Abstract
Under chronic stress, carotenoid-based colouration has often been shown to fade. However, the ecological and physiological mechanisms that govern colouration still remain largely unknown. Colour changes may be directly induced by the stressor (for example through reduced carotenoid intake) or due to the activation of the physiological stress response (PSR, e.g. due to increased blood corticosterone concentrations). Here, we tested whether blood corticosterone concentration affected carotenoid-based colouration, and whether a trade-off between colouration and PSR existed. Using the common lizard (Lacerta vivipara), we correlatively and experimentally showed that elevated blood corticosterone levels are associated with increased redness of the lizard's belly. In this study, the effects of corticosterone did not depend on carotenoid ingestion, indicating the absence of a trade-off between colouration and PSR for carotenoids. While carotenoid ingestion increased blood carotenoid concentration, colouration was not modified. This suggests that carotenoid-based colouration of common lizards is not severely limited by dietary carotenoid intake. Together with earlier studies, these findings suggest that the common lizard's carotenoid-based colouration may be a composite trait, consisting of fixed (e.g. genetic) and environmentally elements, the latter reflecting the lizard's PSR.
Highlights
Colour signals are usually genetically and/or environmentally determined [1,2,3,4,5]
The yellow-orange colour disappeared from the skin within one hour when it was immersed in acetone and it adopted a bluish colour. This shows that the yellow-orange skin colour of common lizards stem from carotenoids and not from melanins or pteridins, neither of which are soluble in acetone [61]
We have investigated the effects of carotenoid availability and blood corticosterone levels on the sexually selected ventral colouration of the common lizard
Summary
Colour signals are usually genetically and/or environmentally determined [1,2,3,4,5]. While genetically determined elements signal an individual’s life history strategy (see [6,7,8] for reptiles and [9] for insects), environmental variance stems from nutritional conditions [1,2,3,4] and health status [10,11,12]. Environmental determination of many colour signals stems from differences in carotenoid deposition. Carotenoids are relevant to the immune system [2,14] and they are thought to fulfil antioxidant functions [15,16] (but see [17]). These multiple functions may create trade-offs in carotenoid-limited animals. The extent to which such trade-offs occur might depend on the role that colouration plays in a given species: signalling individual quality or individual strategy
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