Zoological Institute, University of Basel, Switzerland; Centre d'Écologie Fonctionnelle et Évolutive, Montpellier, France.
Evolution. 2013 Nov;67(11):3233-42. doi: 10.1111/evo.12189. Epub 2013 Jul 10.
Sex allocation theory is considered as a touchstone of evolutionary biology, providing some of the best supported examples for Darwinian adaptation. In particular, Hamilton's local mate competition theory has been shown to generate precise predictions for extraordinary sex ratios observed in many separate-sexed organisms. In analogy to local mate competition, Charnov's mating group size model predicts how sex allocation in simultaneous hermaphrodites is affected by the mating group size (i.e., the number of mating partners plus one). Until now, studies have not directly explored the relationship between mating group size and sex allocation, which we here achieve in the simultaneously hermaphroditic flatworm Macrostomum lignano. Using transgenic focal worms with ubiquitous expression of green-fluorescent protein (GFP), we assessed the number of wild-type mating partners carrying GFP+ sperm from these focal worms when raised in different social group sizes. This allowed us to test directly how mating group size was related to the sex allocation of focal worms. We find that the proportion of male investment initially increases with increasing mating group size, but then saturates as predicted by theory. To our knowledge, this is the first direct test of the mating group size model in a simultaneously hermaphroditic animal.
性分配理论被认为是进化生物学的试金石，为达尔文适应论提供了一些最有力的例证。特别是，汉密尔顿的局部配偶竞争理论已被证明可以对许多雌雄异体生物中观察到的异常性别比例做出精确的预测。类比于局部配偶竞争，查诺夫的交配群体大小模型预测了同时存在的雌雄同体中的性分配如何受到交配群体大小（即交配伙伴的数量加一）的影响。到目前为止，研究尚未直接探讨交配群体大小和性分配之间的关系，我们在同时存在的雌雄同体扁虫 Macrostomum lignano 中实现了这一点。我们使用具有绿色荧光蛋白（GFP）普遍表达的转基因焦点蠕虫，评估了当这些焦点蠕虫在不同的社会群体大小中生长时，携带 GFP+精子的野生型交配伙伴的数量。这使我们能够直接测试交配群体大小与焦点蠕虫性分配的关系。我们发现，雄性投资的比例最初随着交配群体大小的增加而增加，但随后如理论所预测的那样达到饱和。据我们所知，这是对同时存在的雌雄同体动物中的交配群体大小模型的首次直接测试。
