Variation in chemical protection

squeezing moths

Many animals produce or sequester toxic or distasteful chemicals to deter predators. Aposematic species also advertise this protection with signals such as bright colours that aid predator learning. However, the level of defence may not be uniform across all members of a species.

The wood tiger moth produces two distinct defense fluids in response to attack. It also shows considerable polymorphism in its warning colours. In particular, males in many northern populations can be either white or yellow, with bird predators showing greater aversion to the yellow morph. In contrast, females show continuous variation from red to yellow. I am investigating the variation in chemical defense within and between the morphs, and the effect of this variation on the predation pressures experience by the population as a whole.

Photos from left to right: A yellow male, a white male and a female. Courtesy of Bibiana Rojas.
Photos from left to right: A yellow male, a white male and a female. Courtesy of Bibiana Rojas.

My project aims to identify the chemicals used by the moths for defense, as well as how these vary within and between the sexes, colour morphs, and populations. Current evidence suggests that the yellow males not only benefit from a stronger aposematic signal, but also possess stronger chemical defenses that the white morph. If these defenses carry costs or life-history trade-offs this may explain the maintenance of the polymorphism seen in Finland.

I collaborated with the Schulz lab at the Institute of Organic Chemistry, TU Braunschweig to identify the compounds present in the moth defensive fluids. We identified two pyrazines which elicit predator-specific aversive reactions.

A natural predator of the wood tiger moth

I also worked with Dr Bibiana Rojas and Kaisa Suisto to investigate the roles of the two defensive fluids produced by the moths, and the interaction between the colour and chemical signals in predator aversion and learning. Dr Swanne Gordon and I have been working together to study the effect of morph frequency on predator behaviour.

For more information on this work see the Mappes lab webpage and the Center of Excellence in Biological Interactions.