In a recently accepted paper in Molecular Ecology, we conclude that blue tits have colonised the Canary Islands from Africa no less than three times, but contrary to recent suggestions they did not back colonise mainland Africa from the islands. We combined traditional DNA sequencing on a large scale with massively parallel sequencing (“next generation sequencing”) and combine their respective strengths.
A demographic reconstruction reveals that the populations on the eastern Canary Islands Fuerteventura and Lanzarote have undergone recent population bottlenecks, while the long-term population sizes in northwest Africa have been stable, clearly supporting that the mainland populations have acted as a source for the colonisation of Fuerteventura and Lanzarote, and not the other way around.
The phylogenetic relationships between the blue tit populations of the Canary Islands are truly intricate. The first colonisation reached the northwesternmost island La Palma, and constitute a relict population which, surprisingly, is most closely related to a relict population in Libya. A second colonisation wave likely reached Gran Canaria or Tenerife, and spread to all central islands. The third colonisation reached the eastern islands, as described above. Thus, there are presently no less than six distinct populations on the Canary Islands!
Furthermore, we conclude that the access to new sequencing technologies, providing unprecedented amounts of genetic data, requires very careful handling. In another paper in the first issue of Molecular Ecology this year, a Norwegian group performed similar analyses as we did, on the same system. However, as we discuss in our paper, their coalescence analyses did not converge and the many of the results that they discuss are thus not valid.