Pelobates fuscus (Laurenti, 1768)

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 : 138

Pelobates fuscus (Laurenti, 1768)

Diagnosis.

Small spadefoot characterized by pale grayish metatarsal spades and a domed skull. The webbing of the hindfeet is well developed. Males are smaller than females (Fig. 2). The species can be found in a spectrum of gray, brown, or yellowish colors, but rarely greenish (P. Székely pers. comm.), and features patterns such as stripes or blotches of varying sizes; variable presence of orange dots, from almost absent to very abundant (Fig. 3). In Eastern Europe, it differs from its sister species P. vespertinus by most individuals having numerous dark rounded spots on a light dorsum ( Suriadna et al. 2016) and lacking a dark stripe between the eyes ( Lada et al. 2005). Average SVL = 54 mm (range: 37-78 mm) for females (n = 21 populations) and 47 mm (36-65 mm) for males (n = 21 populations) (Suppl. material 1, Table S1; Fig. 2). The karyotype consists of seven large and six small pairs of two-armed chromosomes ( Mészáros 1973; Schmid et al. 1987; Manilo and Radchenko 2004; Manilo and Manuilova 2013; Suriadna 2014). Centromeric C-bands are obvious in pairs 2, 6, and 7-13 ( Schmid et al. 1987). NORs are in the short arm of pair 7 ( Schmid 1980, 1982). The nuclear DNA content (calculated from flow cytometry) averages 8.7-9.0 pg ( Litvinchuk et al. 2013).

Taxonomy.

Originally described as Bufo fuscus Laurenti, 1768; type locality: not specifically designated ("in paludibus, rarissime hospitantur in continenti", in swamps, rarely on the land); type(s): the specimens depicted by Rösel von Rosenhof (1758: pls XVII, XVIII), expressively cited by Laurenti (1768); although controversial (see Nöllert et al. 2012; Frost 2019), the additional mention of pl. XV (p. 122), a drawing of a dissected Pelophylax , could simply be an error. Rösel depicted the amphibians of Germany, and Shaw (1802) accordingly mentioned that Rösel found his specimens in the neighborhood of “Nurenberg” ( Nürnberg), Germany, which could then apply as the type locality. Seven junior synonyms. Rana alliacea Shaw, 1802; type locality: not specifically designated, but Shaw (1802) refers to Rösel’s toads from Nürnberg, Germany; type(s): the toad illustrated by the author (pl. 41), which may very well corresponds to the amplexed female on the top right of pl. XVII in Rösel von Rosenhof (1758), of identical posture and color patterns. Bombinator marmorata Sturm, 1828; type locality: near Penig, Germany; holotype: the frog illustrated by the author. Cultripes minor Müller, 1832; type locality: “unbekannt” (unknown); type(s): not mentioned. Pelobates fuscus var. lividis Koch, 1872: type locality: "von den Wiesen in der Nähe des Röder-Wäldchens bei Frankfurt" (the meadows in the Röder groove near Frankfurt), Germany; type(s): not mentioned; Pelobates insubricus Cornalia, 1873; type locality: nearby Milano, Italy; type(s): not mentioned, most likely deposited at MSNM, but presumably lost since ( Blackburn and Scali 2014). Pelobates latifrons Herón-Royer, 1888; type locality: "environ de Turin" (nearby Torino), Italy; type(s): not mentioned. Pelobates praefuscus Khosatzky, 1985; type locality: Etuliya, Moldova; holotype: ZISP 21N RNA M-1, a Pliocene fossil (according to Frost 2019). The Italian populations, for long considered as a subspecies P. f. insubricus , have been a matter of debate until recently because they bear private mtDNA haplotypes ( Crottini et al. 2007). Litvinchuk et al. (2013) synonymized this taxon with P. fuscus , given the weak divergence of these haplotypes, together with the lack of differentiation of allozyme and genome content. As it stands, P. fuscus should thus be considered a monotypic taxon.

Distribution.

Widespread distribution in western, central and eastern Europe (0-810 m elevation a.s.l.), but absent from the northern European countries and most of southern Europe ( Sillero et al. 2014; Nöllert at al. 2012) (Fig. 1). In the west, it reaches the eastern edge of the Netherlands ( Creemers and Van Delft 2009), the eastern part of Flanders in Belgium ( Bauwens and Claus 1996), the western parts of Nordrhein-Westfalens and the south-east of Rheinland-Pflaz in Germany ( Bitz et al. 1996; Chmela and Kronshage 2011), the north-eastern side of France (particularly along the Rhine River, Eggert and Vacher 2012). In the north, it extends to northern Netherlands ( Creemers and Van Delft 2009), the North Sea coastline of Germany ( Nöllert and Günther 1996) and Denmark, the south of Sweden, as well as the coastline of the Baltic Sea from Germany to Estonia, and eastward until it reaches P. vespertinus in Russia ( Kuzmin 1999; Nyström et al. 2007; Litvinchuk et al. 2013; Sillero et al. 2014). The contact zone with the latter is well delineated from the Kursk region in Russia to the Black Sea coast ( Dufresnes et al. 2019b). From there, it is present westward along the Black Sea coast of Ukraine to north-eastern Bulgaria ( Kuzmin 1999; Stojankov et al. 2011). The southern edges extend along the Danube at the borders of Romania and Bulgaria ( Stojankov et al. 2011) and across Serbia ( Vukov et al. 2013), eastern Croatia, northern Bosnia and Herzegovina, Slovenia ( Džukić et al. 2008, Curić et al. 2018), northern and eastern Austria around the Alps ( Cabela et al. 2001), and southern Germany ( Nöllert and Gunther 1996). The species is also present in a large area of northern Italy, especially in the Po Valley ( Andreone 2006). Last, isolated populations persist in central France (Indre, Loiret, Indre-et-Loire: Eggert and Vacher 2012) and western Bulgaria (around Sofia: Stojankov et al. 2011). IUCN Status: Not Evaluated, considered Least Concern when grouped with P. vespertinus ( Agasyan et al. 2009a). Declines have been reported for more than a century in various parts of Europe, which have caused a regression of the distribution limits ( Džukić et al. 2005; Eggert et al. 2006).

Diversity.

The phylogeographic work by Crottini et al. (2007) and Litvinchuk et al. (2013) characterized two refugial groups for this species (as the "western lineage of P. fuscus "), based on shallow mtDNA divergence and allozyme differentiation: in the Balkans/northern Italy and on the western shores of the Black Sea coast. This seems supported by weak genomic differentiation among Central-European samples ( Dufresnes et al. 2019b). The refugial areas bear nearly all the genetic diversity of the species, which was lost in the derived northern populations, following post-glacial colonizations ( Eggert et al. 2006).