Researcher basic information

• 農学博士, 北海道大学

• https://researchmap.jp/meta_dolly?lang=en

• https://jglobal.jst.go.jp/detail?JGLOBAL_ID=201301006124238152
• http://noah.ees.hokudai.ac.jp/envmi/koizumilab/

• 50572799

• 201301006124238152

• 進化生態学
• 動物生態学
• 分子生態学
• 個体群生態学

• Life Science, Ecology and environment

• Master's degree program, Graduate School of Environmental Science
• Doctoral (PhD) degree program, Graduate School of Environmental Science

Research activity information

• 2017, Ecological Research Paper Award
  Keisuke Atsumi;Itsuro Koizumi
• 2014, 日本動物学会, Zoological Science Award
  Koizumi I;Kanazawa Y;Tanaka Y

• Intersexual size disparity shapes male alternative reproductive tactics in nonparasitic lampreys
  Hironori Mieda; Chiharu Furusawa; Osamu Kishida; Itsuro Koizumi
  Behavioral Ecology and Sociobiology, 80, 9, Springer Science and Business Media LLC, 27 Aug. 2026
  Scientific journal
• Extensive environmental assessments for the national Shinkansen railroad project reveal high occurrence of the endangered Japanese crayfish, Cambaroides japonicus (De Haan, 1841) (Decapoda: Astacidea: Cambaroididae), in undisturbed forest streams
  Wei Jia; Tadashi Kawai; Takeshi Ejima; Naoya Kusuda; Tsuyoshi Urushihara; Kousuke Ikeda; Itsuro Koizumi
  Journal of Crustacean Biology, 46, 3, Oxford University Press (OUP), 07 Jul. 2026
  Scientific journal, Abstract
  
  Freshwater crayfishes are among the most imperiled animal groups worldwide, with many species experiencing rapid local extinctions due to climate change, habitat modification, and biological invasions. The Japanese crayfish, Cambaroides japonicus (De Haan, 1841), the only native crayfish in Japan, is a relict and endemic species of high conservation concern. Although recent reports have suggested ongoing local extinctions, the species persists in numerous habitats, predominantly in headwater streams. Yet, quantitative data at broad spatial scales remain scarce, limiting our understanding of extinction patterns and the ecological conditions that support population persistence. We analyzed extensive environmental assessment data collected for the national Shinkansen Hokkaido railway project in southern Hokkaido, Japan. Because the railway route primarily traverses undisturbed forested areas, distribution data enabling quantitative assessment of the occurrence status of Cambaroides japonicus under near-natural conditions was collected. We employed a two-scale modeling approach: a microhabitat analysis to identify site-specific drivers of abundance, and a macrohabitat analysis using to assess landscape-scale land use. Our results demonstrated a high presence rate of 94.4% across the study area. At the microhabitat scale, the stream width and the presence of large substrate significantly affected catch per unit effort (CPUE). Macro-habitat modeling revealed that total forest area was a significant positive predictor of both presence and CPUE, suggesting that Japanese crayfish can thrive in almost all small headwater streams when shielded from anthropogenic pressures and the introduction of invasive crayfishes. The study demonstrates the success of a tripartite framework connecting developers, consultants, and academics to repurpose infrastructure data for conservation science. Our results highlight the importance of protecting undisturbed forested catchments for this native species.
• An ethanol-based method for quantitative recovery of branchiobdellidans from the crayfish Cambaroides japonicus (De Haan, 1841) (Decapoda: Astacidea: Cambaroididae), with an evaluation of host survival
  Tomoaki Konno; Chiharu Furusawa; Tadashi Kawai; Itsuro Koizumi
  Journal of Crustacean Biology, 46, 3, Oxford University Press (OUP), 07 Jul. 2026
  Scientific journal, Abstract
  
  Accurately quantifying symbiont abundance per host individual is essential for understanding host-symbiont interactions. Crayfish are known to harbor branchiobdellidans on their body surfaces and within their gill chambers, yet quantitative studies of these symbiotic worms remain limited because existing collection methods are typically lethal to the host. We developed a simple, field-applicable isolation method for branchiobdellidans from the Japanese crayfish Cambaroides japonicus (De Haan, 1841). Individual crayfish were sequentially immersed and shaken for 30 seconds each in 70% ethanol in stream water. This procedure recovered, on average, 93.4% of branchiobdellidans from host individuals. Laboratory survival experiments showed no mortality and no significant effects on feeding or growth rate, although a transient reduction in weight gain was observed during the first two weeks after treatment. These results demonstrate that the ethanol-water shaking method provides a simple, quantitative, and non-lethal approach for sampling branchiobdellidans from live crayfish. The method is readily applicable under field conditions, including for threatened species, and facilitates ecological studies of crayfish-symbiont interactions without compromising host populations.
• Mechanisms of local coexistence in juvenile congeneric salmonids in small tributaries with different thermal regimes
  Yohsuke Uemura; Yasuhiko Otsuki; Ryota Hasegawa; Masahiro Naka; Itsuro Koizumi
  Oecologia, 208, 6, Springer Science and Business Media LLC, 21 May 2026
  Scientific journal
• Validating a Past Local Extinction Model Using Site‐Level Disappearances in a Cold‐Adapted Salmonid Under Global Warming
  Yohsuke Uemura; Ryota Hasegawa; Yoshinori Taniguchi; Yoichi Kawaguchi; Koh Hasegawa; Yuma Takeuchi; Natsuki Hara; Yasuhiko Otsuki; Kiyoshi Kasugai; Takeaki Oiso; Kazutaka Shimoda; Hirokazu Urabe; Itsuro Koizumi
  Freshwater Biology, 71, 5, Wiley, 19 May 2026
  Scientific journal, ABSTRACT
  
  Global warming poses an increasing threat to biodiversity by elevating the risk of local extinctions. Species distribution models are widely used to forecast extinction risk under future climate scenarios; however, empirical validation of these models remains rare. Here, we validated a past local extinction model using site‐level disappearances—defined as resurvey‐based absence at sites where the focal species was recorded 20–60 years ago—which can serve as a practical surrogate for local extinction. We focused on a cold‐adapted salmonid fish, the southern Asian Dolly Varden ( Salvelinus curilus ), in Hokkaido, Japan, and further improved extinction risk models by incorporating spatial climate variation, seasonal thermal regimes, subsurface water effects, and biotic interactions.
  
  We resurveyed 138 historical sites between 2018 and 2024 by electrofishing to assess the presence of southern Asian Dolly Varden. Long‐term air temperature data and modelled groundwater temperatures were analysed to estimate warming trends. Multiple disappearance risk models were developed incorporating summer temperature trends and interspecific competition with white‐spotted charr ( S. leucomaenis ), masu salmon ( Oncorhynchus masou ), and rainbow trout ( O. mykiss ), and evaluated using generalised linear mixed models and predictive performance metrics.
  
  Local disappearance was detected at 12 sites (8.70%), double the number predicted by the previous model based on mean annual air temperature (6 sites, 4.35%). No significant correlation was detected between local disappearance and either latitude or elevation. Models incorporating increases in summer air temperature and interspecific competition effects provided the best predictions, whereas those based on annual mean or subsurface temperatures performed poorly.
  
  Our results indicate that seasonal thermal dynamics and biotic interactions, rather than annual mean, exert a critical influence on local disappearance. Limited dispersal ability and habitat specificity likely constrain range shifts that could mitigate the impacts of climate change. Incorporating these complex factors substantially improves the accuracy of disappearance‐based extinction risk models.
  
  By empirically validating a climate‐driven extinction model using local disappearances, this study highlights the importance of ecological realism in extinction risk modelling. The findings offer valuable guidance for international conservation strategies aimed at freshwater species facing global warming.
• A new locality record of the ectoparasitic copepod <i>Salmincola californiensis</i> in Japan: A potential glacial relict population?
  Ryota Hasegawa; Yukihito Sugimoto; Itsuro Koizumi
  Crustacean Research, 54, 1, 7, Carcinological Society of Japan, 18 Feb. 2025
  Scientific journal
• Highly Threatened Status for the Relict Populations of Ectoparasitic Copepod Salmincola californiensis in Japan
  Ryota Hasegawa; Yohsuke Uemura; Yasunori Yamashita; Makoto Inoshita; Itsuro Koizumi
  Aquatic Conservation: Marine and Freshwater Ecosystems, 35, 2, Wiley, 12 Feb. 2025
  Scientific journal, ABSTRACT
  
  Many species have been threatened over the past century because of anthropogenic disturbances. Parasites are among the most vulnerable groups because they rely on host organisms, many of which are now endangered. While many studies have argued and evaluated the risk of parasite extinction, empirical evidence is still lacking, especially from aquatic ecosystems. Here, we show the highly threatened status of relict populations of the ectoparasitic copepod Salmincola californiensis in Japan. S. californiensis attaches to the branchial cavities of freshwater salmonids of the genus Oncorhynchus spp., and only four local populations have been reported from disparate regions of Japan, isolated probably due to range contractions after glacial periods. Through citizen‐led field surveys, we found no copepod infections in half of the S. californiensis populations previously reported, suggesting that local extinction has occurred within the last 50–60 years. The upstream reaches of the Kiso River and the Naka River harboured the only sustained populations, though the Kiso population may also have experienced population decline. Our results indicate that parasites can quickly decline over a large geographic scale, especially at range margins. When focal parasites are visible, citizen science is an effective approach for identifying the distributional range of rare parasites and aiding their conservation.
• Positive feedback between parasite infection and poor host body condition reduces host survival in the wild
  Ryota Hasegawa; Yasuhiko Otsuki; Yohsuke Uemura; Chiharu Furusawa; Masahiro Naka; Yoichiro Kanno; Itsuro Koizumi
  Functional Ecology, 39, 3, 723, 736, Wiley, 27 Jan. 2025
  Scientific journal, Abstract
  
  Host–parasite relationships are ubiquitous on Earth. Although parasites reduce host health, parasite infections also occur due to compromised host health. Both causalities could induce positive feedback, in which infected hosts with poor body conditions may suffer further infection. Such positive feedback could increase host mortality and may finally affect host population dynamics. However, both causalities and how positive feedback affect host population dynamics has rarely been demonstrated in the wild, mainly due to methodological difficulties.
  
  Here, we used a mark‐recapture survey combined with structural equation modelling (SEM) to examine whether both causalities and positive feedback occurred in a host stream salmonid and parasitic copepod system. We also examined the factors affecting the apparent survival of hosts during the mark‐recapture period using a Cormack–Jolly–Seber (CJS) model. Our target parasitic copepod Salmincola markewitschi is relatively large, attaching to the mouth cavity of host white‐spotted charr Salvelinus leucomaenis, which enabled long‐term tracking in natural conditions without sacrificing either host or parasite.
  
  SEM using time‐series snapshot data detected simultaneous occurrence of both causalities, that is the parasitic copepods reduced host body condition and host with poorer body condition were more likely infected by parasites, suggesting the positive feedback. Furthermore, the negative effects of parasites on host body condition were more frequently detected compared to the opposite causal link (high susceptibility to infections in hosts with poor body condition), and the strengths of both causal links fluctuated across seasons and initial infection statuses. The CJS model revealed that both parasite infection and poor host condition reduced apparent survival.
  
  The mouth‐attaching copepods might have reduced host body conditions by altering host foraging behaviour and/or inducing physiological costs such as immunity. High susceptibility in fish with poorer body condition was probably caused by low resource allocations to immunity and behavioural defences against parasites. These direct and indirect processes should incur strong stresses to host fish, finally leading to higher mortality.
  
  Our findings provided the first empirical evidence on how positive feedback between parasite infection and reduced host condition could influence the wild host population via reduction of host survival. Heavily infected hosts created by positive feedback may also play important roles in parasite spreading, for example, as a super spreader. Together, positive feedback would thus be important ecological processes to better understand host and parasite dynamics in the wild populations.
  
  
  
  Read the free Plain Language Summary for this article on the Journal blog.
• Mouth-attaching copepod Salmincola markewitschi reduces the body condition and growth of juvenile salmonids, Salvelinus leucomaenis, by decreasing host feeding activity: evidence from parasite removal experiment
  Leo Murakami; Ryota Hasegawa; Nozomi Aruga; Nobuhiro Sato; Shingo Nakamura; Hiroshi Kajihara; Itsuro Koizumi
  Canadian Journal of Zoology, 103, 1, 8, Canadian Science Publishing, 01 Jan. 2025
  Scientific journal, Ectoparasitic copepods in the genus Salmincola Wilson, 1915 are considered harmful to host salmonids, yet experimental studies on the mechanism by which these copepods affect hosts are critically limited. We evaluated the effects of the mouth-attaching Salmincola markewitschi Shedko & Shedko, 2002 on juvenile white-spotted charr Salvelinus leucomaenis (Pallas, 1814). We used a parasite removal experiment where all individuals were artificially infected, and then parasites were removed in one group (i.e., treatment), while the copepods were left in another group (i.e., control). We hypothesized that the copepods reduce host feeding, thereby reducing host body condition and growth. The alternative hypothesis is that parasites do not change host feeding, or even increase because of the compensation for the negative effect. In this case, host condition and growth would not be reduced. The control group had lower food consumption, body condition, and growth compared to the treatment. Thus, S. markewitschi negatively affected hosts by reducing host feeding, and no behavioral compensation was observed. It remains unknown, however, whether reduced feeding was due to impaired swallowing or physiological stresses caused by infections. Further experiments on gill- and body surface-attaching Salmincola species could provide deeper insights into how these parasites influence host health.
• Host Specificity of the Parasitic Copepod <i>Salmincola markewitschi </i>in an Aquarium
  Ryota Hasegawa; Leo Murakami; Nozomi Aruga; Nobuhiro Sato; Shingo Nakamura; Itsuro Koizumi
  Fish Pathology, 59, 4, 139, 142, The Japanese Society of Fish Pathology, 15 Dec. 2024
  Scientific journal
• Do Mouth‐Infecting Parasites Alter the Foraging Ecology of Host Fish? A Test With the Parasitic Copepod Salmincola markewitschi and White‐Spotted Charr Salvelinus leucomaenis
  Ryota Hasegawa; Itsuro Koizumi
  Freshwater Biology, 70, 1, Wiley, 29 Nov. 2024
  Scientific journal, ABSTRACT
  
  Many parasites infect host mouth cavities and are expected to physically impede host foraging. Despite these potential impacts, few studies have evaluated host foraging activities and their findings are equivocal.
  
  We examined the effects of the mouth‐infecting copepod, Salmincola markewitschi , on wild white‐spotted charr Salvelinus leucomaenis foraging using stomach contents analysis. Because the mouth‐infecting copepod occupies a large space in the host mouth cavity, we hypothesized that infected fish exhibit reduced stomach fullness and total prey consumed compared to uninfected fish. In addition, we also hypothesized that infected fish shift their main diets from terrestrial to aquatic invertebrates because parasites reduce host activity, body condition and competitive ability.
  
  Contrary to our predictions, stomach fullness and total prey consumed were not significantly different between infected and uninfected fish: smaller infected fish consumed more prey. We also found that smaller infected hosts foraged on a lower proportion of terrestrial invertebrates than their uninfected counterparts.
  
  Our results suggest that small infected fish increased foraging activities to compensate for energetic loss induced by infection. They also shifted their diet from large terrestrial to small aquatic invertebrates, possibly due to physical impediments and reduced competitive abilities associated with copepod infection.
  
  Our study indicates that mouth‐infecting parasites affect host foraging ecology, but the impacts are weaker than expected and depend on host body size. Nonetheless, behavioural shifts could have important ecological consequences such as loss of host fitness and strengthening trophic cascades in aquatic ecosystems.
• Form-assortative mating behaviors of individuals from parasitic and non-parasitic populations of Arctic lamprey (Lethenteron camtschaticum)
  Léa Daupagne; Chiharu Furusawa; Hironori Mieda; Osamu Kishida; Emilien Lasne; édric Tentelier; Itsuro Koizumi
  Behavioral Ecology, Oxford University Press (OUP), 21 Sep. 2024
  Scientific journal, Abstract
  
  Evolutionary theory predicts that assortative mating is crucial for sympatric speciation by generating reproductive isolation between diverging populations. Here, we investigate the potential of form-assortative mating, an assumed mating pattern in lampreys, for sympatric speciation. By continuously recording mating activity between anadromous and freshwater-resident forms of L. camtschaticum that greatly differ in body size, we show that lampreys tend to mate with individuals of similar size in experimental conditions. However, we highlight that this pattern does not result from a choice of same-form partner but is the result of the simultaneous action of a preference of males – whatever their size – for large anadromous females, a higher competitive ability of aggressive males and physical constraints on heteroform pairs. Moreover, we do not advocate that sympatric speciation, as the sole consequence of form-assortative mating through sexual selection, is a plausible mechanism for the diversification of lampreys as a significant number of sneaking behaviors were observed in freshwater-resident males toward large anadromous females. Broader attention should be given to mechanisms other than sexual selection that may lead to form-assortative mating, such as variations in spatial or temporal distribution of alternative forms during reproductive season.
• Evaluation of genetic consequences of stocking on the southern‐margin populations of white‐spotted charr
  Taro Masuda; Yoshiko Shimono; Daisuke Kishi; Itsuro Koizumi
  Ecology and Evolution, 14, 8, e70140, Wiley, 09 Aug. 2024, [Peer-reviewed]
  Scientific journal, Abstract
  
  Coldwater‐adapted freshwater fishes, especially their populations along warm‐range margins, are most vulnerable to the climate oscillations associated with global warming. Stocking is a major strategy for avoiding the extinction of these species. However, while stocking can reverse the decline of isolated populations, it may also result in a loss of genetic diversity in the native local population due to the introgressive replacement of hatchery genes. To plan an adequate strategy for conserving locally adapted populations, the genetic impacts of stocking on native lineages should be evaluated from small river branches to wide‐ranging drainage areas. We investigated the population genetic structure of white‐spotted charr (Salvelinus leucomaenis) within its southern range (Lake Biwa basin, Japan). By applying genome‐wide SNP analysis to the population's genetic structure, we assessed the extent of genetic introgression resulting from stocking. White‐spotted charr in the Lake Biwa watershed constitutes a distinctive genetic group, within which apparent genetic differentiation was observed. The hatchery‐reared fish line commonly used for supplementation stocking in the catchment was discernable from the native population, enabling us to analyze genetic introgression across the entire drainage area. Admixed individuals resulting from hatchery introgression were observed in most of the stocked sites that showed relatively high heterozygosity and nucleotide diversity. However, their genetic differentiation was much lower than that of native populations. The supplementation history as well as the road availability contributed substantially to the introgression of hatchery genes. Populations with the native genetic structure remained in the upstream regions of the tested rivers. However, their heterozygosity and nucleotide diversity were low when compared with that of the populations with hatchery supplementation. Our results shed light on the genetic impacts of stocking on isolated native populations and suggest that conventional supplementation methods cannot preserve a unique biodiversity in the distribution margin.
• ‘Ripple effects’ of urban environmental characteristics on cognitive performances in Eurasian red squirrels
  Pizza Ka Yee Chow; Kenta Uchida; Itsuro Koizumi
  Journal of Animal Ecology, 93, 8, 1078, 1096, Wiley, 23 Jun. 2024
  Scientific journal, Abstract
  
  Urban areas are expanding exponentially, leading more species of wildlife living in urban environments. Urban environmental characteristics, such as human disturbance, induce stress for many wildlife and have been shown to affect some cognitive traits, such as innovative problem‐solving performance. However, because different cognitive traits have common cognitive processes, it is possible that urban environmental characteristics may directly and indirectly affect related cognitive traits (the ripple effect hypothesis).
  
  We tested the ripple effect hypothesis in urban Eurasian red squirrels residing in 11 urban areas that had different urban environmental characteristics (direct human disturbance, indirect human disturbance, areas of green coverage and squirrel population size). These squirrels were innovators who had previously repeatedly solved a food extraction task (the original task). Here, we examined whether and how urban environmental characteristics would directly and indirectly influence performance in two related cognitive traits, generalisation and (long‐term) memory. The generalisation task required the innovators to apply the learned successful solutions when solving a similar but novel problem. The memory task required them to recall the learned solution of the original task after an extended period of time.
  
  Some of the selected urban environmental characteristics directly influenced the task performance, both at the population level (site) and at individual levels. Urban environmental characteristics, such as increased direct and indirect human disturbance, decreased the proportion of success in solving the generalisation task or the memory task at the population (site) level. Increased direct human disturbance and less green coverage increased the solving efficiency at individual levels.
  
  We also found an indirect effect in one of the urban environmental characteristics, indirect human disturbance, in the generalisation task, but not the memory task. Such an effect was only seen at the individual level but not at the population level; indirect human disturbance decreased the first original latency, which then decreased the generalisation latency across successes.
  
  Our results partially support the ripple effect hypothesis, suggesting that urban environmental characteristics are stressors for squirrels and have a greater impact on shaping cognitive performance than previously shown. Together, these results provide a better understanding of cognitive traits that support wildlife in adapting to urban environments.
• Behavioural sleep in salmonid fish with flexible diel activity
  Chiharu Furusawa; Itsuro Koizumi
  Animal Behaviour, Mar. 2024
  Scientific journal
• The past, present, and a future for native charr in Japan
  Kurt D. Fausch; Kentaro Morita; Jun-ichi Tsuboi; Yoichiro Kanno; Shoichiro Yamamoto; Daisuke Kishi; Jason B. Dunham; Itsuro Koizumi; Koh Hasegawa; Mikio Inoue; Takuya Sato; Satoshi Kitano
  Ichthyological Research, 71, 4, 461, 485, Springer Science and Business Media LLC, 27 Feb. 2024
  Scientific journal, Abstract
  
  Charrs (Salvelinus) reach their southernmost distribution in Japan, and are uniquely adapted to the short, steep streams of this island archipelago. Southern Asian Dolly Varden (Salvelinus curilus) occur only in Hokkaido Island, whereas white-spotted charr (Salvelinus leucomaenis) range to southern Honshu. Both species diverged from an ancestral lineage during the late Pliocene/early Pleistocene, when lowered sea levels created semi-enclosed water bodies in the seas of Japan and Okhotsk. Genetic analyses showed S. curilus represents the most ancient divergence from the Dolly Varden (Salvelinus malma) - Arctic charr (Salvelinus alpinus) group, and revealed five lineages of S. leucomaenis which align differently than traditional subspecies. Japanese charr display diverse and flexible life histories including anadromous fish with partial migration, and fluvial, adfluvial, and resident forms. In Hokkaido, Dolly Varden are distributed upstream and white-spotted charr downstream. They coexist in narrow sympatric zones through adaptive shifts by Dolly Varden in behavior and morphology that facilitate benthic foraging. Both species hybridize with native and nonnative salmonids, and are displaced from microhabitats and decline in abundance when rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) invade. Japan streams contain over 95,000 erosion control dams which create short stream fragments (medians ~200 m). This has increased extirpation of charr populations via lower genetic diversity and stochastic and demographic factors. Tributaries provide complex rearing habitats, afford refuges from floods, and supply recruits that sustain populations in mainstem fragments and create metapopulations in connected riverscapes. Charr play central roles in linked stream-riparian food webs, and cause direct and indirect effects that cascade to streambed algae and riparian predators when linkages are disrupted by anthropogenic effects or altered by native parasites. Many charr populations are threatened by habitat fragmentation and introgression or invasion by nonnative forms, but efforts to conserve charr are growing. These include restoring connectivity among pure populations above barriers that prevent invasions, protecting tributary nurseries, and instituting angling regulations to protect headwater populations. Key steps include inventorying pure populations, identifying conservation units, selecting appropriate management based on connectivity and biotic interactions, and engaging stakeholders and youth to engender an ethic for conserving irreplaceable charr lineages.
• Host shift to non-native species or ecological dead end? Endangered branchiobdellidans (Annelida: Clitellata) found on introduced Signal Crayfish in Japan
  Tomoaki Konno; Kazunori Tanaka; Itsuro Koizumi
  Knowledge & Management of Aquatic Ecosystems, 26 Feb. 2024, [Peer-reviewed]
  Scientific journal, Symbionts, including parasites, are usually small and thus have been overlooked for their existence and scientific research. In the context of biological invasion, host shifts between native and non-native species occur. Since symbionts often affect host behaviour and survival, it is important to reveal the cryptic invasions and host shifts of such small symbionts. Here, we report the first evidence of the potential host shift of a native endangered branchiobdellidans, ectosymbiotic crayfish worms, to a non-native Signal Crayfish, Pacifastacus leniusculus (Dana 1852), in Hokkaido, Japan. Pacifastacus leniusculus is native to North America and was recently introduced to the Atsubetsu River system in Sapporo. In addition to the North American ectosymbiont, Sathodrilus tetrodonta (Pierantoni, 1906), we found an endangered Japanese species, Cirrodrilus cirratus complex on P. leniusculus. However, C. cirratus complex as well as S. tetrodonta were not found on the native Japanese Crayfish, Cambaroides japonicus (De Haan, 1841), in the same river system, indicating a host shift of the ectosymbiont to invasive crayfish. It remains unclear whether C. cirratus complex will persist for a long time with the non-native host or if this is only a transient leading to local extinction.
• Consistent Negative Correlations between Parasite Infection and Host Body Condition Across Seasons Suggest Potential Harmful Impacts of Salmincola markewitschi on Wild White-Spotted Charr, Salvelinus leucomaenis
  Ryota Hasegawa; Itsuro Koizumi
  Zoological Science, 12 Jan. 2024
  Scientific journal
• Evaluation of multiple behavioral responses of sika deer to human hunting pressures
  Takashi Ikeda; Itsuro Koizumi
  The Journal of Wildlife Management, 88, 1, Wiley, 19 Sep. 2023
  Scientific journal, Abstract
  
  Several ungulate populations have become overabundant worldwide, resulting in ecological and social effects. Wildlife managers must establish effective population control programs to mitigate these negative influences. Hunting is a significant mortality factor for ungulates, which exhibit sensitive behavioral responses toward hunting activities. Wildlife managers need a comprehensive understanding of the ungulate responses to different hunting pressures across seasons. We developed a conceptual method to evaluate multiple behavioral responses to human hunting pressures and applied this to sika deer ( Cervus nippon ) in Hokkaido, Japan, during August and November in 2015. We measured flight behavior, spatial avoidance, and temporal activity shift during non‐hunting and hunting seasons in 4 regions with different hunting pressures. Although we did not observe a clear difference in flight initiation distance among study areas or seasons, sika deer showed significant spatial avoidance during the hunting season in areas with high hunting pressure. Furthermore, sika deer were more active at night in areas with higher hunting pressures, regardless of the season. Collectively, these results suggest that sika deer responded to hunting pressure by changing diel activity to nocturnal throughout the year and avoiding risky areas (i.e., around hunting roads) during hunting season, rather than by increasing flight distance when they encounter humans. Our method can be used for a more efficient population control program for wildlife managers, as it considers the spatiotemporal variations of flexible ungulate behaviors in response to hunting pressures.
• Distribution of ectosymbiotic species of Cirrodrilus (Annelida, Clitellata, Branchiobdellida) in northern Japan, with notes on their taxonomy
  AKIFUMI OHTAKA; TOMOAKI KONNO; ITSURO KOIZUMI; STUART R. GELDER
  Zoosymposia, 23, Magnolia Press, 10 Jul. 2023
  Scientific journal, Twelve species of Cirrodrilus, a genus of ectosymbiotic branchiobdellidans, have been recorded on the Japanese crayfish, Cambaroides japonicus, from the islands of Hokkaido and northern Honshu. To clarify the geographic distribution of these species, we examined branchiobdellidan assemblages from 71 locations on Hokkaido and 59 on northern Honshu. We found 11 morphologically distinct species. The following 8 species: Cirrodrilus digitatus, Ci. cirratus, Ci. uchidai, Ci. sapporensis, Ci. nipponicus, Ci. japonicus, Ci. megalodentatus and Ci. homodontus were exclusively recorded from Hokkaido, while Ci. aomorensis was restricted to Honshu. Two other species, Ci. tsugarensis and Ci. iwakiensis, had previously only been recorded from Honshu but were now also found on Hokkaido. The anomalous record of Ci. digitatus and Ci. uchidai on Honshu is known to be the result of crayfish being translocated from Hokkaido. No significant difference in the species composition was found between eastern and western regions on Hokkaido, where divergent lineages have been detected in the Japanese crayfish host. Overlaps in the diagnostic characters of Ci. cirratus and Ci. uchidai suggest that both taxa belong to either a single species or form a species complex.
• Seasonal changes in the ratio of congeneric charrs in northern Japanese tributaries with different temperature regimes
  Taihei Yamada; Itsuro Koizumi; Futoshi Nakamura
  Research Square Platform LLC, 26 Jun. 2023
  Abstract
  
  Background: The species distributions and community compositions of stream fishes are often shaped by water temperature. Stream salmonids, for example, show longitudinal gradients or marked community differences between spring-fed vs. non-spring-fed streams, which may be a result of species-specific temperature preferences, interspecific competition, or their interaction (i.e., temperature-dependent competition). Despite the widely reported patterns, how such temperature-associated distributions change across seasons remains largely unknown. If temperature is the main driver, the pattern will change across seasons. Alternatively, seasonal patterns will be obscured if other factors, such as species-specific life histories or seasonal aggregation, are important. Here, we investigated the effects of water temperature on the abundance and species ratio of two potentially competing salmonids, southern Asian Dolly Varden Salvelinus curilus and white-spotted charr Salvelinus leucomaenis, in 6 small tributaries with different temperature regimes (i.e., spring-fed and non-spring-fed) across seasons.Results: Across seasons, the southern Asian Dolly Varden dominated in spring-fed tributaries, whereas white-spotted charr dominated in non-spring-fed tributaries. The seasonal variation in the abundance of southern Asian Dolly Varden and species ratio were explained by water temperature fluctuation, whereas that of white-spotted charr was not explained by the temperature fluctuation. No winter aggregation was observed in any of the tributaries. In addition, only the species ratio in summer was explained by the water temperature, and the water temperature did not fully explain the species ratio.Conclusions: Our results indicated that temperature preference and/or the strength of interspecific competition may differ across seasons, which is expected to determine the seasonal distribution patterns in spring-fed and non-spring-fed tributaries. This study underscores the importance of considering seasons when evaluating temperature effects on the distribution of stream salmonids.
• Parasites either reduce or increase host vulnerability to fishing: a case study of a parasitic copepod and its salmonid host
  Ryota Hasegawa; Itsuro Koizumi
  The Science of Nature, Apr. 2023, [Peer-reviewed]
  Scientific journal
• Geology‐Climate Interactions are Key Determinants of Climate‐Change Refugia in Japanese Mountain Streams
  Nobuo Ishiyama; Masanao Sueyoshi; Jorge García Molinos; Kenta Iwasaki; Junjiro N. Negishi; Itsuro Koizumi; Shigeya Nagayama; Akiko Nagasaka; Yu Nagasaka; Futoshi Nakamura
  The Bulletin of the Ecological Society of America, Wiley, 15 Mar. 2023
  Scientific journal
• Underlying geology and climate interactively shape climate change refugia in mountain streams
  Nobuo Ishiyama; Masanao Sueyoshi; Jorge García Molinos; Kenta Iwasaki; Junjiro N. Negishi; Itsuro Koizumi; Shigeya Nagayama; Akiko Nagasaka; Yu Nagasaka; Futoshi Nakamura
  Ecological Monographs, 93, 2, Wiley, 06 Mar. 2023
  Scientific journal, Abstract
  
  Identifying climate‐change refugia is a key adaptation strategy for reducing global warming impacts. Knowledge of the effects of underlying geology on thermal regime along climate gradients and the ecological responses to the geology‐controlled thermal regime is essential to plan appropriate climate adaptation strategies. In the present study, the dominance of volcanic rocks in the watershed is used as a landscape‐scale surrogate for cold groundwater inputs to clarify the importance of underlying geology in stream ecosystems along climate gradients. First, using hundreds of monitoring stations distributed across multiple catchments, we explored the relationship between watershed geology and the mean summer water temperature of mountain streams along climate gradients in the Japanese archipelago. Mean summer water temperature was explained by the interaction between the watershed geology and climate in addition to independent effects. The cooling effect supported by volcanic rocks reached up to 3.3°C among study regions, which was more pronounced in streams with less summer precipitation or lower air temperatures. Next, we examined the function of volcanic streams as cold refugia under contemporary and future climatic conditions. Community composition analyses revealed that volcanic streams hosted distinct stream communities composed of more cold‐water species compared with nonvolcanic streams. Scenario analyses based on multiple global climate models and Representative Concentration Pathways (RCPs) revealed a geology‐related pattern of thermal habitat loss for cold‐water species. Nonvolcanic streams rapidly declined in thermally suitable habitats for lotic sculpins even under the lowest emission scenario (RCP 2.6). In contrast, most volcanic streams will be sustained below the thermal threshold, especially for low‐ and mid‐level emission scenarios (RCP 2.6, 4.5). However, the distinct stream community in volcanic streams and geology‐dependent habitat loss for lotic sculpins was not uniform and were more pronounced in streams with less summer precipitation or lower air temperatures. These findings highlight that underlying geology, climate variability, and their interaction should be considered simultaneously for the effective management of climate‐change refugia in mountain streams.
• Systematic headwater sampling of white‐spotted charr reveals stream capture events across dynamic topography
  Taro Masuda; Yoshiko Shimono; Daisuke Kishi; Itsuro Koizumi
  Journal of Biogeography, Wiley, 26 Dec. 2022
  Scientific journal
• A novel phylogenetic comparative method for evaluating the strength of branch-specific directional selection
  Yusaku Ohkubo; Nobuyuki Kutsukake; Itsuro Koizumi
  Evolution, 77, 1, 63, 82, Oxford University Press (OUP), 08 Dec. 2022
  Scientific journal, Abstract
  
  Phylogenetic comparative methods (PCMs) have played a central role in studying the evolution of phenotypic traits. However, when a trait experienced directional selection, previous PCMs have faced a dilemma between mathematically tractable but restrictive models (i.e., simple Gaussian process models) and flexible but intractable approaches (i.e., a simulation-based process model of phenotype evolution built on population genetics frameworks). This paper proposes a novel Gaussian process macroevolutionary model, called the “branch-specific directional selection (BSDS),” for evaluating the strength of directional selection to reconcile these two approaches. This model is based on a second-order approximation of a previous simulation-based process model but has a closed-form likelihood function. This can also be extended to incorporate intraspecies variations and to linear mixed models, which are necessary for meta-analysis. We conduct numerical experiments to validate the proposed method and apply it to the brain volume of Hominidae species. The results show that the proposed methods yield statistically more reliable inferences and computational time is about hundred thousand times faster than the previous simulation-based methods. Further extensions of the BSDS model are expected to provide a clearer picture of the connection of microevolutionary processes and macroevolutionary patterns.
• Salmincola markewitschi or S. carpionis (Copepoda: Lernaeopodidae)? A requirement for taxonomic revision due to their high morphological variations
  Ryota Hasegawa; Hirotaka Katahira; Itsuro Koizumi
  Folia Parasitologica, 69, 025, Biology Centre, AS CR, 03 Nov. 2022, [Peer-reviewed], [International Magazine]
  English, Scientific journal, Salmincola markewitschi Shedko et Shedko, 2002 (Copepoda: Lernaeopodidae) is an ectoparasitic copepod mainly infecting the buccal cavities of white-spotted charr Salvelinus leucomaenis (Pallas) (Salmonidae). This species has only been recorded from Northeast Asia, where a morphologically similar congener Salmincola carpionis (Krøyer, 1837) is also distributed, using the same host species. These copepods are hard to distinguish from each other because of their similarities. We thus examined the newly collected specimens morphologically and genetically from five populations of white-spotted charr in Japan. Most of the specimens were morphologically consistent with S. markewitschi but showed great variations in the numbers of spines on the exopods of the antennae, shape of the maxilliped myxal palps, and the bulla diameter. Consequently, some specimens shared characteristics with S. carpionis. In addition to the mophological continuities, genetic analyses of 28S rDNA and COI mitochondrial DNA confirmed that all specimens belong to a single species. Further taxonomic revisions are required to draw conclusions of whether S. markewitschi is a valid species different from S. carpionis, by collecting samples from across their wide distributional ranges, such as Europe, North America, and Northeast Asia. A key to identification of species of Salmincola Wilson, 1915 occurring in Japan is also provided.
• Dietary niche breadth influences the effects of urbanization on the gut microbiota of sympatric rodents
  Jason L. Anders; Alexis M. Mychajliw; Mohamed Abdallah Mohamed Moustafa; Wessam Mohamed Ahmed Mohamed; Takashi Hayakawa; Ryo Nakao; Itsuro Koizumi
  Ecology and Evolution, 12, 9, Wiley, Sep. 2022
  Scientific journal,

  Cities are among the most extreme forms of anthropogenic ecosystem
  modification and urbanization processes exert profound effects on animal
  populations through multiple ecological pathways. Increased access to
  human associated food items may alter species’ foraging behavior and
  diet, in turn modifying the normal microbial community of the
  gastrointestinal tract, ultimately impacting their health. It is crucial
  we understand the role of dietary niche breadth and the resulting shift
  in the gut microbiota as urban animals navigate novel dietary resources.
  We combined stable isotope analysis of hair and microbiome analysis of
  four gut regions across the gastrointestinal tract to investigate the
  effects of urbanization on the diet and gut microbiota of two sympatric
  species of rodent with different dietary niches; the omnivorous large
  Japanese field mouse (Apodemus speciosus) and the relatively more
  herbivorous grey red-backed vole (Myodes rufocanus). Both species
  exhibited an expanded dietary niche width within the urban areas
  potentially attributable to novel anthropogenic foods and altered
  resource availability. We detected a dietary shift in which urban A.
  speciosus consumed more terrestrial animal protein and M. rufocanus more
  plant leaves and stems. Such changes in resource use may be associated
  with an altered gut microbial community structure. There was an
  increased abundance of the presumably probiotic Lactobacillus in the
  small intestine of urban A. speciosus and potentially pathogenic
  Helicobacter in the colon of M. rufocanus. Together, these results
  suggest that even taxonomically similar species may exhibit divergent
  responses to urbanization with consequences for the gut microbiota and
  broader ecological interactions.

• Potential negative effects and heterogeneous distribution of a parasitic copepod Salmincola edwardsii (Copepoda: Lernaeopodidae) on Southern Asian Dolly Varden Salvelinus curilus in Hokkaido, Japan
  Ryota Hasegawa; Christopher G. Ayer; Yoshiyuki Umatani; Kazuki Miura; Miyo Ukumura; Hirotaka Katahira; Itsuro Koizumi
  Parasitology International, 87, 102529, 102529, Elsevier BV, Apr. 2022
  Scientific journal
• Comparing the gut microbiome along the gastrointestinal tract of three sympatric species of wild rodents
  Jason L. Anders; Mohamed Abdallah Mohamed Moustafa; Wessam Mohamed Ahmed Mohamed; Takashi Hayakawa; Ryo Nakao; Itsuro Koizumi
  Scientific Reports, 11, 1, 19929, 19929, Springer Science and Business Media LLC, Dec. 2021, [Peer-reviewed], [International Magazine]
  English, Scientific journal, Abstract
  
  Host–microbe interactions within the gastrointestinal tract (GIT) play a pivotal role in shaping host physiology, ecology, and life history. However, these interactions vary across gut regions due to changes in the physical environment or host immune system activity, thereby altering the microbial community. Each animal species may harbor their own unique microbial community due to host species-specific ecological traits such as dietary habits, micro-habitat preferences, and mating behavior as well as physiological traits. While the gut microbiota in wild animals has received much attention over the last decade, most studies comparing closely related species only utilized fecal or colon samples. In this study, we first compared the gut microbial community from the small intestine, cecum, colon, and rectum within three sympatric species of wild rodents (i.e. Apodemus speciosus, A. argenteus, and Myodes rufocanus). We then compared each gut region among host species to determine the effect of both gut region and host species on the gut microbiota. We found that the small intestine harbored a unique microbiome as compared to the lower GIT in all three host species, with the genus Lactobacillus in particular having higher abundance in the small intestine of all three host species. There were clear interspecific differences in the microbiome within all gut regions, although some similarity in alpha diversity and community structure within the small intestine was found. Finally, fecal samples may be appropriate for studying the lower GIT in these species, but not the small intestine.
• Relative importance of host-dependent versus physical environmental characteristics affecting the distribution of an ectoparasitic copepod infecting the mouth cavity of stream salmonid
  Ryota Hasegawa; Itsuro Koizumi
  ECOLOGICAL RESEARCH, Sep. 2021
  English, Scientific journal
• No apparent effects of the buccal cavity attaching parasite, Salmincola sp. (Copepoda: Lernaeopodidae), on a stream salmonid: a mark-recapture study
  Christopher G. Ayer; Kodai Morita; Sho Fukui; Itsuro Koizumi
  ICHTHYOLOGICAL RESEARCH, Aug. 2021
  English, Scientific journal
• Evidence for Introgressive Hybridization Between Native Dolly Varden (Salvelinus curilus (syn. Salvelinus malma)) and Introduced Brook Trout (Salvelinus fontinalis) in the Nishibetsu River of Hokkaido, Japan
  Sho Fukui; Kiyoshi Kasugai; Ayaka Sawada; Itsuro Koizumi
  ZOOLOGICAL SCIENCE, 38, 3, 247, 251, Jun. 2021
  English, Scientific journal
• Local factors affecting winter habitat use of non-native rainbow trout in a boreal stream in northern Japan
  Chiharu Furusawa; Yukiyo Suehiro-Kanazawa; Yuuki Tanaka; Sho Fukui; Chitose Yamazaki; Takuya K. Hosoki; Itsuro Koizumi
  ICHTHYOLOGICAL RESEARCH, Jun. 2021
  English, Scientific journal
• Combined Effects of Summer Water Temperature and Current Velocity on the Distribution of a Cold-Water-Adapted Sculpin (Cottus nozawae)
  Kaiji Suzuki; Nobuo Ishiyama; Itsuro Koizumi; Futoshi Nakamura
  WATER, 13, 7, Apr. 2021
  English, Scientific journal
• Lineage-level distribution models lead to more realistic climate change predictions for a threatened crayfish
  Zhixin Zhang; Jamie M. Kass; Stefano Mammola; Itsuro Koizumi; Xuecao Li; Kazunori Tanaka; Kousuke Ikeda; Toru Suzuki; Masashi Yokota; Nisikawa Usio
  DIVERSITY AND DISTRIBUTIONS, 27, 4, 684, 695, Apr. 2021
  English, Scientific journal
• Characteristics of urban environments and novel problem-solving performance in Eurasian red squirrels
  Pizza Ka Yee Chow; Kenta Uchida; Auguste M. P. von Bayern; Itsuro Koizumi
  PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, 288, 1947, Mar. 2021
  English, Scientific journal
• Temperature-dependent Swimming Performance Differs by Species: Implications for Condition-specific Competition Between Stream Salmonids
  Taihei Yamada; Itsuro Koizumi; Hirokazu Urabe; Futoshi Nakamura
  ZOOLOGICAL SCIENCE, 37, 5, 429, 433, Oct. 2020
  English, Scientific journal
• Are bolder individuals more likely to choose heterospecific mates? A test in cyprinid fishes
  Keisuke Atsumi; Itsuro Koizumi
  JOURNAL OF ETHOLOGY, 38, 2, 247, 251, May 2020
  English, Scientific journal
• Hybrids as potential mediators spreading non-native genes: Comparison of survival, growth, and movement among native, introduced and their hybrid salmonids
  Sho Fukui; Itsuro Koizumi
  Ecology of Freshwater Fish, 29, 2, 280, 288, Blackwell Munksgaard, 01 Apr. 2020
  English, Scientific journal
• Comparison of multiple behavioral traits between urban and rural squirrels
  Kenta Uchida; Tatsuki Shimamoto; Hisashi Yanagawa; Itsuro Koizumi
  Urban Ecosystems, 23, 4, 745, 754, Springer Science and Business Media LLC, 21 Feb. 2020, [Peer-reviewed]
  Scientific journal
• Evaluating a pattern of ecological character displacement: charr jaw morphology and diet diverge in sympatry versus allopatry across catchments in Hokkaido, Japan
  Shigeru Nakano; Kurt D. Fausch; Itsuro Koizumi; Yoichiro Kanno; Yoshinori Taniguchi; Satoshi Kitano; Yo Miyake
  BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, 129, 2, 356, 378, Feb. 2020
  English, Scientific journal
• No evidence of physiological stress in an urban animal: Comparison of fecal cortisol metabolites between urban and rural Eurasian red squirrels
  Tatsuki Shimamoto; Kenta Uchida; Itsuro Koizumi; Motozumi Matsui; Hisashi Yanagawa
  Ecological Research, 35, 1, 243, 251, Wiley, Jan. 2020, [Peer-reviewed]
  Scientific journal
• Decreased vigilance or habituation to humans? Mechanisms on increased boldness in urban animals
  Kenta Uchida; Kei K Suzuki; Tatsuki Shimamoto; Hisashi Yanagawa; Itsuro Koizumi
  Behavioral Ecology, 30, 6, 1583, 1590, Oxford University Press (OUP), Dec. 2019, [Peer-reviewed]
  English, Scientific journal,
  Increased boldness is one of the most prevalent behavioral modifications seen in urban animals and is thought to be a coping response to anthropogenic environmental alterations. Most previous studies have shown enhanced boldness manifested as changes in responses to humans approaching, such as reductions in flight initiation distance (FID). However, this includes two confounding factors related to “boldness,” that is, reduction of vigilance and habituation to humans. Confounding these totally different processes could lead to our misunderstanding of urban adaptation and how to properly manage urban wildlife. Here, we propose a simple framework to separate the two processes using two flight distance measures toward different approaching threats. We considered that the distance at which targeted individuals noticed an approaching object (i.e., alert distance, AD) was related to vigilance, whereas FID represented risk assessment, which is related to habituation. We applied a predictive framework using AD and FID to Eurasian red squirrels’ responses to multiple threats of different risk levels (i.e., humans, model predators, and novel objects). AD was shorter in urban individuals compared with rural ones but not different among the approaching objects. FID was shorter in urban individuals and also varied among the objects with the shortest FID toward humans, whereas rural individuals showed similar FID to the different objects. These results suggest that, although urban individuals showed reduced vigilance, they could still assess different risk levels. Our framework can easily be applied to many animals and could significantly improve our understanding of wild animals’ adaptations to urban environments.
• Visual preference of males for conspecific mates in mutually ornamented fish: possible support for the species recognition hypothesis
  Keisuke Atsumi; Osamu Kishida; Itsuro Koizumi
  Journal of Ethology, 37, 3, 353, 362, Springer Tokyo, 13 Sep. 2019
  English, Scientific journal
• Simple nonlethal identification criteria for two endangered freshwater pearl mussels, Margaritifera laevis and Margaritifera togakushiensis , in Hokkaido, northern Japan
  Kazuki Miura; Nobuo Ishiyama; Keita Kawajiri; Keisuke Atsumi; Michikusa Tachibana; Yu Nagasaka; Yoshiyasu Machida; Gao Yiyang; Junjiro N. Negishi; Itsuro Koizumi; Futoshi Nakamura
  Ecological Research, 34, 5, 667, 677, Wiley, Sep. 2019
  Scientific journal
• Temperature-dependent competition between juvenile salmonids in small streams
  Watz Johan; Otsuki Yasuhiko; Nagatsuka Kenta; Hasegawa Koh; Koizumi Itsuro
  FRESHWATER BIOLOGY, 64, 8, 1534, 1541, Aug. 2019, [Peer-reviewed]
• Comparison of the intestinal helminth community of the large Japanese field mouse (Apodemus speciosus) between urban, rural, and natural sites in Hokkaido, Japan
  Jason L. Anders; Minoru Nakao; Kenta Uchida; Christopher G. Ayer; Mitsuhiko Asakawa; Itsuro Koizumi
  Parasitology International, 70, 51, 57, Elsevier BV, Jun. 2019
  Scientific journal
• Male feeding contribution facilitates multiple brooding in a biparental songbird
  Daisuke Nomi; Teru Yuta; Itsuro Koizumi
  Ibis, 160, 2, 293, 300, Blackwell Publishing Ltd, 01 Apr. 2018, [Peer-reviewed]
  English, Scientific journal
• Seasonal change in sexual differences in nestling size and survival: A framework to evaluate sex-dependent environmental sensitivity in the wild
  Daisuke Nomi; Teru Yuta; Itsuro Koizumi
  Avian Research, 9, 1, BioMed Central Ltd., 19 Mar. 2018, [Peer-reviewed]
  English, Scientific journal
• Facultative multiple breeding as a female conditional strategy in Japanese tits: partner’s quality affects the initiation of second clutches
  Daisuke Nomi; Teru Yuta; Itsuro Koizumi
  Ecological Research, 33, 2, 479, 485, Springer Tokyo, 01 Mar. 2018, [Peer-reviewed]
  English, Scientific journal
• Maladaptive secondary sexual characteristics reduce the reproductive success of hybrids between native and non-native salmonids
  Ecology and Evolution, 2018, [Peer-reviewed]
• Simulated hatching failure predicts female plasticity in extra-pair behavior over successive broods
  Teru Yuta; Daisuke Nomi; Malika Ihle; Itsuro Koizumi
  BEHAVIORAL ECOLOGY, 29, 6, 1264, 1270, 2018, [Peer-reviewed]
  English, Scientific journal
• Seasonal patterns of downstream movement in partially migratory stream-dwelling Dolly Varden
  Christopher G. Ayer; Hirotaka Katahira; Sho Fukui; Itsuro Koizumi
  ECOLOGY OF FRESHWATER FISH, 27, 1, 247, 254, Jan. 2018, [Peer-reviewed]
  English, Scientific journal
• No reduction of hatching rates among F1 hybrids of naturally hybridizing three Far Eastern daces, genus Tribolodon (Cypriniformes, Cyprinidae)
  Keisuke Atsumi; Kazuhiro Nomoto; Yoshiyasu Machida; Masaki Ichimura; Itsuro Koizumi
  Ichthyological Research, 65, 1, 165, 167, Springer Tokyo, 01 Jan. 2018, [Peer-reviewed]
  English, Scientific journal
• Usefulness and limitation of a tiny light-temperature logger to monitor daily activity levels of arboreal squirrels in temperate areas
  Jason L. Anders; Kenta Uchida; Mitsuru Watanabe; Iori Tanio; Tatsuki Shimamoto; Mizuho Hamada; Hisashi Yanagawa; Itsuro Koizumi
  MAMMAL RESEARCH, 62, 4, 397, 404, Oct. 2017, [Peer-reviewed]
  English, Scientific journal
• Web image search revealed large-scale variations in breeding season and nuptial coloration in a mutually ornamented fish, Tribolodon hakonensis
  Keisuke Atsumi; Itsuro Koizumi
  ECOLOGICAL RESEARCH, 32, 4, 567, 578, Jul. 2017, [Peer-reviewed]
  English, Scientific journal
• Mass immigration of juvenile fishes into a small, once-dried tributary demonstrates the importance of remnant tributaries as wintering habitats
  Itsuro Koizumi; Yuuki Tanaka; Yukiyo Kanazawa
  ICHTHYOLOGICAL RESEARCH, 64, 3, 353, 356, Jul. 2017, [Peer-reviewed]
  English, Scientific journal
• BREEDING BIOLOGY OF FOUR SYMPATRIC TITS IN NORTIIERN JAPAN
  Daisuke Nomi; Teru Yuta; Itsuro Koizumi
  WILSON JOURNAL OF ORNITHOLOGY, 129, 2, 294, 300, Jun. 2017, [Peer-reviewed]
  English, Scientific journal
• High frequency of mating without egg release in highly promiscuous nonparasitic lamprey Lethenteron kessleri
  Chitose Yamazaki; Itsuro Koizumi
  JOURNAL OF ETHOLOGY, 35, 2, 237, 243, May 2017, [Peer-reviewed]
  English, Scientific journal
• Extreme winter aggregation of invasive rainbow trout in small tributaries: implications for effective control
  Itsuro Koizumi; Yukiyo Kanazawa; Chitose Yamazaki; Yuuki Tanaka; Kousuke Takaya
  ICHTHYOLOGICAL RESEARCH, 64, 2, 197, 203, Apr. 2017, [Peer-reviewed]
  English, Scientific journal
• Escaping height in a tree represents a potential indicator of fearfulness in arboreal squirrels
  Kenta Uchida; Kei K. Suzuki; Tatsuki Shimamoto; Hisashi Yanagawa; Itsuro Koizumi
  MAMMAL STUDY, 42, 1, 39, 43, Mar. 2017, [Peer-reviewed]
  English, Scientific journal
• Spatial aggregation in small spring-fed tributaries leads to a potential metapopulation structure in a parasitic fish leech
  Parasitology Open, 2017, [Peer-reviewed]
• Early maturation of rosyface dace, Tribolodon sachalinensis (Cyprinidae, Cypriniformes), in a small isolated population
  Atsumi Keisuke; Koizumi Itsuro
  Biogeography, 19, 123, 126, Biogeographical Society of Japan, 2017, [Peer-reviewed]
  English
• Temporal change in the distribution and composition of native, introduced, and hybrid charrs in northern Japan
  Sho Fukui; Shannan L. May-McNally; Hirotaka Katahira; Satoshi Kitano; Itsuro Koizumi
  HYDROBIOLOGIA, 783, 1, 309, 316, Dec. 2016, [Peer-reviewed]
  English, Scientific journal
• Seasonal and Diel Activity Patterns of Eight Sympatric Mammals in Northern Japan Revealed by an Intensive Camera-Trap Survey
  Takashi Ikeda; Kenta Uchida; Yukiko Matsuura; Hiroshi Takahashi; Tsuyoshi Yoshida; Koichi Kaji; Itsuro Koizumi
  PLOS ONE, 11, 10, Oct. 2016, [Peer-reviewed]
  English, Scientific journal
• Socially induced reproductive synchrony in a salmonid: an approximate Bayesian computation approach
  Itsuro Koizumi; Ichiro K. Shimatani
  BEHAVIORAL ECOLOGY, 27, 5, 1386, 1396, Sep. 2016, [Peer-reviewed]
  English, Scientific journal
• Scale dependency of two endangered charismatic species as biodiversity surrogates
  Motoki Higa; Yuichi Yamaura; Masayuki Senzaki; Itsuro Koizumi; Takeshi Takenaka; Yoshiyuki Masatomi; Kunikazu Momose
  BIODIVERSITY AND CONSERVATION, 25, 10, 1829, 1841, Sep. 2016, [Peer-reviewed]
  English, Scientific journal
• Absolute versus Relative Assessments of Individual Status in Status-Dependent Strategies in Stochastic Environments
  Yuuya Tachiki; Itsuro Koizumi
  AMERICAN NATURALIST, 188, 1, 113, 123, Jul. 2016, [Peer-reviewed]
  English, Scientific journal
• Does nest predation risk affect the frequency of extra-pair paternity in a socially monogamous passerine?
  Teru Yuta; Itsuro Koizumi
  JOURNAL OF AVIAN BIOLOGY, 47, 2, 153, 158, Mar. 2016, [Peer-reviewed]
  English, Scientific journal
• Seasonal variation of flight initiation distance in Eurasian red squirrels in urban versus rural habitat
  K. Uchida; K. Suzuki; T. Shimamoto; H. Yanagawa; I. Koizumi
  JOURNAL OF ZOOLOGY, 298, 3, 225, 231, Mar. 2016, [Peer-reviewed]
  English, Scientific journal
• Offspring Sex Ratio of Japanese Tits Parus minor is Related to Laying Date and Clutch Size only in the First Clutches
  Daisuke Nomi; Teru Yuta; Itsuro Koizumi
  Acta Ornithologica, 50, 2, 213, 220, Polish Academy of Sciences, 01 Dec. 2015, [Peer-reviewed]
  English, Scientific journal
• Breeding timing and nest predation rate of sympatric scops owls with different dietary niche breadth
  M. Toyama; N. Kotaka; I. Koizumi
  CANADIAN JOURNAL OF ZOOLOGY, 93, 11, 841, 847, Nov. 2015, [Peer-reviewed]
  English, Scientific journal
• Life-history characteristics and landscape attributes as drivers of genetic variation, gene flow, and fine-scale population structure in northern Dolly Varden (Salvelinus malma malma) in Canada
  Les N. Harris; Robert Bajno; Colin P. Gallagher; Itsuro Koizumi; Lucy K. Johnson; Kimberly L. Howland; Eric B. Taylor; James D. Reist
  CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES, 72, 10, 1477, 1493, Oct. 2015, [Peer-reviewed]
  English, Scientific journal
• Differential effects of spatial network structure and scale on population size and genetic diversity of the ninespine stickleback in a remnant wetland system
  Nobuo Ishiyama; Itsuro Koizumi; Teru Yuta; Futoshi Nakamura
  FRESHWATER BIOLOGY, 60, 4, 733, 744, Apr. 2015, [Peer-reviewed]
  English, Scientific journal
• Mapping large-scale bird distributions using occupancy models and citizen data with spatially biased sampling effort
  Motoki Higa; Yuichi Yamaura; Itsuro Koizumi; Yuki Yabuhara; Masayuki Senzaki; Satoru Ono
  DIVERSITY AND DISTRIBUTIONS, 21, 1, 46, 54, Jan. 2015, [Peer-reviewed]
  English, Scientific journal
• Different habitat salinity between genetically divergent groups of a worm-like goby Luciogobius guttatus: an indication of cryptic species
  Seiya Hashimoto; Itsuro Koizumi; Kotaro Takai; Seigo Higashi
  ENVIRONMENTAL BIOLOGY OF FISHES, 97, 10, 1169, 1177, Oct. 2014, [Peer-reviewed]
  English, Scientific journal
• Potential resource competition between an invasive mammal and native birds: overlap in tree cavity preferences of feral raccoons and Ural owls
  Fumiya Kobayashi; Masahiro Toyama; Itsuro Koizumi
  BIOLOGICAL INVASIONS, 16, 7, 1453, 1464, Jul. 2014, [Peer-reviewed]
  English, Scientific journal
• Geomorphic legacy controls macrophyte distribution within and across disconnected floodplain lakes
  Junjiro N. Negishi; Masashi Soga; Nobuo Ishiyama; Noriyasu Suzuki; Teruaki Yuta; Masanao Sueyoshi; Chitose Yamazaki; Itsuro Koizumi; Shigeru Mizugaki; Kazufumi Hayashida; Masanori Nunokawa; Nobuhiko Yoshimura
  FRESHWATER BIOLOGY, 59, 5, 942, 954, May 2014, [Peer-reviewed]
  English, Scientific journal
• Are hotspring-geothermal areas biodiversity hotspots?
  坂本 洋典; 森 照貴; 小泉 逸郎
  生物科学, 65, 4, 245, 255, 日本生物科学者協会 ; 1949-, 2014, [Peer-reviewed]
  Japanese
• Hybridization between native white-spotted charr and nonnative brook trout in the upper Sorachi River, Hokkaido, Japan
  Satoshi Kitano; Satoshi Ohdachi; Itsuro Koizumi; Koh Hasegawa
  ICHTHYOLOGICAL RESEARCH, 61, 1, 1, 8, Jan. 2014, [Peer-reviewed]
  English, Scientific journal
• Interaction between patch area and shape: lakes with different formation processes have contrasting area and shape effects on macrophyte diversity
  Masashi Soga; Nobuo Ishiyama; Masanao Sueyoshi; Yuichi Yamaura; Kazufumi Hayashida; Itsuro Koizumi; Junjiro N. Negishi
  LANDSCAPE AND ECOLOGICAL ENGINEERING, 10, 1, 55, 64, Jan. 2014, [Peer-reviewed]
  English, Scientific journal
• The Fishermen Were Right: Experimental Evidence for Tributary Refuge Hypothesis During Floods
  Itsuro Koizumi; Yukiyo Kanazawa; Yuuki Tanaka
  ZOOLOGICAL SCIENCE, 30, 5, 375, 379, May 2013, [Peer-reviewed]
  English, Scientific journal
• Fine scale relationships between sex, life history, and dispersal of masu salmon
  Shigeru Kitanishi; Toshiaki Yamamoto; Itsuro Koizumi; Jason B. Dunham; Seigo Higashi
  ECOLOGY AND EVOLUTION, 2, 5, 920, 929, May 2012, [Peer-reviewed]
  English, Scientific journal
• Do small tributaries function as refuges from floods? A test in a salmonid-dominated mountainous river
  Itsuro Koizumi; Koh Hasegawa; Daisuke Kishi
  ECOLOGY OF FRESHWATER FISH, 21, 2, 165, 167, Apr. 2012, [Peer-reviewed]
  English
• Loss of Genetic Diversity Means Loss of Geological Information: The Endangered Japanese Crayfish Exhibits Remarkable Historical Footprints
  Itsuro Koizumi; Nisikawa Usio; Tadashi Kawai; Noriko Azuma; Ryuichi Masuda
  PLOS ONE, 7, 3, Mar. 2012, [Peer-reviewed]
  English, Scientific journal
• Long breeding season and high frequency of multiple brooding in Great Tits in northern Japan
  Teru Yuta; Itsuro Koizumi
  Ardea, 100, 2, 197, 201, 2012, [Peer-reviewed]
  English, Scientific journal
• Integration of ecology, demography and genetics to reveal population structure and persistence: a mini review and case study of stream-dwelling Dolly Varden
  Itsuro Koizumi
  ECOLOGY OF FRESHWATER FISH, 20, 3, 352, 363, Sep. 2011, [Peer-reviewed]
  English, Scientific journal
• Genetic population structure of the invasive signal crayfish Pacifastacus leniusculus in Japan inferred from newly developed microsatellite markers
  Noriko Azuma; Nisikawa Usio; Tomoko Korenaga; Itsuro Koizumi; Noriko Takamura
  Plankton and Benthos Research, 6, 4, 187, 194, 2011, [Peer-reviewed]
  English, Scientific journal
• A case of isolation by distance and short-term temporal stability of population structure in brown trout (Salmo trutta) within the River Dart, southwest England
  Andrew M. Griffiths; Itsuro Koizumi; Dylan Bright; Jamie R. Stevens
  EVOLUTIONARY APPLICATIONS, 2, 4, 537, 554, Nov. 2009, [Peer-reviewed]
  English, Scientific journal
• Guidelines for restoring connectivity around water mills: a population genetic approach to the management of riverine fish
  Joost A. M. Raeymaekers; Dries Raeymaekers; Itsuro Koizumi; Sarah Geldof; Filip A. M. Volckaert
  JOURNAL OF APPLIED ECOLOGY, 46, 3, 562, 571, Jun. 2009, [Peer-reviewed]
  English, Scientific journal
• Evolution, Ecology, and Conservation of Dolly Varden, White-spotted Char, and Bull Trout
  Jason Dunham; Colden Baxter; Kurt Fausch; Wade Fredenberg; Satoshi Kitano; Itsuro Koizumi; Kentaro Morita; Tomoyuki Nakamura; Bruce Rieman; Ksenia Savvaitova; Jack Stanford; Eric Taylor; Shoichiro Yamamoto
  FISHERIES, 33, 11, 537, 550, Nov. 2008, [Peer-reviewed]
  English
• Synchrony in local population dynamics of stream-dwelling Dolly Varden: do genetically similar groups show similar demography?
  Itsuro Koizumi; Shoichiro Yamamoto; Kazuhiro Nomoto; Koji Maekawa
  POPULATION ECOLOGY, 50, 4, 367, 377, Oct. 2008, [Peer-reviewed]
  English, Scientific journal
• Metapopulation structure and persistence of stream-dwelling Dolly Varden in the Shiisorapuchi River, Hokkaido, Japan
  Koizumi, I
  JOURNAL OF FISH BIOLOGY, 69, 226, 227, Dec. 2006, [Peer-reviewed]
  English
• Decomposed pairwise regression analysis of genetic and geographic distances reveals a metapopulation structure of stream-dwelling Dolly Varden charr
  Itsuro Koizumi; Shoichiro Yamamoto; Koji Maekawa
  MOLECULAR ECOLOGY, 15, 11, 3175, 3189, Oct. 2006, [Peer-reviewed]
  English, Scientific journal
• Genetic evaluation of translocation in artificially isolated populations of white-spotted charr (Salvelinus leucomaenis)
  S Yamamoto; K Maekawa; T Tamate; Koizumi, I; K Hasegawa; H Kubota
  FISHERIES RESEARCH, 78, 2-3, 352, 358, May 2006, [Peer-reviewed]
  English, Scientific journal
• Female-biased migration of stream-dwelling Dolly Varden in the Shiisorapuchi River, Hokkaido, Japan
  Koizumi, I; S Yamamoto; K Maekawa
  JOURNAL OF FISH BIOLOGY, 68, 5, 1513, 1529, May 2006, [Peer-reviewed]
  English, Scientific journal
• Introgressive hybridization between Dolly Varden Salvelinus malma and white-spotted charr Salvelinus leucomaenis on Hokkaido Island, Japan
  S Yamamoto; S Kitano; K Maekawa; Koizumi, I; K Morita
  JOURNAL OF FISH BIOLOGY, 68, 68, 85, Mar. 2006, [Peer-reviewed]
  English, Scientific journal
• 河川性サケ科魚類のメタ個体群動態：個人レベルの大規模長期野外調査．
  日本生態学会誌, 2005, [Peer-reviewed]
• Hybridization between endemic Miyabe charr (Salvelinus malma miyabei) and introduced masu salmon (Oncorhynchus masou) in Shikaribetsu Lake.
  Ichthyological Research, 2005, [Peer-reviewed]
• Occurrence of a hybrid between endemic Miyabe charr Salvelinus malma miyabei and introduced masu salmon Onchorhynchus masou masou in Lake Shikaribetsu system, Hokkaido, Japan.
  Koizumi I; Kobayashi H; Maekawa K; Azuma N; Nagase T
  Ichthyological Research, 52, 1, 83, 85, Ichthyological Society of Japan, 2005, [Peer-reviewed]
  English, Scientific journal
• Metapopulation structure of stream-dwelling Dolly Varden charr inferred from patterns of occurrence in the Sorachi River basin, Hokkaido, Japan
  Koizumi, I; K Maekawa
  FRESHWATER BIOLOGY, 49, 8, 973, 981, Aug. 2004, [Peer-reviewed]
  English, Scientific journal
• Genetic differentiation of white-spotted charr (Salvelinus leucomaenis) populations after habitat fragmentation: Spatial-temporal changes in gene frequencies
  S Yamamoto; K Morita; Koizumi, I; K Maekawa
  CONSERVATION GENETICS, 5, 4, 529, 538, Aug. 2004, [Peer-reviewed]
  English, Scientific journal
• Phylogeography of white-spotted charr (Salvelinus leucomaenis) inferred from mitochondrial DNA sequences
  S Yamamoto; K Morita; S Kitano; K Watanabe; Koizumi, I; K Maekawa; K Takamura
  ZOOLOGICAL SCIENCE, 21, 2, 229, 240, Feb. 2004, [Peer-reviewed]
  English, Scientific journal
• Spawning migration of stream-dwelling Dolly Varden in spring-fed tributaries of the Shiisorapuchi River, Japan
  Koizumi, I; K Maekawa
  JOURNAL OF FRESHWATER ECOLOGY, 18, 2, 321, 331, Jun. 2003, [Peer-reviewed]
  English, Scientific journal
• Does the refuge availability influence the spawning behavior of mature male parr in salmonids? A test in the Miyabe charr
  Y Koseki; Koizumi, I; H Kobayashi; K Maekawa
  ENVIRONMENTAL BIOLOGY OF FISHES, 64, 1-3, 87, 93, Jun. 2002, [Peer-reviewed]
  English, Scientific journal

• Elucidating adaptive significance of sleep: relationship between individual sleep pattern and fitness components in brown trout
  古澤千春; 小泉逸郎, 日本生態学会大会講演要旨(Web), 71st, 2024
• Is a lamprey sneaker interrupt a pair spawning or increase female’s reproductive success?
  三枝弘典; 古澤千春; 岸田治; 小泉逸郎, 日本生態学会大会講演要旨(Web), 71st, 2024
• Evaluation of multiple behavioral responses of sika deer to human hunting pressures
  Takashi Ikeda; Itsuro Koizumi, The Journal of Wildlife Management, 88, 1, 19 Sep. 2023
  Abstract
  
  Several ungulate populations have become overabundant worldwide, resulting in ecological and social effects. Wildlife managers must establish effective population control programs to mitigate these negative influences. Hunting is a significant mortality factor for ungulates, which exhibit sensitive behavioral responses toward hunting activities. Wildlife managers need a comprehensive understanding of the ungulate responses to different hunting pressures across seasons. We developed a conceptual method to evaluate multiple behavioral responses to human hunting pressures and applied this to sika deer ( Cervus nippon ) in Hokkaido, Japan, during August and November in 2015. We measured flight behavior, spatial avoidance, and temporal activity shift during non‐hunting and hunting seasons in 4 regions with different hunting pressures. Although we did not observe a clear difference in flight initiation distance among study areas or seasons, sika deer showed significant spatial avoidance during the hunting season in areas with high hunting pressure. Furthermore, sika deer were more active at night in areas with higher hunting pressures, regardless of the season. Collectively, these results suggest that sika deer responded to hunting pressure by changing diel activity to nocturnal throughout the year and avoiding risky areas (i.e., around hunting roads) during hunting season, rather than by increasing flight distance when they encounter humans. Our method can be used for a more efficient population control program for wildlife managers, as it considers the spatiotemporal variations of flexible ungulate behaviors in response to hunting pressures., Wiley
• Sleep ecology in brown trout: when, where and what individuals sleep?
  古澤千春; 小泉逸郎, 日本生態学会大会講演要旨(Web), 70th, 2023
• Fertilization success of sneaking vs. pair-mating Siberian brook lampreys
  三枝弘典; 古澤千春; DAUPAGNE Lea; 岸田治; 小泉逸郎, 日本生態学会大会講演要旨(Web), 70th, 2023
• Behavioral sleep in brown trout
  古澤千春; 小泉逸郎, 日本生態学会大会講演要旨(Web), 69th, 2022
• Behavioral sleep in brown trout
  古澤千春; 小泉逸郎, 日本魚類学会年会講演要旨, 55th (CD-ROM), 2021
• Disentangling the causal relationship between parasite infection and low host condition
  長谷川稜太; 大槻泰彦; 植村洋亮; 古澤千春; 中正大; 小泉逸郎, 日本生態学会大会講演要旨(Web), 68th, 2021
• Do parasite infections cause new parasite infections?: a mark-recapture approach focusing on white-spotted charr and their parasitic copepods Salmincola carpionis
  長谷川稜太; 大槻泰彦; 古澤千春; 植村洋亮; 中正大; 小泉逸郎, 個体群生態学会大会プログラム・講演要旨集(Web), 36th, 2020
• NEWSハイライト：アライグマとフクロウが樹洞を取り合う？
  自然保護, 2014
• 特集「北海道の生物境界」：ブラキストン戦の生物学的意義
  モーリー, 2014, [Invited]
• How useful are molecular tools for the management of alien species?
  KOIZUMI I., Japanese Journal of Ecology, 59, 2, 159, 160, 2009
  The Ecological Society of Japan, Japanese
• Population synchrony in ecological systems
  Akiko Satake; Itsuro Koizumi, POPULATION ECOLOGY, 50, 4, 325, 327, Oct. 2008
  English, Others
• 文化の違いが生み出す研究スタイルの違い : 短時間で高生産、かつリラックスしたフィンランドの研究環境(<連載1>えころじすと@世界(7))
  小泉 逸郎, 日本生態学会誌, 57, 2, 265, 269, 2007
  本稿は私がポスドク中に滞在した北欧フィンランドで感じた日本とフィンランドの研究スタイルの違いについて、文化的側面から考察します。海外の研究において役立つ実践的な話は、えころじすと@世界のバックナンバーでしっかりと紹介されているので、本稿では趣を変えてみました。これまでの寄稿では日本と海外の研究体制の違いが紹介されてきましたが、重要なのはこういった違いが生み出される文化的・歴史的背景を理解し、今後の日本の方向性を考えることだと思います。, 日本生態学会, Japanese
• ミトコンドリアDNA多型に基づくイワナの遺伝的特徴
  山本祥一郎; 森田健太郎; 北野聡; 小泉逸郎; 前川光司; 高村健二, 日本水産学会大会講演要旨集, 2003, 2003

• ヒグマ学への招待 : 自然と文化で考える
  小泉逸郎, 想像を超えたヒグマとサケのつながり―互いに影響する生態と進化、そして生態系全体へ
  北海道大学出版会、67-86, Mar. 2020, 9784832974159, vii, 368p, 図版 [4] p, Japanese, [Contributor]
• 遺伝子・多様性・循環の科学 : 生態学の領域融合へ
  立木佑弥; 堀田淳之介; 小泉逸郎, 代替生活史戦術と個体群動態―行動学的基盤の視点から―、pp. 91-110
  京都大学学術出版会, Feb. 2019, 9784814001903, v, 432p, 図版 [8] p, Japanese, [Contributor]
• Trout and char of the world
  Whiteley AR; Penaluna BE; Taylor EB; Weiss S.; Abadia-Cardoso A.; Gomez-Uchida D.; Koizumi I.; Trotter P., Trout and char: taxonomy, systematics, and phylogeography
  American Fisheries Society, 95-140, 2019, 9781934874547, xxvi, 831 p., English, [Contributor]
• Trout and char of the world
  Muhlfeld CC; Dauwalter DC; D’Angelo VS; Ferguson A.; Glersch J.; Impson D.; Koizumi I.; Kovach RP; Schoeffmann J.; Epifanio J., Global status of freshwater trout and char: conservation challenges in the 21st century
  American Fisheries Society, 717-760, 2019, 9781934874547, xxvi, 831 p., English, [Contributor]
• 系統地理学：DNAで解き明かす生きものの自然史
  小泉逸郎
  2013, [Joint editor]
• サケ科魚類の遺伝的構造 In：「サケ・マスの生態と進化」
  小泉逸郎
  2004, [Contributor]

• 大学院共通授業科目（一般科目）：自然科学・応用科学, 2024年, 修士課程, 大学院共通科目
• 北方生態系の生物多様性基礎論, 2024年, 修士課程, 環境科学院
• 多様性生物学基礎論, 2024年, 修士課程, 環境科学院
• 動物生態学特論Ⅰ, 2024年, 修士課程, 環境科学院
• 大学院共通授業科目（一般科目）：自然科学・応用科学, 2024年, 修士課程, 大学院共通科目
• 動物生態学特論Ⅱ, 2024年, 修士課程, 環境科学院
• 生物圏科学特別講義Ⅱ, 2024年, 修士課程, 環境科学院

• THE ICHTHYOLOGICAL SOCIETY OF JAPAN
• SOCIETY OF EVOLUTIONARY STUDIES, JAPAN
• THE ECOLOGICAL SOCIETY OF JAPAN

• Developing wildlife-friendly farming via elucidation of small-clawed otter ecology: a case of an Indonesian paddyscape
  Grants-in-Aid for Scientific Research Fund for the Promotion of Joint International Research (Fostering Joint International Research (B))
  07 Oct. 2022 - 31 Mar. 2027
  西川 潮; 小泉 逸郎; 富田 幹次; 田中 勝也
  Japan Society for the Promotion of Science, Fund for the Promotion of Joint International Research (Fostering Joint International Research (B)), Kanazawa University, 22KK0172
• Understanding the dynamics of animal communities and the maintenance of biodiversity in interactions among spring-fed and runoff streams
  Grants-in-Aid for Scientific Research
  01 Apr. 2023 - 31 Mar. 2026
  境 優; 小泉 逸郎; 福島 慶太郎; 岩崎 健太; 根岸 淳二郎
  湧水支川・非湧水河川の組み合わせのなかで、(1)「避難場所」として魚類が湧水支川に移入したとき、捕食等により無脊椎動物群集の単純化やバイオマスの減少が起こるかどうか、(2)「産卵場所」として魚類が湧水支川に移入したとき、卵や死体が無脊椎動物等に消費されるかどうか、(3)湧水支川への連結性が高いとき、魚類の個体群の存続性や種多様性が高いかどうかを検証するための調査を始動させた。
  (1)では、魚類の避難行動が卓越すると考えられる夏・冬期を含めて底生無脊椎動物群集の構造・バイオマスの季節変化を定量的に追跡するための調査を開始した。(2)では、秋の産卵期を含めて上記野外調査と並行して炭素・窒素安定同位体比を測定するための試料採集を進めた。(3)では、関連するデータの収集と解析に着手した。これらの調査で収集された試料およびデータの処理を進めることによりそれぞれの仮説を検証するためのデータセットを得ることができる。湧水・非湧水河川で対照的に異なる物理・化学環境を把握するために、流量・温度・水質等についても観測・分析を進めている。以上の野外調査では、湧水・非湧水環境の相互作用に関わる一般性の高い知見を得るために、複数の調査地を対象として上述の調査項目について相補的に調査・観測を進めている。研究開始年度であるため、試料・データの収集が主要な研究目的ではあったものの、本研究に関連した論文発表や講演発表も本年度内に実施することができた。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), National Institute for Environmental Studies, 23K26934
• Metapopulation genomics: integrating population dynamics and genomic using long-term data
  Grants-in-Aid for Scientific Research
  01 Apr. 2021 - 31 Mar. 2025
  小泉 逸郎
  本研究では25年間にわたり50地点の局所個体群で得られた生態データと遺伝データを統合し、野外における小進化や、生態ー進化フィードバックの実態を解明することを目的としている。河川性サケ科魚類オショロコマの長期モニタリングが行われている15－25個体群の動態を解析したところ、温暖化の直接的な影響と競争種を介した間接的な影響が示唆された。過去25年間の温度上昇にともない、より高温に適した競争種であるアメマスが増加し、これがオショロコマ個体数に負の影響を与えていることが示唆された。一方、アメマスが少ない湧水河川においては温暖化はむしろ個体数に正の効果をもたらしていた。また集団の遺伝子頻度は時空間的に大きな変異が見られ、特に小集団においては5年ほどでも大きな時間的分化が認められた。一方で、メタ個体群スケールでは20年間でも安定性が高く、ポートフォリオ効果が示唆された。また、滝などの物理的障壁の有無や湧水と非湧水といった河川環境において、適応的な表現型変異が認められた。そこで表現型が大きく異なる10個体群200個体でゲノムを網羅的に調べたが、残留性や産卵時期など注目していた形質に関する候補遺伝子は得られなかった。中立遺伝子では集団間の分化が認められたにも関わらず候補遺伝子が検出されないのは小、集団に起因する遺伝的浮動の効果が大きいためかもしれない。今後、より極端な形質をもつ個体を数多く解析する必要がある。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 23K21335
• Metapopulation genomics: integrating population dynamics and genomic using long-term data
  Grants-in-Aid for Scientific Research
  01 Apr. 2021 - 31 Mar. 2025
  小泉 逸郎
  本研究では、25年間50個体群50,000個体というかつてないスケールで野外個体群の集団ゲノム解析を実施し、個体群動態論と集団ゲノム学の統合を試みる。これまで申請者は北海道空知川上流の河川性サケ科魚類においてメタ個体群動態を実証し、繁殖時期、発生スピード、回遊性といった適応形質が局所個体群間で分化していることを明らかにしてきた。さらに、長期野外調査のなかで、温暖化や生息地の分断化、台風による大規模攪乱など、進化的変化が起こりうる複数のイベントを目撃してきた。これは理論が先行している生態－進化動態（Eco-evolutionary dynamics）を検証できる貴重な“自然の実験系”を提供している。
  当該年度は14-24年間の継続調査を行ってきた20個体群において個体群センサスを実施しDNAサンプルを採集した。気象データ、環境データと局所・メタ個体群動態の関係性を検討した。現実の空間構造を模したメタ個体群モデルを構築し、現在、遺伝子の動態も取り入れるように改良中である。また、約200個体のゲノムデータを解析して回遊性や繁殖時期などといった生活史形質に関連する遺伝領域を調べて、大規模解析にむけた遺伝子パネルの作成を進めている。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 21H02555
• Genetic basis of adaptive traits in stream salmonids: toward a large scale population genomics
  Grants-in-Aid for Scientific Research
  01 Apr. 2018 - 31 Mar. 2021
  Koizumi Itsuro
  This research established an effective population genomic framework using a model system where long-term ecological data has been accumulated in 50 local populations over the last two decades. I examined large dataset and selected 78 individuals from populations above vs. below physical barriers and with early vs. late reproductive timing. Low coverage whole genome sequence suggested a few candidate genes for affecting residency vs. migratory, as well as for reproductive timing. This enables a cost-effective large scale population genomic analysis by reduced-representation sequencing.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 18K06405
• Evolution of cellular bones in fishes: a phylogenetic comparative approach
  Grants-in-Aid for Scientific Research
  01 Apr. 2016 - 31 Mar. 2018
  koizumi Itsuro; SATO Mari
  Osteocyte or cellular bone is crucial for the survival of tetrapods, affecting metabolisms and immune systems. Surprisingly, however, a considerable proportion of fishes do not possess cellular bones. This study investigates the patterns of gains and losses of cellular bones to infer the functional roles of Osteocyte. Occurrence of cellular (or acellular) bones in more than 500 fishes revealed that the ancestral fishes had cellular bones and some lineages have lost independently. Saltwater fishes tented to have acellular bones, although the pattern was weak. So far, no significant correlate has been found, such as habitat and life history types. Future research should compare bone structures among fishes, amphibians, reptiles and birds to clarify the evolution of bone functions.
  Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, 16K14794
• Understanding genetics and value of wild salmon run
  Grants-in-Aid for Scientific Research
  01 Apr. 2014 - 31 Mar. 2017
  Araki Hitoshi; SATO Shunpei; KOIZUMI Itsuro; O' MALLEY Kathleen
  Salmon is very popular in Japan. While majority of fish in a market is hatchery-reared, ecology of wild salmon is largely unknown. In this study, we investigated genetic basis of wild chum salmon, which returned to their mother rivers at different timings. We found that in some rivers in Japan, early-run population and late-run population are clearly distinct both in timing and the population genetic structure. In addition, the population genetic structure in a river where hatchery fish have been imported was similar to that in its source, despite the fact that the river holds large amount of wild population at this point of time. These results suggest that salmon populations with different run timings are genetically differentiated even within a same river, and that they should be managed differently.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 26292102
• Genetic basis and evolutionary origin of migratory polymorphisms in salmonids
  Grants-in-Aid for Scientific Research
  01 Apr. 2014 - 31 Mar. 2016
  Koizumi Itsuro
  This study examined the genetic basis and evolutionary origin of migratory dimorphisms in salmonids (i.e., sea-run anadromous vs. stream resident), which is among the most remarkable example of phenotypic polymorphism. More than 80 million DNA sequences were determined in 384 individuals of masu salmon and white-spotted charr. Genome-wide association analysis revealed 1-4 candidate genes related to migratory dimorphisms, but the effects of these loci were small. Compared to a draft genome of rainbow trout, candidate loci were different among the 3 species of partially migratory salmonids. This study indicates that salmonids have accomplished similar life history polymorphisms with different genetic mechanisms.
  Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Hokkaido University, 26840136
• Ranking the priority for invasive crayfish control based on phenotypic and genetic characteristics
  Grants-in-Aid for Scientific Research
  01 Apr. 2012 - 31 Mar. 2015
  NISIKAWA Usio; KOIZUMI Itsuro
  We studied behavioural, morphological and genetic differences and factors that explain such phenotypic and genetic variations among invasive signal crayfish populations in Japan. A previous microsatellite DNA analysis has indicated that invasive signal crayfish populations in Japan can be classified into three groups (Lake Mayu in Hokkaido Shiga Prefecture, Akashina in Nagano Shiga Prefecture, Tankai in Shiga Prefecture), and newly discovered invasive populations originate from Lake Masyu. Even among invasive populations that originate from Lake Masyu, aggressiveness differed according to the year of invasion or crayfish abundance. From these results we conclude that newly invaded populations that originate from Lake Masyu should be prioritized for crayfish control or eradication.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), 24510324
• Evaluation of population units considering population dynamics, genetic structure, and life history variation
  Grants-in-Aid for Scientific Research
  2011 - 2013
  KOIZUMI Itsuro
  This study examined "population units" with long-term data on salmonid fish, considering population dynamics, genetic structure, and life history variation. Microsatellite DNA analysis indicated genetic homogeneity for stream groups within 5-10km. However, demographic independency was suggested even among genetically non-divergent groups. In addition, despite significant variations in life history traits among streams, no geographic cluster was observed. This study suggested that population units can vary depending on the entities we focus.
  Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Hokkaido University, 23770013
• Developing management methods for invasive crayfish based on population genetic analysis
  Grants-in-Aid for Scientific Research
  2008 - 2010
  NISIKAWA Usio; KOIZUMI Itsuro; AZUMA Noriko
  In recent decades, the invasive signal crayfish (Pacifastacus leniusculus) has been rapidly expanding its distribution range in Japan. Based on 16S mtDNA analysis, we clarified its origin, genetic variability and dispersal in Japan. We found that the invasive signal crayfish : 1) have undergone genetic admixture following transportation from multiple locations in the native range, 2) have high genetic variability and 3) likely increasing their distribution range through unintended human-mediated introductions.
  We subsequently developed five polymorphic microsatellite markers for signal crayfish, after which the population structure and genetic variability were analysed. Consequently, 5) the invasive signal crayfish populations were grouped into three clusters (Hokkaido, Nagano and Shiga) 6) the newly found population in Tone River drainage appeared to have originated from Hokkaido and 7) the populations with low genetic variability in 16S mtDNA have high genetic variability in microsatellite DNA. These microsatellite markers are useful in identifying dispersal pathways and defining eradication units for the invasive signal crayfish.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), National Institute for Environmental Studies, 20510219
• メタ個体群内における生活史形質の分化:河川性サケ科魚類を用いた実証研究
  科学研究費助成事業
  2007 - 2009
  小泉 逸郎
  平成22年度はDNA実験、データ解析および論文執筆を行った。なお、平成22年10月16日から北海道大学の特任助教に採用になり、特別研究員の実質的な研究は最初の半年に加え就職後の空き時間に行った。
  多くの生物種は自然選択により環境に適応した生活史形質を持っていると考えられている。本研究では、河川性サケ科魚類の繁殖時期に着目して30個体群にもおよぶ大規模な野外調査を行い、自然界での局所適応を調べた。その結果、水温が全く異なり産卵時期が異なると予測される河川においてさえ適応的な形質を持っていないことが示された。マイクロサテライトDNA解析の結果、河川間で遺伝的交流が存在し、それが最適値の実現を妨げていることが示唆された。一方で、滝によって遺伝子流動が阻害されている個体群においては産卵時期が一ヶ月も早く、局所適応していることが示された。遺伝子流動が局所適応を阻害することは多くの理論研究で示されているが、実証研究は数少ない。特に、多数の個体群を網羅的に調べた研究は皆無であり、本研究はこの進化生態学的に重要な仮設を強く立証した世界初の研究となる。現在、投稿間近であり、進化生態学の一流誌Evolutionに投稿予定である。現在、この研究をさらに発展させた遺伝的浮動の影響を加えた解析を行っている。
  日本学術振興会, 特別研究員奨励費, 北海道大学, 07J04509