The cost of producing a sexual signal: Testosterone increases the susceptibility of male lizards to ectoparasitic infestation

According to current evolutionary theory, advertising traits that honestly indicate an organism's genetic quality might be costly to produce or maintain, though the kind of costs involved in this process are controversial. Recently the immunocompetence hypothesis has proposed that testosterone (T) stimulates the expression of male sexually selected traits while decreasing immunocompetence. Even though some recent studies have shown an effect of T on ectoparasite load, the dual effect of the hormone has not been addressed in free-living populations. Here we report results of an experiment in a free-living population of the lizard Psammodromus algirus during the mating season. Males implanted with T had larger patches of breeding color and behaved more aggressively than control males. In T-implanted males, the increase in number of ticks during the mating season was significantly higher than in control males and this negatively affected several hematological parameters. T-males suffered significantly higher mortality than control males during the experiment. The results from the manipulation of T are consistent with the dual effect of this hormone.