Meeting Abstract

23.3  Monday, Jan. 4  Sex Change in Two Species of Calyptraeid Gastropods: Effects of Nutrition and Perceived Mortality Risk COLLIN, R*; MéROT, C; Smithsonian Tropical Research Institute; Smithsonian Tropical Research Institute collinr@si.edu

Although social control of sex-change has been well documented, little is known about other environmental influences that lead to differences in size at or timing of sex change. In protandrous calyptraeid gastropods, laboratory studies have shown that variation in associations with conspecifics do not explain the full range of variation in size at sex change. Therefore we examined how variation in food availability and perceived mortality risk affect size at sex change in two calyptraeids: Crepidula cf. marginalis and Crepidula incurva. High, medium and low food concentrations had significant impact on growth rates in both species, and C. cf. marginalis changed sex at a significantly larger size at high food concentrations than at medium concentrations. The duration of the transitional phase was significantly shorter in the high food than the medium food treatment. In the mortality risk experiment, C. cf. marginalis exposed to crab odor or daily drying did not differ in growth rate from the high food treatment, however animals exposed to the crab control grew faster than the other three treatments. These treatments generally did not affect the size at sex change and duration of sex change. Finally, we found that transitional animals had a higher growth rate than either males or females. Overall these experiments demonstrated that food availability has a significant effect on size at sex change, and that those experiencing harsh conditions show a different pattern, changing sex by losing male characteristics earlier and at smaller sizes, remaining longer in the transitional phase, and becoming female at smaller size. Interpretation of the perceived mortality risk treatment was complicated by the unexpected increased growth in one of the controls, but these treatments had a smaller effect on sex change than did food availability.