Title of Work
Basel, Switzerland [virtual]
In hermaphrodites the impact of mating order on fertilization success may not only shape the evolution of sperm competition but also influence gender roles during copulation. Planorbella trivolvis exhibit strong first sperm precedence – when snails are presented with two mates 24 hours apart, most eggs (over 80%) are fertilized by the first mate. This outcome may be explained if sperm from the first mate fill the storage organ so there is no room for additional sperm. It may also indicate a switch in gender role so that the focal animal acts as male, and not in the female role during the second mating. To test the hypothesis that sperm from a first mate fills the storage organ, preventing the second mate from fertilizing eggs, we conducted three groups of matings: snails mated first to one partner and then another either 48 hours, 4 weeks, or 8 weeks later. If lack of storage capacity prevents second mate sperm from fertilizing eggs, then the longer the lag between matings, the more likely it should be that sperm is depleted and that sperm from the second mate are less successful. Using albinism as a marker of paternity, we observed all embryos from eggs laid within one week of the second mating. There was a significant effect of second mate latency on the proportion of progeny sired by the second mate. Second matings 48 hours after the first resulted in approximately 10% of progeny sired by the second mate whereas an 8 week delay results in more than 50% of embryos sired by the second mate. These data are consistent with sperm storage capacity influencing sperm precedence but do not rule out the influence of previous mating on gender roles in subsequent copulations.
Norton, Cynthia, "Possible mechanism for first sperm precedence in the hermaphroditic freshwater snail Planorbella trivolvis" (2021). Biology Faculty Scholarship. 49.