García-Navas V, Noguerales V, Cordero P J, Ortego J
Department of Integrative Ecology, Estación Biológica de Doñana (EBD-CSIC), Seville, Spain.
Grupo de Investigación de la Biodiversidad Genética y Cultural, Instituto de Investigación en Recursos Cinegéticos IREC (CSIC-UCLM-JCCM), Ciudad Real, Spain.
J Evol Biol. 2017 Aug;30(8):1592-1608. doi: 10.1111/jeb.13131. Epub 2017 Jul 3.
Sexual size dimorphism (SSD) is widespread and variable in nature. Although female-biased SSD predominates among insects, the proximate ecological and evolutionary factors promoting this phenomenon remain largely unstudied. Here, we employ modern phylogenetic comparative methods on eight subfamilies of Iberian grasshoppers (85 species) to examine the validity of different models of evolution of body size and SSD and explore how they are shaped by a suite of ecological variables (habitat specialization, substrate use, altitude) and/or constrained by different evolutionary pressures (female fecundity, strength of sexual selection, length of the breeding season). Body size disparity primarily accumulated late in the history of the group and did not follow a Brownian motion pattern, indicating the existence of directional evolution for this trait. We found support for the converse of Rensch's rule (i.e. females are proportionally bigger than males in large species) across all taxa but not within the two most speciose subfamilies (Gomphocerinae and Oedipodinae), which showed an isometric pattern. Our results do not provide support for the fecundity or sexual selection hypotheses, and we did not find evidence for significant effects of habitat use. Contrary to that expected, we found that species with narrower reproductive window are less dimorphic in size than those that exhibit a longer breeding cycle, suggesting that male protandry cannot solely account for the evolution of female-biased SSD in Orthoptera. Our study highlights the need to consider alternatives to the classical evolutionary hypotheses when trying to explain why in certain insect groups males remain small.
性大小二态性（SSD）在自然界中广泛存在且具有变异性。尽管在昆虫中雌性偏向的SSD占主导，但促进这种现象的直接生态和进化因素在很大程度上仍未得到研究。在此，我们对伊比利亚蝗虫的八个亚科（85个物种）采用现代系统发育比较方法，以检验体型和SSD不同进化模型的有效性，并探讨它们如何受到一系列生态变量（栖息地专业化、底物利用、海拔）的塑造和/或受到不同进化压力（雌性繁殖力、性选择强度、繁殖季节长度）的限制。体型差异主要在该类群历史的后期积累，且不遵循布朗运动模式，这表明该性状存在定向进化。我们发现在所有分类单元中都支持伦施法则的相反情况（即大型物种中雌性比雄性比例更大），但在两个物种最多的亚科（斑翅蝗亚科和斑腿蝗亚科）中不支持，这两个亚科呈现等比模式。我们的结果不支持繁殖力或性选择假说，并且我们没有发现栖息地利用有显著影响的证据。与预期相反，我们发现繁殖窗口较窄的物种在体型上的二态性比繁殖周期较长的物种小，这表明雄性先熟不能单独解释直翅目昆虫中雌性偏向的SSD的进化。我们的研究强调，在试图解释为什么在某些昆虫群体中雄性体型仍然较小时，需要考虑经典进化假说之外的其他因素。
