The distribution and biogeography of slow worms (Anguis, Squamata) across the Western Palearctic, with an emphasis on secondary contact zones

Abstract

The slow-worm lizards (Anguis) comprise five species occurring throughout most of the Western Palearctic. Although these species are relatively uniform morphologically – with the exception of A. cephallonica, which exhibits a quite unique morphology – they are genetically deeply divergent. Here, we provide detailed distribution maps for each species and discuss their biogeography and conservation based on updated genetic data and a robust distribution database. We pay particular attention to the so called ‘grey zone’, which typically represents secondary contact zones and in some cases confirmed or presumed hybrid zones. Four of the five species live in parapatry, while only two species, A. cephallonica and A. graeca from the southern Balkans occur in partial sympatry. Further research should focus on the eco-evolutionary interactions between species in contact, including their hybridization rates, to reveal deeper details of the slow-worm evolutionary and natural history.

Formation of hemiclonal reproduction and hybridogenesis inPelophylax waterfrogs studied with species-specific cytogenomic probes

“…The closest distance between sites of parental taxa was 35 km, while the largest distance between the collected parental taxa for crosses was 380 km. Temperate Central Europe is known for hybrid zones between eastern and western lineages of various taxa (Jablonski et al, 2021;Nürnberger et al, 2016), which probably reflects the genetic divergence that had accumulated between allopatric populations formed during the ice ages. Because the fine-scale phylogeography of Pelophylax taxa in the region is still missing (Hoffmann, 2015;Zeisset & Hoogesteger, 2018), we combined parental individuals from a single or from distinct biogeographic regions, draining into the North Sea and the Baltic Sea.…”

Karyotype stasis but species-specific repetitive DNA patterns in Anguis lizards (Anguidae), in the evolutionary framework of Anguiformes

“…Species identi cation was based on a combination of morphological characters and distribution (Gvoždík et al 2015;Benkovský et al 2021;Jablonski et al 2021), and DNA barcoding using a fragment of mitochondrial DNA (mtDNA; NADH dehydrogenase 2 gene [ND2]) according to previously published protocols (e.g., Gvoždík et al 2010;Jablonski et al 2016). Obtained nucleotide sequences were deposited in GenBank (acc.…”

“…We applied the CGH method on the chromosomes of both sexes to detect sex-speci c regions using competitive hybridization of male-and female-speci c probes. This method has been widely used to search for sex chromosomes in the karyotype of different vertebrates and its success depends on the amount and level of differentiation of sex-speci c genetic content (e.g., Deon et It is also worth noting that the phylogenetically and chromosomally most divergent A. cephallonica occurs in partial sympatry with A. graeca (Jablonski et al 2016(Jablonski et al , 2021, but the two species also probably do not hybridize (Thanou et al 2021). However, how karyotypes change across contact zones of individual species remains to be investigated.…”

“…Slow worms, the semifossorial legless lizards of the genus Anguis (family Anguidae), represent such an example. They are morphologically quite uniform or di cult to distinguish by external characters (Benkovský et al 2021;Jablonski et al 2021) but have been shown to represent genetically relatively deeply divergent lineages harbouring ve currently recognized species (Gvoždík et al 2010(Gvoždík et al , 2013(Gvoždík et al , 2022Jablonski et al 2016).…”

“…It may apply even in relatively deeply divergent, non-sister species such as A. fragilis -A. colchica (Szabó and Vörös 2014; Gvoždík et al 2015; Benkovský et al 2021) or A. fragilis -A. graeca(Mikulíček et al 2018), both of which have the most recent common ancestor (MRCA) dated to 6.7 Mya(Gvoždík et al 2022). In contrast, the sister-species pair A. colchica -A. graeca (MRCA 4.4 Mya) with very similar karyotypes do not hybridize due to lack of geographic contact, as their distribution ranges are separated by the range of A. fragilis(Jablonski et al 2021). Their very similar karyotypes are likely a persistent ancestral condition from their MRCA, although past gene ow cannot be ruled out.…”