Effect of social conditions on sex change and sex determination in two Dascyllus species, D aruanus and D albisella (Family: Pomacentridae)

Abstract

Social control of sex change and sex determination of two Dascyllus species, D. aruanus (protogynous) and D. albisella (gonochoristic), was examined in this study. The difference between gonochoristic and protogynous Dascyllus species could be the difference in the developmental time window for deviation toward maleness, and similar social mechanisms may operate in both processes. In the D. aruanus sex change experiments, males were removed from social groups to induce sex change. Females, however, did not change sex in either the laboratory or the field. This result did not support previous reports that D. aruanus is a protogynous hermaphrodite. In the D. aruanus sex determination experiments, small individuals were reared in different group sizes in the laboratory until they reached sexual maturity. In the first experiment, the largest fish in groups became male, and the sex ratio was female biased. In the second experiment, however, males occurred at every size rank, and the sex ratios did not differ from 1. Varying group sizes did not affect sexual outcome. In the D. albisella sex change experiment, females did not change sex in the laboratory, and this result agrees with previous studies that suggest D. albisella is gonochoristic. In the D. albisella sex determination experiment, both high and low size rank fish became males and the sex ratio was male biased, regardless of the group size. These results indicate that sex determination was not influenced by the social conditions. The male-biased sex ratios, however, indicate that the sex of this species was not determined randomly. One factor that may have affected sex determination was water temperature. Male biased sex ratios were also observed in the field during colder recruitment periods. This study provided no supporting evidence that either sex determination or sex change is socially controlled. The idea that gonochorism and protogyny are variations in the developmental time window could not be examined without knowledge of the actual mechanisms affecting sex change and sex determination in Dascyllus. The lack of a social effect on sex determination suggests that other environmental cues, such as water temperature, may affect sex determination in the genus Dascylllus.