Pelobates vespertinus (Pallas, 1771)

Dufresnes, Christophe, Strachinis, Ilias, Tzoras, Elias, Litvinchuk, Spartak N. & Denoel, Mathieu, 2019, Call a spade a spade: taxonomy and distribution of Pelobates, with description of a new Balkan endemic, ZooKeys 859, pp. 131-158 : 139-141

Pelobates vespertinus (Pallas, 1771)

Diagnosis.

Morphologically close to its sister species P. fuscus , it similarly features pale metatarsal spades and a domed skull. The coloration also spans the gray-yellowish-brownish spectrum, including reddish individuals (Fig. 3); orange dots can be heavily marked or absent (Fig. 3). It differs from P. fuscus by most individuals having three light longitudinal stripes on the dorsum ( Suriadna et al. 2016), as well as a dark stripe between the eyes ( Lada et al. 2005). Sexes of similar size (Fig. 2). Average SVL = 47 mm (range: 29-59 mm) for females (n = 3 populations) and 48 mm (29-61 mm) for males (n = 12 populations) (Suppl. material 1; Table S1, Fig. 2). The karyotype consists of seven large and six small pairs of two-armed chromosomes ( Manilo and Manuilova 2013; Suriadna 2014). NORs (secondary constrictions) are in the short arm of pair 7 ( Manilo and Radchenko 2008). The nuclear DNA content averages 9.2-9.4 pg ( Litvinchuk et al. 2013). As shown in Table 1, P. vespertinus differs from P. fuscus by 2.5% at mtDNA and 0.13% at nuclear DNA ( Dufresnes et al. 2019b). The genome of P. vespertinus is about 5% larger than P. fuscus ( Borkin et al. 2001; Litvinchuk et al. 2013; Suriadna 2014).

Taxonomy.

Originally named Rana vespertina Pallas, 1771; type locality: not specifically designated, but the author mentioned this taxon in Zarbay Creek ("Bach Sarbei", Samara oblast), Russia, which can be considered as the type locality; type(s): not mentioned. Three junior synonyms. Pelobates fuscus var. orientalis Severtsov, 1855; type locality: "Voronezhskaya Gubernia" (Voronezh governorate), Russia; type(s): not mentioned. Pelobates campestris Severtsov, 1855; type locality: between Bityug, Don and Ikorets rivers in today’s Voronezh province, Russia; type(s): not mentioned. Pelobates borkini Zagorodniuk, 2003; proposed for the eastern form of P. fuscus but nomen nudum because neither a type specimen nor a type locality were designated ( Zagorodniuk 2003). Pelobates vespertinus was previously considered a subspecies of the common spadefoot, as Pelobates fuscus vespertinus ( Crochet and Dubois 2004). The significant divergence (~2-3 My) and restricted admixture with P. fuscus , consistent with reproductive isolation, both support the distinction of P. vespertinus as a separate species ( Litvinchuk et al. 2013; Dufresnes et al. 2019b), as also proposed from genome size differences ( Suriadna 2014).

Distribution.

A lowland species (0-830 m elevation a.s.l.) widespread from the contact zone with P. fuscus , to western Siberia and Kazakhstan, and along the Ural River ( Kuzmin 1999) (Fig. 1). However, the exact limits with P. fuscus are not known in the northern 700 km of the distribution range. Detailed genetic data showed that the transition extends between the Kursk region to southern Ukraine ( Litvinchuk et al. 2013; Dufresnes et al. 2019b). In the south, it is present along the Sea of Azov coast to the northern Caucasus ( Kuzmin 1999; Suriadna et al. 2016). Spadefoot populations in the Crimea are attributed to P. vespertinus ( Litvinchuk et al. 2013). The southernmost populations are in Dagestan, where it is sympatric with P. syriacus ( Mazanaeva and Askenderov 2007). IUCN Status: Not Evaluated, as P. vespertinus was previously included in the P. fuscus assessment.

Diversity.

Crottini et al. (2007) and Litvinchuck et al. (2013) provided detailed phylogeographic accounts for this species (as the "eastern lineage of P. fuscus "), which consists of a homogenous clade that expanded from a single glacial refugia located in the eastern shores of the Sea of Azov. Pelobates vespertinus forms a narrow hybrid zone (<20 km) with P. fuscus in eastern Ukraine/western Russia ( Litvinchuk et al. 2013; Dufresnes et al. 2019b).