Résumé
1. Müllerian mimicry between chemically defended preys is a textbook
example of natural selection favouring phenotypic convergence onto a
shared warning signal. Studies of mimicry have concentrated on deciphering
the ecological and genetic underpinnings of dramatic switches in mimicry
association, producing a well-known mosaic distribution of mimicry
patterns across geography. However, little is known about the accuracy of
resemblance between natural co-mimics when the local phenotypic optimum
varies. 2. In this study, using analyses of wing shape, pattern and hue,
we quantify multimodal phenotypic similarity between butterfly co-mimics
sharing the so-called postman pattern in different localities with varying
species composition. 3. We show that subtle but consistent variation
between populations of the localised species, Heliconius timareta
thelxinoe, enhance resemblance to the abundant co-mimics which drive the
mimicry in each locality. 4. Those results suggest that rarer co-mimics
track the changes in the phenotypic optimum caused by gradual changes in
the composition of the mimicry community, providing insights into the
process by which intra-specific diversity of mimetic pattern may arise.
Furthermore, our results suggest a multimodal evolution of similarity,
with coordinated convergence in different features of the phenotype such
as wing outline, pattern and hue. 5. Finally, multilocus genotyping allows
estimating local hybridization rates between H. timareta and co-mimic H.
melpomene in different populations, raising the hypothesis that mimicry
refinement between closely-related co-mimics may be enhanced by adaptive
introgression at loci modifying the accuracy of resemblance.