Responses of intended and unintended receivers to a novel sexual signal suggest clandestine communication

Inadvertent cues can be refined into signals through coevolution between signalers and receivers, yet the earliest steps in this process remain elusive. In Hawaiian populations of the Pacific field cricket, a new morph producing a novel and incredibly variable song (purring) has spread across islands. Here we characterize the current sexual and natural selection landscape acting on the novel signal by (1) determining fitness advantages of purring through attraction to mates and protection from a prominent deadly natural enemy, and (2) testing alternative hypotheses about the strength and form of selection acting on the novel signal. In field studies, female crickets respond positively to purrs, but eavesdropping parasitoid flies do not, suggesting purring may allow private communication among crickets. Contrary to the sensory bias and preference for novelty hypotheses, preference functions (selective pressure) are nearly flat, driven by extreme inter-individual variation in function shape. Our study offers a rare empirical test of the roles of natural and sexual selection in the earliest stages of signal evolution. Parasitoid flies eavesdrop on the mating songs of male Hawaiian crickets, creating conflict between sexual and natural selection. Here, the authors investigate the selection acting on a recently evolved male mating signal, a purring song, which appears to be undetected by parasitoids.

Automated summary

The study investigates the selection acting on a newly evolved male mating signal, a purring song, in Hawaiian populations of field crickets. Contrary to expectations, female crickets respond positively to purring while eavesdropping parasitoids do not, suggesting private communication among crickets. The findings suggest that natural and sexual selection play important roles in the earliest stages of signal evolution.