A Workshop in Ecology and Behaviour seminar hosted by the School of Biological Sciences
Aposematic organisms warn predators of their unprofitability using a combination of defenses, including visual warning signals and aversive or toxic chemical defenses. Using multiple lines of defense can help prey avoid predation by stimulating multiple senses of the predator, acting against multiple predators, or by acting at different stages of predation. Here I focus on the use of multiple chemical defenses in aposematic species using two separate study systems. First, using a taxonomic survey of nudibranch molluscs, I find no clear relationship between palatability and toxicity, but instead demonstrate how defensive compounds can be classified into categories based on these two defensive properties. I also investigate the response of multiple taxa (fish and shrimp) to different nudibranch secondary metabolites. Overall, responses to secondary metabolites were similar between fish and shrimp, except for isonitriles, which were highly unpalatable to shrimp but weakly unpalatable to fish. Next, I use a behavioural experiment to explore how multiple chemical defences disrupt the predation sequence of a polymorphic moth by birds. Moths with two hindwing phenotypes (genotypes: WW/Wy=white, yy=yellow) were manipulated to have aversive smell (methoxypyrazines), taste (pyrrolizidine alkaloids) or both. Colour and smell both contributed to the disruption of early attack stages. After capture, birds only discriminated toxic from non-toxic moths if they had methoxypyrazine smell. Overall, white moths with both smell and taste defences had greatest survival. This work highlights the need to explore the multiple roles chemical defences to better understand the foraging decisions faced by predators, the resultant selection pressures imposed on prey, and the evolution of different anti-predator strategies.