SOCIAL FACILIATION AND SENSORY MEDIATION OF ADULT SEX-CHANGE IN A CRYPTIC, BENTHIC MARINE GOBY

When females of the protogynous gobiid, Coryphopterus glaucofraenum Gi ll 1863, were removed from their natural social system and isolated fr om males in all-female groups, the number of females in a group influe nced both the proportion of groups exhibiting sex change, as well as t he number of females changing sex within groups. Sex change was most p revalent in large, all-female groups; solitary females, however, infre quently changed sex. Therefore, in C. glaucofraenum the presence of ot her female conspecifics promotes sex change. In the presence of larger male(s), the incidence of sex change among experimental females was e ither reduced or negated, depending upon the number of females. Sensor y isolation experiments revealed the importance of two sensory modalit ies in the induction and incidence of sex change. Water-borne cues, pr obably chemical in nature, released by conspecific female groups incre ased the probability of sex change among solitary females. These induc tion cues were both sex- and species-specific. In addition, visual cue s influenced the number of females changing sex within larger, all-fem ale groups. Visual cues, in the absence of other means of information exchange, appear to play a role in determination of group membership a mong female C. glaucofraenum. Lastly, while all females within social groups experienced the same sensory cues, usually only the largest fem ale(s) ultimately changed sex. Thus, while sensory cues mediated the t iming of sex change, other factors (probably social) likely played a p art in determining which individuals within the social group actually changed sex.