Immune challenged male Iberian green lizards may increase the expression of some sexual signals if they have supplementary vitamin E

Abstract

Honesty of sexual signals demands a link between the signal and fitness of the signalers, which can be based on the costs of the signal and trade-offs between signal development and essential physiological functions, such as the immune defense or the antioxidant system. We experimentally challenged the immune system of male lizards Lacerta schreiberi with a bacterial antigen (lipopolysaccharide; LPS). We explored whether the immune activation influenced structural- and pigment-based visual signals and chemical signals. Furthermore, we examined the interactive effects of the immune activation with a vitamin E dietary supplementation, as this vitamin has important antioxidant functions in an immune challenged situation. Contrary to expected, lizards that suffered an immune challenge alone did not decrease the brightness or saturation of visual signals, and even, when challenged lizards had supplementary vitamin E, they were able to increase saturation of UV-blue throat coloration. Similarly, vitamin E supplementation allowed challenged males to maintain high levels of secretion of this vitamin in chemical signals. Males with an immune challenge would have low long-term expectatives of survival and future reproduction and, therefore, these challenged males, especially those with supplementary resources (vitamin E), might try to maximize their current fitness by investing in costly sexual signals, instead of compensating the negative physiological effects of the immune activation. Surprisingly, vitamin E alone did not affect structural and/or melanin-based coloration, but decreased carotenoid-based coloration, which was opposite to a previous experiment when climatic conditions in the year of study were more favorable. This might be explained if females showed flexible mate choice, selecting the type of signals that more reliably indicate male quality under different environmental circumstances. The trade-offs between sexual signals and the immune and antioxidant systems, which allow honesty of signals, are little investigated, especially in reptiles. We examined in a lizard with multiple types of signals (UV-blue throat, yellow chest and green dorsal coloration, and chemical signals) the effects of a simulated immune challenge on these signals. Furthermore, we studied the interactions with vitamin E in the diet, as this is an important antioxidant and immunostimulant. Surprisingly, carotenoid-based signals were not influenced by the immune activation, but throat blue and UV of color patches increased when challenged males had more available vitamin E. This suggests that challenged, apparently ill, males might try to maximize their current mating success because their survivorship probabilities were low. Additionally, climatic differences and flexible female mate choice might explain the different effects of vitamin E observed in different years.