Barreto Felipe S, Avise John C
Behav Ecol Sociobiol. 2011 Aug;65(8):1595-1604. doi: 10.1007/s00265-011-1170-x. Epub 2011 Mar 12.
Male-biased size dimorphism is usually expected to evolve in taxa with intense male-male competition for mates, and it is hence associated with high variances in male mating success. Most species of pycnogonid sea spiders exhibit female-biased size dimorphism, and are notable among arthropods for having exclusive male parental care of embryos. Relatively little, however, is known about their natural history, breeding ecology, and mating systems. Here we first show that Ammothella biunguiculata, a small intertidal sea spider, exhibits male-biased size dimorphism. Moreover, we combine genetic parentage analysis with quantitative measures of sexual selection to show that male body size does not appear to be under directional selection. Simulations of random mating revealed that mate acquisition in this species is largely driven by chance factors, although actual paternity success is likely non-randomly distributed. Finally, the opportunity for sexual selection (I(s)), an indirect metric for the potential strength of sexual selection, in A. biunguiculata males was less than half of that estimated in a sea spider with female-biased size dimorphism, suggesting the direction of size dimorphism may not be a reliable predictor of the intensity of sexual selection in this group. We highlight the suitability of pycnogonids as model systems for addressing questions relating parental investment and sexual selection, as well as the current lack of basic information on their natural history and breeding ecology. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00265-011-1170-x) contains supplementary material, which is available to authorized users.
通常认为，在雄性为争夺配偶而进行激烈竞争的分类群中会进化出雄性偏向的体型二态性，因此它与雄性交配成功率的高方差相关。大多数海蜘蛛类的海蜘蛛表现出雌性偏向的体型二态性，并且在节肢动物中很显著的一点是，它们具有雄性对胚胎的专属亲代抚育。然而，关于它们的自然史、繁殖生态学和交配系统，人们所知相对较少。在这里，我们首先表明，潮间带小海蜘蛛双爪艾氏海蛛表现出雄性偏向的体型二态性。此外，我们将遗传亲权分析与性选择的定量测量相结合，以表明雄性体型似乎并未受到定向选择。随机交配模拟显示，尽管实际的父权成功可能并非随机分布，但该物种的配偶获取在很大程度上是由偶然因素驱动的。最后，双爪艾氏海蛛雄性的性选择机会（I(s)），即性选择潜在强度的间接指标，不到具有雌性偏向体型二态性的海蜘蛛估计值的一半，这表明体型二态性的方向可能不是该类群中性选择强度的可靠预测指标。我们强调海蜘蛛类作为解决与亲代投资和性选择相关问题的模型系统的适用性，以及目前关于它们自然史和繁殖生态学的基础信息的匮乏。电子补充材料：本文的在线版本（doi:10.1007/s00265-011-1170-x）包含补充材料，授权用户可获取。
