Evolutionary Biology, Zoological Institute, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland.
Philos Trans R Soc Lond B Biol Sci. 2013 Jan 21;368(1613):20120052. doi: 10.1098/rstb.2012.0052. Print 2013 Mar 5.
Sex allocation theory predicts the optimal allocation to male and female reproduction in sexual organisms. In animals, most work on sex allocation has focused on species with separate sexes and our understanding of simultaneous hermaphrodites is patchier. Recent theory predicts that sex allocation in simultaneous hermaphrodites should strongly be affected by post-copulatory sexual selection, while the role of pre-copulatory sexual selection is much less clear. Here, we review sex allocation and sexual selection theory for simultaneous hermaphrodites, and identify several strong and potentially unwarranted assumptions. We then present a model that treats allocation to sexually selected traits as components of sex allocation and explore patterns of allocation when some of these assumptions are relaxed. For example, when investment into a male sexually selected trait leads to skews in sperm competition, causing local sperm competition, this is expected to lead to a reduced allocation to sperm production. We conclude that understanding the evolution of sex allocation in simultaneous hermaphrodites requires detailed knowledge of the different sexual selection processes and their relative importance. However, little is currently known quantitatively about sexual selection in simultaneous hermaphrodites, about what the underlying traits are, and about what drives and constrains their evolution. Future work should therefore aim at quantifying sexual selection and identifying the underlying traits along the pre- to post-copulatory axis.
性分配理论预测了有性生物中雄性和雌性繁殖的最佳分配。在动物中，大多数关于性分配的研究都集中在具有不同性别的物种上，而我们对同时存在雌雄同体的理解则更加零散。最近的理论预测，同时存在雌雄同体的性分配应该受到强烈的交配后性选择的影响，而交配前性选择的作用则不太清楚。在这里，我们回顾了同时存在雌雄同体的性分配和性选择理论，并确定了几个强有力的、潜在的不合理的假设。然后，我们提出了一个模型，将分配给有性选择特征的分配视为性分配的组成部分，并探讨了在放松这些假设的情况下分配的模式。例如，当投资于雄性有性选择特征导致精子竞争的倾斜，引起局部精子竞争时，这预计会导致精子产生的分配减少。我们的结论是，理解同时存在雌雄同体的性分配的进化需要详细了解不同的性选择过程及其相对重要性。然而，目前对于同时存在雌雄同体的性选择在定量上知之甚少，不知道潜在的特征是什么，也不知道是什么驱动和限制了它们的进化。因此，未来的工作应该旨在量化性选择，并确定沿交配前到交配后的轴的潜在特征。
