Female preference for hot males

Insects have been used extensively as model systems to study mating preferences based on variation in acoustic signals. In many species, females perform phonotactic approaches towards attractive, long range signals of males, and a decision for final mating may based on further assessment of close range cues. Sound production by males is costly, since only a fraction of muscle energy used to produce the sound is converted into acoustic power. The current proposal is based on the finding that in some katydid and cricket species with long-lasting signalling the male thorax housing the singing muscles increases in temperature by up to 10C after several minutes of singing. Hence, male body temperature could serve an additional cue during mate choice. This would turn the acoustic signal into an inherently bimodal one, where the energy invested in sound production is not wasted but reflected in the elevated thorax temperature of a male, which can be evaluated by females via thermo-sensitive receptor cells located in the long antennae. Preliminary data suggest that these cells respond with high sensitivity to changes in temperature via convective and radiant heat. Since the thorax temperature remains elevated for several minutes even after the male stopped singing, females may evaluate the sound signal indirectly, even if it cannot be perceived by the auditory system. The proposal suggests behavioral, physiological and anatomical approaches to investigate this new idea.

Insects have been used extensively as model systems to study mating preferences based on variation in acoustic signals. Sound production by males is costly, since only a fraction of muscle energy used to produce the sound is converted into acoustic power. The current project was based on the finding that in some insect species the male thorax housing the singing muscles increases in temperature by up to 10C after several minutes of singing. Hence, male body temperature could serve an additional cue during mate choice. Simultaneous measurement of body temperature and the energy required for singing provided data which acoustic signals may provide thermal cues for females, and how costly they are. We evaluated the various sensilla on the long antennae responsible for thermal sensing, and physiological data on the sensitivity enabled to calculate, that they respond to changes of a fraction of a degree Celsius at a distance of several centimeters from a singing male. However, the final behavioural experiments using two different paradigms could not confirm, that females prefer an acoustic stimulus when an additional thermal cue, similar to the one of a male at close range, is presented.