Data from: Deciphering the evolutionary history and developmental mechanisms of a complex sexual ornament: the abdominal appendages of Sepsidae (Diptera)

Male abdomen appendages are a novel trait found within Sepsidae (Diptera). Here we demonstrate that they are likely to have evolved once, were lost three times, and then secondarily gained in one lineage. The developmental basis of these appendages was investigated by counting the number of histoblast cells in each abdominal segment in four species: two that represented the initial instance of appendage evolution, one that has secondarily gained appendages, and one species that did not have appendages. Males of all species with appendages have elevated cell counts for the fourth segment, which gives rise to the appendages. In Perochaeta dikowi, which reacquired the trait, the females also have elevated cell count on the fourth segment despite the fact that females do not develop appendages. The species without appendages has similar cell counts in all segments regardless of sex. These results suggest that the basis for appendage development is shared in males across all species, but the sexual dimorphism is regulated differently in P. dikowi.雄性腹部附肢是扁足蝇科（Sepsidae，双翅目Diptera）中发现的一类新颖性状。本研究证实该性状大概率仅起源一次，随后经历了三次丢失，并在一个演化支中发生了次生获得。 本研究通过计数4个物种各腹节的组织芽细胞（histoblast）数量，探究此类附肢的发育基础：其中2个物种代表附肢演化的初始类群，1个为次生获得附肢的物种，剩余1个物种则不具备该附肢。 所有携带附肢的物种中，雄性的第4腹节（即附肢发育的起源节段）的组织芽细胞数量均显著升高。在重新获得该性状的Perochaeta dikowi中，尽管雌性个体并不会发育出附肢，但其第4腹节的组织芽细胞数量同样显著升高。 不具备附肢的物种，其雌雄个体各腹节的组织芽细胞数量均无显著差异。 上述结果表明，所有物种的雄性个体均共享附肢发育的基础机制，但Perochaeta dikowi的性别二态性调控模式存在差异。