The formation of new species underlies all of life’s biodiversity. Speciation is usually a gradual process, that can occur despite some interbreeding between the emerging gene pools. In fact our work on Heliconius butterflies has revealed that species can remain distinct despite ongoing, occasional hybridisation over a million years after they first started to diverge. So, what are the mechanisms that maintain species differences despite interbreeding?

One answer to this question is that natural selection is able to ‘weed out’ some foreign genes from each population, and thereby maintain some distinctness between the species.

We have been asking where in the genome, and how, these species barriers form. One of the most striking patterns to emerge from our work, and studies in other taxa, is that the local recombination rate influences the effectiveness of species barriers. As a result, there are dramatic differences across the genome in how distinct two species are, and in some cases different parts of the genome even tell a different story of which species is most closely related to which.

Next, we want to know how repeatable these patterns are, and whether large scale changes to the organisation of the genome can change their role in speciation.