Investigating the evolutionary dynamics of chemical defences, warning colouration and predator learning.
In a Nutshell
Aposematism is an antipredator strategy in which chemical defences (e.g. toxicity, distastefulness) are advertised to potential predators using warning signals (such as bright colours, like a bee). Predators learn to avoid such species, and likewise avoid the costs of sub-optimal foraging. The potential prey benefits by not being eaten.
We work on many different aspects of aposematism, but broadly speaking we are interested in the initial evolution of aposematism and its ongoing maintenance. One particular interest is how aposematism is maintained when there is variation in warning signals (which theoretically makes it harder for predators to associate a signal with distastefulness). More recently, we have also become interested in the underlying diversity of <chemical defences> that aposematism signals.
Our studies cover a wide scope, including:
- the selection pressures acting on aposematic prey
- the optimality of signalling
- trade-offs in signal expression
- geographic variation in warning signals
- the evolution of Batesian (harmless prey imitates aposematic prey) and Müllerian (aposematic prey imitates another aposematic prey) mimicry.
Our study systems for aposematism are wood tiger moths, snakes, and poison frogs. We also do many studies using wild bird predators and artificial prey in the lab.
- Alatalo RV & Mappes J. 1996: Tracking the evolution of warning signals – Nature 383: 708-710.
- Mappes J, Marples N, Endler JA. 2005: The complex business of survival by aposematism. Trends in Ecology and Evolution 20: 598-603.
- Thorogood R, Kokko H & Mappes J. 2018: Social transmission of avoidance among predators facilitates the spread of novel prey. Nature Ecology and Evolution 2, 254–261
Signal polymorphism in the wood tiger moth,
Our main study species expresses polymorphic colouration between and within populations despite strong frequency-dependent selection on warning signals (see Lindström et al 2001).
We have discovered that this colour polymorphism is an outcome of multiple, sometimes conflicting, selection pressures.
For example, our experiments show that, in Scandinavia, yellow morphs are better protected against avian predators but white morphs have better mating success (Nokelainen et al. 2012). Attack risk can also vary between morphs depending on the predator community composition: yellow males are better protected when Paridae (e.g. great tits) are abundant, whereas white males have the advantage when Prunellidae (dunnocks) are abundant (Nokelainen et al. 2014).
Furthermore, there are trade-offs between warning signal efficacy and thermoregulation (Hegna et al. 2013). Not to mention genetic correlations between colouration and immunity mechanisms (Nokelainen et al. 2013).
Taken together, our results are indicative of a more complex dynamic between predators and aposematic prey than suggested by classic views of positive frequency-dependent selection favouring local morphs.