Long-Term Sperm Storage in a Superfetatious Live-Bearing Fish (Poeciliopsis gracilis, Poeciliidae)

Sperm storage is a post-copulatory strategy by which females can improve their fecundity by creating asynchrony between mating and fertilization. Sperm storage duration varies across vertebrate species, wherein longer sperm storage is thought to coincide with better reproductive success. Among the vertebrates, live-bearing fishes of the family Poeciliidae are generally assumed to store sperm for extended periods of time, but the temporal dynamics of this process remain unknown for most species. To date, research suggests that superfetatious poeciliids—which give birth to more frequent, temporally overlapping broods—may be able to store sperm longer than non-superfetatious species. However, robust empirical data for superfetatious poeciliids is very limited. Here, we assess the maximum duration of sperm storage and usage in the superfetatious poeciliid Poeciliopsis gracilis by comparing offspring production over time for both sexually isolated (single) and paired fish. We found that (a) the majority of P. gracilis females can store sperm for a maximum of 5 months with a smaller fraction of individuals able to extend this period to nearly 7 months, likely by “skipping broods,” and (b) the number of offspring produced decreases over time post-isolation. With this study, we expand our knowledge of post-copulatory strategies by providing an assessment of both sperm storage longevity and its impact on offspring production over time in a superfetatious, live-bearing fish from the family Poeciliidae. We aim to encourage further research to generate and publish data on sperm storage longevity across the family Poeciliidae to elucidate how sperm storage varies across species with different reproductive strategies.