Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
Proc Biol Sci. 2011 Sep 7;278(1718):2611-20. doi: 10.1098/rspb.2010.2453. Epub 2011 Jan 26.
The role of sexual selection in fuelling genital evolution is becoming increasingly apparent from comparative studies revealing interspecific divergence in male genitalia and evolutionary associations between male and female genital traits. Despite this, we know little about intraspecific variance in male genital morphology, or how male and female reproductive traits covary among divergent populations. Here we address both topics using natural populations of the guppy, Poecilia reticulata, a livebearing fish that exhibits divergent patterns of male sexual behaviour among populations. Initially, we performed a series of mating trials on a single population to examine the relationship between the morphology of the male's copulatory organ (the gonopodium) and the success of forced matings. Using a combination of linear measurements and geometric morphometrics, we found that variation in the length and shape of the gonopodium predicted the success of forced matings in terms of the rate of genital contacts and insemination success, respectively. We then looked for geographical divergence in these traits, since the relative frequency of forced matings tends to be greater in high-predation populations. We found consistent patterns of variation in male genital size and shape in relation to the level of predation, and corresponding patterns of (co)variation in female genital morphology. Together, these data enable us to draw tentative conclusions about the underlying selective pressures causing correlated patterns of divergence in male and female genital traits, which point to a role for sexually antagonistic selection.
性选择在推动生殖器进化方面的作用，正通过揭示同种间雄性生殖器的差异以及雄性和雌性生殖器特征之间的进化关联的比较研究，变得越来越明显。尽管如此，我们对雄性生殖器形态的种内变异，或不同种群中雄性和雌性生殖特征如何协同进化，知之甚少。在这里，我们使用丽鱼科的食蚊鱼（Poecilia reticulata）的自然种群来解决这两个问题，食蚊鱼是一种胎生鱼，其雄性的性行为在种群之间存在明显的差异。最初，我们在一个单一的种群中进行了一系列交配试验，以研究雄性交配器官（交接器）的形态与强制交配成功之间的关系。通过线性测量和几何形态测量学的结合，我们发现交接器的长度和形状的变化分别预测了强制交配中生殖器接触的速度和受精成功率。然后，我们在这些特征上寻找地理上的差异，因为在高捕食压力的种群中，强制交配的相对频率往往更高。我们发现，在与捕食水平相关的雄性生殖器大小和形状上存在一致的变异模式，以及在雌性生殖器形态上相应的（共）变异性模式。这些数据使我们能够初步得出结论，认为雄性和雌性生殖器特征的相关分化模式是由性拮抗选择引起的，这表明性拮抗选择在其中发挥了作用。
