Use of acoustic signals in mating in an eavesdropping frog-biting midge

Abstract

The sensory systems of organisms are shaped by selective pressures imposed by their performance in a variety of contexts. Female frog-biting midges use the mating calls of anurans to locate their host to obtain a blood meal. Although the use of sound in foraging is well documented in this group, it is unknown whether sound is used in other contexts. To investigate the ability to use sound in nonforaging contexts, we experimentally tested the prediction that frog-biting midges (Corethrella appendiculata) use sound in mating. We recorded their wing beats while swarming, in controlled tethered conditions and during different- and same-sex pair interactions. Our results show sexual differences in the acoustic properties of flight tones, with male midges having higher frequency wing beats than females. Wing beats of free-flying individuals were significantly higher in frequency than those recorded from tethered individuals, cautioning the interpretation of recordings obtained following this widely used technique. In addition, interacting, tethered opposite-sex pairs altered their flight tones to match their upper harmonics, converging at the third and fourth harmonic frequencies of males and females, respectively. In male male interactions, however, the frequency of their wing beats diverged. Therefore, flight tones in frog-biting midges may function as courtship signals attracting conspecific females and deterring rival males. We discuss the use of sound in multiple contexts in these midges and potential factors leading to their ability to eavesdrop on anurans.