Mating Season, Egg-Laying Season, and Internal Gametic Association in the Sympatrically Occurring Fluffy Sculpin (Oligocottus snyderi) and Rosy Sculpin (O. rubellio)

Abstract

Some marine sculpins (Psychrolutidae) exhibit an unusual reproductive mode called internal gametic association (IGA), in which sperm transfer between the sexes occurs during copulation, but fertilization is delayed until the eggs are released in seawater. IGA is suggested in many internally inseminating marine sculpins, but experimental evidence of IGA is limited to a few species. The Fluffy Sculpin (Oligocottus snyderi) and its sister species, the Rosy Sculpin (O. rubellio), occur in sympatry in intertidal zones along the central California coast. Although these species likely exhibit internal insemination, their reproductive strategy is not well understood. Here, we investigate reproductive mode, mating season, egg-laying season, and sperm morphology and activity in Fluffy and Rosy Sculpins near Pillar Point, California. Delayed embryonic development was observed for one clutch of eggs of the Rosy Sculpin after exposure to seawater, indicating IGA in this species. We were unable to demonstrate IGA by initiation of development in the Fluffy Sculpin because we were unable to collect females with ovulated oocytes. Nevertheless, we found that sperm morphology with elongated head and high motility in isotonic solution while immotile in seawater in both species represent characteristics associated with IGA. Seasonal changes in gonadosomatic index (GSI) of both sexes revealed asynchronous gonadal maturation between the sexes in the Fluffy Sculpin and suggest a similar pattern in the Rosy Sculpin; however, the latter was affected by small sample size. These patterns indicate that males copulate with females before egg maturation, and females store sperm for several months. Our study supports the generality of IGA across marine sculpins and provides an understanding of its relationship to asynchrony in GSI between the sexes. Further, while Fluffy and Rosy Sculpins are similar in body morphology, habitat, and reproductive mode, the slight difference in mating season (pre-mating isolation) and sperm head and flagellum length (post-mating isolation) may have contributed to divergence in sympatry with reduced probability of hybridization.