Center for Ecological Research, Kyoto University, Hirano 2-509-3, Otsu 520-2113, Japan.
J Theor Biol. 2011 Feb 7;270(1):127-33. doi: 10.1016/j.jtbi.2010.11.008. Epub 2010 Nov 11.
Local mate competition (LMC) may involve some amount of inbreeding between siblings. Because sib-mating is generally accompanied by inbreeding depression, natural selection may favor a reduced rate of sib-mating, possibly affecting the evolution of sex ratio and reproductive group size. The present study theoretically investigated the evolution of these traits under LMC in the presence of inbreeding depression. When the reproductive group size evolves, the determination mechanism of sex ratio is important because the timescale of the sex ratio response to reproductive group size can affect the evolutionary process. We consider a spectrum of sex ratio determination mechanisms from purely unconditional to purely conditional, including intermediate modes with various relative strengths of unconditional and conditional effects. This analysis revealed that both the evolutionarily stable reproductive group size and ratio of males increase with higher inbreeding depression and with a larger relative strength of an unconditional effect in sex ratio determination. Unexpectedly, when the sex ratio is controlled purely conditionally, the reproductive group size cannot exceed three even under the severest level of inbreeding depression (i.e., lethal effect). The present study reveals the conditions for LMC to evolve through the analysis of the joint evolution of reproductive group size and sex ratio.
本地配偶竞争（LMC）可能涉及兄弟姐妹之间的一定程度的近亲交配。由于同胞交配通常伴随着近交衰退，自然选择可能有利于降低同胞交配的速度，这可能会影响性别比例和繁殖群体大小的进化。本研究从理论上研究了存在近交衰退时 LMC 下这些特征的进化。当繁殖群体大小进化时，性别比例的决定机制很重要，因为性别比例对繁殖群体大小的响应时间尺度会影响进化过程。我们考虑了从纯粹无条件到纯粹有条件的性别比例决定机制的范围，包括无条件和有条件效应的相对强度不同的中间模式。这项分析表明，随着近交衰退程度的增加和性别比例决定中无条件效应的相对强度的增大，进化稳定的繁殖群体大小和雄性比例都会增加。出乎意料的是，当性别比例完全由条件决定时，即使在最严重的近交衰退（即致死效应）下，繁殖群体大小也不能超过三个。本研究通过分析繁殖群体大小和性别比例的共同进化，揭示了 LMC 进化的条件。
