Dougherty Liam R, Shuker David M
School of Biology, University of St Andrews, St Andrews, KY16 9TH UK ; Centre for Evolutionary Biology, School of Animal Biology, The University of Western Australia, Crawley, WA 6009 Australia.
School of Biology, University of St Andrews, St Andrews, KY16 9TH UK.
Behav Ecol Sociobiol. 2016;70:625-637. doi: 10.1007/s00265-016-2082-6. Epub 2016 Mar 2.
Sexual selection has been shown to be the driving force behind the evolution of the sometimes extreme and elaborate genitalia of many species. Sexual selection may arise before and/or after mating, or vary according to other factors such as the social environment. However, bouts of selection are typically considered in isolation. We measured the strength and pattern of selection acting on the length of the male intromittent organ (or processus) in two closely related species of lygaeid seed bug: and . In both species, we measured both pre- and post-copulatory selection. For , we also varied the experimental choice design used in mating trials. We found contrasting pre- and post-copulatory selection on processus length in . Furthermore, significant pre-copulatory selection was only seen in mating trials in which two males were present. This selection likely arises indirectly due to selection on a correlated trait, as the processus does not interact with the female prior to copulation. In contrast, we were unable to detect significant pre- or post-copulatory selection on processus length in . However, a formal meta-analysis of previous estimates of post-copulatory selection on processus length in suggests that there is significant stabilising selection across studies, but the strength of selection varies between experiments. Our results emphasise that the strength and direction of sexual selection on genital traits may be multifaceted and can vary across studies, social contexts and different stages of reproduction.
Animal genitalia vary greatly in size and complexity across species, and selection acting on genital size and shape can be complex. In this study, we show that the length of the penis in two species of seed bug is subject to complex patterns of selection, varying depending on the social context and whether selection is measured before or after mating. In one of the species, we show unexpectedly that penis length is correlated with male mating success, despite the fact that the penis does not interact with the female prior to mating. Our results highlight the fact that genitalia may be subject to both direct and indirect selection at different stages of mating and that to fully understand the evolution of such traits we should combine estimates of selection arising from these multiple episodes.
性选择已被证明是许多物种有时极端且复杂的生殖器进化背后的驱动力。性选择可能在交配前和/或交配后出现，或者根据其他因素（如社会环境）而有所不同。然而，选择的各个阶段通常被孤立地考虑。我们测量了作用于两种近缘长蝽科种子椿象雄性交配器官（或阳茎突）长度的选择强度和模式： 和 。在这两个物种中，我们都测量了交配前和交配后的选择。对于 ，我们还改变了交配试验中使用的实验选择设计。我们发现在 中，交配前和交配后的选择对阳茎突长度的作用形成对比。此外，仅在有两只雄性存在的交配试验中观察到显著的交配前选择。这种选择可能是由于对一个相关性状的选择而间接产生的，因为阳茎突在交配前并不与雌性相互作用。相比之下，我们在 中未能检测到对阳茎突长度的显著交配前或交配后选择。然而，对先前关于 中阳茎突长度交配后选择估计的一项正式荟萃分析表明，在各项研究中存在显著的稳定选择，但选择强度在不同实验之间有所变化。我们的结果强调，对生殖器性状的性选择强度和方向可能是多方面的，并且会因研究、社会背景和繁殖的不同阶段而有所变化。
动物生殖器在物种间的大小和复杂性差异很大，作用于生殖器大小和形状的选择可能很复杂。在本研究中，我们表明两种种子椿象的阴茎长度受到复杂的选择模式影响，这取决于社会背景以及选择是在交配前还是交配后进行测量。在其中一个物种中，我们意外地发现阴茎长度与雄性交配成功率相关，尽管阴茎在交配前并不与雌性相互作用。我们的结果突出了这样一个事实，即生殖器在交配的不同阶段可能受到直接和间接选择，并且为了全面理解此类性状的进化，我们应该综合来自这些多个阶段的选择估计。
