Data from: Evasion of predators contributes to the maintenance of male eyes in sexually dimorphic Euphilomedes ostracods (Crustacea)

Sexual dimorphisms have long drawn the attention of evolutionary biologists. However, we still have much to learn about the evolutionary, genetic, and developmental drivers of sexual dimorphisms. Here, we introduce ostracods of the genus Euphilomedes (Myodocopida, Ostracoda, and Crustacea) as a promising new system in which to investigate why and how sexual dimorphisms evolve. First, we ask whether male-skewed selective pressure from pelagic predators may help explain a dramatic sexual dimorphism in which male Euphilomedes have compound eyes, but females do not. Manipulative experiments demonstrate that blindfolding reduces the survival rate of male Euphilomedes when they are exposed to predatory fish. Blindfolding of the female rudimentary eyes (rudiments) does not, however, similarly influence the survival rate of brooding females. Further, numerical estimates of sighting distances, based on reasonable extrapolations from Euphilomedes’s eye morphology, suggest that the eyes of male Euphilomedes are useful for detecting objects roughly the size of certain pelagic predators, but not conspecifics. We conclude that eyes do not mediate direct interactions between male and female Euphilomedes, but that differences in predation pressure—perhaps associated with different reproductive behaviors—contribute to maintaining the sexually dimorphic eyes of these ostracods. Second, through transcriptome sequencing, we examined potential gene regulatory networks that could underlie sexual dimorphism in Euphilomedes’ eyes. From the transcriptome of juvenile male Euphilomedes’ eyes, we identified phototransduction genes and components of eye-related developmental networks that are well characterized in Drosophila and other species. The presence of suites of eye regulatory genes in our Euphilomedes juvenile male transcriptome will allow us, in future studies, to test how ostracods regulate the development of their sexually dimorphic eyes.性二态性长期以来一直是进化生物学家关注的核心研究议题。然而，关于性二态性在进化、遗传及发育层面的驱动机制，学界仍有诸多亟待探索的问题。本研究选取真玻璃介属（Euphilomedes），隶属于壮肢目（Myodocopida）、介形纲（Ostracoda）、甲壳纲（Crustacea），作为研究体系，用以探究性二态性的演化成因与机制，该类群展现出极佳的研究潜力。 其一，本研究旨在验证：远洋捕食者施加的雄性偏向性选择压力，是否可以解释该类群显著的性二态性——即雄性真玻璃介具有复眼结构，而雌性则无复眼。操控实验结果显示：当雄性真玻璃介暴露于掠食性鱼类环境中时，遮光处理会显著降低其存活率；而对雌性的残留眼（rudiments）进行遮光处理，却不会对抱卵雌体的存活率产生类似影响。此外，基于真玻璃介眼部形态的合理外推，本研究对可视距离进行了数值估算，结果表明：雄性真玻璃介的复眼可用于探测体型与部分远洋捕食者相近的物体，但无法识别同种个体。综上，本研究认为，复眼并未介导真玻璃介雌雄个体间的直接互动；而捕食压力的差异——或许与不同的繁殖行为相关——是维持该类介形纲动物性二态性复眼的关键因素。 其二，本研究通过转录组测序（transcriptome sequencing）技术，分析了可能调控真玻璃介眼部性二态性的潜在基因调控网络。我们从雄性幼体真玻璃介的眼部转录组中，鉴定出了光转导基因（phototransduction genes）以及与眼部发育相关的调控网络组分，这些基因和组分在果蝇（Drosophila）及其他物种中已有充分研究。雄性幼体真玻璃介眼部转录组中存在整套眼部调控基因，这为未来研究介形纲动物如何调控其性二态性复眼的发育提供了重要的实验基础。