Colour polymorphism in the leaf beetle genus 'Oreina'

This dissertation investigates the maintenance of colour polymorphism in the leaf beetle genus <i>Oreina</i> CHEVROLAT (Coleoptera; Chrysomelidae). The remarkable colour variation in this seemingly aposematic and chemically defended genus forms a paradox with current scientific views concerning predator learning and mimicry. Using a variety of approaches we explore the selective forces that influence the dynamic colour polymorphic equilibrium. On the basis of a literature review we argue that there isn’t just one selective force of overriding importance but a multitude of factors in a heterogeneous landscape producing a geographic mosaic of coevolution in space and time. Using a phylogenetic approach we analysed the genetic structure and habitat use of <i>Oreina speciosissima</i> populations from the Swiss Alps. Specimens grouped according to their habitat, which was in turn mostly defined by plant associations. Via field experiments we test Müller’s theory of warning colour and mimicry in the wild and prove frequency-dependent selection using tethered beetles exposed to natural predators. By making use of TEM microscopy we prove that colour in <i>Oreina gloriosa</i> is structural and produced by microstructures in the epicuticle. Differences in colour are the result of minute differences in thickness of the electron lucent layers within the chirped multilayer reflector in the beetle’s elytra. I conclude by arguing that there is a multiplicity of factors driving the persisting prevalence of colour polymorphism in <i>Oreina</i> and provide suggestions for further investigation.

Thèse de doctorat : Université de Neuchâtel, 2013