Sexual selection and predator avoidance in an acoustic moth: discriminating females take fewer risks

In: Behaviour

Abstract

Sexual activities in both males and females are expected to incur energetic costs and risk. We tested the expectation that females who exhibit a higher level of discrimination of potential mates' signals incur greater risk than females who are relatively indiscriminate by assaying mate choice and predator evasion in an acoustic moth, Achroia grisella. Female A. grisella evaluate males on the basis of their song, only orienting toward males whose ultrasonic songs are delivered at pulse rates above a lower threshold value. Non-flying females also respond negatively, by ceasing all movement, upon hearing ultrasonic pulses delivered at rates below an upper threshold value; this response is assumed to represent evasion of predatory bats, specifically gleaning species. We found that both the lower and upper pulse-rate thresholds varied considerably among individual females and that the upper pulse-rate threshold for defensive response was always equal to or slightly lower than the lower pulse-rate threshold for a mating response. Thus, females who exhibit heightened discrimination of potential mates' signals experience less, not more, predatory risk. This relationship may reflect the evolutionary origin of acoustic sexual communication in A. grisella as a coöption of the ancestral function of hearing in evasion of predatory bats.

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