Hormones and social behavior of cichlid fishes: a case study in the Mozambique tilapia


The Mozambique tilapia, Oreachrzlrnis rnossambicus, is used as a case study to illustrate different aspects of the relationship between androgens and social behavior in cichlid fish. First the mating system of 0. mossambicus and its variations is described, namely the occurrence of alternative male mating tactics and male-male courtship, and the influence of social status on mating decisions and mating success. A discussion of a two-way causal relationship between androgens and social behavior follows, including the implications of social modulation of androgens for the expression of androgen-dependent male displaying characters (i.e. differential expression of secondary sex characters and male social behavior according to social status). The mechanisms regulating the action of androgens upon male behavior are also discussed with original data on the activity of brain aromatase. It is shown that male 0 . mossambicus have higher levels of brain aromatase activity than females, but aromatase activity is related neither to the gonadosomatic index nor to social status. In contrast, an androgen environment with predominance of the non-aromatizable androgen 1 1 -ketotestosterone over the aromatizable testosterone is indicative of high social status and territorial possession. This suggests that 1 1 -ketotestosterone may be playing a major role in the expression of male characters, both behavioral and morphological. The role of testosterone in female aggression is also discussed. An association between female aggression and plasma testosterone was found during the mouthbrooding cycle. Finally, the relevance of cichlids for comparative studies of vertebrate behavioral endocrinology is highlighted. INTRODUCTION: ANDROGENS AND SOCIAL BEHAVIOUR IN MALE CICHLIDS The relationship between sex steroids and behavior in teleosts has been mainly studied from the point of view of the effects of steroids upon behavior. Androgens in particular have been shown to play a major role in the expression of breeding behaviours (Liley and Stacey, 1983; Villars, 1983; Borg, 1994). Based on early ethological work (e.g.van Iersel, 1953; Wiepkema, 196 1; Baggerman, 1966), which indicated that different motivational systems may be involved in different aspects of breeding behavior, Liley and Stacey (1983) have proposed that the study of the underlying mechanisms to different aspects of breeding behavior should be analyzed separately. The breeding behaviors include: Those that occur before spawning, i.e. the establishment of breeding territories, the preparation of the spawning site (which in some species can be also used as a nest) and the attraction of a mate to the spawning site; The spawning episode, that is male ejaculation and female egg laying behavior in external fertilizers and copulation in species with internal fertilization; The parental behavior, which may involve guarding larvae and/or eggs against potential JOURNAL OF AQUARICULTURE AND AQUATIC SCIENCES CICHLID RESEARCH: STATE OF THE ART VOLUME IX Page 187 Table 1. Effect of exogenous administration of androgens andlor castration on male nuptial coloration incichlidfishes with sexualdichromatism. KT, 1 1-ketotestosterone; 1 1-OHT, 1 1 13-hydroxytestosterone; DHT, 513-dihydrotestosterone; T, testosterone; A, androstenedione. Species Treatment Effect Reference Sarotherodoiz Castration rnacrocephala Testosterone after castration Pseuu'ocrenilahrus Castration rnulticolor Testosterone after castration Testosterone given to females Astatotilapia Testosterone hurtoni propionate Testosterone given to females + + (male coloration) + ("eye bar") + (male coloration with "anal spots") + (melanophores in pelvic fins and in "anal spots" in juveniles) Levy and Aronson, 1955 Levy and Aronson, 1955 Reinboth and Rixner, 1972 Reinboth and Rixner, 1972 Reinboth and Rixner, 1972

7 Figures and Tables

Cite this paper

@inproceedings{Oliveira2006HormonesAS, title={Hormones and social behavior of cichlid fishes: a case study in the Mozambique tilapia}, author={Rui F Oliveira}, year={2006} }