Abstract
Phylogeographic patterns of temperate species from the Mediterranean peninsulas have been investigated intensively. Nevertheless, as more phylogeographies become available, either unique patterns or new lines of concordance continue to emerge, providing new insights on the evolution of regional biotas. Here, we investigated the phylogeography and evolutionary history of the Italian crested newt, Triturus carnifex, through phylogenetic, molecular dating and population structure analyses of two mitochondrial gene fragments (ND2 and ND4; overall 1273 bp). We found three main mtDNA lineages having parapatric distribution and estimated divergence times between Late Pliocene and Early Pleistocene. One lineage (S) was widespread south of the northern Apennine chain and was further geographically structured into five sublineages, likely of Middle Pleistocene origin. The second lineage (C) was widespread throughout the Padano–Venetian plain and did not show a clear phylogeographic structure. The third lineage (N) was observed in only two populations located on western Croatia/Slovenia. Results of analysis of molecular variance suggested that partitioning populations according to the geographic distribution of these lineages and sublineages explains 76% of the observed genetic variation. The phylogeographic structure observed within T. carnifex and divergence time estimates among its lineages, suggest that responses to Pleistocene environmental changes in this single species have been as diverse as those found previously among several codistributed temperate species combined. Consistent with the landscape heterogeneity, physiographic features, and palaeogeographical evolution of its distribution range, these responses encompass multiple refugia along the Apennine chain, lowland refugia in large peri-coastal plains, and a ‘cryptic’ northern refugium.
Highlights
Identifying Pleistocene refugia is a central task of phylogeographical research ([1,2,3] and references therein), and ongoing climate change has led to increased interest in the identification and characterization of these areas [4]
Recent studies have shown that a plethora of microevolutionary processes encompassing demographic size variations, population fragmentations, secondary contacts, and population admixture acted in glacial refugia and contributed to shape the high refugial genetic diversity [3,5,6,7,8,9,10,11,12]
Tree topologies were identical between Maximum Parsimony (MP) and Maximum Likelihood (ML) trees at main nodes, with minor differences at some terminal nodes
Summary
Identifying Pleistocene refugia is a central task of phylogeographical research ([1,2,3] and references therein), and ongoing climate change has led to increased interest in the identification and characterization of these areas [4]. Glacial refugia allowed species to survive during unfavourable climatic phases of the Pleistocene and are often hotspots of current intraspecific diversity. Recent studies have shown that a plethora of microevolutionary processes encompassing demographic size variations, population fragmentations, secondary contacts, and population admixture acted in glacial refugia and contributed to shape the high refugial genetic diversity [3,5,6,7,8,9,10,11,12]. Glacial refugia are important both for long-term preservation of species and for their evolutionary potential. Assessing the geographic location of glacial refugia and understanding what microevolutionary processes were involved in the formation and long-term maintenance of genetic diversity hotspots in these areas have crucial relevance with respect to conservation at multiple levels of biodiversity [4,15,16]. Populations in these areas are expected to be especially threatened by climate change, rising special concerns for their long-term conservation (see [4,15,25,26] for a thorough discussion of the genetic consequences of recent climate change)
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