How male attractiveness mediates the effect of an immune challenge on reproductive traits and sickness behavior in the Texas Field Cricket (Gryllus texensis)

Abstract

Trade offs between life-history traits are well studied; however, most studies examine only two life-history traits at a time. For instance, in invertebrates, there is much evidence for the trade-off between reproduction and immunity but no studies that consider how investment in attractiveness might mediate this trade-off. In this study, I test two hypotheses. First, attractive male crickets (Gryllus texensis) have acquired larger resource pools than unattractive males and can invest more in all life-history traits. Attractive males should therefore have better body condition and show a less pronounced trade-off than unattractive males. Second, that attractive and unattractive males start with similar sized resource pools and allocate these resources differently. Since attractive males have invested some of their limited resources on sexual attractiveness they should have fewer resources left at their disposal than the unattractive males and should have worse body condition and show a more pronounced trade-off between reproduction and immunity than unattractive males. I tested these hypotheses by comparing body condition and testes size in attractive and unattractive males and injecting them with saline or LPS and examining their behavior. Attractive and unattractive males did not differ in their body condition or testes size. Attractive males increased their calling activity when immune-challenged. These results support the hypothesis that attractive and unattractive males have similar sized resource pools and attractive males invest in sexual attractiveness at the expense of immune-competence.