Variation in cricket acoustic mate attraction signalling explained by body morphology and metabolic differences

Males often signal to attract mates and can show extensive variation in how much time they spend signalling. In crickets, some males signal extensively, spending over 50% of their adult lives attempting to attract a mate. At the other end of the continuum, some males are rarely observed to signal. Given that signalling efforts are usually correlated with mating success, all individuals should be selected to signal with high effort. Why then, do males show such variability? Signalling effort variation may stem from differences in physiological capacity that result from disparities in energy stores, metabolic capacities of the muscles used for sexual signalling, the comparative size of the signalling organs, or overall differences in body size. To address the proximate causes underlying variation in signalling effort, we quantified the morphological, physiological and biochemical variation among male European house crickets, Acheta domesticus, and assessed whether it correlated with signalling effort variation. Surprisingly, we found no correlation between signalling effort and activity of the β-oxidation enzyme HOAD, suggesting that the capacity for lipid metabolism is not associated with signalling effort. Instead, signalling effort variation was associated with differences in overall body size and differences in the activity of the glycolytic enzyme pyruvate kinase. Together our findings suggest that the ability to locate and assimilate high-quality diets both during development (to grow large) and into adulthood (capacity for carbohydrate catabolism) may explain some of the variation in signalling effort in this species.