A combination of long term fragmentation and glacial persistence drove the evolutionary history of the Italian wall lizard Podarcis siculus

Gabriele Senczuk,Riccardo Castiglia,Emanuela De Simone,Gaetano Aloise,Paolo Colangelo

doi:10.1186/s12862-016-0847-1

Abstract

BackgroundThe current distribution of genetic diversity is the result of a vast array of microevolutionary processes, including short-term demographic and ecological mechanisms and long-term allopatric isolation in response to Quaternary climatic fluctuations. We investigated past processes that drove the population differentiation and spatial genetic distribution of the Italian wall lizard Podarcis siculus by means of sequences of mitochondrial cytb (n = 277 from 115 localities) and nuclear mc1r and β-fibint7genes (n = 262 and n = 91, respectively) from all its distribution range. The pattern emerging from the genetic data was compared with current and past (last glacial maximum) species distribution modeling (SDM).ResultsWe identified seven deeply divergent parapatric clades which presumably remained isolated in different refugia scattered mainly throughout the Tyrrhenian coast. Conversely, the Adriatic coast showed only two haplogroups with low genetic variability. These results appear to agree with the SDM prediction at the last glacial maximum (LGM) indicating a narrow area of habitat suitability along the Tyrrhenian coast and much lower suitability along the Adriatic one. However, the considerable land exposure of the Adriatic coastline favored a glacial colonization of the Balkan Peninsula.ConclusionsOur population-level historical demography showed a common trend consistent with glacial expansions and regional persistence during the last glacial maximum. This complex genetic signature appears to be inconsistent with the expectation of the expansion-contraction model and post-LGM (re)colonizations from southern refugia. Hence it is one of an increasing number of cases in which these assumptions are not met, indicating that long-term fragmentation and pre-LGM events such as glacial persistence were more prominent in shaping genetic variation in this temperate species.

Highlights

The current distribution of genetic diversity is the result of a vast array of microevolutionary processes, including short-term demographic and ecological mechanisms and long-term allopatric isolation in response to Quaternary climatic fluctuations
These seven clades were supported by spatial principal component analysis (sPCA), performed on the whole Mitochondrial DNA (mtDNA)
The the most recent common ancestors (TMRCA) for this clade was estimated at 846 Thousand years ago (Kya) (95% highest posterior densities (HPD): 1.14 Million years ago (Mya)–573 Kya)

Summary

Introduction

The current distribution of genetic diversity is the result of a vast array of microevolutionary processes, including short-term demographic and ecological mechanisms and long-term allopatric isolation in response to Quaternary climatic fluctuations. Senczuk et al BMC Evolutionary Biology (2017) 17:6 flexibility of the expansion-contraction (EC) model of Pleistocene biogeography [1] and of the expectation of post-last glacial maximum (LGM) demographic expansions from southern refugia These new perspectives suggest that some temperate species could have undergone attenuated or even reverse responses to glacial population contractions, with the absence of a postLGM (re)colonization pattern [13, 14]. This scenario appears plausible considering the strong sea level decrease (as much as 120–135 m) during the LGM, leading to the increase of Mediterranean coastal plains and favoring the formation of new suitable habitats with consequent population expansions. A growing number of taxa reveal evidence of strong phylogeographic structure within the main southern regions ([16,17,18] in the Iberian Peninsula; [19, 20] in the Italian Peninsula; [11, 21, 22] in the Balkan Peninsula)

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