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A large array of species and species complexes from the Iberian Peninsula display strong genetic subdivisions indicative of past population isolation in separate glacial refugia as a result of survival throughout the Pleistocene ice ages. We used mitochondrial and nuclear sequence data to analyse phylogeographic patterns in a group of endemic land snails of the genus Candidula from a valley of central Portugal (Vale da Couda) showing an exceptionally narrow distributional range. Phylogenetic analyses recovered Vale da Couda specimens in two main clades that do not share a common ancestry. Considering the restricted geographic distribution, an unusual high number of haplotypes was found. These haplotypes were unevenly distributed among the sampling sites. Our results show a departure from the expectation that species with restricted distributions have low genetic variability. The putative past and contemporary models of geographic distribution of Vale da Couda lineages are compatible with a scenario of species co-existence in more southern locations during the last glacial maximum (LGM) followed by a post-LGM northern dispersal tracking the species optimal thermal, humidity and soil physical conditions. Mismatch analysis indicated a population expansion during the LGM, which corroborates our biogeographic scenario.
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Bioclimatic variables for current conditions retrieved from WorldClim dataset (Hijmans et al 2005).
Estimates of net evolutionary divergence between haplogroups (axis on the left, dark grey bars ± standard deviation) and within lineages (axis on the right, light grey bars ± standard deviation), based on Tamura-Nei distances.