Data from: Sexual selection on male size drives the evolution of male-biased sexual size dimorphism via the prolongation of male development

Sexual size dimorphism (SSD) arises when the net effects of natural and sexual selection on body size differ between the sexes. Quantitative SSD variation between taxa is common, but directional intraspecific SSD reversals are rare. We combined micro- and macroevolutionary approaches to study geographic SSD variation in closely related black scavenger flies. Common garden experiments revealed stark intra and interspecific variation: Sepsis biflexuosa is monomorphic across the Holarctic, while S. cynipsea (only in Europe) consistently exhibits female-biased SSD. Interestingly, S. neocynipsea displays contrasting SSD in Europe (females larger) and North America (males larger), a pattern opposite to the geographic reversal in SSD of S. punctum documented in a previous study. In accordance with the differential equilibrium model for the evolution of SSD, the intensity of sexual selection on male size varied between continents (weaker in Europe) whereas fecundity selection on female body size did not. Subsequent comparative analyses of 49 taxa documented at least six independent origins of male-biased SSD in Sepsidae, which is likely caused by sexual selection on male size and mediated by bimaturism. Therefore, reversals in SSD and the associated changes in larval development might be much more common and rapid and less constrained than currently assumed.性大小二态性（Sexual size dimorphism，SSD）指自然选择与性选择对两性体型的净效应存在差异的现象。不同类群间的定量SSD差异较为普遍，但种内定向的SSD反转却十分罕见。本研究结合微观与宏观演化研究方法，对近缘食腐黑蝇的地理分布型SSD差异展开探究。同质园实验揭示了显著的种内与种间体型差异：双弯黑蝇（Sepsis biflexuosa）在全北区（Holarctic）范围内均无体型二态性；而仅分布于欧洲的犬蝇黑蝇（S. cynipsea）则始终表现出雌性偏向的SSD。值得注意的是，新犬蝇黑蝇（S. neocynipsea）在欧洲与北美呈现出截然相反的SSD模式：欧洲种群雌性体型更大，北美种群则雄性体型更大，这一模式与此前研究中记载的黑点黑蝇（S. punctum）的SSD地理反转模式恰好相反。依据SSD演化的差异平衡模型，不同大陆间对雄性体型的性选择强度存在差异（欧洲地区的性选择强度较弱），但对雌性体型的繁殖力选择则无此类地理差异。后续对49个类群的比较分析显示，黑蝇科（Sepsidae）中至少存在6次独立起源的雄性偏向SSD，该现象大概率由针对雄性体型的性选择所驱动，并通过发育异时性介导。由此可见，SSD反转及其伴随的幼虫发育变化，或许比当前学界所假设的更为普遍、快速，且受演化约束更少。