Reproduction and immunity trade-offs constrain mating signals and nuptial gift size in a bushcricket

Abstract

Reproduction and immunity often require significant energetic investment and as a result, trade-offs may occur between them. Reproduction is particularly costly for males of the bushcricket Ephippiger diurnus: not only do they produce loud advertisement calls for long periods of time to attract mates but also they offer females a large nuptial gift, a spermatophore, that can be up to 40% of their body weight. Song traits and spermatophore size vary among males, implying that males may differ in their overall reproductive effort or in how their effort is allocated. Males are long-lived, suggesting that survival traits such as immunity may be particularly critical in fitness. Here, we tested the hypothesis that trade-offs exist between reproductive effort and immune response in E. diurnus and that such trade-offs may constrain male mating calls and nuptial gift size. We investigated the relationship between call syllable number, spermatophore size, and immune response in field-collected individuals. We found an inverse relationship in all pairwise comparisons of call syllable number, spermatophore size, and immune response, as well as between overall reproductive effort and immune response. Our results suggest that males exhibit different energy allocation strategies and that their trade-offs ultimately constrain signal evolution.