Behavioral ecology of reproduction in the pomacanthid angelfish, Centropyge potteri

Abstract

The Hawaiian angelfish, Centropyge potteri, was used as a model system to develop and test hypotheses regarding the integration of stimuli from both physical and social environments into reproductive strategies; specifically the social control of sex change, and temporal patterns of mating. Prerequisite to these topics are descriptions of sexual dimorphism and dichromatism, and protogynous sex change. These descriptions include differences between the sexes in meristics, morphometries, and color pattern; a field-test of identification of the sexes; and histological descriptions of the gonads. Encounter-rate models are developed for territorial-haremic fishes. They show how a combination of social-group composition and density may form predictable patterns of contact between social-group members. The patterns of contact are asserted as cues for sex change. The models are tested with S;. potteri by demonstrating that encounters with smaller fish are needed for sex change, encounters with larger fish prevent sex change, and changing the density of a social group alters encounter rates and can induce sex change. Sex change is associated with conditions that yield high smaller-fish encounter, and low larger-fish encounter, for the sex-change candidate. A temporal-threshold model of polygynous mating (TMPM) is developed. This model shows how females that mate with polygynous males may offset polygyny costs by mating during less advantageous times for which fewer females compete. The model's potential for broad applicability is shown to be worthy of study with examples from African elephants and C. potteri. The TMPM is empirically tested using C. potteri. Females compete for mating order. Competition results in a larger variance in daily time of mating, independent of the time required for mating, when females are in a larger group. Females probably disperse mating in time to avoid polygyny costs, including interference by competing females. These results were a priori predictions of the TMPM. The conclusion is that information from both physical and social environments is integrated into C. potteri reproductive strategies. In this way females may minimize potential costs associated with changing sex, and reproducing in a polygynous mating system.