研究者データベース
Last Updated :2024/08/21
研究者情報
マスター
アカウント（マスター）
氏名
相馬 雅代(ソウマ マサヨ), ソウマ マサヨ
所属（マスター）
所属（マスター）
独自項目
syllabus
- 2021, 生命システム科学基礎論, Biosystems Science, 修士課程, 生命科学院, 生命システム, 生命機能, 研究方法論, 研究技術論
- 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, 生命システム, 生命機能, 研究方法論, 研究技術論
- 2021, 多様性生物学基礎論, Fundamental Course in Biological Diversity, 修士課程, 環境科学院, 生物多様性、遺伝的多様性、陸上植物、土壌微生物、藻類、哺乳類、鳥類、魚類、昆虫、陸水生物、海洋動物 Biodiversity, genetic variation, terrestrial plants, soil microorganisms, algae, mammals, birds, fishes, insects, freshwater organisms, marine animals
- 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, 生物多様性、遺伝的多様性、陸上植物、土壌微生物、藻類、哺乳類、鳥類、魚類、昆虫、陸水生物、海洋動物 Biodiversity, genetic variation, terrestrial plants, soil microorganisms, algae, mammals, birds, fishes, insects, freshwater organisms, marine animals
- 2021, 行動システム制御科学特論, Behavioral Control System Sciences, 修士課程, 生命科学院, 行動，脳，中枢神経系，社会性，コミュニケーション，認知，神経回路，ニューロン，最初期遺伝子，感覚情報処理，運動制御，学習，進化
- 2021, 生物多様性概論, Introduction to Biological Diversity, 学士課程, 理学部, 現代生物科学，21世紀に生物科学が解決しなければならない課題，生物の多様性，系統，進化，生物の形態，生命活動の多様性
- 2021, 科学・技術の世界（1単位）, The World of Science and Technology, 学士課程, 全学教育, 現代生物科学，21世紀に生物科学が解決しなければならない課題，生物の多様性，系統，進化，生物の形態，生命活動の多様性
- 2021, 基礎生物学実習, Laboratory Course in Basic Biology, 学士課程, 理学部, 脊椎動物の形態、染色体、細胞、植物、昆虫、土壌動物、ショウジョウバエ、唾腺染色体、博物館標本
- 2021, 生物統計学, Biostatistics, 学士課程, 理学部, 統計，データ解析
- 2021, 生物学Ⅱ, Biology II, 学士課程, 全学教育, 生物の多様性，系統，進化，生物の形態，生命活動の多様性
- 2021, ISP生物科学実習Ⅱ・a, ISP Biological Laboratory Course II･a, 学士課程, 理学部
- 2021, ISP生物科学実習Ⅱ・b, ISP Biological Laboratory Course II･b, 学士課程, 理学部
- 2021, 行動神経生物学実習, Laboratory Course in Behavioral Neurobiology, 学士課程, 理学部, 行動、脳、中枢神経系、脊椎動物、無脊椎動物、組織化学、遺伝子発現、光学計測、社会行動、コミュニケーション
- 2021, 脳と行動の進化, Brain, Behavior and Evolution, 学士課程, 理学部, 動物行動、進化、コミュニケーション、微小脳、視覚、嗅覚、学習、認知
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プロフィール情報
学位
プロフィール情報
姓
相馬, ソウマ名
雅代, マサヨID各種
201301009419073073
対象リソース
業績リスト
研究キーワード
研究分野
経歴
受賞
- 2022年04月 北海道大学 卓越研究者
受賞者: 相馬 雅代 - 2016年 資生堂女性研究者サイエンスグラント
受賞者: 相馬雅代 - 2015年 文部科学大臣表彰 若手科学者賞
受賞者: 相馬雅代 - 2011年 日本鳥学会 黒田賞
受賞者: 相馬雅代 - 2005年 第30 回鳥類内分泌研究会若手奨励賞
受賞者: 相馬雅代
論文
- Makioka H, Lewis RN, Soma MFrontiers in Psychology 2024年08月 [査読有り][招待有り]
- Ayumi Mizuno, Malgorzata Lagisz, Pietro Pollo, Yefeng Yang, Masayo Soma, Shinichi NakagawaeLife 2024年07月30日 [査読有り]
Eyespot patterns have evolved in many prey species. These patterns were traditionally explained by the eye mimicry hypothesis, which proposes that eyespots resembling vertebrate eyes function as predator avoidance. However, it is possible that eyespots are not the mimicry of eyes: according to the conspicuousness hypothesis, eyespots are just one form of vivid aposematic signals where only conspicuousness matters. To test these hypotheses and explore factors influencing predators’ responses, we conducted a meta-analysis with 33 empirical papers focusing on bird responses to lepidopterans having conspicuous patterns (eyespots and non-eyespots). Supporting the latter hypothesis, the results showed no clear difference in predator avoidance efficacy between eyespots and non-eyespots. When comparing geometric pattern characteristics, bigger pattern sizes and smaller numbers of patterns were more effective in preventing avian predation. This finding indicates that paired concentric patterns have weaker deterring effects than single ones. Taken together, our study supports the conspicuousness hypothesis more than the eye mimicry hypothesis. Due to the number and species coverage of published studies so far, the generalisability of our conclusion may be limited. The findings highlight that pattern conspicuousness is key to eliciting avian avoidance responses, shedding a different light on this classic example of signal evolution. - Rebecca N. Lewis, Anthony Kwong, Masayo Soma, Selvino R. de Kort, R. Tucker GilmanAnimal Behaviour 206 61 - 74 2023年12月 [査読無し]
- Jenna Onaga, Masayo SomaPLOS ONE 18 10 e0292074 - e0292074 2023年10月25日 [査読有り]
Conspicuous facial features, such as blushing in primates, can communicate social/emotional/physiological states in animals. However, the role of bare facial features is less well studied in birds than in humans or primates. We investigate the Java sparrow, which is characterised by conspicuous rings of swollen and blushed bare skin around the eye. Eye rings show no clear sex difference, although the swelling is associated with breeding. Java sparrows are socially monogamous, with mutual courtships and long-term pair-bonding. Therefore, it is plausible that eye rings function in within-pair communication. Specifically, do eye rings reflect psychophysiological conditions after pair formation? We assessed variations in ring thickness in pair-bonded birds and compared them with single birds and pairs of non-bonded individuals. Over the 12-week experimental period, pair-bonded males and females had an increased ring thickness, unlike the controls. We suggest eye rings convey breeding motivations or serve as fertility signals. This would be of great importance for ensuring reproductive synchrony in tropical birds like the Java sparrow. Our results contribute to understanding the evolution of facial ornamentation in birds, which was often overlooked in the past studies. - Ayumi Mizuno, Masayo SomaRoyal Society Open Science 10 10 2023年10月18日 [査読有り]
The diverse characteristics of animal signal designs can be explained by the sensory bias hypothesis, which suggests that natural selection shapes sensory bias and preferences associated with signal design. Traditionally, this hypothesis has focused on female sensory biases and male sexual traits. However, considering shared sensory systems between males and females in non-sexual contexts, existing sensory bias possibly contributes to the evolution of shared social and sexual traits. Our previous studies on the family Estrildidae supported this idea. An evolutionary relationship probably existed between diet and white dot plumage, and a species of estrildid finches showed a visual preference for white dot patterns. To investigate this further, we examined hunger-related visual preferences using phylogenetic comparative methods and behavioural experiments. Specifically, we compared the gazing responses of 12 species of estrildids to monochromatic printed white dot and stripe patterns, considering their phylogenetic relationships. The results support our idea that the common estrildid ancestor had a hunger-related visual preference for white dot patterns. Subject species generally preferred white dots to stripes. Furthermore, males and females showed a similar preference towards dots. Our findings provide insights into the role of sensory bias in the evolution of mutual ornamentation. - Ayumi Mizuno, Masayo SomaAnimal Cognition 2022年03月16日 [査読有り][通常論文]
Abstract Many animals have polka dot patterns on their body surface, some of which are known to have signalling functions; however, their evolutionary origins remain unclear. Dot patterns can trigger a fear response (trypophobia) in humans and are known to function as aposematic signals in non-human animals, suggesting that dots may deserve attention for biological reasons. Interestingly in many birds, plumage dot patterns serve for social/sexual signalling. To understand their evolution, we have focused on the sensory bias hypothesis, which predicts the role of pre-existing sensory preference driven by natural selection in shaping signal design. Our previous phylogenetic comparative study supported the hypothesis and showed that diet-driven visual preference promoted the evolution of plumage patterns, as there was an evolutionary correlation between termite-eating (white roundish gregarious prey) and the presence of plumage dot patterns in species of the family Estrildidae. This suggests that these species possess an intrinsic preference for dots. To test this, we compared the responses of an Estrildid species with dot plumage pattern (star finch Neochmia ruficauda) towards simultaneously presented monochrome-printed white dot vs white stripe patterns under both food-deprived and -supplied conditions. Overall, star finches preferred dots to stripes. They showed foraging-like behaviours almost only toward dots when hungry and gazed at dots frequently even when food was available, suggesting both hunger-related and hunger-neutral dot preferences. These results are rather surprising, given how strongly the subjects were attracted to abstract dot patterns without organic structure, but provided good support for the sensory bias hypothesis. - Masayo SomaFrontiers in Physiology 12 2022年01月31日 [査読有り]
The division of cognitive processing between the two hemispheres of the brain causes lateralized eye use in various behavioral contexts. Generally, visual lateralization is shared among vertebrates to a greater extent, with little interspecific variation. However, previous studies on the visual lateralization in mating birds have shown surprising heterogeneity. Therefore, this systematic review paper summarized and analyzed them using phylogenetic comparative methods. The review aimed to elucidate why some species used their left eye and others their right to fixate on individuals of the opposite sex, such as mating partners or prospective mates. It was found that passerine and non-passerine species showed opposite eye use for mating, which could have stemmed from the difference in altricial vs. precocial development. However, due to the limited availability of species data, it was impossible to determine whether the passerine group or altricial development was the primary factor. Additionally, unclear visual lateralization was found when studies looked at lek mating species and males who performed courtship. These findings are discussed from both evolutionary and behavioral perspectives. Possible directions for future research have been suggested. - Nao Ota, Masayo SomaBiotremology: Physiology, Ecology, and Evolution 237 - 259 2022年
- Koen de Reus, Masayo Soma, Marianna Anichini, Marco Gamba, Marianne de Heer Kloots, Miriam Lense, Julia Hyland Bruno, Laurel Trainor, Andrea RavignaniPhilosophical Transactions of the Royal Society B: Biological Sciences 376 1835 20200337 - 20200337 2021年08月23日 [査読有り]
This review paper discussesrhythmic interactions and distinguishes them fromnon-rhythmic interactions. We report on communicative behaviours in social and sexual contexts, as found in dyads of humans, non-human primates, non-primate mammals, birds, anurans and insects. We discuss observed instances of rhythm in dyadic interactions, identify knowledge gaps and propose suggestions for future research. We find that most studies on rhythmicity in interactive signals mainly focus on one modality (acoustic or visual) and we suggest more work should be performed on multimodal signals. Although the social functions of interactive rhythms have been fairly well described, developmental research on rhythms used to regulate social interactions is still lacking. Future work should also focus on identifying the exact timing mechanisms involved. Rhythmic signalling behaviours are widespread and critical in regulating social interactions across taxa, but many questions remain unexplored. A multidisciplinary, comparative cross-species approach may help provide answers. This article is part of the theme issue ‘Synchrony and rhythm interaction: from the brain to behavioural ecology’. - Rebecca N. Lewis, Masayo Soma, Selvino R. de Kort, R. Tucker GilmanFrontiers in Psychology 12 654198 - 654198 2021年06月04日 [査読有り][招待有り]
Social learning of vocalizations is integral to song inheritance in oscine passerines. However, other factors, such as genetic inheritance and the developmental environment, can also influence song phenotype. The relative contributions of these factors can have a strong influence on song evolution and may affect important evolutionary processes such as speciation. However, relative contributions are well-described only for a few species and are likely to vary with taxonomy. Using archived song data, we examined patterns of song inheritance in a domestic population of Java sparrows (Lonchura oryzivora ), some of which had been cross-fostered. Six-hundred and seventy-six songs from 73 birds were segmented and classified into notes and note subtypes (N = 22,972), for which a range of acoustic features were measured. Overall, we found strong evidence for cultural inheritance of song structure and of the acoustic characteristics of notes; sons’ song syntax and note composition were similar to that of their social fathers and were not influenced by genetic relatedness. For vocal consistency of note subtypes, a measure of vocal performance, there was no apparent evidence of social or genetic inheritance, but both age and developmental environment influenced consistency. These findings suggest that high learning fidelity of song material, i.e., song structure and note characteristics, could allow novel variants to be preserved and accumulate over generations, with implications for evolution and conservation. However, differences in vocal performance do not show strong links to cultural inheritance, instead potentially serving as condition dependent signals. - Ayumi Mizuno, Masayo SomaEthology Ecology & Evolution 1 - 13 2020年08月 [査読有り]
- Masayo Soma, Henrik BrummBiology Letters 16 8 20200399 - 20200399 2020年08月 [査読有り]
The duets of birds have intrigued biologists for a long time, yet much remains unknown about the evolution of these striking collective displays. This is partly because previous studies on duet evolution have been biased to songbirds and neglected other bird groups. In songbirds, the absence of migration has been found to predict the occurrence of duetting, indirectlysupporting the idea that duet communication is linked with pair bonding. Here, we used phylogenetic comparative analyses in a sedentary clade of non-songbirds, the barbets (Capitonidae), to reveal new correlates of duet evolution. We found (i) that duets evolved several times independently in different barbet lineages and (ii) that duetting evolved in association with group living (i.e. the presence of helpers or non-breeding adults during the breeding period), but not with sexual monochromatism or habitat type. Our findings are consistent with a duet function in mate guarding and dominance against subordinate group members as well as joint territory defence. Altogether, the results highlight the importance of the social environment for the evolution of collective signalling. - ブンチョウのオス同性間にみられる「つがい」の絆形成安達寛子, 相馬雅代日本性科学会誌 37 1 45 - 54 2019年07月 [査読有り][招待有り]
- Soma M, Iwama M, Nakajima R, Endo RRoyal Society Open Science 6 190563 2019年06月 [査読有り][通常論文]
- Ayumi MIZUNO, Yutaka MARUYAMA, Masayo SOMA日本鳥学会誌 68 1 67 - 71 2019年04月23日 [査読有り]
- Vocalization can mediate male-male sexual interactions in Java sparrowsHiroko Adachi, Masayo SomaAnimal Biology 2018年12月 [査読有り][招待有り]
- Ota N, Gahr M, Soma MScience Advances 4 10 eaat4779 2018年10月 [査読有り][通常論文]
- 歌鳥の雌雄の音声コミュニケーション相馬雅代騒音制御 42 4 161 - 164 2018年08月 [査読有り][招待有り]
- Masayo Soma, László Zsolt GaramszegiBehavioral Ecology 29 3 676 - 685 2018年05月09日 [査読有り][通常論文]
Color patterns, such as bars or dots that cover the body surface of animals are generally thought to play roles in signaling and camouflage. In birds, however, the macroscopic aspects of plumage coloration are less well understood, as past studies typically described plumage colorations by using spectrophotometric analyses. To provide insight into the evolution of plumage patterns as sexual signals, we characterized interspecific and intersexual variations in the plumage patterns of estrildid finches and tested their associations with other courtship signals and life-history traits using a comparative phylogenetic approach. Our results support the idea that plumage patterns in estrildids are favored by sexual selection because large-sized conspicuous plumage patterns are possessed by species with an elaborate courtship dance. These plumage patterns may also play roles in social signaling because patterns are more conspicuous in species with intraspecific brood parasitism. We predict that pattern traits can be favored by mate choice or intrasexual competition when they can serve as honest indicators of individual condition. As our results are consistent between the sexes, we suggest that the same selective force is acting on the evolution of plumage patterns in males and females in parallel. Finally, we also found a trade-off between large size and vivid color patterns, suggesting that too conspicuous patterns are costly, presumably because of the risk of catching the eyes of potential predators. Therefore, plumage patterns are also shaped by natural selection. - Masayo SomaJapanese Journal of Animal Psychology 2018年 [査読有り][招待有り]
- A. C. R. Gomes, C. Funghi, M. Soma, M. D. Sorenson, G. C. CardosoJOURNAL OF EVOLUTIONARY BIOLOGY 30 7 1336 - 1346 2017年07月 [査読有り][通常論文]
Sexual traits (e.g. visual ornaments, acoustic signals, courtship behaviour) are often displayed together as multimodal signals. Some hypotheses predict joint evolution of different sexual signals (e.g. to increase the efficiency of communication) or that different signals trade off with each other (e.g. due to limited resources). Alternatively, multiple signals may evolve independently for different functions, or to communicate different information (multiple message hypothesis). We evaluated these hypotheses with a comparative study in the family Estrildidae, one of the largest songbird radiations, and one that includes many model species for research in sexual selection and communication. We found little evidence for either joint evolution or trade-offs between song and colour ornamentation. Some negative correlations between dance repertoire and song traits may suggest a functional compromise, but generally courtship dance also evolved independently from other signals. Instead of correlated evolution, we found that song, dance and colour are each related to different socio-ecological traits. Song complexity evolved together with ecological generalism, song performance with investment in reproduction, dance with commonness and habitat type, whereas colour ornamentation was shown previously to correlate mostly with gregariousness. We conclude that multimodal signals evolve in response to various socio-ecological traits, suggesting the accumulation of distinct signalling functions. - Masayo Soma, Midori IwamaPLOS ONE 12 3 e0172655 2017年03月 [査読有り][通常論文]
Mutual interactions between sexes have multiple signalling functions. Duet singing in songbirds is related to mutual mate guarding, joint resource defence, and signalling commitment. Coordinated visual displays of mating pairs are thought to perform similar functions, but are less well understood. The current study evaluated mutual interactions in an Estrildid species to explore the relative importance of duet dancing and male singing in mating success of pairs in a first encounter. When Java sparrows (Lonchura oryzivora) court prospective mates, only males sing. However, both males and females perform courtship dances, often in a duet-like manner. These dances are typically terminated by female copulation solicitation displays (CSDs). In the current study, we observed higher mating success when courtship dances were mutually exchanged, and when males sang. However, the sex initiating the courtship did not affect mating success. Most females produced CSDs after duet dancing but before hearing the entire song, indicating that duet dancing played a crucial role in mating. This finding highlights an unexplored aspect of duetting behaviour in the process of mutual mate choice. These results conflict with the majority of past songbird research, which has interpreted songs as primary behavioural sexual signals. - Nao Ota, Manfred Gahr, Masayo SomaBIOACOUSTICS-THE INTERNATIONAL JOURNAL OF ANIMAL SOUND AND ITS RECORDING 26 2 161 - 168 2017年 [査読有り][通常論文]
Vocalizations have been elucidated in previous songbird studies, whereas less attention has been paid to non-vocal sounds.In the bluecapped cordon-bleu (Uraeginthus cyanocephalus), both sexes perform courtship displays that are accompanied by singing and distinct body movements (i.e.dance).Our previous study revealed that their courtship bobbing includes multiple rapid steps.This behaviour is quite similar to human tap dancing, because it can function as both visual and acoustic signals.To examine the acoustic signal value of such steps, we tested if their high-speed step movements produce non-vocal sounds that have amplitudes similar to vocal sounds. We found that step behaviour affected step sound amplitude. Additionally, the dancing step sounds were substantially louder than feet movement sounds in a non-courtship context, and the amplitude range overlapped with that of song notes.These results support the idea that in addition to song cordon-bleus produce acoustic signals with their feet. - Kentaro Yamada, Masayo SomaJOURNAL OF AVIAN BIOLOGY 47 6 865 - 870 2016年12月 [査読有り][通常論文]
Song is a notable sexual signal of birds, and serves as an honest indicator of male quality. Condition dependence of birdsong has been well examined from the viewpoint of the developmental stress hypothesis, which posits that complex songs assure fitness because learned acoustic features of songs are especially susceptible to early-life stress that young birds experience in song learning periods. The effect of early stress on song phenotypes should be crucial, especially in age-limited song learners which sing stereotyped songs throughout life. However, little attention has been paid to non-learned song features that can change plastically even in adulthood of age-limited song-learners. Although it has been shown that food availability affects song rate in wild songbirds, there is limited evidence of the link between favorable nutritional conditions and song phenotypes other than song rate. Under the prediction that singing behavior reflects an individual's recent life history, we kept adult Bengalese finch males under high-nutrition or normal diet for a short term, and examined changes in body mass and songs. We found that birds on a high-nutrition diet showed higher song output (e.g. song rate and length) compared with those of the control group, while changes in body mass were moderate. In addition, note repertoire became more consistent and temporal structures got faster in both nutrition and control groups, which indicates that songs were subject to other factors than nutrition. Considering that female estrildid finches, including Bengalese and zebra finches, show a preference toward complex songs as well as longer songs and higher song rate, it is plausible that different aspects of singing behavior signal different male qualities, and provide multifaceted clues to females that choose mates. - Nao Ota, Manfred Gahr, Masayo SomaSCIENTIFIC REPORTS 5 2015年11月 [査読有り][通常論文]
According to classical sexual selection theory, complex multimodal courtship displays have evolved in males through female choice. While it is well-known that socially monogamous songbird males sing to attract females, we report here the first example of a multimodal dance display that is not a uniquely male trait in these birds. In the blue-capped cordon-bleu (Uraeginthus cyanocephalus), a socially monogamous songbird, both sexes perform courtship displays that are characterised by singing and simultaneous visual displays. By recording these displays with a high-speed video camera, we discovered that in addition to bobbing, their visual courtship display includes quite rapid step-dancing, which is assumed to produce vibrations and/or presumably non-vocal sounds. Dance performances did not differ between sexes but varied among individuals. Both male and female cordon-bleus intensified their dance performances when their mate was on the same perch. The multimodal (acoustic, visual, tactile) and multicomponent (vocal and non-vocal sounds) courtship display observed was a combination of several motor behaviours (singing, bobbing, stepping). The fact that both sexes of this socially monogamous songbird perform such a complex courtship display is a novel finding and suggests that the evolution of multimodal courtship display as an intersexual communication should be considered. - Masayo Soma, Chihiro MoriPLOS ONE 10 5 2015年05月 [査読有り][通常論文]
Music and dance are two remarkable human characteristics that are closely related. Communication through integrated vocal and motional signals is also common in the courtship displays of birds. The contribution of songbird studies to our understanding of vocal learning has already shed some light on the cognitive underpinnings of musical ability. Moreover, recent pioneering research has begun to show how animals can synchronize their behaviors with external stimuli, like metronome beats. However, few studies have applied such perspectives to unraveling how animals can integrate multimodal communicative signals that have natural functions. Additionally, studies have rarely asked how well these behaviors are learned. With this in mind, here we cast a spotlight on an unusual animal behavior: nonvocal sound production associated with singing in the Java sparrow (Lonchura oryzivora), a songbird. We show that male Java sparrows coordinate their bill-click sounds with the syntax of their song-note sequences, similar to percussionists. Analysis showed that they produced clicks frequently toward the beginning of songs and before/after specific song notes. We also show that bill-clicking patterns are similar between social fathers and their sons, suggesting that these behaviors might be learned from models or linked to learning-based vocalizations. Individuals untutored by conspecifics also exhibited stereotypical bill-clicking patterns in relation to song-note sequence, indicating that while the production of bill clicking itself is intrinsic, its syncopation appears to develop with songs. This paints an intriguing picture in which non-vocal sounds are integrated with vocal courtship signals in a songbird, a model that we expect will contribute to the further understanding of multimodal communication. - Soma M, Garamszegi LZFrontiers in Ecology and Evolution 3 4 2015年02月 [査読有り][通常論文]
- Nao Ota, Masayo SomaJOURNAL OF AVIAN BIOLOGY 45 6 566 - 573 2014年11月 [査読有り][通常論文]
Birdsong is a sexual signal that serves as an indicator of male quality. There is already abundant evidence that song elaboration reflects early life-history because early developmental stress affects neural development of song control systems, and leaves irreversible adverse effects on song phenotypes. Especially in closed-ended vocal learners, song features crystallized early in life are less subject to changes in adulthood. This is why less attention has been paid to lifelong song changes in closed-ended learners. However, in the eyes of female birds that gain benefits from choosing mates based on male songs, not only past but also current conditions encoded in songs would be meaningful, given that even crystallized songs in closed-ended learners would not be identical in the long term. In this study, we examine within-individual song changes in the Java sparrow Lonchura oryzivora, with the aim of shedding light on the relationship between song and long-term life history. Specifically, we compared song length, tempo, and song complexity measures between the point just after song crystallization and around 1 yr later, and also compared those traits between fathers and sons to clarify the effect of vocal learning. While it is not surprising that song complexity did not differ depending on age or between fathers and sons, we found that song length and tempo increased with age. Follow-up analyses have revealed that frequency bandwidth and peak frequency of song notes also elevated with age. Our results show that song performance related to motor skills can be improved even after song crystallization. We also suggest that song performance in closed-ended vocal learners gives a reliable clue for mate choice by reflecting male quality with aging. - Hiroko Kagawa, Masayo SomaBEHAVIOURAL PROCESSES 99 138 - 144 2013年10月 [査読無し][通常論文]
Bird songs have evolved under sexual selection pressure. Songs include multiple features that are subject to female preference, but recent comparative research has indicated evolutionary tradeoffs between song performance and complexity in some species. Trill, a repetition of the same sound, is a performance-related song trait; higher trill performance can be achieved at the cost of song complexity at the among-species or population level. The aim of this study was to examine whether such tradeoffs also account for within-species variation in Java sparrow songs, which include both multiple trill types and non-trill parts. We found a great individual variation in trill proportion, trill performance, and song complexity. A positive association between trill performance and body size suggested that trills can serve as an indicator of male quality. However, contrary to the tradeoffs predicted by previous studies based on other passerine species, trill performance and song complexity, i.e., note repertoire, were positively correlated: males in better condition can sing songs with larger note repertoires and higher trill performance, which may explain how trills and non-trill notes are both maintained and have co-evolved by sexual selection in Java sparrow songs. (C) 2013 Elsevier B.V. All rights reserved. - M. Soma, K. OkanoyaBEHAVIOUR 150 13 1491 - 1508 2013年 [査読有り][通常論文]
Postmating sexual selection plays an important part in the evolution of secondary sexual characters. Based on differential allocation theory that predicts biased reproductive investment of females depending on the attractiveness of mates, a number of previous studies have shown that egg production is related in various ways to ornamental sexual traits of males, but evidence for behavioural sexual traits is less abundant. In this study we examine such maternal effects in relation to birdsong. Because the Bengalese finch is a monomorphic songbird, courtship song serves a key role in mate choice. To take into account individual female differences in egg production performance, we sequentially paired naive, captive, female Bengalese finches to two different males, and investigated if their reproductive investment (clutch size, egg mass and hatchling sex ratio) was related to the song traits of their mates. We found that clutch size and egg mass were highly repeatable within individual females while sex ratio was not. Despite the inflexibility of egg mass within each female, egg mass increased when females were mated to males with longer songs. In addition, we found a non-significant weak tendency toward male-biased sex ratio in relation to longer song duration of mates. Our findings suggest that females mated to better mates adjusted their reproductive investment by producing heavier eggs and possibly offspring of the more costly sex. - Masayo F. SomaORNITHOLOGICAL SCIENCE 10 2 89 - 100 2011年12月 [査読無し][通常論文]
Birdsong is an important sexually selected trait, and its acoustic features are socially transmitted in the process of song learning. Though a great deal of research has been conducted to shed light on the mechanisms and functions of song learning, we still do not have clear answers as to why for some species, including Estrildid finches and humans, the ability of "social" vocal learning has evolved. Therefore, this paper addresses social factors responsible for song learning, especially focusing on tutor choice in Estrildid finches, with the aim of elucidating what is already clear about how the social environment shapes songs and what is needed in future studies. - Ai Hasegawa, Masayo Soma, Toshikazu HasegawaORNITHOLOGICAL SCIENCE 10 1 73 - 80 2011年06月 [査読有り][通常論文]
Estrildine finches are important model species in experimental studies on female mating preferences, but research has focused on only two species from this family, namely, the Zebra Finch Taeniopygia guttata and the Bengalese Finch Lonchura striata var. domestica, and we know comparatively little about other closely related species. Therefore, we investigated sexual dimorphism and female choice in the Java Sparrow Padda oryzivora, which also belongs to the family Estrildidae, to open up the potential for comparative research and to better understand sexual selection in this family. First, we took measurements of eight morphological traits of six male and six female Java Sparrows: natural wing length, maximum wing length, tarsus length, tail length, exposed culmen length, bill width, bill depth and body mass. We quantitatively confirmed that Java Sparrows show sexual dimorphism in bill depth, with males having deeper bills than females. Second, we examined individual variation in male courtship songs by analyzing their acoustic and syntactical structure. After collecting data on male morphological and song-related traits, we conducted two-way choice tests to ask which kinds of male traits predicted which males were preferred by female Java Sparrows. In the choice tests, we put a cage with a female in between two cages each containing one male and recorded the position of the female every 30 seconds by point sampling. We performed a stepwise regression analysis to assess the relationship between the time females spent in front of each male and male morphological and song-related traits. The results indicated that females base their preference upon large body size, which is likely to act as a good indicator of male quality. However, no preference was observed for song-related traits or sexually dimorphic bill depth. Perhaps the sexual dimorphism in bill size is instead the evolutionary outcome of male-male competition. - Masayo Soma, Laszlo Zsolt GaramszegiBEHAVIORAL ECOLOGY 22 2 363 - 371 2011年03月 [査読無し][通常論文]
The theory of sexual selection predicts a relationship between male sexual traits and reproductive success. This prediction has been tested extensively using the complexity of birdsong as a model for trait elaboration. However, contradictory results have emerged. Some studies have demonstrated that males with large repertoires enjoy a reproductive advantage, whereas other studies have failed to support this prediction. To make general inferences from this mixed evidence, we quantitatively reviewed the relevant literature using a meta-analytic approach. The mean effect size for the song/mating success association was significant, but the effects were generally weak, affected by publication bias, confounded by uncontrolled variables, and differing across the traits examined. Effect sizes were heterogeneous across studies due to species-specific effects, differences in mating systems, and song phenotypes. The degree of association between song complexity and reproductive success was independent of the strength of sexual selection, as assessed by the degree of polygyny and extrapair paternity. Our results highlight the importance of considering various biological factors to understand the role of repertoires in mediating mating success in different species. - Masayo Soma, Mariko Hiraiwa-Hasegawa, Kazuo OkanoyaANIMAL BEHAVIOUR 78 5 1107 - 1113 2009年11月 [査読無し][通常論文]
Birdsong is an important sexually selected trait, and its acoustic features are socially transmitted in the process of song learning. The preference of some female songbirds for song complexity as measured by repertoire size has driven the evolution of many song traits and song-learning programs in males. If juvenile birds adopt the attractiveness of model birds by copying their repertoires, tutor choice in the early song-learning period should be crucial for future reproductive success. Thus, we hypothesized that the song quality of tutors influences the tutor choice of chicks in the Bengalese finch, Lonchura striata var. domestica. Each subject chick was reared by a foster pair in an individual breeding cage. At around the fledging period, we introduced another unrelated adult male (subtutor) into each cage to simulate the natural social environment in which chicks have opportunities to hear the songs of nonfather males after fledging. Subject chicks learned from both tutors when the total note repertoire size of the two models was small; they tended to learn from the subtutor when the father had a smaller note repertoire size. The acquired note repertoire size was not affected by whether subjects learned songs from the foster father or not. Song learning from the subtutor contributed to a larger note repertoire. Observed patterns in tutor choice, in particular song learning from a subtutor, could be an adaptive strategy that helps chicks compensate for exposure to smaller repertoire size in models. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. - Masayo Soma, Mariko Hiraiwa-Hasegawa, Kazuo OkanoyaBEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 63 3 363 - 370 2009年01月 [査読無し][通常論文]
Birdsong differs from other sexual traits in that the acquisition process involves learning. Especially in close-ended learning species like the Bengalese finch, conditions experienced during the critical song-learning period can have a profound influence on song quality. Therefore, to understand song evolution from a life-history perspective, we investigated early ontogenetic effects on song quality. In particular, we focused on maternal effects and sibling competition. In asynchronously hatching bird species, the age hierarchy among nestlings affects physical development due to competition for food; mothers may influence this competition by adjusting their investment in each egg according to its sequence in the laying order. To independently assess these effects, chicks of the Bengalese finch were cross-fostered so that the age hierarchies formed in fostered broods were independent of the laying order. Our results indicate that song quality partially reflects early ontogenetic conditions, whereas song duration and note-type repertoire were independent of either laying order or age hierarchy. The syntactical complexity of note order declined over the laying sequence. This finding suggests that the song learning ability is influenced by within-clutch variation in maternal investment toward eggs. Considering that song syntactical complexity is subject to female preference in the Bengalese finch, it is likely that maternal resource allocation strategies play a role in song evolution. - Masayo Soma, Toshikazu Hasegawa, Kazuo OkanoyaJOURNAL OF AVIAN BIOLOGY 39 1 101 - 107 2008年01月 [査読無し][通常論文]
Recent studies of the vocal mechanisms of songbirds have shown that there are physical effects on sound production. Interspecific and phylogenetic comparisons have shown that body mass and bill morphology are two major factors affecting vocalizations such as songs. We analyzed the distance calls of female Bengalese finches Lonchurastriata var. domestica, the non-vocal learning sex, to assess the potential physical effects on the acoustic structure of vocalizations. By experimentally controlling rearing condition using cross-fostering we could examine the effects of the developmental environment and genetic background. None of the tested factors affected the peak frequency of the distance calls, but we found that larger-billed birds tended to produce shorter bout calls with higher trill rates. These results suggest that the divergence of bill morphology can affect acoustic features at the within-population level. We also found that the birds reared in the same foster brood and siblings from the same genetic parents tended to produce calls with similar trill rates. This implies that the trill rate is under the influence of developmental and genetic factors. - Masayo Soma, Daichi S. Saito, Toshikazu Hasegawa, Kazuo OkanoyaBEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 61 11 1695 - 1705 2007年09月 [査読無し][通常論文]
Maternal effects, such as investment in eggs, have profound effects on offspring fitness. Mothers are expected to skew their investment depending on the laying order and sex when unequal sibling competition occurs within a brood because of sex-specific vulnerability and age hierarchy caused by asynchronous hatching. The Bengalese finch hatches asynchronously and shows a moderate reversed sexual size dimorphism. However, contrary to commonly accepted assumptions of size-dependent vulnerability, the smaller sex (male) is more vulnerable to developmental stress caused by sibling competition. We investigated whether maternal investment would be biased by the position in laying order and the sex of eggs, and also explored the possible differences in growth patterns depending on sex, laying order, and age hierarchy by observing chicks fostered to experimentally manipulated broods where brood composition was controlled and age hierarchy was more enhanced than in natural breeding conditions. We found that overall patterns of maternal investment favored the disadvantageous sectors of sibling competition, i.e., eggs of later laying order and sons over those of early laying order and daughters. We also examined the effect of laying order on adult body size and sex differences in growth patterns. When reared in the subordinate age hierarchy, females could compensate for the deficit of decreased growth rate by taking longer to mature, whereas males could not. We suggest that this sex-specific growth pattern could be the cause of sex differences in vulnerability to early developmental stress. - Masayo Soma, Miki Takahasi, Maki Ikebuchi, Hiroko Yamada, Madoka Suzuki, Toshikazu Hasegawa, Kazuo OkanoyaETHOLOGY 112 11 1071 - 1078 2006年11月 [査読無し][通常論文]
Birdsong is an acoustic ornament. According to indicator models, a trait must be costly to act as an honest signal, but the potential costs of elaborate songs are still poorly understood. The developmental stress hypothesis Suggests that learned song characteristics Could be an honest indicator of early developmental conditions because the brain structures associated with learning songs are susceptible to early developmental stress, which could thus affect song development. Unlike previous studies of developmental stress that examined the effect of a stress hormone or restricted nutrition, we observed Bengalese finches under semi-natural breeding conditions in captivity to investigate the relationship between early rearing conditions (e.g., brood size and sex ratio) and the subsequent variation in body size and song among individuals. Our results suggest that the early rearing environment directly affects body size and song complexity, whereas song output is determined mainly by' body size. These results support the developmental stress hypothesis. Moreover, Our findings are the first to show that developmental condition affects not only the number of note types but also the syntactical complexity of the song. - Masayo Soma, Toshikazu Hasegawa, Miki Takahasi, Kazuo Okanoya, Kazuo OkanoyaOrnithological Science 5 1 77 - 84 2006年 [査読有り][通常論文]
A birdsong involves multiple traits that may have evolved under sexual selection pressure. There are two types of song traits: performance-related and elaboration-related traits. These two aspects of songs are partially independent, reflecting neural development and physical condition, respectively, but some song traits might interact with each other because they share the same mechanism for song production. Understanding the evolution of multiple ornaments requires knowledge of correlations among ornaments in the same individual. We explored the potential relationships between the following five song measures. We measured song duration and note rate as performance-related traits and average note types, linearity index score, and entropy as elaboration-related traits for the analysis. First, we found a significant relationship between linearity and entropy, indicating that syntactical complexity was consistently measured in both different variables. However, note type repertoire was not significantly associated with the two measures of syntactical complexity. Different song nuclei are responsible for each aspect of hierarchically organized song structures. Specifically, a lower-order song nucleus (RA) codes note type, while higher-order song nuclei (HVC and Nif) program transition patterns. Considering that female Bengalese Finches prefer syntactically complex songs, sexual selection, especially female choice, has played a role in shaping brains however, the sexual selection pressure for each song nucleus may differ in its intensity. Our investigation also revealed that those birds having a larger repertoire of note types tended to sing at lower speeds and require longer song bouts to sing syntactically complex songs. Hence, these results indicate that there are trade-offs and correlations between distinct aspects of performance-related and elaboration-related traits. © 2006, The Ornithological Society of Japan. All rights reserved. - M Soma, T HasegawaBEHAVIOUR 141 1121 - 1134 2004年09月 [査読無し][通常論文]
Social foraging is a far more complex phenomenon than individual foraging because of the many social interactions and communications that affect individual behaviour. Social dominance and social learning markedly influence the foraging efficiency of individuals in an unfamiliar environment. This study investigated how these two factors affect the costs and benefits of social foraging. We presented a novel feeding environment to captive budgerigars, Melopsittacus undulatus, and then compared the latency to feeding and number of pecks at the food for social and individual conditions, and for high-, middle-, and low-ranking birds. When in the social condition, birds started foraging faster and pecked more food than in the individual condition. Presumably, this lowered neophobia and enhanced foraging efficiency in the social condition was caused by social facilitation. Low-ranking birds had less resource accessibility in the social condition, probably because they were constrained by the existence of higher-ranking birds when it came to accessing the feeder. Nevertheless, the food intake of low-ranking birds almost equaled that of high- or middle-ranking birds in the social condition. In summary, high status is definitely an advantage, while low status adds some costs to individuals. Nevertheless, low-ranking birds compensate for this through enhanced foraging. It was clear that social foraging provides a great advantage to foragers of each rank, because of social facilitation.
MISC
- 相馬雅代, 長谷川寿一, 岡ノ谷一夫 認知科学 12 (3) 166 -176 2005年09月 [査読無し][通常論文]
- 相馬雅代, 長谷川寿一 日本鳥学会誌 52 (2) 97 -106 2003年12月31日 [査読無し][通常論文]
鳥類や哺乳類に関するいくつかの研究では,餌資源に集まる群れは,餌を発見した個体が同種他個体を引きつける集合音声を発することにより,形成されることが報告されている.ハシブトガラス Corvus macrorhynchos は群れで採餌を行うことがあり,そこでは「kakaka」という特徴的な音声が発声される.そこで,人工的に設置した餌場へのハシブトガラスの集合過程での「kakaka」声の頻度, その前後の群れサイズの変化の観察と「kakaka」声の再生実験を行うことにより,「kakaka」声が集合音声として機能しているのかどうかを調べた.観察の結果,「kakaka」声が発声されると群れサイズが上昇しており,この回数と採餌群れの大きさとの間には正の相関関係がみられた.また,「kakaka」声の再生は,何も再生しなかった統制実験を比べて多くの個体を引きつけた.これより,「kakaka」声は,餌資源への集合音声として機能していると考えられる.様々な理由から,動物は群れを形成することによって採餌上の利益を得ており,それが採餌効率の上昇につながる場合も多いことが,いくつかの研究において指摘されている.ハシブトガラスは,採餌群れを形成することによって,採餌効率を上昇させているのかどうか検討するため,そのついばみ速度と採餌群れの大きさを計測した.この結果,これらの2 変数の間には正の相関関係がみられた.これにより,ハシブトガラスは多数の個体が集まることで採餌効率を上昇させている可能性が示された.
書籍等出版物
- Soma M, Shibata M (担当:共著範囲:Chapter 6 Dancing in Singing Songbirds: Choreography in Java Sparrows)
Springer 2023年 (ISBN: 9789819908301) viii, 231 p. - Biotremology: Physiology, Ecology, and EvolutionOta N, Soma M (担当:共著範囲:10 Vibrational Signals in Multimodal Courtship Displays of Birds)
Springer 2022年 (ISBN: 9783030974183) - 動物行動学 原書11版J. Alcock (原著), D. R. Rubenstein (原著), 松島 俊也 (翻訳), 相馬 雅代 (翻訳), 的場 知之 (翻訳)
丸善出版 2021年01月 - 生物音響学会 (範囲:第５章共編共著)
朝倉書店 2019年11月 (ISBN: 9784254171679) xii, 441, 4p, 図版 [4] p - 上田, 恵介, 田中, 啓太, 伊澤, 栄一, 森本, 元, 相馬, 雅代, 三上, かつら, 関, 伸一, 齋藤, 武馬, 杉田, 典正, 泉, 洋江, 久井, 貴世, 江田, 真毅, 田中, 康平, 綿貫, 豊, 出口, 智広, 笠原, 里恵, 森, さやか(環境学), 森口, 紗千子, 浅井, 芝樹, 佐藤, 雪太
一色出版 2019年11月 (ISBN: 9784910389080) 431p - 日本生態学会, 沓掛, 展之, 古賀, 庸憲 (範囲:第８章)
共立出版 2012年06月 (ISBN: 9784320057388) xi, 275p, 図版 [4] p - Eldredge, Niles, 長谷川, 真理子, 長谷川, 寿一, 相馬, 雅代
麗澤大学出版会 2012年06月 (ISBN: 9784892056123) xv, 253p
共同研究・競争的資金等の研究課題
- 日本学術振興会：科学研究費助成事業 基盤研究(C)研究期間 : 2020年04月 -2023年03月代表者 : 相馬 雅代本研究課題は，鳥類の目付近の形態が示す特徴の多様性に焦点をあて，その視覚信号としての進化要因解明を目指している．これまで，形態形質自体に着目し，種内および種間変異を検討してきた．これを発展させてきたのに加え，本年度は，視覚系の果たす役割についても，種間比較と行動実験の両面から検討をおこなった．一般に，視覚信号の進化は，視覚情報処理や視覚的注意と切り離すことができない問題である．この観点から以下のような研究成果を得ている． (1) 視覚の側方性 本課題の研究対象でるカエデチョウ科鳥類は，顔から体側にかけてしばしば模様を持ち，これらが雌雄が隣同士に並び立っておこなう求愛において重要な役割をになっていることがすでに指摘されている．また，鳥類は視覚情報処理において，左右での機能局在が著しく，求愛にも片側の目（視野）を使う傾向が高い（利き目が存在する）ことはよく知られている．一方で，求愛に左右どちらの目を使うかに関しては，異なる分類群で真逆の報告がなされており，スズメ目あるいはカエデチョウ科は，鳥類の中では特異な性質を示す可能性が高い．それがなぜであるのか，進化と機能の観点から解析をおこなった． (2) 視覚的注意 特定の模様特徴が視覚信号として機能しているならば，その特性だけを抽出した抽象的な視覚刺激に対しても，鳥は視覚的注意を向ける可能性がある．そこで，抽象的な模様呈示による注視実験をおこない，選好注視による刺激弁別および選好の定量により成果を得た． 以上の結果は，いずれも論文および学会発表として年度内に発表済みである．
- 日本学術振興会：科学研究費助成事業 若手研究(A)研究期間 : 2016年04月 -2020年03月代表者 : 相馬 雅代旧年度からの研究に引きつづき，カエデチョウ科鳥類を対象に，なぜ複数モダリティにまたがる「派手な」装飾形質や行動が進化し，それがときに雌雄に備わるかを明らかにするため，(1)行動研究と(2)種間比較研究とを並行しておこなった．
(1) 行動研究においては，特に求愛に用いられる視覚ディスプレイ（求愛ダンス）がなぜ雌雄に共有されるのか，について多角的に見当し，多くの成果を得た．これまでの鳴禽類鳥類の研究では，雌雄に共有される視聴覚ディスプレイがある場合，これを双方向的に同期させることで，有効なコミュニケーションシグナルとして機能していることがしばしば指摘されてきた．しかし，カエデチョウ科の一種であるブンチョウによる研究からは，実際には雌雄で求愛ダンスを同期しているというよりは，個体内でのリズムが求愛ダンスの表出に影響を与えていることが明らかになった．さらに，メスのコンディションが求愛ダンスの表出に影響を与えることも分かったことから，一見同期しているかに見える求愛ダンスは，実際にはさほど同期性が高くなく，単に高頻度な求愛が一見同期しているように見えている可能性が高い．
(2) 種間比較研究においては，引き続き視覚シグナルに関しての検討を行っている．これまでの研究では，カエデチョウ科の求愛ダンスの複雑さは，色の派手さではなく，模様の派手さと相関進化しており，そのことは，模様の性的信号としての有効性を間接的に示唆している．実際に，いくつかの種について求愛ダンスと模様の関連に着目し調査をおこなったところ，模様のある部分の羽だけを逆立てて求愛ダンスを呈することが判明した．これに関し，カエデチョウ科ではなぜ模様が性的シグナルとして機能しうるのか，感覚便乗仮説からの説明が可能ではないかという洞察を得て，さらなる検討をすすめようとしている． - 日本学術振興会：科学研究費助成事業 若手研究(A)研究期間 : 2011年04月 -2015年03月代表者 : 相馬 雅代鳴禽類の中でもカエデチョウ科は，歌・ダンス・装飾的羽装，という複数の性淘汰形質を持っている．本研究では特に歌とダンスに主な焦点をあて，なぜ複数シグナルが進化し機能しているか検討した．カエデチョウ科の鳥達は，複数の要素にまたがるシグナル（ダンス・歌・嘴音）をうまく協調させて同時に求愛ディスプレイ中に表出していることが分かった．のみならず，発達のごく早い時期からダンスの「練習」様の行動がみられるのは，ダンスと歌の協調を発達させるためである可能性がある．しかし，歌とダンスの協調した表出がみられるにもかかわらず，系統進化史的には両行動は独立に進化しており，メカニズムと機能面も独立であることもわかった．
- 日本学術振興会：科学研究費助成事業 研究活動スタート支援研究期間 : 2010年 -2011年代表者 : 相馬 雅代ヒトを含む脊椎動物のコミュニケーションは多くの場合,視聴覚シグナルの複合的行動として表出される.本研究で対象とする鳥類(鳴禽類)においては,これまで発声行動がもっぱら着目されてきたものの,音声と身体動作との複合シグナルが雌雄間コミュニケーションに重要な役割を果たしている.このため,複数モダリティを介した情報伝達行動の進化を考える上で,このような視覚シグナルをも含む複雑なコミュニケーション行動に着目することは有用である.本研究では,その中でも求愛ディスプレイ行動の機能と特徴に焦点をあて,性淘汰の見地から社会行動の進化を明らかにすることを目指している.本年度は,ブンチョウを対象とした視覚シグナルに関わる種内研究と,鳴禽類全般を対象とした発声シグナルに関わる系統種間比較研究とを行った.前者においては,ブンチョウの性的形質の中でもとりわけ視覚シグナリングに重要と考えられる嘴の色および形の個体差について定量的検討を行い,嘴の大きさに性的二型が見られるだけでなく,色(赤さ)にも性差があり,ここから,オスの赤く盛り上がった嘴が繁殖期の求愛文脈において,オスの「質」と結びついている可能性が示唆された.後者の系統種間比較研究においては,求愛ディスプレイ行動の発声面での複雑さが繁殖成功とどの程度結びついており,それがどのような生態学的要因と結びついているかメタ分析の手法を用いて検討し,発声行動の進化に関わる性淘汰圧のレベルを明らかにした
- 日本学術振興会：科学研究費助成事業 特別研究員奨励費研究期間 : 2007年 -2009年代表者 : 相馬 雅代卵生の動物のメスにとって産卵量の調節は,限られた繁殖資源を配分投資し,自身とさらに子の適応度を最適化するという面で,重要な繁殖パラメータである.一般的に,卵1個に対する栄養投資量が多いほど子の生存率は高まる一方,メスには総投資量として大きな負担を強いることになる.また,一度の繁殖で産む卵は多いほうが,効率的に子の数を増やすことができ,適応度に寄与する可能性もあるが,他方で,育児・育雛のコストが大きくなり兄弟間競争が激化するぶん,メス自身や子の各個体にとって必ずしも利益となるとは限らない.そのため,産卵量の調節は,繁殖コンディションの影響を鋭敏に反映するのではないかと予測されている。このような産卵量の調節に関わるのが,繁殖コンディションやつがい相手オスの質である.ジュウシマツのような鳴禽類は,性淘汰形質として発声行動(歌)を求愛ディスプレイに用いる.そこでメスは,どのような歌をうたうオスとつがうと産卵投資を増加させるのか検討を行った. その結果,それぞれのメスがつがった相手の歌の音響特性が,初期発達期にさらされた歌とどれだけ似ているかどうかという指標が,卵重・一腹卵数・性比の増減に関連していた.メスの配偶投資に反映される選好性には,父親よりも,発達初期に社会交渉のあった非父親オスの歌の方が影響を与えていることが示唆された.このことは,初期聴覚記憶にもとづく性的刷り込み学習が繁殖投資に影響している一方で,近親交配を促進するような,すなわち父親の歌を選好するような傾向は無いことを示唆している.この結果については,学会において発表を行い,論文を準備中である.
- 日本学術振興会：科学研究費助成事業 特別研究員奨励費研究期間 : 2005年 -2006年代表者 : 相馬 雅代昨年度までの研究によって,ジュウシマツヒナの発達コンディションの影響の受けやすさに性差があることが示唆された.この理由として,(1)母性効果の性差,(2)性特異的な成長パターンという2つの要因を考え検討した. (1)母性効果の性差:卵順と性によって卵に量的差異が生じている可能性について検討した.卵重には性と卵順の交互作用の影響がみとめられた.すなわち母親は,産卵順が遅いほど重い卵を産む傾向があった.この傾向はメス卵よりもオス卵でより顕著で,また全般に,メスよりオスで卵重が重かった.このことは,母親がヒナ間競争で不利になりやすい孵化順の遅い卵,脆弱な性であるオスの卵に多く投資し,ヒナの減少を回避しようとする戦略を反映すると考えられる.しかしこれらの結果から,オスの脆弱性を母性効果で説明することはできなかった. (2)成長パターンの性差:性および卵順がヒナ間競争中での発達におよぼす影響を検討するため,里子実験によってヒナ間に実験的に日齢差をもうけることで,ヒナ間競争に有利な年長個体と不利な年少個体との身体発達(体重増加)を比較した.発達初期にヒナの性判定を行い,実験巣が全て両性とも2羽ずつ,各性年少・年長1羽ずつになるようヒナを配置した.各ヒナの体重増加を成長曲線にあてはめ,最終体重と成長速度に影響を与えている要因を分析した.この結果,成長速度には性と日齢差の影響が,最終体重には卵順・性・日齢差の影響がみられた.実験巣で年少群に割り当てられたヒナは成長速度の低減がみられ,特にメスにおいて顕著であった.しかし,最終体重は,年長群・年少群ともメスの方が大きかった.つまり,不利なヒナ間競争下でのメスは成長速度の大幅な低減を示すが,成長期間を柔軟に長くとることで補完していたと考えられる.他方オスは,成長期間の可塑性が低いことが,発達ストレスに対する脆弱性の原因であることが示唆された.