Researcher Database

Hitoshi Araki
Research Faculty of Agriculture Fundamental AgriScience Research Agrobiology and Bioresources

Researcher Profile and Settings


  • Research Faculty of Agriculture Fundamental AgriScience Research Agrobiology and Bioresources

Job Title

  • Professor

J-Global ID

Research Interests

  • fish   gene   anthoropogenic changes   Adaptation   Evolution   

Research Areas

  • Life sciences / Biodiversity and systematics
  • Life sciences / Ecology and environmental science
  • Life sciences / Evolutionary biology

Academic & Professional Experience

  • 2013/04 - Today Hokkaido University Research Faculty of Agriculture, Devision of Environmental Resources Professor
  • 2008/01 - 2013/03 Eawag, Swiss Federal Institute of Aquatic Science and Technology Department of Fish Ecology and Evolution Group leader
  • 2004/07 - 2007/12 Oregon State University Department of Zoology Postdoctoral research associate
  • 2001/04 - 2004/06 University of Chicago Department of Ecology and Evolution Postdoctoral fellow


  • 1997/04 - 2001/03  Kyushu University  Graduate School of Medical Science
  • 1995/04 - 1997/03  Kyushu University  Graduate School of Science
  • 1991/04 - 1995/03  Kyushu University  Faculty of Science  Department of Biology

Research Activities

Published Papers

  • Tetsu Yatsuyanagi, Ryotaro Ishida, Masayuki K. Sakata, Takashi Kanbe, Hiroki Mizumoto, Yumi Kobayashi, Shoko Kamada, Satoko Namba, Hisaya Nii, Toshifumi Minamoto, Hitoshi Araki
    Environmental DNA 2 (2) 130 - 139 2637-4943 2020/04 [Refereed][Not invited]
  • Miyamoto Kouta, Araki Hitoshi
    HYDROBIOLOGIA 840 (1) 103 - 112 0018-8158 2019/09 [Refereed][Not invited]
  • Morita Kentaro, Sahashi Genki, Miya Masaki, Kamada Shouko, Kanbe Takashi, Araki Hitoshi
    HYDROBIOLOGIA 840 (1) 207 - 213 0018-8158 2019/09 [Refereed][Not invited]
  • Yuki Minegishi, Marty Kwok-Shing Wong, Takashi Kanbe, Hitoshi Araki, Tomomi Kashiwabara, Minoru Ijichi, Kazuhiro Kogure, Susumu Hyodo
    PLOS ONE 14 (9) e0222052  1932-6203 2019/09 [Refereed][Not invited]
    To understand the ecology of juvenile chum salmon during early marine life after their downstream migration, we developed a quantitative PCR-based environmental DNA (eDNA) method specific for chum salmon and investigated the spatiotemporal distribution of eDNA in Otsuchi Bay, Iwate, Japan. Indoor aquarium experiments demonstrated the following characteristics of chum salmon eDNA: (1) the eDNA shedding and degradation were time- and water temperature-dependent and the bacterial abundance could contribute to the eDNA decay, (2) fecal discharge may not be the main source of eDNA, and (3) a strong positive Pearson correlation was found between the number of juveniles and the eDNA amounts. As we discovered strong PCR inhibition from the seawater samples of the bay, we optimized the eDNA assay protocol for natural seawater samples by adding a further purification step and modification of PCR mixture. The intensive eDNA analysis in the spring of 2017 and 2018 indicated that juvenile chum salmon initially inhabited in shallow waters in the shorefront area and then spread over the bay from January to June. The eDNA data also pointed out that outmigration of juvenile chum salmon to open ocean temporarily suspended in April, possibly being associated with the dynamics of the Oyashio Current as suggested by a previous observation. The eDNA method thus enables us large-scale and comprehensive surveys without affecting populations to understand the spatiotemporal dynamics of juvenile chum salmon.
  • 気候変動下における日本系サケの持続可能な保全管理のあり方とその研究課題
    帰山雅秀, 荒木仁志, 宮下和士, 永田光博, 佐々木義隆, 浦和茂彦
    海洋と生物 40 (5) 459 - 466 2018/10 [Not refereed][Not invited]
  • 環境変動下におけるサケの持続可能な資源管理:国際サーモン年に向けたプロローグ
    浦和茂彦, 荒木仁志, 宮下和士, 永田光博, 佐々木義隆, 帰山雅秀
    海洋と生物 40 (4) 315 - 318 2018/08 [Not refereed][Not invited]
  • Castellani M, Heino M, Gilbey J, Araki H, Svåsand T, Glover KA
    Evolutionary applications 11 (6) 1010 - 1025 1752-4571 2018/07 [Refereed][Not invited]
  • Mizumoto Hiroki, Urabe Hirokazu, Kanbe Takashi, Fukushima Michio, Araki Hitoshi
    LIMNOLOGY 19 (2) 219 - 227 1439-8621 2018/04 [Refereed][Not invited]
  • Miyamoto Kouta, Squires Theodore E, Araki Hitoshi
    MARINE AND FRESHWATER RESEARCH 69 (3) 446 - 454 1323-1650 2018 [Refereed][Not invited]
  • Urawa Shigehiko, Araki Hitoshi, Miyashita Kazushi, Nagata Mitsuhiro, Sasaki Yoshitaka, Kaeriyama Masahide
    NIPPON SUISAN GAKKAISHI 84 (5) 921  0021-5392 2018 [Refereed][Not invited]
  • Araki Hitoshi, Kanbe Takashi, Mizumoto Hiroki, Kamada Shoko, Sato Shunpei
    NIPPON SUISAN GAKKAISHI 84 (5) 936  0021-5392 2018 [Refereed][Not invited]
  • Kevin A. Glover, Monica F. Solberg, Phil McGinnity, Kjetil Hindar, Eric Verspoor, Mark W. Coulson, Michael M. Hansen, Hitoshi Araki, Oystein Skaala, Terje Svasand
    FISH AND FISHERIES 18 (5) 890 - 927 1467-2960 2017/09 [Refereed][Not invited]
    Atlantic salmon (Salmo salar) is one of the best researched fishes, and its aquaculture plays a global role in the blue revolution. However, since the 1970s, tens of millions of farmed salmon have escaped into the wild. We review current knowledge of genetic interactions and identify the unanswered questions. Native salmon populations are typically genetically distinct from each other and potentially locally adapted. Farmed salmon represent a limited number of wild source populations that have been exposed to 12 generations of domestication. Consequently, farmed and wild salmon differ in many traits including molecular-genetic polymorphisms, growth, morphology, life history, behaviour, physiology and gene transcription. Field experiments have demonstrated that the offspring of farmed salmon display lower lifetime fitness in the wild than wild salmon and that following introgression, there is a reduced production of genetically wild salmon and, potentially, of total salmon production. It is a formidable task to estimate introgression of farmed salmon in wild populations where they are not exotic. New methods have revealed introgression in half of similar to 150 Norwegian populations, with point estimates as high as 47%, and an unweighted average of 6.4% across 109 populations. Outside Norway, introgression remains unquantified, and in all regions, biological changes and the mechanisms driving population-specific impacts remain poorly documented. Nevertheless, existing knowledge shows that the long-term consequences of introgression is expected to lead to changes in life-history traits, reduced population productivity and decreased resilience to future challenges. Only a major reduction in the number of escapees and/or sterility of farmed salmon can eliminate further impacts.
  • Kouta Miyamoto, Hitoshi Araki
    FISHERIES SCIENCE 83 (2) 245 - 250 0919-9268 2017/03 [Refereed][Not invited]
    Predation after release is one of the major concerns of hatchery fish propagation. However, size-specific interaction between predator and prey on the survival of hatchery-released salmonid fish is largely unknown. To understand the size-selective predation risk, 24-h predation experiments were conducted on masu salmon Oncorhynchus masou in tanks. Four ranges of fork length (FL) were examined for masu salmon as a prey, in combination with three ranges of FL for white-spotted charr Salvelinus leucomaenis as a predator. The results show that not only predator and prey sizes, but also interaction between prey size and predator size, strongly affected the survival rate of masu salmon. Predation on masu salmon with the FL exceeding 40% of the FL of white-spotted charr was rare in the experiment. A logistic regression suggests that 37% relative FL of masu salmon to white-spotted charr results in the 50% survival of masu salmon. Our results suggest that adjusting relative size of hatchery fish to the size of local fish predators at the time of hatchery release will have a significant impact on the survival of hatchery fish in the wild. From this perspective, site-specific, adaptive management might be important to improve the effectiveness of hatchery fish propagation.
  • Makiko Mimura, Tetsukazu Yahara, Daniel P. Faith, Ella Vazquez-Dominguez, Robert I. Colautti, Hitoshi Araki, Firouzeh Javadi, Juan Nunez-Farfan, Akira S. Mori, Shiliang Zhou, Peter M. Hollingsworth, Linda E. Neaves, Yuya Fukano, Gideon F. Smith, Yo-Ichiro Sato, Hidenori Tachida, Andrew P. Hendry
    EVOLUTIONARY APPLICATIONS 10 (2) 121 - 139 1752-4571 2017/02 [Refereed][Not invited]
    Intraspecific variation is a major component of biodiversity, yet it has received relatively little attention from governmental and nongovernmental organizations, especially with regard to conservation plans and the management of wild species. This omission is ill-advised because phenotypic and genetic variations within and among populations can have dramatic effects on ecological and evolutionary processes, including responses to environmental change, the maintenance of species diversity, and ecological stability and resilience. At the same time, environmental changes associated with many human activities, such as land use and climate change, have dramatic and often negative impacts on intraspecific variation. We argue for the need for local, regional, and global programs to monitor intraspecific genetic variation. We suggest that such monitoring should include two main strategies: (i) intensive monitoring of multiple types of genetic variation in selected species and (ii) broad-brush modeling for representative species for predicting changes in variation as a function of changes in population size and range extent. Overall, we call for collaborative efforts to initiate the urgently needed monitoring of intraspecific variation.
  • Martin M. Turcotte, Hitoshi Araki, Daniel S. Karp, Katja Poveda, Susan R. Whitehead
    PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES 372 (1712) 0962-8436 2017/01 [Refereed][Not invited]
    Agriculture is a dominant evolutionary force that drives the evolution of both domesticated and wild species. However, the various mechanisms of agriculture-induced evolution and their socio-ecological consequences are not often synthetically discussed. Here, we explore how agricultural practices and evolutionary changes in domesticated species cause evolution in wild species. We do so by examining three processes by which agriculture drives evolution. First, differences in the traits of domesticated species, compared with their wild ancestors, alter the selective environment and create opportunities for wild species to specialize. Second, selection caused by agricultural practices, including both those meant to maximize productivity and those meant to control pest species, can lead to pest adaptation. Third, agriculture can cause nonselective changes in patterns of gene flow in wild species. We review evidence for these processes and then discuss their ecological and sociological impacts. We finish by identifying important knowledge gaps and future directions related to the eco-evolutionary impacts of agriculture including their extent, how to prevent the detrimental evolution of wild species, and finally, how to use evolution to minimize the ecological impacts of agriculture. This article is part of the themed issue 'Human influences on evolution, and the ecological and societal consequences'.
  • Satoshi Yamamoto, Reiji Masuda, Yukuto Sato, Tetsuya Sado, Hitoshi Araki, Michio Kondoh, Toshifumi Minamoto, Masaki Miya
    SCIENTIFIC REPORTS 7 40368  2045-2322 2017/01 [Refereed][Not invited]
    Environmental DNA (eDNA) metabarcoding has emerged as a potentially powerful tool to assess aquatic community structures. However, the method has hitherto lacked field tests that evaluate its effectiveness and practical properties as a biodiversity monitoring tool. Here, we evaluated the ability of eDNA metabarcoding to reveal fish community structures in species-rich coastal waters. High-performance fish-universal primers and systematic spatial water sampling at 47 stations covering similar to 11 km(2) revealed the fish community structure at a species resolution. The eDNA metabarcoding based on a 6-h collection of water samples detected 128 fish species, of which 62.5% (40 species) were also observed by underwater visual censuses conducted over a 14-year period. This method also detected other local fishes (>= 23 species) that were not observed by the visual censuses. These eDNA metabarcoding features will enhance marine ecosystem-related research, and the method will potentially become a standard tool for surveying fish communities.
  • Yamamoto S, Minami K, Fukaya K, Takahashi K, Sawada H, Murakami H, Tsuji S, Hashizume H, Kubonaga S, Horiuchi T, Hongo M, Nishida J, Okugawa Y, Fujiwara A, Fukuda M, Hidaka S, Suzuki KW, Miya M, Araki H, Yamanaka H, Maruyama A, Miyashita K, Masuda R, Minamoto T, Kondoh M
    PloS one 11 (4) e0153291  1932-6203 2016/04/04 [Refereed][Not invited]
  • Satoshi Yamamoto, Kenji Minami, Keiichi Fukaya, Kohji Takahashi, Hideki Sawada, Hiroaki Murakami, Satsuki Tsuji, Hiroki Hashizume, Shou Kubonaga, Tomoya Horiuchi, Masamichi Hongo, Jo Nishida, Yuta Okugawa, Ayaka Fujiwara, Miho Fukuda, Shunsuke Hidaka, Keita W. Suzuki, Masaki Miya, Hitoshi Araki, Hiroki Yamanaka, Atsushi Maruyama, Kazushi Miyashita, Reiji Masuda, Toshifumi Minamoto, Michio Kondoh
    PLOS ONE 11 (3) 1932-6203 2016/03 [Refereed][Not invited]
    Recent studies in streams and ponds have demonstrated that the distribution and biomass of aquatic organisms can be estimated by detection and quantification of environmental DNA (eDNA). In more open systems such as seas, it is not evident whether eDNA can represent the distribution and biomass of aquatic organisms because various environmental factors (e.g., water flow) are expected to affect eDNA distribution and concentration. To test the relationships between the distribution of fish and eDNA, we conducted a grid survey in Maizuru Bay, Sea of Japan, and sampled surface and bottom waters while monitoring biomass of the Japanese jack mackerel (Trachurus japonicus) using echo sounder technology. A linear model showed a high R-2 value (0.665) without outlier data points, and the association between estimated eDNA concentrations from the surface water samples and echo intensity was significantly positive, suggesting that the estimated spatial variation in eDNA concentration can reflect the local biomass of the jack mackerel. We also found that a best-fit model included echo intensity obtained within 10-150 m from water sampling sites, indicating that the estimated eDNA concentration most likely reflects fish biomass within 150 m in the bay. Although eDNA from a wholesale fish market partially affected eDNA concentration, we conclude that eDNA generally provides a 'snapshot' of fish distribution and biomass in a large area. Further studies in which dynamics of eDNA under field conditions (e.g., patterns of release, degradation, and diffusion of eDNA) are taken into account will provide a better estimate of fish distribution and biomass based on eDNA.
  • Tomotaka Matsumoto, Katsuhiko Mineta, Naoki Osada, Hitoshi Araki
    FRONTIERS IN GENETICS 6 (NOV) 1664-8021 2015/11 [Refereed][Not invited]
    Recent studies suggest the existence of a stochasticity in gene expression (SGE) in many organisms, and its non-negligible effect on their phenotype and fitness. To date, however, how SGE affects the key parameters of population genetics are not well understood. SGE can increase the phenotypic variation and act as a load for individuals, if they are at the adaptive optimum in a stable environment. On the other hand, part of the phenotypic variation caused by SGE might become advantageous if individuals at the adaptive optimum become genetically less adaptive, for example due to an environmental change. Furthermore, SGE of unimportant genes might have little or no fitness consequences. Thus, SGE can be advantageous, disadvantageous, or selectively neutral depending on its context. In addition, there might be a genetic basis that regulates magnitude of SGE, which is often referred to as "modifier genes," but little is known about the conditions under which such an SGE-modifier gene evolves. In the present study, we conducted individual-based computer simulations to examine these conditions in a diploid model. In the simulations, we considered a single locus that determines organismal fitness for simplicity, and that SGE on the locus creates fitness variation in a stochastic manner. We also considered another locus that modifies the magnitude of SGE. Our results suggested that SGE was always deleterious in stable environments and increased the fixation probability of deleterious mutations in this model. Even under frequently changing environmental conditions, only very strong natural selection made SGE adaptive. These results suggest that the evolution of SGE-modifier genes requires strict balance among the strength of natural selection, magnitude of SGE, and frequency of environmental changes. However, the degree of dominance affected the condition under which SGE becomes advantageous, indicating a better opportunity for the evolution of SGE in different genetic models.
  • Marco Castellani, Mikko Heino, John Gilbey, Hitoshi Araki, Terje Svasand, Kevin A. Glover
    PLOS ONE 10 (9) 1932-6203 2015/09 [Refereed][Not invited]
    Ecology and genetics can influence the fate of individuals and populations in multiple ways. However, to date, few studies consider them when modelling the evolutionary trajectory of populations faced with admixture with non-local populations. For the Atlantic salmon, a model incorporating these elements is urgently needed because many populations are challenged with gene-flow from non-local and domesticated conspecifics. We developed an Individual-Based Salmon Eco-genetic Model (IBSEM) to simulate the demographic and population genetic change of an Atlantic salmon population through its entire life-cycle. Processes such as growth, mortality, and maturation are simulated through stochastic procedures, which take into account environmental variables as well as the genotype of the individuals. IBSEM is based upon detailed empirical data from salmon biology, and parameterized to reproduce the environmental conditions and the characteristics of a wild population inhabiting a Norwegian river. Simulations demonstrated that the model consistently and reliably reproduces the characteristics of the population. Moreover, in absence of farmed escapees, the modelled populations reach an evolutionary equilibrium that is similar to our definition of a 'wild' genotype. We assessed the sensitivity of the model in the face of assumptions made on the fitness differences between farm and wild salmon, and evaluated the role of straying as a buffering mechanism against the intrusion of farm genes into wild populations. These results demonstrate that IBSEM is able to capture the evolutionary forces shaping the life history of wild salmon and is therefore able to model the response of populations under environmental and genetic stressors.
  • M. Miya, Y. Sato, T. Fukunaga, T. Sado, J. Y. Poulsen, K. Sato, T. Minamoto, S. Yamamoto, H. Yamanaka, H. Araki, M. Kondoh, W. Iwasaki
    ROYAL SOCIETY OPEN SCIENCE 2 (7) 150088  2054-5703 2015/07 [Refereed][Not invited]
    We developed a set of universal PCR primers (MiFish-U/E) for metabarcoding environmental DNA (eDNA) from fishes. Primers were designed using aligned whole mitochondrial genome (mitogenome) sequences from 880 species, supplemented by partial mitogenome sequences from 160 elasmobranchs (sharks and rays). The primers target a hypervariable region of the 12S rRNA gene (163-185 bp), which contains sufficient information to identify fishes to taxonomic family, genus and species except for some closely related congeners. To test versatility of the primers across a diverse range of fishes, we sampled eDNA from four tanks in the Okinawa Churaumi Aquarium with known species compositions, prepared dual-indexed libraries and performed paired-end sequencing of the region using high-throughput next-generation sequencing technologies. Out of the 180 marine fish species contained in the four tanks with reference sequences in a custom database, we detected 168 species (93.3%) distributed across 59 families and 123 genera. These fishes are not only taxonomically diverse, ranging from sharks and rays to higher teleosts, but are also greatly varied in their ecology, including both pelagic and benthic species living in shallow coastal to deep waters. We also sampled natural seawaters around coral reefs near the aquarium and detected 93 fish species using this approach. Of the 93 species, 64 were not detected in the four aquarium tanks, rendering the total number of species detected to 232 (from 70 families and 152 genera). The metabarcoding approach presented here is non-invasive, more efficient, more cost-effective and more sensitive than the traditional survey methods. It has the potential to serve as an alternative (or complementary) tool for biodiversity monitoring that revolutionizes natural resource management and ecological studies of fish communities on larger spatial and temporal scales.
  • M. Miya, Y. Sato, T. Fukunaga, T. Sado, J. Y. Poulsen, K. Sato, T. Minamoto, S. Yamamoto, H. Yamanaka, H. Araki, M. Kondoh, W. Iwasaki
    ROYAL SOCIETY OPEN SCIENCE 2 (7) 0831-2796 2015/07 [Refereed][Not invited]
    We developed a set of universal PCR primers (MiFish-U/E) for metabarcoding environmental DNA (eDNA) from fishes. Primers were designed using aligned whole mitochondrial genome (mitogenome) sequences from 880 species, supplemented by partial mitogenome sequences from 160 elasmobranchs (sharks and rays). The primers target a hypervariable region of the 12S rRNA gene (163-185 bp), which contains sufficient information to identify fishes to taxonomic family, genus and species except for some closely related congeners. To test versatility of the primers across a diverse range of fishes, we sampled eDNA from four tanks in the Okinawa Churaumi Aquarium with known species compositions, prepared dual-indexed libraries and performed paired-end sequencing of the region using high-throughput next-generation sequencing technologies. Out of the 180 marine fish species contained in the four tanks with reference sequences in a custom database, we detected 168 species (93.3%) distributed across 59 families and 123 genera. These fishes are not only taxonomically diverse, ranging from sharks and rays to higher teleosts, but are also greatly varied in their ecology, including both pelagic and benthic species living in shallow coastal to deep waters. We also sampled natural seawaters around coral reefs near the aquarium and detected 93 fish species using this approach. Of the 93 species, 64 were not detected in the four aquarium tanks, rendering the total number of species detected to 232 (from 70 families and 152 genera). The metabarcoding approach presented here is non-invasive, more efficient, more cost-effective and more sensitive than the traditional survey methods. It has the potential to serve as an alternative (or complementary) tool for biodiversity monitoring that revolutionizes natural resource management and ecological studies of fish communities on larger spatial and temporal scales.
  • Katsuhiko Mineta, Tomotaka Matsumoto, Naoki Osada, Hitoshi Araki
    GENE 562 (1) 16 - 21 0378-1119 2015/05 [Refereed][Not invited]
    The role of stochasticity in evolutionary genetics has long been debated. To date, however, the potential roles of non-genetic traits in evolutionary processes have been largely neglected. In molecular biology, growing evidence suggests that stochasticity in gene expression (SGE) is common and that SGE has major impacts on phenotypes and fitness. Here, we provide a general overview of the potential effects of SGE on population genetic parameters, arguing that SGE can indeed have a profound effect on evolutionary processes. Our analyses suggest that SGE potentially alters the fate of mutations by influencing effective population size and fixation probability. In addition, a genetic control of SGE magnitude could evolve under certain conditions, if the fitness of the less-fit individual increases due to SGE and environmental fluctuation. Although empirical evidence for our arguments is yet to come, methodological developments for precisely measuring SGE in living organisms will further advance our understanding of SGE-driven evolution. (C) 2015 Elsevier B.V. All rights reserved.
  • Long Wang, Weina Si, Yongfang Yao, Dacheng Tian, Hitoshi Araki, Sihai Yang
    PLOS ONE 7 (12) 1932-6203 2012/12 [Refereed][Not invited]
    Pseudogenes (Psi s), including processed and non-processed Psi s, are ubiquitous genetic elements derived from originally functional genes in all studied genomes within the three kingdoms of life. However, systematic surveys of non-processed Psi s utilizing genomic information from multiple samples within a species are still rare. Here a systematic comparative analysis was conducted of Psi s within 80 fully re-sequenced Arabidopsis thaliana accessions, and 7546 genes, representing similar to 28% of the genomic annotated open reading frames (ORFs), were found with disruptive mutations in at least one accession. The distribution of these Psi s on chromosomes showed a significantly negative correlation between Psi s/ORFs and their local gene densities, suggesting a higher proportion of Psi s in gene desert regions, e. g. near centromeres. On the other hand, compared with the non-Psi loci, even the intact coding sequences (CDSs) in the Psi loci were found to have shorter CDS length, fewer exon number and lower GC content. In addition, a significant functional bias against the null hypothesis was detected in the Psi s mainly involved in responses to environmental stimuli and biotic stress as reported, suggesting that they are likely important for adaptive evolution to rapidly changing environments by pseudogenization to accumulate successive mutations.
  • Akiko Satake, Hitoshi Araki
    THEORETICAL ECOLOGY 5 (2) 283 - 296 1874-1738 2012/05 [Refereed][Not invited]
    Releasing captive-bred fish into natural environments (stocking) is common in fisheries worldwide. Although stocking is believed to have a positive effect on fish abundance over the short term, little is known about the long-term consequences of recurrent stocking and its influence on natural populations. In fact, there are growing concerns that genetically maladapted captive-bred fish can eventually reduce the abundance of natural population. In this study, we develop a simple model to quantitatively investigate the condition under which recurrent stocking has long-term effects on the natural population. Using a population dynamics model that takes into account a density-dependent recruitment, a gene responsible for the fitness difference between wild and captive-bred fish, and hybridization between them, we show that there is little or no contribution of recurrent stocking to the stock enhancement without a replacement of the wild gene pool by the captive-bred gene pool. The model further predicted that stocking of an intermediate level causes a reduction, rather than enhancement, of population size over the long term. The population decline due to stocking was attributed to the fitness disadvantage of captive-bred fish and strong overcompensation at recruitment stage. These results suggest that it would be difficult to simultaneously attain population size recovery and conservation of the local gene pool when captive-bred fish have fitness disadvantage in the wild, although caution is needed when applying the predictions from the simplified model to a specific species or population.
  • Etienne Bezault, Patricia Balaresque, Aboubacar Toguyeni, Yves Fermon, Hitoshi Araki, Jean-Francois Baroiller, Xavier Rognon
    BMC GENETICS 12 102  1471-2156 2011/12 [Refereed][Not invited]
    Background: Reconstructing the evolutionary history of a species is challenging. It often depends not only on the past biogeographic and climatic events but also the contemporary and ecological factors, such as current connectivity and habitat heterogeneity. In fact, these factors might interact with each other and shape the current species distribution. However, to what extent the current population genetic structure reflects the past and the contemporary factors is largely unknown. Here we investigated spatio-temporal genetic structures of Nile tilapia (Oreochromis niloticus) populations, across their natural distribution in Africa. While its large biogeographic distribution can cause genetic differentiation at the paleo-biogeographic scales, its restricted dispersal capacity might induce a strong genetic structure at micro-geographic scales. Results: Using nine microsatellite loci and 350 samples from ten natural populations, we found the highest genetic differentiation among the three ichthyofaunal provinces and regions (Ethiopian, Nilotic and Sudano-Sahelian) (R(ST) = 0.38 - 0.69). This result suggests the predominant effect of paleo-geographic events at macro-geographic scale. In addition, intermediate divergences were found between rivers and lakes within the regions, presumably reflecting relatively recent interruptions of gene flow between hydrographic basins (R(ST) = 0.24 - 0.32). The lowest differentiations were observed among connected populations within a basin (R(ST) = 0.015 in the Volta basin). Comparison of temporal sample series revealed subtle changes in the gene pools in a few generations (F = 0 - 0.053). The estimated effective population sizes were 23 - 143 and the estimated migration rate was moderate (m similar to 0.094 - 0.097) in the Volta populations. Conclusions: This study revealed clear hierarchical patterns of the population genetic structuring of O. niloticus in Africa. The effects of paleo-geographic and climatic events were predominant at macro-geographic scale, and the significant effect of geographic connectivity was detected at micro-geographic scale. The estimated effective population size, the moderate level of dispersal and the rapid temporal change in genetic composition might reflect a potential effect of life history strategy on population dynamics. This hypothesis deserves further investigation. The dynamic pattern revealed at micro-geographic and temporal scales appears important from a genetic resource management as well as from a biodiversity conservation point of view.
  • Tingting Gu, Shengjun Tan, Xiaoxi Gou, Hitoshi Araki, Dacheng Tian
    GENETICS 186 (3) 1077 - U490 0016-6731 2010/11 [Refereed][Not invited]
    Protein is an essential component for life, and its synthesis is mediated by codons in any organisms on earth. While some codons encode the same amino acid, their usage is often highly biased. There are many factors that can cause the bias, but a potential effect of mononucleotide repeats, which are known to be highly mutable, on codon usage and codon pair preference is largely unknown. In this study we performed a genomic survey on the relationship between mononucleotide repeats and codon pair bias in 53 bacteria, 68 archaea, and 13 eukaryotes. By distinguishing the codon pair bias from the codon usage bias, four general patterns were revealed: strong avoidance of five or six mononucleotide repeats in codon pairs; lower observed/expected (o/e) ratio for codon pairs with C or G repeats (C/G pairs) than that with A or T repeats (A/T pairs); a negative correlation between genomic GC contents and the o/e ratios, particularly for C/G pairs; and avoidance of C/G pairs in highly conserved genes. These results support natural selection against long mononucleotide repeats, which could induce frameshift mutations in coding sequences. The fact that these patterns are found in all kingdoms of life suggests that this is a general phenomenon in living organisms. Thus, long mononucleotide repeats may play an important role in base composition and genetic stability of a gene and gene functions.
  • Jia-Xing Yue, Jinpeng Li, Dan Wang, Hitoshi Araki, Dacheng Tian, Sihai Yang
    BMC PLANT BIOLOGY 10 1471-2229 2010/11 [Refereed][Not invited]
    Background: Rates of molecular evolution vary widely among species. While significant deviations from molecular clock have been found in many taxa, effects of life histories on molecular evolution are not fully understood. In plants, annual/perennial life history traits have long been suspected to influence the evolutionary rates at the molecular level. To date, however, the number of genes investigated on this subject is limited and the conclusions are mixed. To evaluate the possible heterogeneity in evolutionary rates between annual and perennial plants at the genomic level, we investigated 85 nuclear housekeeping genes, 10 non-housekeeping families, and 34 chloroplast genes using the genomic data from model plants including Arabidopsis thaliana and Medicago truncatula for annuals and grape (Vitis vinifera) and popular (Populus trichocarpa) for perennials. Results: According to the cross-comparisons among the four species, 74-82% of the nuclear genes and 71-97% of the chloroplast genes suggested higher rates of molecular evolution in the two annuals than those in the two perennials. The significant heterogeneity in evolutionary rate between annuals and perennials was consistently found both in nonsynonymous sites and synonymous sites. While a linear correlation of evolutionary rates in orthologous genes between species was observed in nonsynonymous sites, the correlation was weak or invisible in synonymous sites. This tendency was clearer in nuclear genes than in chloroplast genes, in which the overall evolutionary rate was small. The slope of the regression line was consistently lower than unity, further confirming the higher evolutionary rate in annuals at the genomic level. Conclusions: The higher evolutionary rate in annuals than in perennials appears to be a universal phenomenon both in nuclear and chloroplast genomes in the four dicot model plants we investigated. Therefore, such heterogeneity in evolutionary rate should result from factors that have genome-wide influence, most likely those associated with annual/perennial life history. Although we acknowledge current limitations of this kind of study, mainly due to a small sample size available and a distant taxonomic relationship of the model organisms, our results indicate that the genome-wide survey is a promising approach toward further understanding of the mechanism determining the molecular evolutionary rate at the genomic level.
  • Michael S. Blouin, Virginie Thuillier, Becky Cooper, Vindhya Amarasinghe, Laura Cluzel, Hitoshi Araki, Christoph Grunau
    CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES 67 (2) 217 - 224 0706-652X 2010/02 [Refereed][Not invited]
    When salmonid fish that have been raised in hatcheries spawn in the wild, they often produce fewer surviving adult offspring than wild fish. Recent data from steelhead (Oncorhynchus mykiss) in the Hood River (Oregon, USA) show that even one or two generations of hatchery culture can result in dramatic declines in fitness. Although intense domestication selection could cause such declines, it is worth considering alternative explanations. One possibility is heritable epigenetic changes induced by the hatchery environment. Here, we show, using methylation-sensitive amplified fragment length polymorphism, that hatchery and wild adult steelhead from the Hood River do not appear to differ substantially in overall levels of genomic methylation. Thus, although altered methylation of specific DNA sites or other epigenetic processes could still be important, the hatchery environment does not appear to cause a global hypo- or hypermethylation of the genome or create a large number of sites that are differentially methylated.
  • Wei-Kuang Wang, Chuan-Wen Ho, Kuo-Hsiang Hung, Kuo-Hsiung Wang, Chi-Chun Huang, Hitoshi Araki, Chi-Chuan Hwang, Tsai-Wen Hsu, Naoki Osada, Tzen-Yuh Chiang
    NEW PHYTOLOGIST 188 (2) 488 - 500 0028-646X 2010 [Refereed][Not invited]
    P>Outcrossing Arabidopsis species that diverged from their inbreeding relative Arabidopsis thaliana 5 million yr ago and display a biogeographical pattern of interspecific sympatry vs intraspecific allopatry provides an ideal model for studying impacts of gene introgression and polyploidization on species diversification. Flow cytometry analyses detected ploidy polymorphisms of 2x and 4x in Arabidopsis lyrata ssp. kamchatica of Taiwan. Genomic divergence between species/subspecies was estimated based on 98 randomly chosen nuclear genes. Multilocus analyses revealed a mosaic genome in diploid A. l. kamchatica composed of Arabidopsis halleri-like and A. lyrata-like alleles. Coalescent analyses suggest that the segregation of ancestral polymorphisms alone cannot explain the high inconsistency between gene trees across loci, and that gene introgression via diploid A. l. kamchatica likely distorts the molecular phylogenies of Arabidopsis species. However, not all genes migrated across species freely. Gene ontology analyses suggested that some nonmigrating genes were constrained by natural selection. High levels of estimated ancestral polymorphisms between A. halleri and A. lyrata suggest that gene flow between these species has not completely ceased since their initial isolation. Polymorphism data of extant populations also imply recent gene flow between the species. Our study reveals that interspecific gene flow affects the genome evolution in Arabidopsis.
  • Hitoshi Araki, Corinne Schmid
    AQUACULTURE 308 (Suppl.1) S2 - S11 0044-8486 2010 [Refereed][Not invited]
    Hatchery fish stocking for stock enhancement has been operated at a massive and global scale. However, the use of hatchery fish as a means of stock enhancement is highly controversial, and little is known about its effects on wild stock and consequences for stock enhancement. Here we review the scientific literature on this subject in order to address a fundamental - question is hatchery stocking a help or harm for wild stock and stock enhancement? We summarized 266 peer-reviewed papers that were published in the last 50 years, which describe empirical case studies on ecology and genetics of hatchery stocks and their effects on stock enhancement. Specifically, we asked whether hatchery stock and wild stock differed in fitness and the level of genetic variation, and whether stocking affected population abundance. Seventy studies contained comparisons between hatchery and wild stocks, out of which 23 studies showed significantly negative effects of hatchery rearing on the fitness of stocked fish, and 28 studies showed reduced genetic variation in hatchery populations. None of these studies suggested a positive genetic effect on the fitness of hatchery-reared individuals after release. These results suggest that negative effects of hatchery rearing are not just a concern but undeniably present in many aquaculture species. In a few cases, however, no obvious effect of hatchery rearing was observed, and a positive contribution of hatchery stock to the abundance of fish populations was indicated. These examples suggest that there is a chance to improve hatchery practices and mitigate the negative effects on wild stocks, although scientific data supporting the positive effect on stock enhancement are largely missing at this moment. Technically, microsatellite-based parentage assignments have been proven as a useful tool for the evaluation of reproductive fitness in natural settings, which is a key for stock enhancement by hatchery-based stocking. We discuss implications of these results, as well as their limitations and future directions. (C) 2010 Elsevier B.V. All rights reserved.
  • Hitoshi Araki, Becky Cooper, Michael S. Blouin
    BIOLOGY LETTERS 5 (5) 621 - 624 1744-9561 2009/10 [Refereed][Not invited]
    Supplementation of wild populations with captive-bred organisms is a common practice for conservation of threatened wild populations. Yet it is largely unknown whether such programmes actually help population size recovery. While a negative genetic effect of captive breeding that decreases fitness of captive-bred organisms has been detected, there is no direct evidence for a carry-over effect of captive breeding in their wild-born descendants, which would drag down the fitness of the wild population in subsequent generations. In this study, we use genetic parentage assignments to reconstruct a pedigree and estimate reproductive fitness of the wild-born descendants of captive-bred parents in a supplemented population of steelhead trout (Oncorhynchus mykiss). The estimated fitness varied among years, but overall relative reproductive fitness was only 37 per cent in wild-born fish from two captive-bred parents and 87 per cent in those from one captive-bred and one wild parent (relative to those from two wild parents). Our results suggest a significant carry-over effect of captive breeding, which has negative influence on the size of the wild population in the generation after supplementation. In this population, the population fitness could have been 8 per cent higher if there was no carry-over effect during the study period.
  • Liucun Zhu, Qiang Wang, Ping Tang, Hitoshi Araki, Dacheng Tian
    MOLECULAR BIOLOGY AND EVOLUTION 26 (10) 2353 - 2361 0737-4038 2009/10 [Refereed][Not invited]
    Spontaneous mutations are not randomly distributed throughout a genome. Although mutation hotspots are found on genomes of a variety of species, mechanisms that generate the hotspots are not well understood. In eukaryotes, strong association between a regional nucleotide Substitution rate and insertions/deletions (indels) was reported in a previous study, and the "indel-induced mutation" hypothesis was proposed. However, it is unknown whether the association exists even in prokaryote genomes. In this study, we conducted a systematic survey for the association in 262 complete genomes from 73 bacterial species. In these bacteria, the level of nucleotide diversity was negatively correlated with the distance from the closest indel, which is consistent with the eukaryote data. The same pattern was observed even after excluding noncoding sequences, indicating that the difference in functional constraints among genomic regions is not a primary cause of the correlation. In addition, the increase of nucleotide substitution rate was detected disproportionally on a lineage carrying a derived indel mutation, confirming the indel-nucleotide diversity association in the bacterial genomes. In some cases, the level of nucleotide diversity was more than 100 times higher in regions close to indels than in distant regions. Although further understanding of the molecular mechanism is required to test the hypothesis, these results suggest that the same mechanism for the indel-nucleotide diversity associations might exist in eukaryotes and prokaryotes and play an important role in molecular evolution.
  • Jianchang Du, Tingting Gu, Hao Tian, Hitoshi Araki, Yong-Hua Yang, Dacheng Tian
    GENE 426 (1-2) 1 - 6 0378-1119 2008/12 [Refereed][Not invited]
    While information for single nucleotide polymorphism is accumulating in many organisms, little is known about the magnitude and the occurrence of nucleotide dimorphism or higher order structural polymorphisms (grouped nucleotide polymorphisms or GNPs). To address these questions, we systematically investigated the genetic variations of 996 loci in 96 Arabidopsis accessions. Our data suggest that GNP loci are highly frequent in the genomes (40.4% of 996 loci), and that 66.7% of genetic variation in 996 loci is attributed to GNPs. The frequency distribution and the linkage analysis of GNP loci demonstrate that GNPs occurred randomly, locally, ceaselessly and independently in general, although they are particularly abundant in the region near centromeres. The age distribution of GNP loci shows that the majority of these loci are under a transient phase of neutral evolution. The characteristics of GNPs imply that a molecular isolation exists in GNP loci, and most likely the indels caused isolation, which could explain how GNPs are generated and maintained. (c) 2008 Elsevier B.V. All rights reserved.
  • Wen Zhang, Xiaoqin Sun, Huizhong Yuan, Hitoshi Araki, Jue Wang, Dacheng Tian
    MOLECULAR GENETICS AND GENOMICS 280 (4) 351 - 361 1617-4615 2008/10 [Refereed][Not invited]
    Little is known about variation of nucleotide insertion/deletions (indels) within species. In Arabidopsis thaliana, we investigated indel polymorphism patterns between two genome sequences and among 96 accessions at 1215 loci. Our study identified patterns in the variation of indel density, size, GC content and distribution, and a correlation between indels and substitutions. We found that the GC content in indel sequences was lower than that in non-indel sequences and that indels typically occur in regions with lower GC content. Patterns of indel frequency distribution among populations were more consistent with neutral expectation than substitution patterns. We also found that the local level of substitutions is positively correlated with indel density and negatively correlated with their distance to the closed indel, suggesting that indels play an important role in nucleotide variation.
  • Dacheng Tian, Qiang Wang, Pengfei Zhang, Hitoshi Araki, Sihai Yang, Martin Kreitman, Thomas Nagylaki, Richard Hudson, Joy Bergelson, Jian-Qun Chen
    NATURE 455 (7209) 105 - U70 0028-0836 2008/09 [Refereed][Not invited]
    Mutation hotspots are commonly observed in genomic sequences and certain human disease loci(1-7), but general mechanisms for their formation remain elusive(7-11). Here we investigate the distribution of single- nucleotide changes around insertions/ deletions ( indels) in six independent genome comparisons, including primates, rodents, fruitfly, rice and yeast. In each of these genomic comparisons, nucleotide divergence ( D) is substantially elevated surrounding indels and decreases monotonically to near-background levels over several hundred bases. D is significantly correlated with both size and abundance of nearby indels. In comparisons of closely related species, derived nucleotide substitutions surrounding indels occur in significantly greater numbers in the lineage containing the indel than in the one containing the ancestral ( non- indel) allele; the same holds within species for single- nucleotide mutations surrounding polymorphic indels. We propose that heterozygosity for an indel is mutagenic to surrounding sequences, and use yeast genome- wide polymorphism data to estimate the increase in mutation rate. The consistency of these patterns within and between species suggests that indel- associated substitution is a general mutational mechanism.
  • Hitoshi Araki, Barry A. Berejikian, Michael J. Ford, Michael S. Blouin
    EVOLUTIONARY APPLICATIONS 1 (2) 342 - 355 1752-4571 2008/05 [Refereed][Not invited]
    Accumulating data indicate that hatchery fish have lower fitness in natural environments than wild fish. This fitness decline can occur very quickly, sometimes following only one or two generations of captive rearing. In this review, we summarize existing data on the fitness of hatchery fish in the wild, and we investigate the conditions under which rapid fitness declines can occur. The summary of studies to date suggests: nonlocal hatchery stocks consistently reproduce very poorly in the wild; hatchery stocks that use wild, local fish for captive propagation generally perform better than nonlocal stocks, but often worse than wild fish. However, the data above are from a limited number of studies and species, and more studies are needed before one can generalize further. We used a simple quantitative genetic model to evaluate whether domestication selection is a sufficient explanation for some observed rapid fitness declines. We show that if selection acts on a single trait, such rapid effects can be explained only when selection is very strong, both in captivity and in the wild, and when the heritability of the trait under selection is high. If selection acts on multiple traits throughout the life cycle, rapid fitness declines are plausible.
  • Hitoshi Araki, Flideki Innan, Martin Kreitman, Joy Bergelson
    GENETICS 177 (2) 1031 - 1041 0016-6731 2007/10 [Refereed][Not invited]
    The bacterial pathogen Pseudomonas viridiflava possesses two pathogenicity islands (PAIs) that share many gene homologs, but are structurally and phenotypically differentiated (T-PAI and S-PAI). These PAIs are paralogous, but only one is present in each isolate. While this dual presence/absence polymorphism has been shown to be maintained by balancing selection, little is known about the molecular evolution of individual genes on the PAIs. Here we investigate genetic variation of 12 PAI gene loci (7 on T-PAI and 5 on SPAI) in 96 worldwide isolates of R viridiflava. These genes include avirulence genes (hopPsyA and avrE), their putative chaperones (shcA and avrF), and genes encoding the type III outer proteins (hrpA, hrpZ, and hrpW). Average nucleotide diversities in these genes (pi = 0.004-0.020) were close to those in the genetic background. Large numbers of recombination events were found within PAIs and a sign of positive selection was detected in avrE. These results suggest that the PAI genes are evolving relatively freely from each other on the PAIs, rather than as a single unit tinder balancing selection. Evolutionarily stable PAIs may be preferable in this species because preexisting genetic variation enables P. viridiflava to respond rapidly to natural selection.
  • Hitoshi Araki, Becky Cooper, Michael S. Blouin
    SCIENCE 318 (5847) 100 - 103 0036-8075 2007/10 [Refereed][Not invited]
    Captive breeding is used to supplement populations of many species that are declining in the wild. The suitability of and long-term species survival from such programs remain largely untested, however. We measured lifetime reproductive success of the first two generations of steelhead trout that were reared in captivity and bred in the wild after they were released. By reconstructing a three-generation pedigree with microsatellite markers, we show that genetic effects of domestication reduce subsequent reproductive capabilities by similar to 40% per captive-reared generation when fish are moved to natural environments. These results suggest that even a few generations of domestication may have negative effects on natural reproduction in the wild and that the repeated use of captive-reared parents to supplement wild populations should be carefully reconsidered.
  • Undral Orgil, Hitoshi Arakit, Samantha Tangchaiburana, Robert Berkey, Shunyuan Xiao
    GENETICS 176 (4) 2317 - 2333 0016-6731 2007/08 [Refereed][Not invited]
    The RPW8 locus of Arabidopsis thaliana confers broad-spectrum resistance to powdery mildew pathogens. In many A. thaliana accessions, this locus contains two homologous genes, RPW8.1 and RPW8.2. In some susceptible accessions, however, these two genes are replaced by HR4, a homolog of RPW8.1. Here, we show that RPW8.2 from A. lyrata conferred powdery mildew resistance in A. thaliana, suggesting that RPW8.2 might have gained the resistance function before the speciation of A. thaliana and A. lyrata. To investigate how RPW8 has been maintained in A. thaliana, we examined the nucleotide sequence polymorphisms in RPW8 from 51 A. thaliana accessions, related disease reaction phenotypes to the evolutionary history of RPW8.1 and RPW8.2, and identified mutations that confer phenotypic variations. The average nucleotide diversities were high at RPW8.1 and RPW8.2, showing no sign of selective sweep. Moreover, we found that expression of RPW8 incurs fitness benefits and costs on A. thaliana in the presence and absence of the pathogens, respectively. Our results suggest that polymorphisms at the RPW8 locus in A. thaliana may have been maintained by complex selective forces, including those from the fitness benefits and costs both associated with RPW8.
  • Sihai Yang, Ke Jiang, Hitoshi Araki, Jing Ding, Yong-Hua Yang, Dacheng Tian
    GENE 394 (1-2) 87 - 95 0378-1119 2007/06 [Refereed][Not invited]
    High levels of inter-specific diversity are expected due to genetic isolation, the reproductive or geographical barriers, which lead to the accumulation of nucleotide variation. However, high levels of genetic variation are repeatedly observed even within species, notably at loci of the human major histocompatability complex and of plant resistance genes. Are molecular isolations responsible for the high intra-specific variation? To address this issue, we performed a genome-wide survey of the relationship between the possible factors that could cause genetic isolation, and the level of polymorphism, based on two rice genome comparisons. Here, we show that the levels of polymorphism in rice genes are positively correlated with the proportions of non-alignable flanking sequences, and that the correlation is observed even in single-copy genes. The physical locations of the genes were also investigated, and a strong association between the asymmetric architecture of genomes and the levels of polymorphism was revealed. These results suggest that the flank heterogeneity and the asymmetric architecture between genomes serve as isolation mechanisms at the molecular level that result in accumulation of higher genetic variation. This mechanism is of fundamental importance to understand natural genetic variation within species. (C) 2007 Elsevier B.V. All rights reserved.
  • Jing Ding, Hitoshi Araki, Qiang Wang, Pengfei Zhang, Sihai Yang, Jian-Qun Chen, Dacheng Tian
    BMC GENOMICS 8 1471-2164 2007/06 [Refereed][Not invited]
    Background: Individuals in the same species are assumed to share the same genomic set. However, it is not unusual to find an orthologous gene only in small subset of the species, and recent genomic studies suggest that structural rearrangements are very frequent between genomes in the same species. Two recently sequenced rice genomes Oryza sativa L. var. Nipponbare and O. sativa L. var. 93-11 provide an opportunity to systematically investigate the extent of the gene repertoire polymorphism, even though the genomic data of 93-11 derived from whole-short-gun sequencing is not yet as complete as that of Nipponbare. Results: We compared gene contents and the genomic locations between two rice genomes. Our conservative estimates suggest that at least 10% of the genes in the genomes were either under presence/absence polymorphism (5.2%) or asymmetrically located between genomes (4.7%). The proportion of these "asymmetric genes" varied largely among gene groups, in which disease resistance (R) genes and the RLK kinase gene group had 11.6 and 7.8 times higher proportion of asymmetric genes than housekeeping genes ( Myb and MADS). The significant difference in the proportion of asymmetric genes among gene groups suggests that natural selection is responsible for maintaining genomic asymmetry. On the other hand, the nucleotide diversity in 17 R genes under presence/absence polymorphism was generally low ( average nucleotide diversity = 0.0051). Conclusion: The genomic symmetry was disrupted by 10% of asymmetric genes, which could cause genetic variation through more unequal crossing over, because these genes had no allelic counterparts to pair and then they were free to pair with homologues at non-allelic loci, during meiosis in heterozygotes. It might be a consequence of diversifying selection that increased the structural divergence among genomes, and of purifying selection that decreased nucleotide divergence in each R gene locus.
  • Hitoshi Araki, Robin S. Waples, Michael S. Blouin
    MOLECULAR ECOLOGY 16 (11) 2261 - 2271 0962-1083 2007/06 [Refereed][Not invited]
    Indirect genetic methods are frequently used to estimate the effective population size (N-e) or effective number of breeders (N-b) in natural populations. Although assumptions behind these methods are often violated, there have been few attempts to evaluate how accurate these estimates really are in practice. Here we investigate the influence of natural selection following a population admixture on the temporal method for estimating N-e. Our analytical and simulation results suggest that N-e is often underestimated in this method when subpopulations differ substantially in allele frequencies and in reproductive success. The underestimation is exacerbated when true N-e and the fraction of the low-fitness group are large. As an empirical example, we compared N-b estimated in natural populations of steelhead trout (Oncorhynchus mykiss) using the temporal method (N-b[temp]) with estimates based on direct demographic methods (N-b[demo]) and the linkage disequilibrium method (N-b[LD]). While N-b[LD] was generally in close agreement with N-b[demo], N-b[temp] was much lower in sample sets that were dominated by nonlocal hatchery fish with low reproductive success, as predicted by the analytical results. This bias in the temporal method, which arises when genes associated with a particular group of parents are selected against in the offspring sample, has not been widely appreciated before. Such situations may be particularly common when artificial propagation or translocations are used for conservation. The linkage disequilibrium method, which requires data from only one sample, is robust to this type of bias, although it can be affected by other factors.
  • Jing Ding, Houlong Cheng, Xinqing Jin, Hitoshi Araki, Yonghua Yang, Dacheng Tian
    GENETICA 129 (3) 235 - 242 0016-6707 2007/03 [Refereed][Not invited]
    Heterogeneities in evolutionary pattern among different loci are commonly observed. To see whether the heterogeneity can also be observed among allelic groups in a single locus, we investigated the coding sequence and the flanking regions of Rpp13, a disease resistance gene in up to 60 accession lines from worldwide populations in Arabidopsis thaliana. An extraordinarily high level of polymorphism (pi=0.098) and four distinct clades were found in the leucine-rich repeat (LRR) region in this gene. No obvious geographic relationship with the clades was observed, and such clades were not observed in the other regions in and around this gene. The average genetic diversity among the clades ranged from 10 to 14.6% in the LRR. The levels of polymorphism within each clade varied largely, and significant heterogeneity in evolutionary rates among clades was detected. A statistically significant departure from neutrality was also detected by Fu & Li's tests. These results suggest that both directional and diversifying selection are working on this locus, and that natural selection can cause heterogeneity in evolutionary rate, even among allele groups in a locus.
  • Hitoshi Araki, Robin S. Waples, William R. Ardren, Becky Cooper, Michael S. Blouin
    MOLECULAR ECOLOGY 16 (5) 953 - 966 0962-1083 2007/03 [Refereed][Not invited]
    The effective population size is influenced by many biological factors in natural populations. To evaluate their relative importance, we estimated the effective number of breeders per year (N(b)) and effective population size per generation (N(e)) in anadromous steelhead trout (Oncorhynchus mykiss) in the Hood River, Oregon (USA). Using demographic data and genetic parentage analysis on an almost complete sample of all adults that returned to the river over 15 years (> 15 000 individuals), we estimated N(b) for 13 run years and N(e) for three entire generations. The results are as follows: (i) the ratio of N(e) to the estimated census population size (N) was 0.17-0.40, with large variance in reproductive success among individuals being the primary cause of the reduction in N(e)/N; (ii) fish from a traditional hatchery program (H(trad): nonlocal, multiple generations in a hatchery) had negative effects on N(b), not only by reducing mean reproductive success but also by increasing variance in reproductive success among breeding parents, whereas no sign of such effects was found in fish from supplementation hatchery programs (H(supp): local, single generation in a hatchery); and (iii) N(b) was relatively stable among run years, despite the widely fluctuating annual run sizes of anadromous adults. We found high levels of reproductive contribution of nonanadromous parents to anadromous offspring when anadromous run size is small, suggesting a genetic compensation between life-history forms (anadromous and nonanadromous). This is the first study showing that reproductive interaction between different life-history forms can buffer the genetic impact of fluctuating census size on N(e).
  • Hitoshi Araki, William R. Ardren, Erik Olsen, Becky Cooper, Michael S. Blouin
    CONSERVATION BIOLOGY 21 (1) 181 - 190 0888-8892 2007/02 [Refereed][Not invited]
    Population supplementation programs that release captive-bred offspring into the wild to boost the size of endangered populations are now in Place for many species. The use of hatcheries for supplementing salmonid populations has become particularly popular Nevertheless, whether such programs actually increase the size of wild populations remains unclear, and predictions that supplementation fish drag down the fitness of wild fish remain untested. To address these issues, we performed DNA-based parentage analyses on almost complete samples of anadromous steelhead (Oncorhynchus mykiss) in the Hood River in Oregon (U.S.A.). Steelhead from a supplementation hatchery (reared in a supplementation hatchery and then allowed to spawn naturally in the wild) had reproductive success indistinguishable from that of wild fish. In contrast, fish from a traditional hatchery (nonlocal origin, multiple generations in hatcheries) breeding in the same river showed significantly lower fitness than wild fish. In addition, crosses between wild fish and supplementation fish were as reproductively successful as those between wild parents. Thus, there was no sign that supplementation fish drag down the fitness of wild fish by breeding with them for a single generation. On the other band, crosses between hatchery fish of either type (traditional or supplementation) were less fit than expected, suggesting a possible interaction effect These are the first data to show that a supplementation program with native brood stock can provide a single-generation boost to the size of a natural steelhead population without obvious short-term fitness costs. The long-term effects of population supplementation remain untested.
  • H Araki, DC Tian, EM Goss, K Jakob, SS Hallclorsdottir, M Kreitman, J Bergelson
    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 103 (15) 5887 - 5892 0027-8424 2006/04 [Refereed][Not invited]
    The contribution of arms race dynamics to plant-pathogen coevolution has been called into question by the presence of balanced polymorphisms in resistance genes of Arabidopsis thaliana, but less is known about the pathogen side of the interaction. Here we investigate structural polymorphism in pathogenicity islands (PAIS) in Pseudomonas viridiflava, a prevalent bacterial pathogen of A. thaliana. PAIS encode the type III secretion system along with its effectors and are essential for pathogen recognition in plants. P. viridiflava harbors two structurally distinct and highly diverged PAI paralogs (T- and S-PAI) that are integrated in different chromosome locations in the A viridiflava genome. Both PAIS are segregating as presence/absence polymorphisms such that only one PAI ([T-PAI, del S-PAI] and [del T-PAI, S-PAI]) is present in any individual cell. A worldwide population survey identified no isolate with neither or both PAL T-PAI and S-PAI genotypes exhibit virulence differences and a host-specificity tradeoff. Orthologs of each PAI can be found in conserved syntenic locations in other Pseudomonas species, indicating vertical phylogenetic transmission in this genus. Molecular evolutionary analysis of PAI sequences also argues against "recent" horizontal transfer. Spikes in nucleotide divergence in flanking regions of PAI and del-PAI alleles suggest that the dual PAI polymorphism has been maintained in this species under some form of balancing selection. Virulence differences and host specificities are hypothesized to be responsible for the maintenance of the dual PAI system in this bacteria[ pathogen.
  • JD Shen, H Araki, LL Chen, JQ Chen, DC Tian
    GENETICS 172 (2) 1243 - 1250 0016-6731 2006/02 [Refereed][Not invited]
    While the presence/absence polymorphism is commonly observed in disease resistance (R-) genes in Arabidopsis, only a few R-genes under the presence/absence polymorphism (R-P/A) have been investigated. To understand the mechanism of the molecular evolution of R-P/A, the investigated genetic variation of nine R-P/A in A. thaliana from worldwide populations. The number of possessed R-genes varied widely among accessions (two to nine, on average 4.3 +/- 1.6/accession). No pair of accessions shared the same haplotype, and no clear geographic differentiation was observed with respect to the pattern of presence/absence of the R-genes investigated. Presence allele frequencies also varied among loci (25-70%), and no linkage disequilibrium was detected among them. Although the LRR region in regular R-genes is known to be highly polymorphic and has a high K-a/K-s ratio in A. thaliana, nucleotide sequences of this region in the R-P/A showed a relatively low level of genetic variation (pi = 0.0002-0.016) and low K-a/K-s (0.03-0.70, <1). In contrast, the nucleotide diversities around the deletion junction of R-P/A were constantly high between presence and absence accessions for the R-genes (D-xy = 0.031-0.103). Our results suggest that R-P/A loci evolved differently from other R-gene loci and that balancing selection plays an important role in molecular evolution of R-P/A.
  • H Araki, MS Blouin
    MOLECULAR ECOLOGY 14 (13) 4097 - 4109 0962-1083 2005/11 [Refereed][Not invited]
    Parentage assignment is widely applied to studies on mating systems, population dynamics and natural selection. However, little is known about the consequence of assignment errors, especially when some parents are not sampled. We investigated the effects of two types of error in parentage assignment, failing to assign a true parent ( type A) and assigning an untrue parent ( type B), on an estimate of the relative reproductive success (RRS) of two groups of parents. Employing a mathematical approach, we found that (i) when all parents are sampled, minimizing either type A or type B error insures the minimum bias on RRS, and (ii) when a large number of parents is not sampled, type B error substantially biases the estimated RRS towards one. Interestingly, however, (iii) when all parents were sampled and both error rates were moderately high, type A error biased the estimated RRS even more than type B error. We propose new methods to obtain an unbiased estimate of RRS and the number of offspring whose parents are not sampled (zW(z)), by correcting the error effects. Applying them to genotypic data from steelhead trout ( Oncorhynchus mykiss), we illustrated how to estimate and control the assignment errors. In the data, we observed up to a 30% assignment error and a strong trade-off between the two types of error, depending on the stringency of the assignment decision criterion. We show that our methods can efficiently estimate an unbiased RRS and zW(z) regardless of assignment method, and how to maximize the statistical power to detect a difference in reproductive success between groups.
  • K Jakob, EM Goss, H Araki, T Van, M Kreitman, J Bergelson
    MOLECULAR PLANT-MICROBE INTERACTIONS 15 (12) 1195 - 1203 0894-0282 2002/12 [Refereed][Not invited]
    We report the isolation and identification of two natural pathogens of Arabidopsis thaliana, Pseudomonas viridiflava and Pseudomonas syringae, in the midwestern United States. P viridiflava was found in six of seven surveyed Arabidopsis thaliana populations. We confirmed the presence in the isolates of the critical pathogenicity genes hrpS and hrpL. The pathogenicity of these isolates was verified by estimating in planta bacterial growth rates and by testing for disease symptoms and hypersensitive responses to A. thaliana. Infection of 21 A. thaliana ecotypes with six locally collected P. viridiflava isolates and with one P. syringae isolate showed both compatible (disease) and incompatible (resistance) responses. Significant variation in response to infection was evident among Arabidopsis ecotypes, both in terms of symptom development and in planta bacterial growth. The ability to grow and cause disease symptoms on particular ecotypes also varied for some P. viridiflava isolates. We believe that these pathogens will provide a powerful system for exploring coevolution in natural plant-pathogen interactions.
  • DC Tian, H Araki, E Stahl, J Bergelson, M Kreitman
    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 99 (17) 11525 - 11530 0027-8424 2002/08 [Refereed][Not invited]
    Natural selection and genetic linkage cause DNA segments to have genealogical histories resembling those of the selected sites. When a polymorphism maintained by selection is old, it will have an island of enhanced sequence variability surrounding it, which represents a detectable "signature of selection." We investigate the structure of single-nucleotide polymorphisms (SNPs) in a 20-kb interval containing the Arabidopsis thaliana disease resistance gene RPS5, a locus containing common alleles for the presence/ absence of the entire locus. The alleles are considerably diverged at surrounding sites, indicative of an old polymorphism maintained by selection. The island of "enhanced" variability extends several kilobases to either side of the RPS5 deletion junction, and these SNPs are in nearly complete linkage disequilibrium with the RPS5 insertion/deletion. At a distance of 10 kb to either side of the locus, however, we find low levels of polymorphism and the absence of linkage disequilibrium between individual SNPs and RP55 alleles. Our results show that the interval of enhanced variability surrounding this balanced polymorphism in Arabidopsis is large enough to be readily detected, but small enough to span the focal gene and few others. For this species it should be possible to identify the complete set of genes with long-lived polymorphisms, a potentially important subset of genes segregating for functional variants.


Awards & Honors

  • 2007 Society of Evolutionary Studies, Japan Awards for encouragement of young scientist
    受賞者: Hitoshi Araki

Research Grants & Projects

Educational Activities

Teaching Experience

  • Applied Animal Ecology
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 農学院
    キーワード : 進化、生態、保全 Evolution, Ecology and Conservation
  • Advanced Ecology and Systematics Ⅱ
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 農学院
    キーワード : 野生動植物の生態・進化と保全, 生物多様性
  • Field Training of Animal Ecology
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 農学部
    キーワード : センサス、フィールド科学センター、野外実習、密度、多様性
  • Applied Zoology
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 農学部
    キーワード : 生態進化学
  • Arts and Science Courses in English 1
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 国際本部
    キーワード : Ecology, Evolution and Conservation
  • Introduction to Animal Ecology
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 農学部
    キーワード : 生態、進化、適応、遺伝、保全、生物多様性
  • General Genetics
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 農学部
    キーワード : 遺伝、生命現象、メンデル、ダーウィン、変異、進化、保全
  • Environment and People
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : サケ、回遊、人工ふ化放流、分類、気候変化、資源変動、生活史、個体群密度効果、生物多様性、バイオロギング、母川回帰、嗅覚、物質循環、海水適応、ゲノム、性統御、始原生殖細胞、流通、ハサップ(HACCP)、先住民族、市民運動、魚病

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