The speciation history of Heliconius : inferences from multilocus DNA sequence data
Heliconius butterflies, which contain many intermediate stages between local varieties, geographic races, and sympatric species, provide an excellent biological model to study evolution at the species boundary. Heliconius butterflies are warningly coloured and mimetic, and it has been shown that these traits can act as a form of reproductive isolation. I present a species-level phylogeny for this group based on 3834bp of mtDNA (COI, COII, 16S) and nuclear loci (Efla, dpp, ap, wg). Using these data I test the geographic mode of speciation in Heliconius and whether mimicry could drive speciation. Recent sister species display variable degrees of geographic overlap, ranging from almost complete overlap (sympatry) to complete non-overlap (parapatry or allopatry). There are frequent shifts in colour pattern within and between sister species which have a positive and significant correlation with species diversity this suggests that speciation is facilitated by the evolution of novel mimetic patterns. My data is also consistent with the idea that two major innovations in Heliconius , adult pollen feeding and pupal-mating, each evolved only once. By comparing gene genealogies from mtDNA and introns from nuclear Tpi and Mpi genes, I investigate recent speciation in two sister species pairs, H. erato/H. himera and H. melpomene/ H. cydno. There is highly significant discordance between genealogies of the three loci, which suggests recent speciation with ongoing gene flow. Finally, I explore the phylogenetic relationships between races of H. melpomene using an AFLP band tightly linked to the Yb colour pattern locus (which determines the yellow bar in the hindwing). At this locus, races group according to geographical location rather than clades inferred from colour pattern phenotype. This and similar loci can be used to facilitate comparative mapping with other Heliconius species. In summary, the patterns at each phylogenetic level using different gene regions are consistent with a scenario of rapid, adaptively driven divergence and speciation in this group.