In many animal species, parents provide care for their offspring, but the parental roles of the two sexes differ considerably between and within species. Here, we use an individual-based simulation approach to investigate the evolutionary emergence and stability of parental roles. Our conclusions are in striking contrast to the results of analytical models. In the absence of initial differences between the sexes, our simulations do not predict the evolution of egalitarian care, but either female-biased or male-biased care. When the sexes differ in their pre-mating investment, the sex with the highest investment tends to evolve a higher level of parental care; this outcome does not depend on non-random mating or uncertainty of paternity. If parental investment evolves jointly with sexual selection strategies, evolution results in either the combination of female-biased care and female choosiness or in male-biased care and the absence of female preferences. The simulations suggest that the parental care pattern drives sexual selection, and not vice versa. Finally, our model reveals that a population can rapidly switch from one type of equilibrium to another one, suggesting that parental sex roles are evolutionarily labile. By combining simulation results with fitness calculations, we argue that all these results are caused by the emergence of individual variation in parental care strategies, a factor that was hitherto largely neglected in sex-role evolution theory.

中文翻译：

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父母照料的个体差异导致性别角色的差异

在许多动物物种中，父母为他们的后代提供照料，但是两个性别之间的父母角色在物种之间和内部有很大差异。在这里，我们使用基于个体的模拟方法来研究父母角色的进化出现和稳定性。我们的结论与分析模型的结果形成鲜明对比。在没有性别之间的初始差异的情况下，我们的模拟不能预测平均主义照护的发展，而可以预测女性偏爱或男性偏爱的照护。当两性在婚前投资方面有所不同时，投资最高的性别往往会发展更高水平的父母照料；这个结果不取决于非随机的交配或父权的不确定性。如果父母的投资与性选择策略共同发展，进化导致女性偏向照护和女性选择的结合，或者男性偏向照护和女性偏好的缺失。模拟表明，父母的照料方式会驱动性选择，反之则不然。最后，我们的模型表明，人口可以迅速从一种平衡类型转变为另一种平衡类型，这表明父母的性别角色在进化上不稳定。通过将模拟结果与适应性计算相结合，我们认为所有这些结果都是由父母护理策略中个体差异的出现引起的，而迄今为止，这一角色在性别角色进化理论中一直被忽略。反之亦然。最后，我们的模型表明，人口可以迅速从一种平衡类型转变为另一种平衡类型，这表明父母的性别角色在进化上不稳定。通过将模拟结果与适应性计算相结合，我们认为所有这些结果都是由父母护理策略中个体差异的出现引起的，而迄今为止，这一角色在性别角色进化理论中一直被忽略。反之亦然。最后，我们的模型表明，人口可以迅速从一种平衡类型转变为另一种平衡类型，这表明父母的性别角色在进化上不稳定。通过将模拟结果与适应性计算相结合，我们认为所有这些结果都是由父母护理策略中个体差异的出现引起的，而迄今为止，这一角色在性别角色进化理论中一直被忽略。