Birth of a hotspot of intraspecific genetic diversity: notes from the underground

Abstract

Hotspots of intraspecific diversity have been observed in most species, often within areas of putative Pleistocene refugia. They have thus mostly been viewed as the outcome of prolonged stability of large populations within the refugia. However, recent evidence has suggested that several other microevolutionary processes could also be involved in their formation. Here, we investigate the contribution of these processes to current range-wide patterns of genetic diversity in the Italian endemic mole Talpa romana, using both nuclear (30 allozyme loci) and mitochondrial markers (cytochrome b sequences). Southern populations of this species showed an allozyme variation that is amongst the highest observed in small mammals (most populations had an expected heterozygosity of 0.10 or above), which was particularly unexpected for a subterranean species. Population genetic, phylogeographic and historical demographic analyses indicated that T. romana populations repeatedly underwent allopatric differentiations followed by secondary admixture within the refugial range in southern Italy. A prolonged demographic stability was reliably inferred from the mitochondrial DNA data only for a population group located north and east of the Calabrian peninsula, showing comparatively lower levels of allozyme variability, and lacking evidence of secondary admixture with other groups. Thus, our results point to the admixture between differentiated lineages as the main cause of the higher levels of diversity of refugial populations. When compared with the Pleistocene evolutionary history recently inferred for species from both the same and other geographic regions, these results suggest the need for a reappraisal of the role of gene exchange in the formation of intraspecific hotspots of genetic diversity.

What triggers the rising of an intraspecific biodiversity hotspot? Hints from the agile frog

“…The discovery of hotspots and the causes of their formation have become vigorous areas of research12345678910. Indeed, hotspots are increasingly seen as excellent opportunities for the study of long-debated themes in ecology and evolutionary biology, including the microevolutionary processes leading to the formation of latitudinal patterns of biodiversity, the role of divergence with or without gene flow in moulding current biodiversity, the role of hybridization in evolution, and the geographic mosaic of coevolutionary interactions561112. On the other hand, these areas are also of the utmost importance for long-term survival and conservation of species, since they frequently harbour most species' resources for coping with natural and anthropogenic environmental changes131415.…”

“…This geographic area has recently emerged as a hotspot of genetic diversity and as a site of multiple refugia for many temperate animal species, including amphibians6212728293031. Here we adopted a dense sampling strategy within this area, with the following aims: i) to assess the phylogeographic and population genetic structure, and the historical demographic trends of R. dalmatina within its prospected glacial refugium, ii) to investigate the microevolutionary processes that have moulded its genetic diversity within this area; and iii) to evaluate the main implications of our results for the conservation of this species.…”

Lifting the curtain on the freshwater mussel diversity of the Italian Peninsula and Croatian Adriatic coast

“…Moreover, while the southern part of the Italian Peninsula has been identified as a major hotspot of genetic diversity, as a glacial/interglacial refugium and as a source for later (re)colonizations of northern areas (e.g. Magri 2008;Canestrelli et al 2010), its northern part has long been acknowledged as an area of postglacial (re)colonization (e.g. Salvi et al 2013;Vilaça et al 2014).…”

Evaluation of large‐scale genetic structure in complex demographic and historical scenarios: The mitochondrial DNA and Y‐chromosome pools of the Iberian Atlantic façade

“…While the merits of such an approach are numerous (Holsinger and Weir, 2009), several equally significant models can only be compared on the basis of their raw within-group variance (Canestrelli et al, 2010;de Filippo et al, 2011), a drawback when assessing complex population structures such as those proposed in the present study.…”