The Stress Response of the Highly Social African Cichlid Neolamprologus pulcher
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In group-living species, dominant individuals are frequently aggressive toward subordinates, and such dominant aggression can lead to chronic stress, higher glucocorticoid levels, and decreased fitness for subordinates. However, in many cooperatively breeding species, it is surprisingly the dominants rather than the subordinates that exhibit higher levels of glucocorticoids, a possible consequence of the demands of maintaining high social rank and socially suppressing the reproduction of other group members. This study investigates the relationship between social status and circulating plasma cortisol in groups of the cooperatively breeding African cichlid Neolamprologus pulcher. Baseline (resting) levels of cortisol were quantified, as was the cortisol response following an acute stressor. Dominants had the higher cortisol concentrations, and these were not related to their social behavior. Cortisol concentrations correlated (positively) with social behaviors and general activity levels only in subordinate males, arguably the individuals with the least stability in the social group. No status-dependent differential responses to acute stress were detected, suggesting that the status-induced chronic stress has little effect on the capacity to mount a full stress response to large-scale, life-threatening risk.
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