Polymorphism in aposematic animals and coexistence of multiple mimicry rings within a habitat are not predicted by classical Müllerian mimicry. The butterfly Heliconius numata Cramer (Lepidoptera: Nymphalidae; Heliconiinae) is both polymorphic and aposematic. The polymorphism is due to variation at a single locus (or 'supergene') which determines colour patterns involved in Müllerian mimicry. We sampled 11 sites in a small area (approx. 60 × 30 km) of Northeastern Peru for H. numata and its co-mimics in the genus Melinaea and Athyrtis (Ithomiinae), and examined the role of temporal and spatial heterogeneity in the maintenance of polymorphism. Colour-patterns of Melinaea communities, which constitute the likely 'mimetic environment' for H. numata, are differentiated on a more local scale than morphs of H. numata, but the latter do show a strong and significant response to local selection for colour-pattern. In contrast, analysis of enzyme polymorphism in H. numata across the region revealed no spatial structure, which is consistent with a high mobility of this species. Differences in spatial variability in the two taxa may have caused H. numata to become polymorphic, while temporal variability, not significant in this study, probably has a lesser effect. The mimetic polymorphism is therefore explained by means of multiple selection-migration clines at a single locus, a similar process to that which explains narrow hybrid zones between geographic races of other Heliconius butterflies.
Bibliographical noteFunding Information:
We are grateful to Moisés Abanto, Gorky Valencia and Andrew Brown who helped collecting butterflies, and to Rainer Schulte who improved our local mobility. John Allen and an anonymous reviewer provided useful comments on the manuscript. INRENA granted permission to export biological material. The work was funded by financial aid from the Institut Klorane and from the Centre National de la Recherche Scientifique to MJ and by a collaborative grant from the French Ministry of Foreign Affairs and the British Council to JM and MJ. This is publication ISEM-2000-82 of the Institut des Sciences de l'Evolution, Montpellier.
- Frequency-dependent selection
- Heliconius numata
- Müllerian mimicry
- Population genetic structure
- Spatial heterogeneity