ANDROGENIZATION OF DOMINANT MALES IN A CICHLID FISH - ANDROGENS MEDIATE THE SOCIAL MODULATION OF SEXUALLY DIMORPHIC TRAITS

We present data on the relationship between social status and male sec ondary sex traits, both morphological and ethological, in Oreochromis mossambicus at the onset of sexual maturation. There is a differential expression of morphological (dorsal fin height, anal fin height, mand ible width and premaxilla length) and behavioural (nuptial coloration, per cent time defending a territory, spawning pit volume, pit hoverin g and courtship rate) traits according to social status, with dominant s presenting the highest expression of these dimorphic traits. Social status also affects the development of the genital papillae, which is considered to be a good predictor of androgen levels in cichlid fishes . The results support a causal model in which social status modulate a ndrogen levels that in turn modulate the expression of behavioural and morphological male traits.