Interspecific mtDNA transfer, selection and adaptation to cold in hares

Three of the five hare species that naturally occur in Europe are present in the Iberian Peninsula. From these three species, L. granatensis and L. castroviejoi are endemic to this region. The other species, L. europaeus, is restricted to northern Iberia and its range extends throughout Europe. Recently Alves et al. (2003) found in different hare populations of the three Iberian species the introgression of mtDNA from L. timidus, although the latter species inhabits Northern Eurasia and the Alps. Preliminary data obtained by our research group (POCTI/BSE/41457/2001) revealed a gradient from highly introgressed populations in the north to pure populations in the south of the peninsula. They also demonstrate that multiple hybridisation events were at the origin of this introgression. 

The analysis of all available mtDNA data has shown that such introgression from mountain hare was not restricted to Iberia, but also occurred into other northern hare species (e.g. L. oiostolus, L. arcticus, L. othus, and L. towensendii). Because the introgression appears to have occurred in the same direction into several species, we raise the hypothesis that it could be mediated by natural selection. In this project, we wish to confirm the selective advantage of mountain hare mtDNA, and assess whether this mitochondrial type confers a better resistance to cold. To test this hypothesis we propose to accomplish three main goals. 

First we aim to demonstrate that the gradient of mountain hare introgression in Iberia is due to selection since is not paralleled by a similar gradient for neutral nuclear markers (microsatellites).

Second, we intend to assess the nuclear gene phylogeny of several Lepus species in order to confirm the supposed mountain hare mtDNA introgression as a repeated and a widespread phenomenon.

Finally we plan to pinpoint mutations specific to the introgressive lineage that might be related to thermal adaptation, by sequencing the complete mitochondrial genome in different hare species. With this approach, we intend to demonstrate that reticulate evolution has played an important role in the evolution and adaptation of hare species to important climatic changes. We expect that our results would significantly contribute to a better understanding of mitochondrial evolution and demonstrate the permeability of species barriers to the spread of genetic novelty conferring adaptation.