The physiological effects of social status in the cooperatively breeding cichlid Neolamprologus pulcher A. S. B UCHNER *, K. A. S LOMAN † AND S. B ALSHINE *‡ *Department of Psychology, McMaster University, Hamilton, Ontario, L8S 4K1, Canada and †Department of Biological Sciences, Brunel University, Uxbridge, Middlesex, UB8 3PH, U.K. (Received 27 June 2003, Accepted 7 July 2004) The physiological effects of social rank were examined in three different experiments with Neolamprologus pulcher a cooperatively breeding cichlid, endemic to Lake Tanganyika, East Africa. 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) were examined. A third experiment mimicked the natural social structure in the wild; pairs were observed with other group members including breeders. The effect of social position was investigated 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. In the absence of breeders, dominant individuals (of helper pairs) had higher liver glycogen levels and dominant fish (held in groups of four) grew most. These results support previous coopera- tively breeding mammal studies and suggest that dominant individuals experience higher cortisol levels as well as higher growth rates. # 2004 The Fisheries Society of the British Isles Key words: dominance; energy; growth; helpers; Neolamprologus pulcher. INTRODUCTION Dominance hierarchies are most commonly seen in permanent or semi-permanent social groups (Drickamer et al., 1996) and are believed to reduce the amount of severe aggression among members of a group (Krebs & Davies, 1997). While these social hierarchies may benefit group stability, many physiological costs and benefits have been associated with the social position of individuals. The conventional view is that social subordination is stressful. The physiological costs to subordinate animals have been described for many mammalian species and have also been demonstrated in fishes (Sloman & Armstrong, 2002). While physiological correlates ofsocialrankhavebeenstudiedinasmallnumberofnon-salmonidspeciesoffishes (Fox etal., 1997; Winberg etal., 1997; Hofmann etal., 1999; Hofmann & Fernald, 2001), no study to date has considered the physiological effects of social status in a cooperatively breeding species of fish with a long-term stable social hierarchy. ‡Author to whom correspondence should be addressed. Tel.: þ19055259140 ext. 23024; fax: þ19055296225; email: sigal@mcmaster.ca JournalofFishBiology (2004) 65, 1080–1095 doi:10.1111/j.1095-8649.2004.00517.x,availableonlineathttp://www.blackwell-synergy.com 1080 # 2004TheFisheriesSocietyoftheBritishIsles