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.

Diversity and flexibility of sex-change strategies in animals

“…This assumption has been overturned by an increasing list of fish species in which multiple sex reversals can occur ( [13,[46][47][48] and references therein) and by the recognition of ecological conditions that favour repetitive sex change [49,50].…”

“…Importantly, recent research has shown that the decision to become a primary male might be a plastic response to local social conditions [47], just as adult sex change is in many species. It now seems that there could be a continuum in the timing of sexual differentiation in some species that transcends ontogenetic boundaries.…”

The influence of social factors on juvenile sexual differentiation in a diandric, protogynous grouper Epinephelus coioides

“…The largest individual was a primary female, the second largest one a male, and the smallest one remained sexually undifferentiated in social units of triplets (Wood 1986;Bruslé-Sicard et al 1994). In the bi-directional sex-changing Cephalopholis boenak, all isolated, single, juveniles differentiated as primary males, and the largest ones in social units of pairs, triplets and quartets were always primary males (Liu and Sadovy 2004a;Sadovy de Mitcheson and Liu 2008). The study suggested that growth rate played a role in C. boenak sexual differentiation with faster growth associated with maleness.…”

“…Recently, studies have demonstrated experimentally that social factors can influence juvenile sexual differentiation in sequentially hermaphroditic teleosts, reflecting the plasticity of sex expression at different life stages in this group of fishes. Examples include the bi-directional sex change in the Chocolate hind Cephalopholis boenak (Serranidae, Epinephelinae) (Liu and Sadovy 2004a;Sadovy de Mitcheson and Liu 2008) and the Rippled coralgoby Gobiodon erythrospilus (Gobiidae) (Hobbs et al 2004), and protogyny in the Bluehead wrasse Thalassoma bifasciatum (Labridae) (Munday et al 2006b); the initial sex in these species was influenced experimentally by the number of juveniles in social units.…”

Mathematical Modeling Describing the Effect of Fishing and Dispersion on Hermaphrodite Population Dynamics

“…Some females can reach 26 years old without changing sex [5,20,21]. However, a dependence on the sex ratio of the population and social control of the sexual inversion exists [16]. In our case, we assume that sexual inversion occurs for all groupers at a fixed length.…”