Quantitative genetic variation in courtship song and its covariation with immune function and sperm quality in the field cricket Teleogryllus oceanicus

Acoustic signals used by males to attract females are among the most prominent examples of secondary sexual traits, yet we have only limited understanding of their genetic architecture. Male crickets produce a calling song to attract females and then switch to a courtship song that incites mounting by females once they are at close range. Although we know much about the genetics of cricket calling song, no study has yet examined the quantitative genetics of courtship song. Here, we conduct a quantitative genetic analysis of courtship song using the Australian cricket Teleogryllus oceanicus. We find substantial levels of additive genetic variation in courtship song parameters and genetic covariances between courtship song parameters that reflect female preferences. We also found evidence for a negative relationship between the amount of trill in the courtship song and the ability of males to mount an immune response and to produce an ejaculate containing a high proportion of viable sperm. Trade-offs between immunity and sexual signaling are a prerequisite for immunocompetence handicap models of preference evolution, whereas a trade-off between gaining matings and fertilizations is a fundamental assumption underlying sperm competition theory. These life-history trade-offs are likely to constrain evolutionary responses to selection from female choice, and to maintain additive genetic variance in courtship song.