Temperature effects on interspecific eavesdropping in the wild

Abstract Mating signals are targets of conspecific signal recognition and sexual selection but are also subject to abiotic temperature effects and to biotic interspecific eavesdroppers. In crickets, the male calling song becomes faster at warmer temperatures, and female crickets’ recognition of male song tracks temperature in a coordinated manner, termed “temperature coupling.” But, female crickets are not the only ecologically relevant listeners: some cricket species are parasitized by Ormia ochracea, a parasitoid fly which finds its cricket hosts by eavesdropping on male cricket song. How temperature affects parasitoid fly phonotaxis to song is largely unexplored, with only one previous study conducted under field conditions. Here, we explore 6 possible patterns of thermal effects on fly responses to cricket song, including temperature coupling, using field playbacks of synthetic Gryllus lineaticeps songs designed to be species-typical at various temperatures. We find that temperature does affect fly response, but that the temperature deviation of songs from ambient does not impact numbers of flies caught. We extend this finding by comparing the temperatures of the air (where flies search for their hosts) and the ground (where their host crickets signal) to show that temperature coupling is unlikely to be effective given microhabitat variation and differential rates of cooling in the evening hours when flies are most active. Our results can be interpreted more broadly to suggest (1) temperature effects on intraspecific communication systems may be more tightly coupled than are effects on interspecific eavesdropping and (2) variation in thermal microhabitats in the field make it difficult to translate laboratory physiological responses to natural selection in the wild. Mating signals are sometimes intercepted by predators or parasites, but temperature affects the expression of mating signals, potentially making it difficult for predators and parasites to recognize them. By using playbacks of cricket song in the wild, we show that temperature changes do affect the response of a parasitoid fly to cricket song. However, parasitoid responses are not tightly coupled to temperature-induced changes in cricket song, in part due to unpredictable variation in microhabitat temperatures typical of crickets and flies.