Research Article |
Corresponding author: Christophe Dufresnes ( christophe.dufresnes@hotmail.fr ) Academic editor: Angelica Crottini
© 2019 Christophe Dufresnes, Ilias Strachinis, Elias Tzoras, Spartak N. Litvinchuk, Mathieu Denoël.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Dufresnes C, Strachinis I, Tzoras E, Litvinchuk SN, Denoël M (2019) Call a spade a spade: taxonomy and distribution of Pelobates, with description of a new Balkan endemic. ZooKeys 859: 131-158. https://doi.org/10.3897/zookeys.859.33634
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The genomic era contributes to update the taxonomy of many debated terrestrial vertebrates. In an accompanying work, we provided a comprehensive molecular assessment of spadefoot toads (Pelobates) using genomic data. Our results call for taxonomic updates in this group. First, nuclear phylogenomics confirmed the species-level divergence between the Iberian P. cultripes and its Moroccan relative P. varaldii. Second, we inferred that P. fuscus and P. vespertinus, considered subspecies until recently, feature partial reproductive isolation and thus deserve a specific level. Third, we evidenced cryptic speciation and diversification among deeply diverged lineages collectively known as Pelobates syriacus. Populations from the Near East correspond to the Eastern spadefoot toad P. syriacus sensu stricto, which is represented by two subspecies, one in the Levant (P. s. syriacus) and the other in the rest of the range (P. s. boettgeri). Populations from southeastern Europe correspond to the Balkan spadefoot toad, P. balcanicus. Based on genetic evidence, this species is also polytypic: the nominal P. b. balcanicus inhabits the Balkan Peninsula; a new subspecies P. b. chloeae ssp. nov. appears endemic to the Peloponnese. In this paper, we provide an updated overview of the taxonomy and distribution of all extant Pelobates taxa and describe P. b. chloeae ssp. nov.
Amphibian, Palearctic, Pelobates balcanicus, Pelobates balcanicus chloeae, Pelobates vespertinus, Pelobatidae, phylogenomics, phylogeography, spadefoot toad
The revolution initiated by high-throughput sequencing techniques has reached the field of phylogeography (
Until recently, Pelobates included four recognized extant species. First, the sister taxa P. cultripes (Cuvier, 1829) and P. varaldii Pasteur & Bons, 1959 are found north and south of the Strait of Gibraltar, respectively (
Our accompanying paper (
In this paper, we integrate these recent findings into an updated overview of the Pelobates radiation, including comparative diagnosis, current taxonomy, distribution, and diversity of the resulting eight extant taxa (Fig.
Phylogeny and distribution of Pelobates taxa. The tree is adapted from the phylogenomic analysis of
In order to attribute names to the newly documented Pelobates species and subspecies, we examined nomina available in the literature. To this end, we first referred to the Amphibian Species of the World online database (
We reviewed phenotypic (coloration, morphology) and genetic (genome size, karyotype, and sequence divergence) variation of the considered taxa. Coloration is illustrated by high-quality photographs of known geographic origins, taken by us and credited photographers. Besides detailing general characteristics, we compiled a dataset of snout-vent length (SVL) from published studies (Suppl. material
We briefly described the karyotype of each taxon based on the literature and further report nuclear DNA content as a proxy to genome size, obtained from flow cytometry. In addition, sequence divergence, available from our phylogeographic study (
We detailed the distribution of each Pelobates taxon, based on available literature, i.e. national and regional atlas, as well as scientific articles informative of distribution. Boundaries between cryptic taxa were inferred from genetic studies, and thus remain unclear for parapatric ranges for which no molecular survey has been conducted. Distribution layers were originally obtained from the IUCN Red List of Threatened Species (https://www.iucnredlist.org/), and meticulously reshaped with the drawing tools of ArcMap 10.3.
In order to describe the new P. balcanicus subspecies from southern Greece, we conducted a short fieldwork expedition to the only recently confirmed locality of this taxon, Strofylia meadows in Peloponnese (38.1239°N, 21.3858°E) on December 2018. Collection of live animals was authorized by permit ΑΔΑ: ΩΣΜ34653Π8-9ΣΟ issued by the Greek Ministry of Environment, Energy and Climate Change. Pelobates usually breed during spring (March–April) in this area but are active all-year round providing proper weather conditions. A total of 18 individuals could be captured in the evening of December 10th, under heavy rains. The largest 12 individuals (putatively adults) were measured for 11 standard morphometric variables, i.e. SVL: snout-vent length; HW: head width; HL: head length; ED: eye diameter; EE: inter-eye distance; NN: inter-nostril distance; EN: eye-nostril distance; ML: metatarsal tubercle length; MH: metatarsal tubercle height; HLL: hind leg length; TTL: tibia + tarsus length. HLL and TTL were measured with a ruler (1 mm precision); all other variables were measured with a digital caliper (0.1 mm precision). For the sake of comparison, only one of us (IS) measured all individuals. Note that we did not discriminate the sex of individuals as it was unclear whether all specimens were adults.
Toads were subsequently released at their place of capture, except for two females that were chosen as holotype and paratype, sent to the Natural History Museum of Crete (NHMC). Our choice for a small type series was bounded by the rarity of this taxon, so far confirmed from a single locality, with unknown population trends.
We updated the distributions and taxonomy of Eurasian spadefoot toads (genus Pelobates). Following recent molecular results (
From our SVL dataset, there was a significant global effect of species (P < 0.001) but not of sex (P = 0.08), neither of their interaction (P = 0.42) (two way ANOVA). The species effect was mainly due to differences between the large P. cultripes, P. syriacus, and P. balcanicus versus the smaller P. varaldii, P. fuscus, and P. vespertinus: all pairwise comparisons between these two groups were significant (P < 0.001), but none within groups (P > 0.05) (Tukey test). Females were significantly larger than males in P. cultripes (P = 0.002, n = 16 populations with both sexes), P. fuscus (P < 0.001, n = 21), but not in P. balcanicus (P = 0.58, n = 15) (paired t-test). Sample size precluded similar analyses in the remaining taxa.
The following present accounts for each taxon. We could successfully access the original literature for all but one description, and herein report the primary information as it was published. The only exception is Pelobates praefuscus Khosatzky, 1985, and we rely on
The largest Pelobates species, P. cultripes differs from the other Eurasian spadefoots by metatarsal spades being entirely black and a flat skull. Sizes largely overlap between sexes although males are generally smaller than females (Fig.
First named Rana cultripes Cuvier, 1829; holotype: MNHNP 0.4554; type locality: “notre midi”, corresponds to southern France, as noted by
The species inhabits south-western Europe (0–1770 m elevation a.s.l.) (
Combining mtDNA and microsatellite data,
A smaller version of P. cultripes (Fig.
Between-population variation of average size (snout–vent length – SVL) for each Pelobates species, measured separately for females (pink) and males (blue). This compiles average size-data from 82 populations, representing at least 6,004 individuals (Suppl. material
Color variation in Pelobates cultripes, P. varaldii, P. fuscus and P. vespertinus. Photo credits and origins as follows a CD (Hérault, France) b, c CD (Algarve, Portugal) d A Sanchez Vialas (Spain) e G Martinez (Kenitra, Morocco) f–h A Sanchez Vialas (Tanger, Morocco) i, j N Suriadna (Ukraine) k CD (Wojewodztwo podkarpackie, Poland) l A Nöllert (Burgenland, Austria) m–p N Suriadna (Ukraine).
Pairwise % of genetic differences between Pelobates taxa (from the data of
P. cultripes | P. varaldii | P. fuscus | P. vespertinus | P. s. syriacus | P. s. boettgeri | P. b. balcanicus | P. b. chloeae | |
P. cultripes | – | 0.40 | 0.66 | 0.75 | 0.72 | 0.70 | 0.74 | 0.73 |
P. varaldii | 6.0 | – | 0.83 | 0.92 | 0.89 | 0.88 | 0.92 | 0.90 |
P. fuscus | 10.1 | 10.0 | – | 0.13 | 0.63 | 0.62 | 0.65 | 0.64 |
P. vespertinus | 9.7 | 9.6 | 2.5 | – | 0.71 | 0.70 | 0.74 | 0.73 |
P. s. syriacus | 9.1 | 8.6 | 9.1 | 8.9 | – | 0.01 | 0.32 | 0.30 |
P. s. boettgeri | 9.2 | 8.9 | 9.2 | 9.0 | 1.7 | – | 0.31 | 0.29 |
P. b. balcanicus | 9.2 | 8.6 | 8.5 | 8.5 | 7.2 | 7.0 | – | 0.02 |
P. b. chloeae | 9.2 | 8.2 | 8.5 | 8.6 | 7.7 | 7.7 | 2.8 | – |
The nomen Pelobates varaldii Pasteur & Bons, 1959 is the only one ever proposed for the Moroccan populations of spadefoot toads; holotype: MNHN-RA-1959.1; type locality: Merja Samora, Morocco. The ancient split of P. varaldii, dating back to the Messinian Salinity Crisis (5.3 My), supports its specific distinction from P. cultripes (
It is endemic to north-western Morocco (0–350 m elevation a.s.l.), found along the Atlantic coast, from the south of Tanger to Oualidia, where it is rare (
To our knowledge, P. varaldii has not been the focus of any phylogeographic or population genetic work.
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.
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
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 (
The phylogeographic work by
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.
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 (
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 (
Large spadefoot with whitish metatarsal spades and a flat skull. Webbing of the hind feet less developed than in P. fuscus and P. vespertinus. Sexes of similar size (Fig.
Color variation in Pelobates syriacus and P. balcanicus. Photo credits and origins as follows a, b G Hamoivitch (Israël) c R Winkler (Israël) d G Martinez (Israël) e IS (Limnos, Greece) f SNL (European Turkey) g IS (Limnos, Greece) h A Nöllert (Dagestan, Russia) i MD (Danube Delta, Romania) j IS (Thrace, Greece) k IS (Macedonia, Greece) l IS (Evia, Greece) m–o IS (Peloponnese, Greece) p CD (Peloponnese, Greece).
Described from the Levant region as Pelobates syriacus Boettger, 1889; type locality: “Haiffa in Syrien” (Haifa), Israel; type: SMF 1437.1a (
Scattered distribution; mainly present in the Middle East with 0–2000 m elevation a.s.l. (
Using mtDNA and genomic data,
Similar to the nominal subspecies, notably in terms of cranial characters (
The oldest nomen available for Anatolian/Caucasian spadefoots is Pelobates syriacus boettgeri Mertens, 1923; type locality: Belesuwar, southeastern Azerbaijan; holotype: SMF 1725 (originally 1437.2a,
See the accounts for P. syriacus.
Resembling P. syriacus with which it was previously considered a synonym (
Originally described as a subspecies of the Eastern spadefoot, Pelobates syriacus balcanicus Karaman, 1928; type locality: Dojran Lake, North Macedonia; type(s): most likely include the skeleton described by
Pelobates balcanicus is restricted to the Balkan Peninsula, 0–920 m a.s.l. (
Using mtDNA and genomic data,
Strofylia meadows, near the village of Metochi, Peloponnese, Greece (38.1239°N, 21.3858°E, 1 m a.s.l.). Coastal sandy meadows with shallow ponds (Fig.
Description of Pelobates balcanicus chloeae. Top live photograph of the holotype, NHMC 80.2.15.10 (CD, taken on December 10th 2018); middle dorsal and lateral views of the type specimens (left NHMC 80.2.15.10; right NHMC 80.2.15.11) post-mortem (IS); bottom Strofylia meadows, the type locality in Peloponnese, Greece (ET).
NHMC 80.2.15.10, adult female captured on December 10th 2018 by CD, IS and ET at Strofylia meadows, Greece (38.1239°N, 21.3858°E, 1 m a.s.l.); subsequently deposited at the Natural History Museum of Crete (NHMC); mitochondrial cyt-b haplotype BAL19 (
Morphometric measurements (mm) of Pelobates balcanicus chloeae at the type locality (Strofylia meadows), based on 12 adults (both sexes combined), and detailed for the type specimens. SVL: snout-vent length; HW: head width; HL: head length; ED: eye diameter; EE: inter-eye distance; NN: inter-nostril distance; EN: eye-nostril distance; ML: metatarsal tubercle length; MH: metatarsal tubercle height; HLL: hind leg length; TTL: tibia + tarsus length.
Strofylia population | Holotype NMHC 80.2.15.10 | Paratype NMHC 80.2.15.11 | |
SVL | 71.5 ± 3.4 | 78.7 | 74.1 |
HW | 23.7 ± 1.1 | 26.6 | 25.5 |
HL | 21.8 ± 0.9 | 23.4 | 23.1 |
ED | 7.4 ± 0.24 | 7.2 | 7.1 |
EE | 15.9 ± 0.7 | 16.7 | 17.3 |
NN | 4.4 ± 0.2 | 4.6 | 4.2 |
EN | 6.0 ± 0.3 | 6.7 | 6.0 |
ML | 6.1 ± 0.4 | 7.1 | 6.5 |
MH | 2.6 ± 0.1 | 2.6 | 2.8 |
HLL | 83.7 ± 3.6 | 92 | 90 |
TTL | 64.2 ± 3.1 | 72 | 69 |
NHMC 80.2.15.11, adult female captured on December 10th 2018 by CD, IS and ET at Strofylia meadows, Greece (38.1239°N, 21.3858°E, 1 m a.s.l.); subsequently deposited at the Natural History Museum of Crete (NHMC); mitochondrial cyt-b haplotype BAL20 (
Supposedly similar morphologically to the nominal subspecies and reliably diagnosed only by molecular data. So far studied from the type locality only (Strofylia). Like the nominal subspecies, Pelobates balcanicus chloeae is a large spadefoot with whitish metatarsal spades, a flat skull and incomplete webbing on the hind feet (Fig.
Following
No name is available for spadefoots from the Peloponnese or Greece in general. We hence attribute it a new nomen, Pelobates balcanicus chloeae, as a reference to the young daughter of CD, Chloé, who played a decisive role in guiding his research towards European biogeography and herpetology. Moreover, “Chloé” is an ancient Greek name (“Χλόη”) designating the young green grass spurring from the ground in spring, reminiscent of spadefoots unearthing themselves to breed in mass. The name is also associated with Dimitra (Δήμητρα), the Ancient Greek goddess of agriculture who protected traditional farmlands in which so many amphibians used to thrive.
From current knowledge, this subspecies is endemic to the Peloponnese in southern Greece (
Never studied as such, but this subspecies most likely shares a similar ecology as the nominal subspecies (P. b. balcanicus). Inhabits open, flat, lowland areas with soft sandy soil near shallow ponds or ditches with aquatic vegetation for breeding, as described for P. balcanicus (
Our P. b. chloeae samples featured the lowest nuclear genetic diversity recorded across the entire ranges of P. balcanicus and P. syriacus (
Conservation Status –
Based on our updated overview of the taxonomy and distribution of Pelobates, we hereby provide a key to summarize the main discriminating features within this group. Because several taxa are cryptic and lack diagnostic phenotypic differences, geographic origin remains an essential information.
1 | Black spades on the hind legs | 2 |
– | Spades of light coloration | 3 |
2 | Large body (6–9 cm) without orange dots, spades entirely black; Spain, Portugal and southern France | P. cultripes |
– | Small body (<6 cm) with orange dots, spades bordered with black; Morocco | P. varaldii |
3 | Domed skull, developed webbing, and small body (<6 cm) | 4 |
– | Flat skull, partial webbing, and large body (6–8 cm) | 5 |
4 | Dorsum stripes rare; Central and northwestern Europe, west of a Crimea–Moscow imaginary line | P. fuscus |
– | Three dorsum stripes often present; Eastern Europe and Central Asia, east of a Crimea–Moscow imaginary line | P. vespertinus |
5 | Levantine region (Israel, Lebanon, and Syria) | P. syriacus syriacus |
– | Caucasus and Caspian Sea shores, Anatolia, and European Turkey | P. syriacus boettgeri |
– | Balkan Peninsula, except Peloponnese | P. balcanicus balcanicus |
– | Peloponnese | P. balcanicus chloeae |
Our phylogeographic analyses of Pelobates (
We thank M. Pajković for translating publications from Serbo-Croatian, P. Lymberakis (NHMC) for processing the type series of P. b. chloeae, A. Nöllert, G. Haimovitch, G. Martinez, and A. Sanchez Vialas for sharing their pictures, P.-A. Crochet for taxonomic advices and Nicolas Perrin for support. We are also grateful to T. Vukov, O. Zinenko, A. Ohler, L. Ceriaco, and A. Crottini, as well as an anonymous reviewer, for their expertise and useful feedback. M.D. is Research Director at Fonds de la Recherche scientifique (FNRS). This study was founded by a grant from the Swiss National Science Foundation (SNSF) to Nicolas Perrin (no. 31003A_166323), and a SNSF fellowship to CD (no. P2LAP3_171818).
Average snout-vent length in Pelobates populations
Data type: measurement