Zero(2007) A Comparative Study of Sex Roles in African Cichlid fishes of the Genus Julidochromis: Implications for Sexual Selection and Sexual Conflict Theory.

Sex roles are those behaviors that may be performed predominantly by one sex or the other, and are generally thought of as fixed for a species. However, these roles may be determined by a variety of social and environmental factors. In most animals, males compete for access to females, while females are faced with a choice of potential mates. This is generally explained by the ability of males to produce a larger number of offspring per unit time than females and places the ma jority of selection pressure, in the form of sexual selection, on males. The mechanisms which determine sex roles and the strength of sexual selection are still much debated. The five species of the African cichlid genus Julidochromis are an ideal model for studies of these issues because some are reported to be sex role conventional and others reversed. Furthermore, these roles may be plastic in response to body size, mating system, and environmental conditions. In order to validate claims of sex role reversal, it is necessary to conduct a rigorous behavioral comparison. This study is the first genus-wide analysis of behavior for Julidochromis to be conducted using standardized measures. I examined the effect of species, sex, body size, and reproductive stage on the amount of aggression and parental care in all five species of Julidochromis. This study provides evidence to support the importance of sex and size for aggression and parental roles, particularly for J. marlieri. In female-largest pairs, females were more dominant than males. This study also shows that the intensity of sex roles responds to changes associated with the development of offspring. Julidochromis ornatus were observed to anticipate egg laying by increasing territoriality, and spent more time in the nest once eggs were laid. Hence these species exhibit temporal plasticity in sex roles and flexibility in their responses to the social environment.

Due to its comparative nature, and the inclusion of all five Julidochromis species, this study offers novel insights into sex and species differences in this genus. Sexual conflict was addressed through the division of roles, relative sizes within a pair, dominance relationships, parental behaviors and reproductive tradeoffs. While few sex-specific traits were conclusively demonstrated to differ between species, the descriptive data provided by this this is broadly applicable to future investigations of sex role behavior. Division of roles may exist in Julidochromis, but sex roles were not as strongly diverged as I had predicted for these species.