Many animals face a life in a multi-enemy world. In order to survive, they have evolved different defensive strategies that vary in their nature and efficacy. Aposematic organisms display warning signals that are coupled with some form of unprofitability, for example chemical defences. Wood tiger moths (Arctia plantaginis) are aposematic; males display conspicuous colouration in their hindwings (either yellow or white) and secrete defensive fluids from both their abdomen and their prothoracic glands.
Previous work done by my colleague Ossi Nokelainen and his collaborators showed that white moths are more attacked than yellow ones. This suggests that yellow is a more efficient warning signal against predators, but nothing is known about how deterrent the chemical defences are and why. Although chemical defences are thought to be costly, wood tiger moths have two types of defensive secretions.
I am investigating the reactions of two types of predators (ants and birds) to the two types of chemical secretions of A. plantaginis, when information on colour is not available. This will hopefully provide some information on whether one of the morphs has more deterrent chemical defences, and whether predators react differently to the two types of secretions.
Multi-modal warning signals
In experiments with blue tits we aim to determine which signal (either visual or chemical) is more important for predator deterrence in wood-tiger moths. For this purpose, we are using fake paper moths with a nutritious lard + flour body that we rub with the moths’ chemical defences. Birds seem to easily identify our models as food!
Costs of chemical defences produced de novo, and potentially honest warning signals
It has long been assumed that most chemical defences in insects are sequestered from the plants they feed on, but it has not been experimentally tested whether there is some degree of de novo production. We are currently investigating whether that is the case in wood tiger moths, by raising larvae under different diet regimes. In addition to that, we are studying whether or not these chemical defences are costly and, if so, what kind of costs these moths incur during their production and/or sequestration. Finally, we are interested in the possibility that female colouration (which varies continuously from yellow through to red) is an honest signal of the strength of their chemical defences.
These studies are being done in collaboration with Emily Burdfield-Steel and Kaisa Suisto, and MSc students Morgan Brain and Miriam Furlanetto.