Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland.
Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
J Anim Ecol. 2021 Aug;90(8):1831-1843. doi: 10.1111/1365-2656.13487. Epub 2021 May 4.
Sexes often differ more obviously in secondary sexual characteristics than in traits that appear naturally selected, despite conceivable benefits to intersexual niche partitioning. Genetic constraints may play a role in limiting sex-specific niche evolution; however, it is not clear why this limit should apply to naturally selected traits more than those under sexual selection; the latter routinely produces dimorphism. We ask whether ecological factors and/or features of the mating system limit dimorphism in resource use, or conversely, what conditions are the most permissible ones for sexual niche differences. The scale of mating competition and spatial variation in resource availability can help predict sexually dimorphic niches or the lack thereof. We investigate why and when dimorphism might fail to evolve even if genetic covariation between the sexes posed no constraint. Our analytical model incorporates the first aspect of spatial interactions (scale of mating competition). It is followed by simulations that explore broader conditions, including multiple resources with habitat heterogeneity, genetic correlations and non-Gaussian resource-use efficiency functions. We recover earlier known conditions for favourable conditions for the evolution of niche partitioning between sexes, such as narrow individual niche and low degrees of genetic constraint. We also show spatial considerations to alter this picture. Sexual niche divergence occurs more readily when local mating groups are small and different resources occur reliably across habitats. Polygyny (medium-sized or large mating groups) can diminish the prospects for dimorphism even if no genetic constraints are present. Habitat heterogeneity typically also disfavours niche dimorphism but can also lead to polymorphism within a sex, if it is beneficial to specialize to be very competitive in one habitat, even at a cost to performance in the other. Sexual conflict is usually used to explain dimorphic traits or behaviours. Our models highlight that introducing conflict (achieved by switching from monogamy to polygamy) can also be responsible for sexual monomorphism. Under monogamy, males benefit from specializing to consume other resources than what feeds the female best. Polygyny makes males disregard this female benefit, and both sexes compete for the most profitable resource, leading to overlapping niches.
性别之间的第二性征差异通常比自然选择产生的特征更为明显，尽管两性之间的生态位分化可能会带来益处。遗传限制可能在限制特定性别生态位进化方面发挥作用；然而，不清楚为什么这种限制应该更适用于自然选择产生的特征，而不是性选择产生的特征；后者通常会产生二态性。我们想知道生态因素和/或交配系统的特征是否限制了资源利用的二态性，或者相反，哪些条件最有利于性生态位差异。交配竞争的规模和资源可利用性的空间变化可以帮助预测两性异形的生态位，或者缺乏两性异形的生态位。我们研究为什么即使性别之间的遗传相关性没有限制，二态性也可能无法进化。我们的分析模型结合了空间相互作用的第一个方面（交配竞争的规模）。随后进行了模拟，探索了更广泛的条件，包括具有栖息地异质性的多种资源、遗传相关性和非正态资源利用效率函数。我们恢复了先前已知的性别之间生态位分化进化有利条件，例如狭窄的个体生态位和较低的遗传限制程度。我们还展示了空间因素如何改变这种情况。当地交配群体较小时，两性之间的生态位差异更容易发生，不同的资源可靠地存在于不同的栖息地中。即使没有遗传限制，多配偶制（中等或大的交配群体）也会降低二态性的可能性。栖息地异质性通常也不利于生态位二态性，但如果在一个栖息地中非常有竞争力的专业化对物种有利，即使这会对另一个栖息地的表现造成代价，它也可以导致同一性别内的多态性。性冲突通常用于解释二态性特征或行为。我们的模型强调，引入冲突（通过从一夫一妻制转变为多配偶制来实现）也可能导致性同态性。在一夫一妻制下，雄性从专门食用雌性最佳食物以外的其他资源中获益。多配偶制使雄性忽视了这种雌性益处，雌雄两性都为最有利可图的资源而竞争，导致生态位重叠。
