The physiological cost of courtship: field cricket song results in anaerobic metabolism

During courtship interactions, males typically perform displays that are assumed to demonstrate some aspect of their quality. While some displays are elaborate and spectacular in appearance, others involve comparatively simple repetitive actions. The functions of these dynamic repeated courtship displays are hypothesized to fall into two broad categories. Either the signal is repeated as a process of validation to counter errors in transmission, or the process of repetition itself advertises the ability to bear signalling costs. The function of any repetitive courtship display can thus be identified by investigating the nature of production costs as well as the pattern of repetition. In the present study, I investigated the function of signal repetition using a commonly used organism, the Mediterranean field cricket, Gryllus bimaculatus. Male G. bimaculatus court females by producing acoustic signals using rapid, repeated movements of their wings. I tested for the presence of energetic costs by analysing haemolymph lactate concentrations after time-controlled courtship interactions. Males that had performed 5 min of courtship were found to have higher levels of haemolymph lactate relative to controls. Furthermore, those individuals producing more rapid song had higher levels of haemolymph lactate. The song produced by courting crickets therefore incurs significant energetic costs, and probably serves to advertise the energetic cost capacity of the calling male. Thus, I confirm that stridulation is an energetically costly signal and demonstrate that anaerobic metabolism appears to be a significant cost of repeated courtship displays.