The influence of social factors on adult sex change and juvenile sexual differentiation in a diandric, protogynous epinepheline, Cephalopholis boenak (Pisces, Serranidae)

Abstract

Adult sex change and juvenile sexual differentiation in the protogynous epinepheline Cephalopholis boenak were demonstrated in captivity to be influenced by social factors. Adult sex change in C. boenak occurred in two directions, female to male and male to female. The presence or absence of a larger male plays an important role in adult female sex change; female(s) did not change sex in the presence of a larger male, but sex change occurred after the removal of the larger males in the same social groups. In male pairs, either the larger or the smaller male changed sex. Male to female sex change has not been reported previously in Cephalopholis, and only rarely in epinephelines. This is the first report of direct male sexual differentiation from juveniles (i.e. primary male development), through manipulating the number of juveniles, in a protogynous epinepheline. All isolated, single, juveniles differentiated directly as males, and male to female sex ratios did not differ significantly from 1:1 in all experimental social groups of two to four juveniles. Differentiating males grew significantly faster than differentiating females and undifferentiated juveniles during the 57-week experimental period. The role of growth rate in sex determination in C. boenak is not known but clearly plays a part in juvenile sexual differentiation and merits further investigation. Social factors influencing bi-directional adult sex change and juvenile sexual differentiation are a reflection of plasticity of sexual expression in C. boenak, in particular, and the Serranidae in general.