We are interested in the processes of divergence and admixture during speciation. As species diverge in their ecology, behaviour and other traits, how does this translate into divergence in the genome. A popular recent metaphor has been that of ‘islands of divergence’, whereby some regions are maintained as distinct by selection, while other regions of the genome homogenise through ongoing gene flow and resultant admixture. However, it remains unclear the extent to which this metaphor applies in the real world.
We have used whole genome sequencing to show that patterns of divergence are highly heterogeneous across the genome (Martin et al., Genome Research In Press). Nonetheless, geographic sampling can be used to show that up to 40% of the genome of sympatric taxa is influenced by admixture. Furthermore there is good evidence that this admixture has been ongoing throughout the history of speciation. There is evidence that the size of divergent ‘blocks’ in the genome increases during speciation, as well as recruitment of more divergent regions (Nadeau et al., 2013).
We have also shown that regions controlling divergence in wing pattern are indeed ‘islands’ of divergence, with higher Fst as compared to the surrounding genome (Nadeau et al., 2012).
We are currently using coalescent models to generate more explicit hypotheses for the history of divergence and admixture during speciation in the butterflies.