Abstract
Two non-independent theories in evolutionary ecology, the immunocompetence and the oxidative handicap hypotheses, may explain maintenance of genetic variation and signal honesty through genic capture in sexual selection biology. Thus, polygenic traits, like body condition, could help maintain variation in signalling traits under strong, directional sexual selection while maintaining signal honesty. The immunocompetence and oxidative handicap hypotheses are complementary in this regard in that hormones (most often steroids) essential for sexual signalling also carry costs, including increases in potentially damaging reactive oxygen species (ROS). Here we combine (at least) two of these hypotheses in a study of morph-specific condition and free radical effects on signalling traits (head coloration) in males of a polymorphic lizard, the Australian painted dragon (Ctenophorus pictus). Males differ in head colour (red, orange, yellow, hereto forth collectively ‘yellow-reds’), with these morphs showing reproductive tactics and behaviour in a graded fashion of aggression and dominance (red highest levels). A blue morph recently emerged in our study population and has never been behaviourally characterised. Body condition varied significantly in its relationship with superoxide among the four morphs, with males in better condition showing higher superoxide levels in ‘yellow-reds’ (least so in red males). Blue males contrasted markedly by showing lower superoxide levels in males in better condition, perhaps facilitated by no (or reduced) dermal deposition of pigmentation. Colour degradation with loss in condition from yellow to red males, suggesting that red males (i.e., genes associated within a more aggressive morph) is more able to maintain colour with superoxide acting as a potential handicap. This result is consistent with handicap principles in that males with the more pronounced signal carry a higher cost (higher ROS levels) when being in better body condition, while maintaining more vivid coloration (the condition-dependent trait).
Highlights
Genic capture supposes that trait expression depends on overall condition (Rowe and Houle, 1996)
Given the relationship between color morph and associated reproductive tactics, superoxide and BCI, we predicted that the red morph with correlated suite of traits forged by an evolutionary history of higher aggression (Healey et al, 2007; Olsson et al, 2007a,b) would have evolved the capacity to better ameliorate a trade-off between body condition and level of superoxide
Our results paint a complex picture of morph-specific differences in levels of superoxide and its relationship to body condition and coloration
Summary
Genic capture supposes that trait expression depends on overall condition (Rowe and Houle, 1996). Experimental lowering of superoxide using a superoxide dismutase mimetic (EUK 134) reduces color fading over the breeding season (Olsson et al, 2012), suggesting superoxide production is linked to color degradation Given these differences between the two best described morphs, we might expect different aspects of condition (e.g., BCI and superoxide) to vary among these morphs due to past selection to optimize the different morph-specific reproductive strategies and to be reflected in color-fading sexually active males. Given the relationship between color morph and associated reproductive tactics, superoxide and BCI, we predicted that the red morph with correlated suite of traits forged by an evolutionary history of higher aggression (Healey et al, 2007; Olsson et al, 2007a,b) would have evolved the capacity to better ameliorate a trade-off between body condition and level of superoxide. Yellow morphs are predicted to show a negative— and red morphs a positive—relationship with body condition and color maintenance
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