Acoustic ranging in meadow katydids: female preference for attenuated calls

ABSTRACT For many insects advertisement calls made by males are the primary method of mate choice. Females often have a preference for higher amplitude calls. However, if a male is capable of making a louder call than his neighbour he still might be perceived as the quieter of the two, if he is farther away from the female. There is a huge amount of information encoded in male calls and among those is information on distance, or range. As calls travel through air, higher frequency components attenuate faster than lower frequency components. This excess high-frequency attenuation could act as a ranging aid to females. If she hears two males making calls of equal amplitude, but one male has fewer high-frequency components in his call, he is likely farther away. If so, he must be able to make the higher absolute-amplitude call (the amplitude of the call at the sender) of the two. We tested this in Orchelimum pulchellum, a meadow katydid that uses broad spectrum calls. We found that females are more likely to do positive phonotaxis towards a call with excess high-frequency attenuation. This preference exists even when the calls with excess attenuation are quieter.