Evolution and maintenance of variation in warning signals

Aposematic organisms display warning signals (for example conspicuous colours, distinctive odours or sounds) that inform predators about their possession of secondary defences (such as toxins, spines, irritant hairs, etc.). Predators learn about this association, and eventually learn to avoid defended prey, but this becomes very difficult if the warning signals are variable. The wood tiger moth (Arctia plantaginis) and the dyeing poison frog (Dendrobates tinctorius) are examples of species with within-population variation in warning signals. The main objective of my doctoral and postdoctoral research has been to understand how this colour pattern variability in aposematic species is maintained.

Wood Tiger Moths

In certain populations of this species both males with yellow and white hindwings can co-occur. Various studies have shown that yellow males are better protected from predators, which raises the question of why white males still exist, and why yellow males have not taken over. I teamed-up with my colleague Swanne Gordon, to run an experiment in semi-natural enclosures that aimed to test the role of  frequency-dependent sexual selection (Gordon et al. 2015)  and frequency-dependent flight activity (Rojas et al. 2015) on the maintenance of this colour polymorphism. We have also run a capture-mark-recapture study over two consecutive years, in the wild, in order to study movement patterns, population dynamics, and whether or not there are differences between the morphs, and the sexes, in their temporal occurrence within a given flying season. The latter study has been done in collaboration with Andrés López-Sepulcre and Juan Galarza.

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Dyeing Poison Frogs

I have studied the dyeing poison frog at Les Nouragues Reserve in French Guiana since 2009, mostly trying to understand how its phenotypic diversity can persist within a population. I have addressed the possible roles of natural and sexual selection (Rojas & Endler 2013), the link between colour-pattern geometry and behaviour (Rojas et al. 2014a) , the effect of differences in light environment (Rojas et al. 2014) , and spatial patterns of predators and prey (Endler & Rojas 2009) as possible (non-mutually exclusive) explanations for the maintenance of warning signal variation.

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But warning signal variation can also occur between populations of a given species (polytypism). In collaboration with Brice Noonan and JP Lawrence (University of Mississippi, USA), Johanna Mappes (University of Jyväskylä, Finland), Antoine Fouquet (CNRS, France), Ralph Saporito (John Carroll University, USA) and Elodie Courtois (CNRS, French Guiana), I’m trying to get a better understanding of the origin of the phenotypic diversity displayed by the dyeing poison frog across populations, and investigate the possible selective pressures leading to it.

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