Sex differences in immune investment and infection rate are predicted due to the divergent life histories of males and females, where females invest more toward immunity due to the fitness consequences of a reduced lifespan and males allocate less toward immunity due to increased resource investment in traits critical to sexual selection. Consequently, males are expected to fight infection less adeptly, resulting in higher parasite loads relative to females across all taxa. Wild animals rarely face a single parasite within their given environment, yet nearly all studies on sex-biased infection rates have focused on a single host–parasite relationship. Here, we investigate how simultaneous natural infections of ecto- and endosymbionts (i.e. both parasitic and phoretic taxa) correlate with sex biases in host immune response and reproductive investment in a field-caught cricket, Gryllus texensis. Our comprehensive analysis found no significant sex differences in two measures of immune response (melanization and nodulation), and found no strong evidence of a sex bias in the prevalence or intensity of parasitism by the three most common parasites infecting wild G. texensis field crickets (Eutrombidiidae, gregarines, and nematodes). Two traits related to female fitness, egg number and egg size, showed no relation to parasitic infection; however, males having wider heads and poorer body condition were significantly more infected by eutrombidiid mites, gregarines, and nematodes. Despite frequent predictions of male-biased parasitism in the literature, our results concur with many other studies indicating that the divergent life histories of males and females alone are not sufficient to explain natural infection rates in wild insects.
All Science Journal Classification (ASJC) codes
- Insect Science