Abstract
Mediterranean peninsulas are major biodiversity hotspots, and cold-adapted species are an important component of this biodiversity. However, cold-adapted species contributed surprisingly little to our knowledge of the intimate links between Quaternary environmental changes, species’ responses to these changes, and current patterns of intraspecific biodiversity. Here, we investigated the genetic structure and evolutionary history of a cold-adapted amphibian, the Alpine newt Ichthyosaura alpestris, within the Italian peninsula. Nuclear and mitochondrial markers consistently identified three distinct genetic lineages, whose divergence dates to the Early Pleistocene (1.9 and 0.8 million years ago). Our results show that the Italian peninsula provided multiple Pleistocene refugia to this cold-adapted species, and suggest that allopatric fragmentation followed by secondary admixture have been key events in the formation of its current pattern of genetic diversity. Indeed, estimates of population genetic diversity clearly identified contact populations as those achieving the highest levels of diversity. Such concordance among cold-adapted and temperate species in terms of processes triggering the formation of regional patterns of genetic diversity provides strong support for the hypothesis that gene exchange between divergent lineages, rather than long-term stability of refugial populations, has been the main step toward the formation of hotspots of intraspecific biodiversity.
Highlights
Mediterranean peninsulas are major biodiversity hotspots, and cold-adapted species are an important component of this biodiversity
In the combined mitochondrial DNA (mtDNA) dataset (1277 bp), we found 13 haplotypes defined by 35 variable positions, 31 of which were parsimony informative
In the β-fibrinogen gene (β-FIB) alignments, we found six haplotypes that were identified by eight variable sites, seven of which were parsimony informative; h = 0.365 (±0.041 SD) and π = 0.0041 (±0.001 SD)
Summary
Mediterranean peninsulas are major biodiversity hotspots, and cold-adapted species are an important component of this biodiversity. By promoting cycles of contraction and expansion in species’ ranges, they triggered the formation of range-wide patterns of genetic diversity, such as the so-called “southern richness and northern purity” pattern[8,9,10,11] Through their interactions with the topographical complexity of the Mediterranean peninsulas and their influence on sea-level changes, Pleistocene climatic oscillations contributed to the formation of complex patterns of population genetic structure and divergence within these regions, such as the so-called “refugia-within-refugia”[12]. We investigated the genetic structure and evolutionary history of a cold-adapted amphibian, the Alpine newt Ichthyosaura alpestris (Laurenti, 1768), within the Italian peninsula This species is widely distributed in central and eastern Europe, while in the Apennines its distribution is fragmented and closely linked to midand high-altitude ponds[35] (Fig. 1). Phylogenetic analyses have confirmed that populations in the Italian peninsula belong to a distinct evolutionary unit, and have estimated their divergence from other European clades (including populations in the Alps) to the Late Miocene[39,40,41]
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