Institute of Biology I, University of Freiburg, Hauptstraße 1, D-79104 Freiburg, Germany.
Theoretical and Experimental Ecology Station, CNRS, 2 route du CNRS, 09200 Moulis, France.
Philos Trans R Soc Lond B Biol Sci. 2023 May 8;378(1876):20220283. doi: 10.1098/rstb.2022.0283. Epub 2023 Mar 20.
Anisogamy-the size dimorphism of gametes-is the defining difference between the male and female sexual strategies. Game-theoretic thinking led to the first convincing explanation for the evolutionary origins of anisogamy in the 1970s. Since then, formal game-theoretic models have continued to refine our understanding of when and why anisogamy should evolve. Such models typically presume that the earliest anisogamous organisms had separate sexes. However, in most taxa, there is no empirical evidence to support this assumption. Here, we present a model of the coevolution of gamete size and sex allocation, which allows for anisogamy to emerge alongside either hermaphroditism or separate sexes. We show that hermaphroditic anisogamy can evolve directly from isogamous ancestors when the average size of spawning groups is small and fertilization is relatively efficient. Sex allocation under hermaphroditism becomes increasingly female-biased as group size decreases and the degree of anisogamy increases. When spawning groups are very small, our model also predicts the existence of complex isogamous organisms in which individuals allocate resources equally to two large gamete types. We discuss common, but potentially unwarranted, assumptions in the literature that could be relaxed in future models. This article is part of the theme issue 'Half a century of evolutionary games: a synthesis of theory, application and future directions'.
雌雄配子大小差异——即配子异型性——是雄性和雌性性策略之间的决定性区别。20 世纪 70 年代，博弈论思维首次为雌雄配子异型性的进化起源提供了令人信服的解释。从那时起，正式的博弈论模型不断深化我们对何时以及为何会出现配子异型性的理解。这些模型通常假定最早的雌雄配子异型性生物具有不同的性别。然而，在大多数分类群中，没有经验证据支持这一假设。在这里，我们提出了一个关于配子大小和性别分配共同进化的模型，该模型允许雌雄配子异型性与雌雄同体或不同性别同时出现。我们表明，当产卵群体的平均大小较小时，并且受精相对有效，那么雌雄配子异型性可以直接从同型配子祖先进化而来。随着群体大小的减小和异型性程度的增加，雌雄同体中的性别分配变得越来越偏向雌性。当产卵群体非常小时，我们的模型还预测了复杂同型生物的存在，其中个体将资源平等地分配给两种大型配子类型。我们讨论了文献中常见但可能没有根据的假设，这些假设在未来的模型中可以被放宽。本文是主题为“半个世纪的进化博弈：理论、应用和未来方向的综合”的一部分。
