Summary:

Dominance is a widespread mechanism by which the phenotype of heterozygotes is determined. In polymorphic loci, dominance thus plays an important role in the dynamic of the phenotypic polymorphism because of the high number of heterozygotes. This talk focuses on dominance in a striking case of colour polymorphism caused by Müllerian mimicry. In the unpalatable butterfly species Heliconius numata, several wing colour patterns are co-existing and these patterns exhibit high resemblance with other unpalatable species. Colour patterns thus seem to act as a warning signal of toxicity for predators. In H. numata, this protective mimicry is adapted to the spatial variation in communities of unpalatable butterflies, leading to a stable polymorphism of wing colour patterns due to selection/migration equilibrium. These complex wing colour patterns are mainly controlled by a single locus, the supergene P, which contains about 18 co-segregating genes. Dominance relationships among the haplotypes at the supergene P are predicted to be under high selective constraint due to an increased predation risk for non-mimetic intermediate heterozygotes. Using an original morphological approach based on automatic detection of pattern variation, we quantify the coefficient of dominance between haplotypes at the supergene P. The study of controlled crosses between sympatric and allopatric morphs suggests a complete dominance among haplotypes occurring within populations whereas mosaic of dominance is mainly observed in allopatric haplotypes. This highlights the important role of dominance in the polymorphism of distinct wing colour patterns involved in mimicry relationships and allow us to open research on the possible mechanisms of dominance at the supergene P.

Summary:

Mimicry as a defensive strategy is one of the most compelling example of adaptation. Mimicry communities often involve numerous species, and both mutualistic (Müllerian) and deceptive (Batesian) mimics coexist. In deceptive mimicry, palatable prey mimic unprofitable species (e.g. chemically defended prey which predators avoid) with a negative impact on avoidance learning by predators. In mutualistic mimicry, appearances of defended prey converge on a similar warning signal, thereby reinforcing it and decreasing the per-capita cost of training predators. Theoretical and experimental studies on mimicry phenotypes abound, but studies empirically testing their predictions in real mimicry communities remain scarce. Indeed, the quantitative distribution of phenotypes within and among mimicry complexes is largely unknown, and how phenotypic variations are influenced by the type of mimicry, selection intensity, and/or phylogeny remains unaddressed. We first developed a novel framework that enables for the automatic and precise quantification and comparison of colour pattern. We then used this tool on over 2000 specimens, consisting of 130 butterfly species, collected from distinct Neotropical butterfly communities in the Peruvian Amazon. We quantified the distribution of phenotypes and their structure into a number of separate mimicry optima, using a morphological space encompassing the variation and frequencies of all coexisting colours patterns. We analysed this structure to extract the ecological and phylogenetic patterns underlying the coexistence of multiple mimicry groups within a given locality. We then demonstrated the influence of deceptive vs. mutualistic mimics on phenotypic variability around a mimicry optimum in order to address the effective impact of deception on mimicry.