Heliconius butterflies show striking Müllerian mimicry between species. In other words, unrelated species resemble one another because this helps in teaching predators that they are distasteful. We have demonstrated that mimicry plays a key role in speciation. For example, the sister sympatric species Heliconius cydno and H. melpomene differ in their mimetic warning colour patterns, and we have shown that 1) mimetic patterns are directly involved as cues in mate finding and 2) changes in mimicry are associated with changes in habitat. Mimetic shifts are also expected to generate strong disruptive selection because hybrids have intermediate and non-mimetic colour patterns. There is therefore potential for the rapid evolution of new Heliconius species due to shifts in mimicry. Mimicry is therefore a ‘magic trait’ that is both under ecological selection, but that also generates reproductive isolation between populations and hence leads to speciation.
We are currently interested in the genetic basis of mate preference in speciation. Richard Merrill carried out crosses between Heliconius cydno and H. melpomene and has shown that there are genetic associations between mate preference and colour patterning genes. This is exciting as it suggests a genetic architecture that could facilitate speciation with gene flow.
Also, in collaboration with Mauricio Linares and his group in Colombia, Camilo Salazar and others have shown that the colombian endemic species, H. heurippa, has most likely arisen as a result of a hybridisation event. The H. heurippa pattern can be reconstructed by crossing H. melpomene and H. cydno, and its pattern plays an important role in reproductive isolation from the parental species. More recently Maria-Clara Melo has shown that even first generation backcross hybrids with ‘heurippa-like’ patterns show the same mating preferences – this suggests that the mating preference of H. heurippa was also generated through hybridisation.
A good place to read more about speciation in Heliconius is my review article in BioScience Ecological speciation in mimetic butterflies.