Anura

Speybroeck, Jeroen, Beukema, Wouter & Crochet, Pierre-André, 2010, A tentative species list of the European herpetofauna (Amphibia and Reptilia) — an update, Zootaxa 2492, pp. 1-27 : 6-8

Anura

Hofman et al. (2007) and Zheng et al. (2009) investigated the phylogeography of fire-bellied toad species ( Bombina ). Their mtDNA data showed Bombina pachypus (Italian Yellow-bellied Toad) to be nested within B. variegata (Yellow-bellied Toad) lineages, with Carpathian populations occupying the most basal position within the phylogeny of variegata s.l. Pending more detailed studies of genetic variation and level of introgression in contact zones in this complex, we prefer to consider this Italian taxon at subspecies rank as Bombina variegata pachypus , rather than treating it as a full species.

Gonçalves et al. (2009) established high levels of genetic divergence within the Iberian Midwife Toad ( Alytes cisternasii ), but considered these to be within the range of typical intraspecific variation in amphibians.

Carretero et al. (2009) disagreed with Zangari et al. ’s (2006) decision to treat the Eastern Iberian Painted Frog as a subspecies, Discoglossus galganoi jeanneae . They found additional support for the species rank of these two taxa in Velo-Antón et al. (2008) and stated that, given the lack of more detailed studies allowing assessment of gene flow between both taxa in secondary contact areas, there is no reason to treat them as conspecific. This is in conflict with our fundamental appraisal that splitting a species can only be valid if the split is substantiated by scientific evidence, rather than considering taxa as species because of lack of reason to treat them as conspecific. As long as this is not the case, we promote conspecificity to be the rule. In fact, Velo-Antón et al. ’s (2008) results are in agreement with Zangari et al. ’s (2006) work. The fact that both studies found the same low level of nuclear differentiation with independent markers certainly calls for a reassessment of the validity of the specific status of jeanneae and reinforces our reluctance to treat is as a valid species.

The comprehensive work of Frost et al. (2006) on amphibian systematics has provoked contrasting responses, including (among quite some others) a rather strong critique by Wiens (2007), which saw a subsequent rebuttal by Frost et al. (2008). Indirectly, Pauly et al. (2009) also criticised Frost et al. (2006), and also received a response (Frost et al. 2009). Overall, Speybroeck and Crochet’s (2007) treatment of the proposed changes seems to have been largely in correspondence to what other authors have concluded. An exception deserves, however, our renewed attention. While Speybroeck and Crochet (2007) proposed to attribute the European ‘true toad’ species to 2 genera ( Bufo and Epidalea ), general consent in this case seems to be towards conserving Bufo as the genus for all, at least for the time being ( Vences 2007; Bour et al. 2008; Lescure 2008). These authors argue that cases of natural hybridisation (e.g. a very recent record of hybridisation Bufo bufo x viridis by Duda 2008) should encourage rejection of a genus level split, as proposed by Dubois (1988) and applied to the case of Bufo for the first time by Dubois and Dinesh (2007). Concerning European species, Van Bocxlaer et al. (2009) provide some support for the generic arrangement proposed by Frost et al. (2006), which might very well make attribution of Green Toad ( Bufo viridis (s.l. - see below)) to the genus Pseudepidalea and the Natterjack ( Bufo calamita ) to Epidalea a valid arrangement. Yet, with different relationships turning up from different studies (cf. also Pramuk et al. 2008) and many taxa still in need of investigation, it seems cautious not to draw any taxonomical conclusions just yet. Pending additional research, we therefore place all European species back in the single genus Bufo . Additionally, we note that according to Dubois and Bour (in press), the use of the name Pseudepidalea should be abandoned for that of the junior synonym Bufotes Rafinesque, 1815 , while the name Epidalea Cope, 1864 remains available.

We have previously been reluctant to accept Stöck et al. ’s (2006) Bufo viridis (Green Toad) splits ( Speybroeck and Crochet 2007). Stöck et al. (2008a) described yet another new species from Sicily, Bufo siculus (Sicilian Green Toad) . Despite Carretero et al. ’s (2009) adoption of these new species, we still believe that mtDNA lineages alone cannot be used to substantiate new species, and that the level of divergence of the taxa, which are also supported by other characters (e.g. siculus which is also supported by nuclear and morphological data, albeit without comparing the taxon morphologically with its closest African relatives), is not high enough to be in itself evidence of specific status. To a certain degree at least, this seems to be corroborated by Van Bocxlaer et al. (2009): divergence between the Green Toad splits viridis and ‘ cf. variabilis ’ appears to be smaller than between the Common Toad (sub)species bufo and spinosus. We also treat the latter two taxa as conspecific. While we do not claim that the green toads of the Western Palearctic definitely belong to a single species, we maintain that the available information cannot (yet) support any species level split.

As noted by Razzetti (2008), the correct name for the green toads of peninsular Italy, Corsica , Sardinia and northeastern Sicily is still controversial. Balletto et al. (2007), based on specimens from Venice, used Bufo lineatus Ninni, 1879 (type locality: surroundings of Venice - Frost, 2009) as the valid nomen for the clade of peninsular Italy, while Stöck et al. (2006, 2008a) considered Bufo lineatus as a junior synonym of Bufo viridis , because they found specimens from Padua and Trieste that belong to the nominotypical lineage.

Stöck et al. (2008b) studied the phylogeography of the genus Hyla (tree frogs) around the Mediterranean. They identified three deeply divergent mitochondrial lineages in populations currently classified as Hyla arborea , each of them being supported by variation in one nuclear intron. In their mitochondrial tree (but not in their nuclear tree), treating H. sarda and H. intermedia as valid species could render H. arborea paraphyletic, because the three mitochondrial lineages identified within arborea are not necessarily each other's closest relatives. Since the specific status of intermedia is well supported by reproductive isolation in contact zones (Verardi et al. 2009), and since sarda displays distinct and well-known morphological and acoustic characters ( Schneider 1974; Lanza 1983; Rosso et al. 2001, 2004; Castellano et al. 2002), we maintain them as valid species. As a consequence, the mitochondrial data provide strong evidence for recognising the Iberian taxon molleri and the eastern taxon orientalis (currently only known in Europe from the Black Sea Coast of Romania and European Turkey) as valid species as well. Nevertheless, the distributional limits of these two taxa remain unknown. There is no evidence of reproductive isolation in the continuous range of tree frogs in the Balkans, no known obvious morphological characters to separate them, and no obvious acoustic difference between molleri and arborea , nor orientalis and arborea ( Schneider 1974, 2002). Accepting these two new European species would thus rest entirely on mtDNA data from a very small number of specimens (seven orientalis and only two molleri ). Therefore, while a species level split is likely to be required, we prefer to wait for additional data, as specified, before recognising molleri and/or orientalis as valid species.

Detailed study by Gvoždík et al. (2008) uncovered a complex pattern of geographical variation in morphology among populations of Hyla arborea and Hyla savignyi . The similarity among populations is not necessarily greater within species that between species. On the contrary, populations of different species inhabiting neighbouring regions are often more similar than populations of the same species inhabiting distant regions. Groups of populations defined by morphology do not correspond to the mitochondrial lineages defined by Stöck et al. (2008) either. In fact, Gvoždík et al. (2008) suggest that morphological variation of Hyla is more linked to climate variation than to evolutionary history.

Stöck et al. ’s (2008b) unnamed clade of Hyla cf. intermedia from Switzerland corresponds with the northern clade of Canestrelli et al. (2007a). Allozyme divergence between this northern clade and the southcentral clade of H. intermedia s.l. is typical of intraspecific level of divergence: Nei’s distance value of 0.07 according to Canestrelli et al. (2007b), to be compared with Nei’s distance of 0.55 between arborea and intermedia (Verardi et al. 2009) . Thus, in our opinion, the various clades within Hyla intermedia s.l. might well prove to constitute valid subspecies, but are unlikely to represent distinct species. In any case, we strongly advocate detailed analyses of contact zones prior to any formal proposal.

A detailed phylogeographic analysis of the Pool Frog in Italy ( Canestrelli and Nascetti 2008) supported the subspecific status of Pelophylax lessonae bergeri suggested by Crochet and Dubois (2004) and followed by Speybroeck and Crochet (2007). The same study confirmed that Sicilian pool frogs should also be recognised as a distinct subspecies (see also Santucci et al. 1996).

Lymberakis et al. (2007) investigated Eastern Mediterranean water frog phylogeny by means of mitochondrial DNA. Their results reinforce the idea that Pelophylax kurtmuelleri (Greek Marsh Frog) should be treated as conspecific with central European populations of the P. ridibundus complex (Marsh Frog), as previously established with allozyme data (Beerli 1994). The precise status of these populations should be investigated in a range-wide analysis of the P. ridibundus complex. As long as mating call differences are the only support for specific treatment ( Schneider et al. 1993), we suggest to no longer recognise kurtmuelleri as a valid species.

Alleged contact zones between ridibundus and kurtmuelleri in Thrace ( Schneider et al. 1993) seem to be in fact contact zones with Pelophylax bedriagae (Bedriaga’s Water Frog) rather than ridibundus , as Beerli (1994) identified Thracian water frogs unambiguously as Pelophylax bedriagae . This seems to have been confirmed by Lymberakis et al. ’s (2007) results, which included a sample from Thrace (Dadia) attributed to P. bedriagae and closely related to Lesbos and Chios populations. However, their results also attributed a sample from a very nearby location, as well as other Thracian samples, to Pelophylax ridibundus . All these results suggest that bedriagae and “European ridibundus ” form a contact zone in Thrace, where these two taxa are reproductively isolated ( Schneider et al. 1993). This indicates that the two subclades B5 and B6 of Lymberakis et al. (2007) are valid biological species and thus supports the widely accepted species status of P. bedriagae and P. ridibundus (sensu lato). However, Lymberakis et al. (2007) did not include samples from the type locality of ridibundus (northern Caspian Sea area), so it remains to be determined if European populations of Marsh Frogs are conspecific with sensu stricto P. ridibundus or not. If not, the names Pelophylax ranaeformis (Laurenti, 1768) and Pelophylax fortis (Boulenger, 1884) might apply to the European Marsh Frog ( Dubois & Ohler 1995a, b). The former name relates (at least) to the populations of the Greek island Limnos ( Dubois & Ohler 1995b).

Lymberakis et al. (2007) found Pelophylax cerigensis (Karpathos Water Frog) to be nested within their subclade B5, corresponding to P. bedriagae . We note that these authors also attributed Rhodes populations to P. cerigensis , whereas the original description only considered this to be a possibility (Beerli et al. 1994). Indeed, based on biochemical data, Plötner (2005) placed Rhodes and Karpathos water frogs together, different from both bedriagae and ridibundus , and attributed populations from “Karpathos and probably Rhodes” to cerigensis . However, to our knowledge, no subsequent papers have provided definite evidence ascertaining the specific status of Rhodes water frogs. The results of Lymberakis et al. (2007) invalidate a P. cerigensis limited to Karpathos and Rhodes. Apart from the authors’ suggestion that P. c e r i g e n s i s could be treated as a junior synonym for P. bedriagae , alternative arrangements seem compatible with the available evidence: to restrict the name P. bedriagae to (at least some of) the more eastern populations ( Syria and some surrounding areas, also Cyprus), whereas populations from Turkey, the eastern Aegean islands, including Karpathos and Rhodes could be attributed to P. caralitanus (Arıkan 1988) , for which cerigensis ( Beerli, Hotz, Tunner, Heppich and Uzzell 1994) would be a junior synonym. A second alternative could include splitting of the latter group, with the Karpathos populations being attributed to P. cerigensis and treating the Turkish, eastern Aegean and Rhodes populations as a different species. Under either of these alternative hypotheses, several other species would need to be recognised for Anatolian and Middle Eastern water frog populations. Our second alternative might result in retaining the validity of P. cerigensis (for Karpathos populations only). However, for the time being, we believe material from geographically intermediate populations is required to warrant these alternative arrangements, and therefore preliminarily consider P. cerigensis to represent a part of P. bedriagae rather than a separate species. The most recent available results about the contact zones between the western and central Anatolian lineages of water frogs ( Akın et al. 2010) support the view that at least part of the genetic diversity within the bedriagae complex represents intraspecific variation. We thus suggest to recognise, for the time being, a single species of Middle East water frog, whose name should be either bedriagae or ranaeformis , depending on the identity of the water frogs of Limnos. The nomen cerigensis thus currently becomes a synonym of bedriagae at the species rank.