Lorenzi M C, Sella G
Department of Animal and Human Biology, University of Turin, Turin, Italy.
J Evol Biol. 2008 May;21(3):827-33. doi: 10.1111/j.1420-9101.2008.01513.x. Epub 2008 Feb 29.
The role of sexual selection in shaping the mating system of hermaphrodites is currently widely accepted. However, a quantification of the intensity of sexual selection in hermaphroditic animals has never been accomplished. We evaluated the opportunity for sexual selection for both the female and the male functions in the simultaneous outcrossing hermaphrodite Ophryotrocha diadema by measuring focal hermaphrodites' paternal and maternal offspring in experimental replicated monogamous and promiscuous populations, using genetic markers to estimate paternity. Opportunity for sexual selection for each of the two sexual functions was quantified by means of the Crow's index, i.e. the ratio of variance in progeny number to the squared mean number of progeny. In addition, the extent to which the reproductive success was shared among competing individuals was estimated by means of the Nonacs's B index. We documented that the strength of selection on the male and female function in hermaphrodites with external fertilization depends on the reproductive context. Under a promiscuous regime, hermaphrodites have higher opportunities for selection for both the male and the female function than under the monogamous regime. Moreover, the reproductive skew for the female function becomes greater than that for the male function, moving from monogamy to promiscuity. In our model system, allocation to one sexual function is opposed by any degree of allocation to the other, indicating that sex-specific patterns of selection operate in this model species.
性选择在塑造雌雄同体生物交配系统中的作用目前已被广泛接受。然而，对雌雄同体动物中性选择强度的量化工作从未完成。我们通过在实验性重复的一夫一妻制和滥交种群中测量焦点雌雄同体生物的父本和母本后代，利用遗传标记来估计亲权，从而评估了同时异体受精的雌雄同体生物——王冠鳃蚕（Ophryotrocha diadema）中雌性和雄性功能的性选择机会。通过克劳指数（Crow's index），即后代数量方差与后代平均数量平方的比值，对两种性功能各自的性选择机会进行了量化。此外，通过诺纳克斯B指数（Nonacs's B index）估计了竞争个体间生殖成功的共享程度。我们记录到，体外受精的雌雄同体生物中，对雄性和雌性功能的选择强度取决于生殖环境。在滥交模式下，雌雄同体生物在雄性和雌性功能上的选择机会均高于一夫一妻制模式。此外，从一夫一妻制转变为滥交时，雌性功能的生殖偏斜比雄性功能的更大。在我们的模型系统中，对一种性功能的资源分配会受到对另一种性功能任何程度分配的对抗，这表明在这个模型物种中存在性别特异性的选择模式。
