Male dwarf chameleons assess risk of courting large, aggressive females.

Conflict between the sexes has traditionally been studied in terms of costs of mating to females and female resistance. However, courting can also be costly to males, especially when females are larger and aggressively resist copulation attempts. We examined male display intensity towards females in the Cape dwarf chameleon, Bradypodion pumilum, in which females are larger than males and very aggressive. We assessed whether aggressive female rejection imposes potential costs on males and whether males vary their display behaviour with intensity of female rejection, female size or relative size differences. Males persisted in courtship after initial female rejection in 84% of trials, and were bitten in 28% of trials. Attempted mounts were positively associated with males being bitten. Males reduced courtship with increased intensity of female rejection. Male courtship behaviour also varied with female size: males were more likely to court and approach smaller females, consistent with the hypothesis that larger females can inflict more damage. These results suggest that, in addition to assessing female willingness to mate, male dwarf chameleons may use courtship displays to assess potential costs of persistence, including costs associated with aggressive female rejection, weighed against potential reproductive pay-offs associated with forced copulation.

Sexual selection, natural selection and the evolution of dimorphic coloration and ornamentation in agamid lizards.

Both sexual selection and natural selection can influence the form of dimorphism in secondary sexual traits. Here, we used a comparative approach to examine the relative roles of sexual selection and natural selection in the evolution of sexually dimorphic coloration (dichromatism) and ornamentation in agamid lizards. Sexual dimorphism in head and body size were used as indirect indicators of sexual selection, and habitat type (openness) as an index of natural selection. We examined separately the dichromatism of body regions "exposed to" and "concealed from" visual predators, because these body regions are likely to be subject to different selection pressures. Dichromatism of "exposed" body regions was significantly associated with habitat type: males were typically more conspicuously coloured than females in closed habitats. By contrast, dichromatism of "concealed" body regions and ornament dimorphism were positively associated with sexual size dimorphism (SSD). When we examined male and female ornamentation separately, however, both were positively associated with habitat openness in addition to snout-vent length and head SSD. These results suggest that natural selection constrains the evolution of elaborate ornamentation in both sexes as well as sexual dichromatism of body regions exposed to visual predators. By contrast, dichromatism of "concealed" body regions and degree of ornament dimorphism appear to be driven to a greater degree by sexual selection.

Evolution of color variation in dragon lizards: quantitative tests of the role of crypsis and local adaptation.

Many animal species display striking color differences with respect to geographic location, sex, and body region. Traditional adaptive explanations for such complex patterns invoke an interaction between selection for conspicuous signals and natural selection for crypsis. Although there is now a substantial body of evidence supporting the role of sexual selection for signaling functions, quantitative studies of crypsis remain comparatively rare. Here, we combine objective measures of coloration with information on predator visual sensitivities to study the role of crypsis in the evolution of color variation in an Australian lizard species complex (Ctenophorus decresii). We apply a model that allows us to quantify crypsis in terms of the visual contrast of the lizards against their natural backgrounds, as perceived by potential avian predators. We then use these quantitative estimates of crypsis to answer the following questions. Are there significant differences in crypsis/conspicuousness among populations? Are there significant differences in crypsis conspicuousness between the sexes? Are body regions "exposed" to visual predators more cryptic than "hidden" body regions? Is there evidence for local adaptation with respect to crypsis against different substrates? In general, our results confirmed that there are real differences in crypsis/conspicuousness both between populations and between sexes; that exposed body regions were significantly more cryptic than hidden ones, particularly in females; and that females, but not males, are more cryptic against their own local background than against the background of other populations [corrected]. Body regions that varied most in contrast between the sexes and between populations were also most conspicuous and are emphasized by males during social and sexual signaling. However, results varied with respect to the aspect of coloration studied. Results based on chromatic contrast ("hue" of color) provided better support for the crypsis hypothesis than did results based on achromatic contrast ("brightness" of color). Taken together, these results support the view that crypsis plays a substantial role in the evolution of color variation and that color patterns represent a balance between the need for conspicuousness for signaling and the need for crypsis to avoid predation.