Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA.
Proc Biol Sci. 2010 Oct 7;277(1696):2951-6. doi: 10.1098/rspb.2010.0311. Epub 2010 May 12.
Taxa in which males alone invest in postzygotic care of offspring are often considered good models for investigating the proffered relationships between sexual selection and mating systems. In the pycnogonid sea spider Pycnogonum stearnsi, males carry large egg masses on their bodies for several weeks, so this species is a plausible candidate for sex-role reversal (greater intensity of sexual selection on females than on males). Here, we couple a microsatellite-based assessment of the mating system in a natural population with formal quantitative measures of genetic fitness to investigate the direction of sexual selection in P. stearnsi. Both sexes proved to be highly polygamous and showed similar standardized variances in reproductive and mating successes. Moreover, the fertility (number of progeny) of males and females appeared to be equally and highly dependent on mate access, as shown by similar Bateman gradients for the two sexes. The absence of sex-role reversal in this population of P. stearnsi is probably attributable to the fact that males are not limited by brooding space but have evolved an ability to carry large numbers of progeny. Body length was not a good predictor of male mating or reproductive success, so the aim of future studies should be to determine what traits are the targets of sexual selection in this species.
在雄性独自为后代进行合子后护理的物种中，通常被认为是研究性选择与交配系统之间提出的关系的良好模型。在球蛛形纲海蜘蛛 Pycnogonum stearnsi 中，雄性会在身体上携带大的卵块数周，因此该物种是性别角色反转（雌性比雄性受到更强的性选择压力）的合理候选者。在这里，我们将自然种群中的交配系统的基于微卫星的评估与遗传适应性的正式定量测量相结合，以调查 P. stearnsi 中的性选择方向。两性均被证明是高度多配偶的，并且在生殖和交配成功方面表现出相似的标准化方差。此外，正如两性的 Bateman 梯度所表明的那样，雄性和雌性的生育力（后代数量）似乎同样高度依赖于配偶的获取。在该 P. stearnsi 种群中没有性别角色反转，这可能归因于这样一个事实，即雄性不受孵化空间的限制，而是进化出了携带大量后代的能力。体长不是雄性交配或生殖成功的良好预测指标，因此未来研究的目标应该是确定在该物种中哪些特征是性选择的目标。
