Terminal phase males stimulate ovarian function and inhibit sex change in the protogynous wrasse Thalassoma duperrey

Abstract

Under experimental conditions, the probability of sex change in the protogynous wrasse Thalassoma duperrey is determined largely by an individual's relative size within a social group. Natural populations, however, contain two distinct male phenotypes that may also play a role in regulating sex change. To investigate potential effects of male phenotype, the ability to change sex, ovarian histology and serum estradiol-17β levels were examined in females maintained under controlled social settings. Large females housed with smaller or larger terminal phase males had significantly larger gonadosomatic indices than females housed singly, with other females or with smaller initial phase males. Similarly, ovaries of females housed with terminal phase males showed no histological evidence of sex change, whereas large females from other social groupings were in advanced stages of sex change. These results demonstrate terminal phase males inhibit sex change regardless of their size relative to the female. Furthermore, gonadosomatic indices, ovarian histology, and serum estradiol-17β levels of females housed with terminal phase males indicate normal ovarian function whereas ovaries of other treatment groups appear quiescent or are undergoing sex change. Consequently, terminal phase males may be required for normal ovarian development which may, in turn, inhibit sex change in T. duperrey.