The influence of females on the initiation of female-to-male sex change in a coral reef fish

Abstract

In the protogynous coral reef fish Anthias squamipinnis (Peters), all males are sex-reversed females. A sexually mature female can be induced to change sex by removing a male from her social group. The influence of non-sex-changing females on the initiation of sex change was evaluated in 109 social groups in the Gulf of Eilat. When the male and largest female were removed from each of 12 single-male groups, the second-largest female changed sex in 9 groups. This result distinguished between two behavioral hypotheses suggested by previous work and made it tenable that a particular behavioral measure, the profile of behavior-received, that depends on adult females, is critical to the initiation of sex change. This species forms all-female groups as well as bisexual groups. All-female groups can be expected to have some mechanism for the production of a male. The removal of the largest female from each of 8 all-female groups failed to induce sex change in any group. The dominant female in these groups thus does not function in the same way as does the male in bisexual groups, at least in terms of the initiation of sex change. Following the removal of the male from each of 8 bisexual groups containing five or fewer adult females, a female changed sex in only 4 groups. This 50% incidence of sex reversal was lower than the 77–80% incidence in control groups containing more than five adult females. Data suggest that a minimum of four adult females is probably required for the probability of sex change after male removal to equal 75%.