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。类群间的定量SSD差异较为普遍，但定向的种内SSD逆转却十分罕见。本研究结合微进化与宏进化研究方法，对近缘黑蝇科（Sepsidae）昆虫的地理格局SSD变异展开研究。

同质园实验结果揭示了显著的种内与种间变异：弯脉黑蝇（Sepsis biflexuosa）在全北界范围内均表现为体型二态性缺失；仅分布于欧洲的西普黑蝇（S. cynipsea）则始终呈现雌性偏向的SSD（即雌性体型大于雄性）。

有趣的是，新西普黑蝇（S. neocynipsea）在欧洲与北美洲表现出截然相反的SSD模式：欧洲种群为雌性体型更大，而北美洲种群则为雄性体型更大——这一模式与既往研究中记载的斑点黑蝇（S. punctum）的SSD地理逆转现象恰好相反。

契合SSD演化的差异平衡模型，雄性体型所受性选择的强度在两大洲间存在差异（欧洲地区的选择强度较弱），而雌性体型所受的繁殖力选择则未表现出地理差异。

后续对49个类群的比较分析显示，黑蝇科中至少存在6次雄性偏向SSD的独立起源事件，这一现象大概率由雄性体型所受的性选择驱动，并通过两性发育异时性（bimaturism）介导。

因此，SSD逆转及其伴随的幼虫发育变化，或许比当前学界的假设更为普遍、快速且受约束程度更低。