Species are defined by their ability to interbreed and by their inability of breed successfully with other species. Thus, the formation of new species, a key step in the origin of biological diversity, is dependent on the evolution of traits that prevent interbreeding between populations that were previously part of one species. Closely-related species are typically isolated from one another by multiple traits of this type. However, the evolutionary origin of individual barrier traits and the ways in which multiple traits are brought together to form strong barriers are not well understood. At a time when biological diversity is under threat from rapidly changing environments and human-mediated dispersal, it is crucial to manage natural populations in ways that maintain evolutionary potential. This includes the potential to form new species. Therefore, understanding the speciation process is important both for interpreting and conserving biological diversity.
The focus of this project is on the accumulation of barriers to gene exchange and the processes underlying increasing reproductive isolation between populations that have gone part of the way to being new species. I use the power of natural contact zones, where these populations hybridize, combined with novel manipulative experiments and modern genetic techniques, to separate the processes that underlie differentiation between populations and the barrier effects of differentiated traits. The model system is a common coastal snail, Littorina saxatilis. In many places around Europe, this snail forms distinct populations adapted to different parts of the shore environment, with areas of hybridization where environments meet. Our objective is to understand the traits that reduce interbreeding and lower fitness of hybrids, the genetic basis of the traits and the way they combine to limit gene exchange. We then model the underlying processes to predict the circumstances in which populations are most likely to evolve complete reproductive isolation and so become new species.
Our project has advanced understanding of the speciation process. We have shown that it is nearer to completion in Spanish populations than in Swedish populations, probably because the contact there is older and more extensive. A particular form of genetic variant, chromosomal inversions, have been shown to be critical to the progress of adaptation and speciation through their effects of traits that fit organisms to their environment and also impact on mating behaviour.
