Effect of changing harem on timing of sex change in female cleaner fish Labroides dimidiatus

Abstract

The cleaner wrasse Labroides dimidiatus has a haremic mating system. When the territorial dominant male disappears, the largest female of the harem changes sex and takes it over. During a 2.5-year field study on a high-density population, females sometimes temporarily intruded into neighbouring harems. Almost half of these females transferred to harems that they had frequently visited, suggesting that females may assess the social conditions of the harem during these visits. After the transfer, females increased in rank or escaped from similar-sized competitors in their former harem. As a result, such females could become the dominant male earlier than females that never changed harem. The females that transferred were reproductively active, but less fecund than females that did not. Their low spawning success as females may be offset by their earlier sex change to become a dominant male. We suggest that changing harems has developed as a life history tactic in high-density conditions where females, in a fish whose sex is socially controlled, compete to become male.