Frequency-dependent physiological trade-offs between competing colour morphs

• Published in: Biology letters (2005) Vol. 3; no. 5; pp. 494 - 497
• Main Authors: Pryke, Sarah R, Astheimer, Lee B, Buttemer, William A, Griffith, Simon C
• Format: Journal Article
• Language: English
• Published: London The Royal Society 22.10.2007
• Subjects: Alternative Strategies; Animals; Biological Evolution; Colour Polymorphism; Competitive Behavior; Corticosterone - blood; Erythrura gouldiae; Evolutionary Biology; Finches - genetics; Finches - physiology; Immune Tolerance; Immunocompetence; Male; Pigmentation - genetics; Polymorphism, Genetic; Social Dominance; Steroid Hormones
• ISSN: 1744-9561; 1744-957X
• DOI: 10.1098/rsbl.2007.0213

Evolutionary theory suggests that alternative colour morphs (i.e. genetically controlled phenotypes) may derive similar fitness under frequency-dependent selection. Here we experimentally demonstrate opposing effects of frequency-dependent social environments on plasma hormone levels (testosterone and corticosterone) and immune function between red- and black-headed male morphs of the Gouldian finch (Erythrura gouldiae). Red-headed males are highly sensitive to changes in the social environment, especially towards the relative density of their own aggressive morph, exhibiting high stress responses and immunosuppression in socially competitive environments. In contrast, the non-aggressive black-headed males follow a more passive strategy that appears to buffer them against social stresses. The differential effect of hormones on aggressive behaviour and immune performance reinforces the contrasting behavioural strategies employed by these colour morphs, and highlights the importance of the social environment in determining the individual basis of behavioural and physiological responses.