Abstract
The aim of the present study was to investigate the genetic structure of the Valais shrew (Sorex antinorii) by a combined phylogeographical and landscape genetic approach, and thereby to infer the locations of glacial refugia and establish the influence of geographical barriers. We sequenced part of the mitochondrial cytochrome b (cyt b) gene of 179 individuals of S. antinorii sampled across the entire species' range. Six specimens attributed to S. arunchi were included in the analysis. The phylogeographical pattern was assessed by Bayesian molecular phylogenetic reconstruction, population genetic analyses, and a species distribution modelling (SDM)-based hindcasting approach. We also used landscape genetics (including isolation-by-resistance) to infer the determinants of current intra-specific genetic structure. The phylogeographical analysis revealed shallow divergence among haplotypes and no clear substructure within S. antinorii. The starlike structure of the median-joining network is consistent with population expansion from a single refugium, probably located in the Apennines. Long branches observed on the same network also suggest that another refugium may have existed in the north-eastern part of Italy. This result is consistent with SDM, which also suggests several habitable areas for S. antinorii in the Italian peninsula during the LGM. Therefore S. antinorii appears to have occupied disconnected glacial refugia in the Italian peninsula, supporting previous data for other species showing multiple refugia within southern refugial areas. By coupling genetic analyses and SDM, we were able to infer how past climatic suitability contributed to genetic divergence of populations. The genetic differentiation shown in the present study does not support the specific status of S. arunchi.
Highlights
Understanding the factors that both determine the distribution of species and contribute to the formation and the maintenance of population genetic structure is a central tenet of biogeography
The southern European peninsulas are often assumed to have been single areas from which species recolonized higher latitudes after the Last Glacial Maximum (LGM; Hewitt, 2000; Petit et al, 2003), it has recently been suggested that populations within species in a single southern peninsula may have been distributed among multiple disconnected refugia (Gómez & Lunt, 2007)
At the LGM, S. antinorii was apparently restricted to the Italian Peninsula, which itself was subdivided into multiple suitable areas, concordant with the ‘refugia within refugia’ concept (Gómez & Lunt, 2007)
Summary
Understanding the factors that both determine the distribution of species and contribute to the formation and the maintenance of population genetic structure is a central tenet of biogeography. Such an understanding enables the prediction of the consequences of global change, such as future range contraction and loss of genetic variation. The three southern European peninsulas (Iberian, Italian, and Balkan) have traditionally been recognized as glacial refugia during these ice ages, and are currently considered as species-rich areas, as well as hotspots of intra-specific diversity (Bilton et al, 1998; Hewitt, 2000; Petit et al, 2003; Ruedi et al, 2008). The causes of genetic structure should be investigated using multiple approaches, including both species distribution modelling (SDM; Guisan & Zimmermann, 2000; Waltari et al, 2007) and the use of current landscape features to infer which factor(s) are most responsible for shaping intra-specific genetic subdivision
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