Sex change in Crepidula fornicata: Influence of environmental factors on reproductive success and the timing of sex change
Many organisms experience a sex change at some point in their life cycle. In order for this life history strategy to be adaptive, lifetime reproductive success must be maximized. The size advantage hypothesis predicts a universal size at sex change for all individuals; however, for most species, size at sex change varies both across and within populations, indicating that the reproductive success of the first sex is influenced by external factors. The objective of this research was to investigate the influence of environmental variables on the sex, reproductive success, and timing of sex change of the protandrous sequential hermaphrodite, Crepidula fornicata. ^ To determine whether the sex of individuals can be predicted using environmental cues, variables at 4 different sites along the Rhode Island coastline were measured and the relationships between those variables and sex ratio at 3 spatial scales were evaluated. Logistic regression models were also constructed to predict an individual's sex. A set of microsatellite loci were developed and used to establish paternal relationships. Through paternity analysis, reproductive success for potential fathers was estimated and related to their position within the stack. ^ Substrate availability, population density, and stack height did not affect sex ratio at the population, patch, or stack scale. Instead, a tendency for C. fornicata to exist in a 1:1 sex ratio was observed. According to the logistic regression models, size, position, stack height and sex ratio were significant indicators of sex, with position being the best indicator. Using genotypic data, I was able to identify the true father for 96% of the offspring tested and paternity analysis revealed that as a male's distance from the female increased, his reproductive success decreased. Low reproductive success for males in higher positions suggests that the males closest to the female have a competitive advantage. Despite being the strongest competitors, they can fall victim to decreased reproductive success as a result of increased competition. If these males suffer a decrease in reproductive success that is greater than the loss they would suffer by switching sex at a small size, then they should change sex. ^
Dina A Proestou,
"Sex change in Crepidula fornicata: Influence of environmental factors on reproductive success and the timing of sex change"
Dissertations and Master's Theses (Campus Access).