Data from: Female-biased dispersal in a bat with a female-defence mating strategy

The ultimate causes for predominant male-biased dispersal (MBD) in mammals and female-biased dispersal (FBD) in birds are still subject to much debate. Studying exceptions to general patterns of dispersal, for example, FBD in mammals, provides a valuable opportunity to test the validity of proposed evolutionary pressures. We used long-term behavioural and genetic data on individually banded Proboscis bats (Rhynchonycteris naso) to show that this species is one of the rare mammalian exceptions with FBD. Our results suggest that all females disperse from their natal colonies prior to first reproduction and that a substantial proportion of males are philopatric and reproduce in their natal colonies, although male immigration has also been detected. The age of females at first conception falls below the tenure of males, suggesting that females disperse to avoid father–daughter inbreeding. Male philopatry in this species is intriguing because Proboscis bats do not share the usual mammalian correlates (i.e. resource-defence polygyny and/or kin cooperation) of male philopatry. They have a mating strategy based on female defence, where local mate competition between male kin is supposedly severe and should prevent the evolution of male philopatry. However, in contrast to immigrant males, philopatric males may profit from acquaintance with the natal foraging grounds and may be able to attain dominance easier and/or earlier in life. Our results on Proboscis bats lent additional support to the importance of inbreeding avoidance in shaping sex-biased dispersal patterns and suggest that resource defence by males or kin cooperation cannot fully explain the evolution of male philopatry in mammals.

哺乳动物中普遍存在的雄性偏向扩散（male-biased dispersal, MBD）以及鸟类中雌性偏向扩散（female-biased dispersal, FBD）的终极成因，至今仍存在诸多学术争议。针对扩散通用模式的例外情况（例如哺乳动物中的雌性偏向扩散FBD）开展研究，可为检验已提出的进化压力假说的合理性提供宝贵契机。本研究依托对佩戴个体识别环的长鼻蝙蝠（Rhynchonycteris naso）开展的长期行为学与遗传学监测数据，证实该物种是少数呈现雌性偏向扩散的哺乳动物例外类群之一。研究结果显示，所有雌性个体均会在首次繁殖前离开其出生群；尽管已检测到雄性迁入现象，但绝大多数雄性会留居出生地，并在出生群内完成繁殖。雌性首次受孕的年龄低于雄性的任职时长，这表明雌性扩散的核心动因是避免父女近交。该物种的雄性留居现象颇为引人关注，因为长鼻蝙蝠并不具备雄性留居的典型哺乳动物关联特征——即资源防御型多配偶制与/或亲属合作。它们的交配策略基于配偶防御，据推测雄性亲属间的局部配偶竞争会十分激烈，本应阻碍雄性留居的演化进程。然而，与迁入雄性不同，留居雄性可凭借对出生地觅食地的熟悉度，在种群中更早、更轻松地获得统治地位。本研究针对长鼻蝙蝠的结果，进一步支持了近交回避在塑造性偏向扩散模式中的重要性，同时表明雄性的资源防御行为或亲属合作，并不能完全解释哺乳动物中雄性留居现象的演化。