The physiological effects of social status in the cooperatively breeding cichlid Neolamprologus pulcher

The physiological effects of social rank were examined in three different experiments withNeolamprologus pulcher a cooperatively breeding cichlid, endemic to Lake Tanganyika, EastAfrica. The effects of rank on physiology between pairs of dominant and subordinate size-matched fish (experiment 1) and among groups of four size-matched fish (experiment 2) wereexamined. A third experiment mimicked the natural social structure in the wild; pairs wereobserved with other group members including breeders. The effect of social position wasinvestigated on growth rates, liver concentrations of adenosine triphospate (ATP), lipids,proteins, creatine phosphate (CrP), glucose and glycogen as well as plasma cortisol. In natur-alistic group settings, dominants displayed higher levels of liver protein and plasma cortisol. Inthe absence of breeders, dominant individuals (of helper pairs) had higher liver glycogen levelsand dominant fish (held in groups of four) grew most. These results support previous coopera-tively breeding mammal studies and suggest that dominant individuals experience highercortisol levels as well as higher growth rates.