Inter-group movement of females of the polygynous gobiid fish Trimma okinawae in relation to timing of protogynous sex change

Social conditions and function of inter-group movement of females of the polygynous goby, Trimma okinawae, have been studied at Akamizu Beach, Kagoshima, Japan. Some females moved from their original groups, where the male was still present, to other groups. Before the movement females sometimes temporarily visited the group into which they subsequently moved, suggesting they were able to assess social conditions during the visit. By moving, the females increased in size rank or escaped from similar-sized female competitors in their previous groups. Although the social ranks of the moving females in their original groups were lower than those of the resident females, the ratio of the number of females that changed sex to the number of females surviving at the end of the study did not differ for the two types of female. Inter-group movement of females may increase the probability of their changing sex to become a dominant male. © 2006 Japan Ethological Society and Springer-Verlag.