Seasonal reproductive anatomy and sperm storage in pleurocerid gastropods (Cerithioidea: Pleuroceridae)

Abstract

Life histories, including anatomy and behavior, are a critically understudied component of gastropod biology, especially for imperiled freshwater species of Pleuroceridae. This aspect of their biology provides important insights into understanding how evolution has shaped optimal reproductive success and is critical for informing management and conservation strategies. One particularly understudied facet is seasonal variation in reproductive form and function. For example, some have hypothesized that females store sperm over winter or longer, but no study has explored seasonal variation in accessory reproductive anatomy. We examined the gross anatomy and fine structure of female accessory reproductive structures (pallial oviduct, ovipositor) of four species in two genera (round rocksnail, Leptoxis ampla (Anthony, 1855); smooth hornsnail, Pleurocera prasinata (Conrad, 1834); skirted hornsnail, Pleurocera pyrenella (Conrad, 1834); silty hornsnail, Pleurocera canaliculata (Say, 1821)). Histological analyses show that despite lacking a seminal receptacle, females of these species are capable of storing orientated sperm in their spermatophore bursa. Additionally, we found that they undergo conspicuous seasonal atrophy of the pallial oviduct outside the reproductive season, and there is no evidence that they overwinter sperm. The reallocation of resources primarily to somatic functions outside of the egg-laying season is likely an adaptation that increases survival chances during winter months.