Passive anti-bat defences in nocturnal Lepidoptera

: novel wingbeat-powered sound production in deaf microlepidoptera, and acoustic crypsis in moths

Abstract

Nocturnal moths and echolocating bats have been in a co-evolutionary arms race for 65 million years. Resulting adaptations are complex, diverse, and often convergently evolved. Notable examples include anti-bat hearing providing an early warning of approaching predators, sound production to startle, warn, or jam an approaching bat, and potential acoustic camouflage afforded by the wing scales and body fur of nocturnal moths. Here, I investigate two aspects of passive anti-bat defence, wingbeat-powered anti-bat sound and acoustic camouflage.
I present the first combined description and acoustic characterisation of the novel wing-embedded sound-producing structure in the microlepidopteran genus Yponomeuta, which I term the aeroelastic tymbal (AT). By investigating the life history of Yponomeuta and comparing their acoustic characteristics with those of moth sounds in the literature, I conclude that they are acoustic Müllerian mimics of the chemically defended Arctiinae. I then show that ATs likely convergently evolved 15 times in the microlepidoptera, confirming sound production from five (including Yponomeuta) of the 15 examples. Due to their acoustic characteristics being similar to known anti-bat sounds and the life histories of some taxa placing them at high risk of bat predation, I conclude that these ATs too produce anti-bat sounds.
Research into potential acoustic camouflage in moths has previously focussed on small numbers of species, so I present the first species-rich, phylogenetically widespread study on the topic. Using acoustic tomography, I compare the ultrasonic retroreflection of nocturnal moths and two groups of diurnal Lepidoptera, butterflies and diurnal moths. Unlike previous work I find no differences between moths based on their diel (day-night) activity; however, moths as a whole show reduced echo intensity over all the tested frequencies for both their bodies and wings when compared to butterflies. It appears that moths are adapted for broadband acoustic camouflage against bats; whereas, butterflies are not.

Date of Award	23 Jan 2020
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Daniel Robert (Supervisor) & Marc W Holderied (Supervisor)