SYMPOSIUM Evasion of Predators Contributes to theMaintenance ofMale Eyes in Sexually Dimorphic Euphilomedes ostracods (Crustacea)

Synopsis 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 extrapo-lations 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 inter-actions 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 dimor-phism in Euphilomedes ’ eyes. From the transcriptome of juvenile male Euphilomedes ’ eyes, we identified phototransduc