Polyphyly and gene flow between non-sibling Heliconius species.
BACKGROUND
The view that gene flow between related animal species is rare and evolutionarily unimportant largely antedates sensitive molecular techniques. Here we use DNA sequencing to investigate a pair of morphologically and ecologically divergent, non-sibling butterfly species, Heliconius cydno and H. melpomene (Lepidoptera: Nymphalidae), whose distributions overlap in Central and Northwestern South America.


RESULTS
In these taxa, we sequenced 30-45 haplotypes per locus of a mitochondrial region containing the genes for cytochrome oxidase subunits I and II (CoI/CoII), and intron-spanning fragments of three unlinked nuclear loci: triose-phosphate isomerase (Tpi), mannose-6-phosphate isomerase (Mpi) and cubitus interruptus (Ci) genes. A fifth gene, dopa decarboxylase (Ddc) produced sequence data likely to be from different duplicate loci in some of the taxa, and so was excluded. Mitochondrial and Tpi genealogies are consistent with reciprocal monophyly, whereas sympatric populations of the species in Panama share identical or similar Mpi and Ci haplotypes, giving rise to genealogical polyphyly at the species level despite evidence for rapid sequence divergence at these genes between geographic races of H. melpomene.


CONCLUSIONS
Recent transfer of Mpi haplotypes between species is strongly supported, but there is no evidence for introgression at the other three loci. Our results demonstrate that the boundaries between animal species can remain selectively porous to gene flow long after speciation, and that introgression, even between non-sibling species, can be an important factor in animal evolution. Interspecific gene flow is demonstrated here for the first time in Heliconius and may provide a route for the transfer of switch-gene adaptations for Müllerian mimicry. The results also forcefully demonstrate how reliance on a single locus may give an erroneous picture of the overall genealogical history of speciation and gene flow.
Bull
Vanessa
V
Galton Laboratory, Department of Biology, University College London, 4 Stephenson Way, London NW1 2HE, UK. Vanessa.Bull@fss.pnn.police.uk
Beltrán
Margarita
M
Jiggins
Chris D
CD
McMillan
W Owen
WO
Bermingham
Eldredge
E
Mallet
James
J
D000818:Animals; D005075:Biological Evolution; D002080:Butterflies / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D004296:Dopa Decarboxylase / Q000235:genetics; D029721:Drosophila Proteins / Q000235:genetics; D003576:Electron Transport Complex IV / Q000235:genetics; D051456:Gene Flow; D006239:Haplotypes; D007438:Introns; D008359:Mannose-6-Phosphate Isomerase / Q000235:genetics; D008957:Models, Genetic; D010802:Phylogeny; D013045:Species Specificity; D014157:Transcription Factors / Q000235:genetics; D014305:Triose-Phosphate Isomerase / Q000235:genetics
D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D014157:Transcription Factors; C092937:ci protein, Drosophila; D003576:Electron Transport Complex IV; D004296:Dopa Decarboxylase; D014305:Triose-Phosphate Isomerase; D008359:Mannose-6-Phosphate Isomerase