Abstract
A growing body of evidence suggests that resources invested in sexual signals and other reproductive traits often come at the expense of the ability to mount an immune response. Male sagebrush crickets, Cyphoderris strepitans, offer an unusual nuptial food gift to females during mating: females chew on the tips of males' fleshy hind wings and ingest hemolymph seeping from the wounds they inflict. Previous research has shown that once a male has mated, his probability of obtaining an additional copulation is reduced relative to that of a virgin male seeking his first mating. One hypothesis to account for this effect is that wing wounding triggers an energetically costly immune response, such that non virgin males are unable to sustain the costly acoustical signaling needed to attract additional females. To test this hypothesis, we injected virgin males with lipopolysaccharides (LPS), a non-living component of bacterial cell walls that leads to upregulation of the insect immune system. Males were released in the field and recaptured over the course of the breeding season to monitor their mating success. Over two breeding seasons, LPS-injected males took significantly longer to secure matings than sham-injected virgin males. An encapsulation rate assay showed no difference in the encapsulation response of males of different mating status, but virgin males had significantly higher levels of phenoloxidase than non-virgin males. These results suggest that males trade off investment in reproduction and investment in immunity.