A geographic mosaic of evolutionary lineages within the insular endemic newt Euproctus montanus

Abstract

Islands are hotspots of biodiversity, with a disproportionately high fraction of endemic lineages, often of ancient origin. Nevertheless, intra-island phylogeographies are surprisingly scarce, leading to a scanty knowledge about the microevolutionary processes induced on island populations by Plio-Pleistocene climatic oscillations, and the manner in which these processes contributed to shape their current genetic diversity. We investigated the phylogeography, historical demography and species distribution models of the Corsican endemic newt Euproctus montanus (north-western Mediterranean). As for many island endemics, the continuous distribution of E. montanus throughout its range has hitherto been considered as evidence for a single large population, a belief that also guided the species' categorization for conservation purposes. Instead, we found a geographic mosaic of ancient evolutionary lineages, with five main clades of likely Pliocene origin (2.6-5.8 My), all but one restricted to northern Corsica. Moreover, the copresence between main lineages in the same population was limited to a single case. As also suggested by growing literature on intra-island phylogeographic variation, it seems that the extensive use of simplifying assumption on the population structure and historical demography of island populations--both in theoretical and applicative studies--should be carefully reconsidered, a claim that is well exemplified by the case presented here.

Digging up the roots of an insular hotspot of genetic diversity: decoupled mito-nuclear histories in the evolution of the Corsican-Sardinian endemic lizard Podarcis tiliguerta

“…The high genetic diversity, phylogeographic complexity and intra-island differentiation found within P. tiliguerta clearly challenges these simplified assumptions. Similar findings stand out from recent phylogeographic studies on Corsican Sardinian endemic vertebrates [13, 20, 32] as well as on other insular systems [e.g. [98, 99]] indicating that the complexity of evolutionary histories which took place in environmentally complex islands such as the Tyrrhenian islands engendered a wealth of diversity comparable to or even higher than that observed in continental settings.…”

“…If on one hand we have little evidence that the transitory separations between Corsica and Sardinian may have triggered the vicariance between the P. tiliguerta lineages of each island, on the other hand the geologic evolution of Corsica and Sardinia is clearly not associated to the ancient (Miocenic) intra-island divergence estimated between west and east Corsican (Lineage 1 and 2) lineages and between north and south Sardinian (Lineage 3 and 4) lineages. Deep phylogeographic partitions have been found in north Corsica, but not in Sardinia, for the endemic lizard A. bedriagae [12] and the Corsican newt Euproctus montanus [13] as well as in the snail Solatopupa guidoni [29]. While a possible association with an exceptionally dry period during the Pliocene may explain the allopatric divergence between the newt lineages [13], to date we still have no clues on possible historical (environmental) barriers which may have driven intra-island diversification in the former species.…”

“…Deep phylogeographic partitions have been found in north Corsica, but not in Sardinia, for the endemic lizard A. bedriagae [12] and the Corsican newt Euproctus montanus [13] as well as in the snail Solatopupa guidoni [29]. While a possible association with an exceptionally dry period during the Pliocene may explain the allopatric divergence between the newt lineages [13], to date we still have no clues on possible historical (environmental) barriers which may have driven intra-island diversification in the former species.…”

“…These islands offer an ideal setting for investigating the evolutionary processes behind the origin and the structure of current patterns of insular biodiversity hotspots because: (i) they have a complex topography with a diversity of landscapes and microclimatic regions, spanning from Mediterranean to alpine climates [5, 6], which combined with the imprints of Plio-Pleistocene climatic oscillations [7–10] contribute to the diversification and persistence of old lineages [11–13]; (ii) the palaeogeographical evolution of the Corsican-Sardinian system within the Western Mediterranean is well established [14–18], thus providing a useful framework for biogeographic and molecular inferences [19]; and (iii) emerging phylogeographic and phylogenetic data on many endemics allow conclusions to be drawn within a comparative framework [see e.g. [19, 20].…”

“…In the last decade, Corsican-Sardinian species have been the subject of intensive phylogeographic surveys, especially regarding amphibians and reptiles [12, 13, 20–34], which have revealed how an essential component of the Tyrrhenian biodiversity hotspot is represented by the genetic variation held within and among populations of these endemic species. A significant realization of these studies is that the current patterns of genetic structure and diversity of these endemic species have been historically shaped by an unexpectedly diverse array of evolutionary and demographic processes acting across unrelated spatial and temporal scales [20].…”