Abstracts (first author)
The hidden history of the Snowshoe hare (Lepus americanus): deep intraspecific divergence and massive mitochondrial DNA introgression
The analysis of molecular variation in wild populations often allows uncovering fundamental evolutionary processes that could otherwise remain unknown. Lepus americanus is the most widespread North American hare and its ecology has been vastly studied. However, knowledge on its evolutionary history is very scarce. A recent work based on microsatellite and mtDNA data suggested that this species is structured in three major units, which may have resulted from fragmentation during Pleistocene glaciations. Also, it suggested that the mtDNA lineage of one of these units is more closely related to that of a neighboring southern species, Lepus californicus, which could result from introgression or sharing ancestral polymorphism. Here, we sequenced nine loci, representative of all inheritance compartments (6774 bp), and shed light on the evolutionary history of L. americanus (48 specimens), taking also into account the evolution of L. californicus (30 specimens) and a third North American species, L. townsendii (18 specimens). Using a coalescent-based species tree inference method we show that the three evolutionary units of L. americanus have genealogical relevance and that one of the groups, widely distributed along the Boreal region, diverged at about 2 Mya, i.e. at the same time scale of the split between L. californicus and L. townsendii (1.6 Mya), without obvious morphological or ecological divergence. Also, coalescent simulations based on parameters of speciation inferred using the IM model, suggest that massive ancient mtDNA introgression occurred 680 kya from L. californicus into the Pacific Northwest populations of L. americanus. Interestingly, the specimens in this region have a peculiar morphology, since some do not molt to the white winter coat, an uncommon phenotypic variation in L. americanus. The snowshoe hare is thus a valuable model to understand cryptic divergence, adaptation and speciation in the presence of gene flow.