Nonchalant Flight in Tiger Moths (Erebidae: Arctiinae) Is Correlated With Unpalatability

Nicolas J Dowdy,William E Conner

doi:10.3389/fevo.2019.00480

Nicolas J Dowdy, William E Conner

Open Access

https://doi.org/10.3389/fevo.2019.00480

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Abstract

Many aposematic animals are well-known to exhibit generally sluggish movements. However, less is known about their escape responses when under direct threat of predation. In this study, we characterize the anti-bat escape responses of 5 species of tiger moth (Erebidae: Arctiinae), a subfamily of Lepidoptera which possess ultrasound-sensitive ears. These ears act as an early-warning system which can detect the ultrasonic cries of nearby echolocating bats, allowing the moths to enact evasive flight behaviors in an effort to escape predation. We examine the role that unpalatability plays in predicting the likelihood that individuals of a given species will enact escape behaviors in response to predation. We hypothesized that more unpalatable species would be less likely to exhibit escape maneuvers (i.e., more nonchalant) than their less unpalatable counterparts. Our results demonstrate significant interspecific variation in the degree to which tiger moths utilize evasive flight behaviors to escape bat predators as well as in their degree of unpalatability. We provide evidence for the existence of a nonchalance continuum of anti-bat evasive flight response among tiger moths and show that species are arrayed along this continuum based on their relative unpalatability to bat predators. Relatively unpalatable prey more often exhibit nonchalant flight behaviors whereas palatable prey more often employ evasive dives. Our findings demonstrate that the degree to which certain animals are protected by potent chemical defenses can influence the likelihood that they will exhibit evasive escape behaviors. Further, we argue that the bat-moth predator-prey system is an ideal model for future studies of escape behaviors of prey which overcomes some of the limitations inherent to current model systems.

Highlights

Aposematic animals have long been recognized to exhibit sluggish movements
The phenomenon of sluggishness was later incorporated into the “chemical defense syndrome” (CDS), a general suite of characteristics commonly exhibited by chemically protected animals
In this study we examine the role that unpalatability plays in predicting the likelihood that individuals of a given species will enact escape behaviors in response to the threat of predation

Summary

Introduction

Aposematic animals have long been recognized to exhibit sluggish movements. Bates was the first to observe this, describing several strikingly colored butterflies as possessing “weak, slow flight” (Bates, 1862; Poulton, 1890). There are several hypotheses which seek to explain why aposematic animals exhibit these sluggish behaviors One such hypothesis is that these slow movements evolved because they avoid triggering the attack responses of motion-oriented, ambush predators like frogs and praying mantids (Hatle and Faragher, 1998; Hatle et al, 2002). Expanding on Bates’ early observations, a comparative study of butterfly species has quantitatively shown that distasteful species fly relatively more slowly than palatable species, indicating that sluggish flight can honestly signal prey defenses (i.e., “locomotor mimicry”; Chai and Srygley, 1990; Srygley, 1994, 2004) Another non-mutually exclusive hypothesis posits that these slow movements may make visual aposematic signals more apparent to predators, increasing the effectiveness of such signals (i.e., “raised exposure”; Speed et al, 2010)

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