Reconstructing hotspots of genetic diversity from glacial refugia and subsequent dispersal in Italian common toads (Bufo bufo)

Abstract

Genetic diversity feeds the evolutionary process and allows populations to adapt to environmental changes. However, we still lack a thorough understanding of why hotspots of genetic diversity are so 'hot'. Here, we analysed the relative contribution of bioclimatic stability and genetic admixture between divergent lineages in shaping spatial patterns of genetic diversity in the common toad Bufo bufo along the Italian peninsula. We combined population genetic, phylogeographic and species distribution modelling (SDM) approaches to map ancestral areas, glacial refugia, and secondary contact zones. We consistently identified three phylogeographic lineages, distributed in northern, central and southern Italy. These lineages expanded from their ancestral areas and established secondary contact zones, before the last interglacial. SDM identified widespread glacial refugia in peninsular Italy, sometimes located under the present-day sea-level. Generalized linear models indicated genetic admixture as the only significant predictor of the levels of population genetic diversity. Our results show that glacial refugia contributed to preserving both levels and patterns of genetic diversity across glacial-interglacial cycles, but not to their formation, and highlight a general principle emerging in Mediterranean species: higher levels of genetic diversity mark populations with substantial contributions from multiple genetic lineages, irrespective of the location of glacial refugia.

Evidence for multiple refugia and hotspots of genetic diversity for Westralunio carteri, a threatened freshwater mussel in south‐western Australia

“…The BSPs detected demographic expansion within all three haplogroups (Figure 6); WcII and WcIII appear to have begun a Identifying hotspots of intraspecific diversity and areas of historical refugia is important for the conservation of imperilled taxa (Petit et al, 2003;Canestrelli et al, 2010;Chiocchio et al, 2021). Mussels in Mediterannean-climate regions are more imperilled and face a wider range of threats than other mussels globally, but the phylogeographical research effort on this group has not been equal among these regions (Benson et al, 2021).…”

“…Traditionally, this process has been described as a contraction to major refugia, where a panmictic, stable and genetically diverse population is maintained (Hewitt, 2000). More recently, numerous authors have shown that the process may actually involve ‘refugia‐within‐refugia’, whereby multiple isolated populations persist within the broader refugial area (Byrne, 2008; Canestrelli et al, 2010; Canestrelli et al, 2014; Chiocchio et al, 2021). In this scenario, hotspots are ‘melting pots’ generated by (a) localized contraction and divergence of these populations and (b) subsequent admixture during re‐expansion (Canestrelli et al, 2010).…”

“…‘Hotspots’ of intraspecific genetic diversity (areas of exceptionally high diversity) are increasingly recognized as key targets for species conservation and management (Petit et al, 2003; Canestrelli et al, 2010; Chiocchio et al, 2021). Hotspots not only contain populations with greater evolutionary potential, but also often have important environmental resources that may allow those populations to persist when facing stressful conditions (Canestrelli et al, 2014).…”

Genetic diversity and demography of Bufo japonicus and B. torrenticola (Amphibia: Anura: Bufonidae) influenced by the Quaternary climate

“…There are two endemic Bufo species on the Japanese mainland, Bufo japonicus Temminck and Schlegel, 1838 and B. torrenticola Matsui, 1976 ( Matsui & Maeda, 2018 ). Although the effects of the Quaternary climate on European toads have been examined in detail ( e.g ., Garcia-Porta et al, 2012 ; Arntzen et al, 2018 ; Chiocchio et al, 2021 ), limited information is currently available on B. japonicus and B. torrenticola . Bufo japonicus is widely distributed in Honshu, Shikoku, Kyushu, and some adjacent islands and is a lentic breeder, similar to the majority of congeneric species.…”

Spatial differentiation of background matching strategies along a Late Pleistocene range expansion route

“…During periods of unsuitable climatic conditions, species’ ranges contracted into climatic refugia, whereas range expansions followed the re-establishment of suitable conditions (Hewitt, 1996; 2000; 2011a; Weiss & Ferrand, 2007). The legacies of range dynamics on species genetic structures have been widely investigated during the last decades (Hewitt, 2000; Avise, 2009; Hewitt, 2011b; Lucati et al, 2020; Chiocchio et al, 2021), whereas evidence on their role in moulding intra-specific phenotypic variation is scarce. Yet, phenotypic traits are likely to vary in response to dispersal processes, especially during range expansions (Canestrelli et al, 2016a).…”