Extreme Duty Cycles in the Acoustic Signals of Tiger Moths: Sexual and Natural Selection Operating in Parallel.

Y Fernández,W E Conner,N J Dowdy

doi:10.1093/iob/obaa046

Y Fernández, W E Conner + Show 1 more

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https://doi.org/10.1093/iob/obaa046

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Abstract

SynopsisSound production in tiger moths (Erebidae: Arctiinae) plays a role in natural selection. Some species use tymbal sounds as jamming signals avoiding bat predation. High duty cycle signals have the greatest efficacy in this regard. Tiger moth sounds can also be used for intraspecific communication. Little is known about the role of sound in the mating behavior of jamming species or the signal preferences underlying mate choice. We recorded sound production during the courtship of two high duty cycle arctiines, Bertholdia trigona and Carales arizonensis. We characterized variation in their acoustic signals, measured female preference for male signals that vary in duty cycle, and performed female choice experiments to determine the effect of male duty cycle on the acceptance of male mates. Although both species produced sound during courtship, the role of acoustic communication appears different between the species. Bertholdia trigona was acoustically active in all intraspecific interactions. Females preferred and ultimately mated with males that produced higher duty cycles. Muted males were never chosen. In C. arizonensis however, sound emissions were limited during courtship and in some successful matings no sound was detected. Muted and clicking males were equally successful in female mate-choice experiments, indicating that acoustic communication is not essential for mating in C. arizonensis. Our results suggest that in B. trigona natural and sexual selection may work in parallel, to favor higher duty cycle clicking.

Highlights

Sexual selection molds male traits across a wide range of species (Greenfield 2016)
In the tiger moths Bertholdia trigona and Carales arizonensis, tymbal sounds jam bat echolocation causing bats to miss their target— natural selection—and we explore the role of tymbal sound in female mate choice—sexual selection
We address two hypotheses: the first is that females will show an open-ended preference for male courtship sounds with high duty cycles, and second that this preference will result in female mate choice for males with high duty cycle “phenotypes.”

Summary

Introduction

Sexual selection molds male traits across a wide range of species (Greenfield 2016). When the preference function is open-ended, sexual selection drives the evolution of selected traits toward more conspicuous and exaggerated signals until they become too costly to maintain. There is a tradeoff, where sexual and natural selection functions antagonistically. Sexual selection and natural selection are at odds Another example is the extinct Irish elk (Megaloceros giganteus) whose males sported enormous antlers that were once used during male– male competition for females. This sexually selected trait came at a cost; over evolutionary time males reallocated calcium from their bones to produce larger antlers (Emlen 2014). In some moth species, including Achroia grisella (Pyralidae), the lesser wax moth, this antagonism is seen when acoustic signals produced by males both attract predators (gleaning bats) and mates (Rodriguez and Greenfield 2004)

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