Genomics

We have sequencecd the genome of Heliconius melpomene, and this is now being used in a wide variety of evolutionary and genomic studies. The genome was published in Nature in 2012. It is now available at LepBase.

Why Heliconius?

A major challenge in evolutionary biology is to identify the genes underlying the diversity of morphologies and adaptations within populations and among species. We would like to know how developmental pathways are modified to produce evolutionary novelty; which genes underlie evolutionary radiations or adaptive change and whether they share particular characteristics or modes of action.

Examples of recent evolutionary novelty are also useful for studying genetic variation in the genome surrounding a locus under strong selection. Strong selection can reduce genetic variation in surrounding regions and might be an important cause of genetic drift . This ‘signature of selection’ is used to detect genes in human disease gene association studies, but we are still lacking empirical studies of the expected pattern under different selection regimes. Butterfly wing patterns are excellent examples of adaptation, as they have a long history of field studies demonstrating their adaptive value, they are highly diverse even between very closely related taxa, and they are amenable to manipulation studies during development. In particular many species show striking convergence of pattern due to mimicry, which offers an opportunity to study how different species produce the same phenotype: how repeatable is adaptation in different genetic backgrounds?

Heliconius butterflies are a long-standing example of mimicry adaptation in a group that are particularly well suited to this kind of study. The Mullerian co-mimics, H. melpomene and H. erato, are well known for precise mimicry between the two species but also a great diversity of geographic races. Thus, the two species look identical in any one site, but their pattern changes between geographic locations. We have recently found striking evidence for homology between a cluster of tightly linked patterning loci in H. melpomene and a region controlling similar phenotypic effects in H. erato. More surprisingly, the same locus is homologous to a single pattern switch gene in a third species, H. numata. The latter has a very different pattern of diversity with locally polymorphic populations having several divergent morphs flying together, whose phenotypes are controlled by a single genetic switch locus. This ‘supergene’ architecture appears to have been assembled by increasing linkage between existing, loosely linked loci in the ancestral lineage (Joron et al.,2006).

In addition closely related species such as H. melpomene and H. cydno also differ in colour pattern controlled by the same genes. There is even evidence for mate preference genes being genetically associated with those controlling colour pattern, such that a yellow/white colour pattern switch and the preference for yellow versus white is controlled by the same genomic region (Kronforst et al, 2006). The same genomic regions are therefore evolutionarily important in different lineages within Heliconius and in speciation. Thus, the genetic analysis of genes controlling colour patterns in Heliconius will offer insights into the developmental control of evolutionary novelty, the repeatability of natural evolution, and the influence of different selection regimes on the genome in terms of patterns of variability and genome organisation.

Genome size

Heliconius melpomene 295MB
Heliconius erato 380MB

References

Joron, M., R. Papa, M. Beltrán, N. Chamberlain, J. Mavárez, et al. 2006. A conserved supergene locus controls wing pattern diversity in Heliconius butterflies. PLoS Biology 4(10): e303.

Kronforst, M., L.G. Young, L., D. D. Kapan, C. McNeely, R. J. O’Neill, and L. E. Gilbert. 2006. Linkage of butterfly mate preference and wing color preference cue at the genomic location of wingless. PNAS 103:6575-6580