Hybridisation, Adaptation and Speciation
The evolution of genetic information underlies the dynamics of biodiversity, and among the avatars generated by this information at higher levels of organization, species are considered an important unit of evolution. The pertinence of this level of organization depends on our understanding of the relationship between the process of speciation and that of adaptation to the environment and the level of coupling/uncoupling between the two, a major challenge of modern evolutionary theory. This can be addressed at the early stages of the speciation process by determining how genetic information is partitioned among incipient species that continue to exchange part of it. We are using this approach in two well studied mammalian models (hares and house mice) and one reptile (the Iberian Wall Lizards complex) for which we have gathered evidence of extensive but differential genetic exchanges between closely related taxa in the recent past, at the favour of changes in the environment, presumably range shifts linked to climatic fluctuations during the last glaciation.
In the three models, the amount of introgression varies a lot among hybrid zones and among loci, and some populations show evidence of massive introgression for some loci. This variance in introgression levels suggests that selection and drift were both involved in shaping patterns of interspecific gene flow. We are expanding these observations of the apportionment and exchange of genetic diversity between taxa genome‐wide, thanks to the recent progress of high throughput sequencing technologies. With this extensive dataset we will infer the historical conditions of the genetic exchanges between the taxa since their initial divergence, and determine their variations along the genome. We are also studying the population genetics of genomic regions with varying patterns of introgression, in order to take apart the influence of demographic processes from that of selection in promoting introgression.
This research is expected to deliver unprecedented understanding, on several biological models, of the genetic architecture of reproductive isolation, the role of species range‐shifts and natural selection in promoting introgression, and will contribute to elucidate the possible dual role of sex chromosomes and genetic conflicts in driving reproductive isolation vs. promoting gene flow.