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The biogeography of Elaphe sauromates (Pallas, 1814), with a description of a new rat snake species

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RT @thePeerJ: The biogeography of Elaphe sauromates (Pallas, 1814), with a description of a new rat snake species https://t.co/nopabFGfiq h…
The biogeography of Elaphe sauromates (Pallas, 1814), with a description of a new rat snake species https://t.co/nopabFGfiq https://t.co/D66GDmu8ey
https://t.co/HSWHgnEZp5 A new species of Elaphe! Reading this paper took me to Kazakhstan tourism website, because of the Caspian Sea! #Elaphe #newreptilespecies
And #newspecies again: #Evolution and #taxonomy of rat #snakes https://t.co/n5zNKrbrGK prostřednictvím @thePeerJ

Introduction

The Western Palearctic region is home to great diversity of herpetofauna (Sindaco & Jeremčenko, 2008; Sindaco, Venchi & Grieco, 2013). Among the most emblematic members are the rat snakes of the genus Elaphe Fitzinger in Wagler, 1833, once a large genus with distribution in temperate, subtropical, and tropical zones of both eastern and western hemisphere (Schulz, 1996). With the rise of molecular taxonomy in the last decades of the 20th century, the complicated relationships among dozens of species have been studied with a new rigor, resulting in the New-World as well as most Old-World species being identified as new or resurrected genera (Helfenberger, 2001; Lenk, Joger & Wink, 2001; Utiger et al., 2002; Chen et al., 2017). As a consequence, the genus Elaphe is comprised of 15 species (Wallach, Williams & Boundy, 2014; Chen et al., 2017), with most occurring exclusively in Asia. The high diversity in Asia supports the hypothesis of the origin of the genus in this region (Lenk, Joger & Wink, 2001; Utiger et al., 2002; Chen et al., 2017). Outside of Asia, three Elaphe species are also found in southern-eastern and eastern Europe: Elaphe sauromates (Pallas, 1814), E. quatuorlineata (Bonnaterre, 1790), the species with the western-most distribution of all Elaphe, and E. dione (Pallas, 1773) with mainly Asian distribution (Sindaco, Venchi & Grieco, 2013). Elaphe sauromates is also the type species of the genus Elaphe.

Elaphe sauromates is a robustly built snake whose biology has been systematically understudied and, despite its relatively large size, is only rarely encountered in the wild (Böhme & Ščerbak, 1993). It was described as a separate species under the name Elaphis sauromates (see: Strauch, 1873), followed by being synonymized with Coluber quatuorlineatus Bonnaterre, 1790, and subsequently treated as its subspecies C. quatuorlineatus sauromates (Boulenger, 1894). At the beginning of the 21st century, morphological and molecular-phylogenetic studies justified the species status of E. sauromates (Helfenberger, 2001; Lenk, Joger & Wink, 2001; Utiger et al., 2002) and this view has been largely accepted to date (Sindaco, Venchi & Grieco, 2013; Sillero et al., 2014; Wallach, Williams & Boundy, 2014; Jablonski, Soltys & Simonov, 2019). Aside from confirming the separate species status of E. sauromates, early genetic studies found a surprisingly high genetic distance between populations from Kazakhstan and eastern Turkey (5.0–6.5% in Lenk, Joger & Wink, 2001 or even 7.6% in Huang et al., 2012), which was quite similar to the distances between E. sauromates and E. quatuorlineata, E. dione and E. bimaculata Schmidt, 1925, E. quadrivirgata (Boie, 1826) and E. carinata (Günther, 1864), or between E. quadrivirgata and E. schrenckii (Strauch, 1873) (Utiger et al., 2002; Huang et al., 2012). In addition to genetic divergence, some morphological and color variation seems to be geographically correlated, indicating possible phenotypic differentiation of at least two genetic forms (Zinner, 1972; Tiedemann & Häupl, 1978; Schulz, 1996). Thus, there is a clear indication that the taxonomy of E. sauromates requires a revision based on a detailed study of both genetic and morphological variation.

Here, we studied the genetic structure and morphology of E. sauromates in biogeographic framework using robust geographic sampling, with the aim of elucidating the levels of divergence and phylogenetic relationships among the populations originating from most areas of the known taxon range. We analyzed sequences of mitochondrial and nuclear DNA fragments, snake measurements and pholidosis and have revealed the existence of cryptic diversity within E. sauromates. As a result, we describe a new species of a rat snake of the genus Elaphe.

Material and Methods

Tissue sampling, DNA extraction, and PCR amplification

Between 2000 and 2017 we collected tissue samples of E. sauromates sensu lato (s.l.) from an area extending from the eastern Balkans to western Kazakhstan. We covered almost the entire distribution range except for the central-southern Turkey, northern Iran, Turkmenistan, Uzbekistan, and the Levant (Israel, Lebanon, Syria; Fig. 1). In total we obtained 90 tissue samples of E. sauromates s. l., and 63 of them were subsequently used in our molecular analyses. All sample information (DNA working codes, sampling localities, GenBank Accession Numbers, and comments) is presented in Table 1. We collected blood samples, ventral scales, and saliva from living specimens, while muscle and liver samples were collected from the dead (road-kills) or museum deposited individuals. All tissue samples were preserved in 96% ethanol or frozen and stored at −25 or −80 °C.

Geographic distribution of the samples used in the molecular-phylogenetic (A) and morphological (D) analyses.

Figure 1: Geographic distribution of the samples used in the molecular-phylogenetic (A) and morphological (D) analyses.

The colors correspond to the species and to individual COI and ND4 haplotypes. Inset images (B and C) show the haplotype networks of both mtDNA genes analyzed. The stars indicate the type localities of Elaphe sauromates (yellow; photo by Mark Pestov) and E. urartica sp. nov. (red; photo by Ilya Korshunov). For more details on samples and localities, refer to Tables 1 and 2.
Table 1:
List of the material used in the molecular-phylogenetic analyses.
Code Taxon Country Locality Coordinates GenBank accession number Museum voucher References
N E COI ND4 RAG1 PRLR CMOS MC1R
Oocatochus rufodorsatus NC_022146 NC_022146 Li et al. (2014)
Zamenis lineatus HQ392546 DQ902319 Musilová et al. (2011)/Burbrink & Lawson (2007)
LSUMZ 40626 E. quatuorlineata AY486955 Nagy et al. (2004)
1509 E. quatuorlineata Northern Macedonia Crkvino 41.66 21.82 MK640236 MK640366 MK640344 MK640300 MK640325 This study
3195 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.37 44.68 MK640260 MK640407 MK640362 MK640316 MK640341 TuRE ES 0000003301 This study
3196 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.37 44.68 MK640261 MK640408 MK640317 TuRE ES 0000003300 This study
3197 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.37 44.68 MK640262 MK640409 MK640318 This study
3408 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.37 44.68 MK640263 MK640410 MK640363 MK640342 This study
3409 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.37 44.68 MK640264 MK640411 This study
3410 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.37 44.68 MK640265 MK640412 This study
3411 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.37 44.68 MK640266 MK640413 This study
6582 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.27 44.63 MK640270 MK640417 This study
6583 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.27 44.63 MK640271 MK640418 This study
6584 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.27 44.63 MK640272 MK640419 This study
6585 E. urartica. sp. nov. Armenia Mt. Gutanasar, Abovyan 40.27 44.63 MK640273 MK640420 This study
3449 E. urartica. sp. nov. Armenia Mt. Atis, Kotayikskoe Plateau 40.31 44.73 MK640267 MK640414 MK640364 TuRE ES 0000003303 This study
3450 E. urartica. sp. nov. Armenia Mt. Atis, Kotayikskoe Plateau 40.36 44.61 MK640268 MK640415 TuRE ES 0000003302 This study
3655 E. urartica. sp. nov. paratype Azerbaijan Guzdak, Qobustan 40.37 49.68 MK640269 MK640416 MK640365 MK640343 IZANAS T17 This study
1409 E. sauromates Bulgaria Pomorie 42.59 27.60 MK640290 This study
2494 E. sauromates Bulgaria Poda 42.44 27.46 MK640297 MK640385 MK640307 MK640335 This study
2495 E. sauromates Bulgaria Letnitsa 43.31 25.13 MK640298 MK640386 MK640350 This study
2605 E. sauromates Bulgaria Svistov 43.62 25.32 MK640237 MK640387 This study
2609 E. sauromates Bulgaria Svistov 43.62 25.31 MK640238 MK640388 MK640351 This study
6130 E. sauromates Bulgaria Djuni 42.36 27.71 MK640253
1179 E. sauromates “Crimea” Solenoe Ozero 45.94 34.46 MK640288 MK640377 MK640348 MK640304 MK640322 MK640331 This study
1180 E. sauromates “Crimea” Cape Kazantip 45.46 35.84 MK640289 MK640378 This study
2372 E. sauromates “Crimea” Zolotoe, Kerch 45.40 36.12 MK640291 MK640379 This study
2373 E. sauromates “Crimea” Yuzhnoe 45.13 35.60 MK640292 MK640380 This study
2374 E. sauromates “Crimea” Primorskyi 45.13 35.59 MK640293 MK640381 This study
2375 E. sauromates “Crimea” Opuk 45.08 36.29 MK640294 MK640382 MK640305 MK640323 MK640332 This study
2378 E. sauromates “Crimea” Yarkoe 45.14 35.74 MK640296 MK640384 MK640349 MK640334 This study
3406 E. sauromates “Crimea” Cape Kazantip II 45.47 35.85 MK640244 MK640394 MK640356 MK640338 This study
4418 E. sauromates “Crimea” Nauchnyi 44.73 34.01 MK640248 MK640398 This study
4526 E. sauromates “Crimea” Yurkino 45.44 36.57 MK640249 MK640399 This study
6024 E. sauromates “Crimea” Kara–Tobe 45.13 33.62 MK640251 This study
6025 E. sauromates “Crimea” Nikolaevka 44.97 33.60 MK640252 This study
3089 E. urartica. sp. nov. Georgia Tbilisi 41.69 44.80 MK640256 MK640403 MK640359 MK640312 MK640340 This study
3090 E. urartica. sp. nov. Georgia Tbilisi 41.69 44.80 MK640257 MK640404 MK640313 This study
3095 E. urartica. sp. nov. Georgia Tbilisi 41.69 44.80 MK640258 MK640405 MK640360 MK640314 This study
3096 E. urartica. sp. nov. Georgia Tbilisi 41.69 44.80 MK640259 MK640406 MK640361 MK640315 This study
3447 E. sauromates Kazakhstan Mangystau Peninsula 43.60 51.57 MK640246 MK640396 MK640358 MK640339 This study
3448 E. sauromates Kazakhstan Mangystau Peninsula 43.60 51.57 MK640247 MK640397 This study
892 E. sauromates Russia Novorossijsk 44.70 37.73 MK640277 This study
893 E. sauromates Russia Novorossijsk 44.70 37.73 MK640278 This study
2376 E. sauromates Russia Bol’shoy Bogdo Mt. 48.14 46.86 MK640295 MK640383 MK640306 MK640333 This study
3193 E. sauromates Russia Razdorskaya 47.54 40.64 MK640242 MK640392 MK640354 MK640337 This study
3194 E. sauromates Russia Iki–Burul, Kalmykia 45.72 44.56 MK640243 MK640393 MK640355 MK640310 This study
3407 E. sauromates Russia Iki–Burul, Kalmykia 45.72 44.56 MK640245 MK640395 MK640357 This study
5338 E. sauromates Russia Taganrogskyi Gulf 46.99 39.01 MK640250 ZISP 26197 This study
6670 E. urartica. sp. nov. Russia (Dagestan) Leninkent 42.96 47.35 MK640274 MK640421 ZM MSU 10784 This study
6671 E. urartica. sp. nov. Russia (Dagestan) Yersi 42.02 48.01 MK640275 MK640422 ZM MSU 11043 This study
6672 E. sauromates Russia Varvarovka 44.82 37.38 MK640254 MK640400 ZM MSU 14729 This study
6673 E. sauromates Russia Varvarovka 44.77 37.39 MK640255 MK640401 ZM MSU 14731 This study
278 E. sauromates Turkey Iskenderun 41.63 26.68 MK640276 MK640367 MK640345 MK640301 MK640319 MK640326 This study
1124 E. urartica. sp. nov. holotype Turkey Kısıklı, Süphan Mts., Bitlis 38.93 42.91 MK640299 MK640402 MK640311 MK640324 ZDEU 26/2012 This study
1125 E. sauromates Turkey Akcay–Elmalı 36.55 29.79 MK640279 MK640368 MK640302 MK640320 MK640327 ZDEU 108/2011 This study
1126 E. sauromates Turkey Göltara, Elmalı 36.56 29.89 MK640280 MK640369 MK640303 MK640321 MK640328 ZDEU 298/2013 This study
2891 E. sauromates Turkey İhsaniye–Eyüp, İstanbul 41.28 28.75 MK640239 MK640389 ZDEU 180/2014 This study
2892 E. sauromates Turkey Öksüt Village–Develi 38.28 35.51 MK640240 MK640390 MK640352 MK640308 MK640336 ZDEU 15/2015 This study
2893 E. sauromates Turkey Yağmurlusayobası 39.25 33.94 MK640241 MK640391 MK640353 MK640309 ZDEU 14/2015 This study
SH556 E. urartica. sp. nov. Turkey Mt. Ararat 39.68 44.20 AY122713 Utiger et al. (2002)
SH972 E. sauromates Turkey Selçuk 37.95 27.37 AY122711 Utiger et al. (2002)
1172 E. sauromates Ukraine Egorivka 46.71 30.40 MK640281 MK640370 This study
1173 E. sauromates Ukraine Egorivka 46.71 30.40 MK640282 MK640371 This study
1174 E. sauromates Ukraine Egorivka 46.71 30.40 MK640283 MK640372 This study
1175 E. sauromates Ukraine Egorivka 46.71 30.40 MK640284 MK640373 This study
1176 E. sauromates Ukraine Zayichevske 47.04 32.09 MK640285 MK640374 MK640346 MK640329 This study
1177 E. sauromates Ukraine Davydovka 46.37 35.18 MK640286 MK640375 MK640347 MK640330 This study
1178 E. sauromates Ukraine Chongar 46.02 34.50 MK640287 MK640376 This study
DOI: 10.7717/peerj.6944/table-1

Note:

Museum abbreviations: IZANAS, Institute of Zoology, Azerbaijan, National Academy of Sciences, Baku, Republic of Azerbaijan; TuRE, Zoological Department of Tula State Regional Exotarium, Ministry of Culture of Tula Region, Tula, Russia; ZDEU, Zoology Department of Ege University, Turkey; ZISP, Institute of Zoology, Russian Academy of Sciences, Saint Petersburg, Russia; ZMMSU, Zoological Museum of Moscow State University, Moscow, Russia.

Total genomic DNA was extracted using the NucleoSpin Tissue kit (MACHEREY—NAGEL, Duren, Germany), following the manufacturer’s instructions. Sequences of two mitochondrial (mtDNA) and four nuclear DNA (nDNA) genes were targeted: the DNA barcoding segment of cytochrome c oxidase subunit 1 (COI), the mitochondrial protein-coding segment of NADH dehydrogenase subunit 4 (ND4) (including the flanking tRNAs Serine, Histidine, and part of Leucine), and the nuclear protein-coding genes for the prolactin receptor (PRLR), the oocyte maturation factor Mos (C-MOS), recombination activation gene 1 (RAG1), and melanocortin 1 receptor (MC1R). Primers used for PCR amplifications are listed in Table S1. All amplification procedures involved an initial cycle of denaturation at 94 °C for 3–7 min, 35–40 subsequent cycles at 94, 48–63, and 72 °C for 1 min each, followed by a final extension step at 72 °C for 5–10 min. PCR products were purified with ExoSAP-IT™ PCR Product Cleanup Reagent (USB Europe GmbH, Staufen, Germany; manufacturer’s protocol). Sequencing was performed by Macrogen Inc. (Seoul, South Korea or Amsterdam, Netherlands; http://www.macrogen.com) with the ABI PRISM 3100 capillary sequencer using the PCR amplification primers. All newly obtained sequences have been deposited in GenBank (Table 1).

Alignment, genetic divergence and model selection

DNA sequences were manually checked, aligned, and inspected using BioEdit 7.0.9.0 (Hall, 1999). No stop codons were detected with into amino acid translated sequences using the vertebrate genetic code in the program DnaSP 5.10 (Librado & Rozas, 2009). The same program was used to calculate uncorrected p-distances among the main clades and to estimate the haplotype diversity (Hd), number of segregating sites (S), variables (V), nucleotide diversity (π), and parsimony informative (Pi) sites for the selected groups. Heterozygous positions in nuclear genes were manually identified based on the presence of double peaks in chromatograms. Identified heterozygous loci were coded according to the IUPAC ambiguity codes. The best-fit codon-partitioning schemes and the best-fit substitution models for phylogenetic analyses with concatenated dataset (COI 581 bp + ND4 810 bp) were selected using PartitionFinder v1.1.1. (Lanfear et al., 2012) with the following parameters: Bayesian approach (BA)—linked branch length; all models; BIC model selection; greedy schemes search; data blocks by codons for each used marker. The best partitioning scheme and models of nucleotide substitutions were: first and second positions (HKY+G), third position (K80). The Maximum likelihood (ML) analysis followed the same approach; the best substitution model in this case was GTR+G+I with a single partition.

Phylogenetic and haplotype network analysis

Concatenated (COI + ND4) mitochondrial phylogenetic trees were inferred using the BA performed with MrBayes 3.2.1 (Ronquist et al., 2012) and ML analysis performed with RAxML 8.0 (Stamatakis, 2014). The BA analysis was set as follows; two separate runs, with four chains for each run, 10 million generations with trees sampled every 100th generation. The first 20% of trees were discarded as the burn–in after inspection for stationarity of log–likelihood scores of sampled trees in Tracer 1.6 (Rambaut et al., 2013; all parameters had effective sample sizes (ESSs) of >200). A majority-rule consensus tree was drawn from the post-burn-in samples and posterior probabilities were calculated as the frequency of samples recovering any particular clade. Nodes with posterior probability values ≥ 0.95 were considered as strongly supported. The ML clade support was assessed by 1,000 bootstrap pseudoreplicates. Sequences of other, closely related Eurasian rat snakes, Oocatochus rufodorsatus (Cantor, 1842) and Zamenis lineatus (Camerano, 1891) (for GenBank accession numbers see Table 1), were used in the analyses included as outgroups (Utiger et al., 2002; Chen et al., 2017).

In order to obtain better support for putative species boundaries of the divergent lineages of Elaphe, we employed three species delimitation methods: (i) Bayesian implementation of the Poisson tree processes model (bPTP; Zhang et al., 2013, https://species.h-its.org/), (ii) multi-rate Poisson Tree Processes (mPTP; Kapli et al., 2016) model, using the webserver (http://mptp.h-its.org/), and (iii) the general mixed yule-coalescent model (GMYC; Pons et al., 2006). For species delimitations analysis we used as input an ultrametric tree of mtDNA haplotypes constructed with BEAST 2.1 (Bouckaert et al., 2014). BEAST analyses were run under the uncorrelated log-normal relaxed clock approach with a Yule tree prior. Two independent runs were conducted with a chain length of 5 × 107 iterations. Tracer 1.6 (Rambaut et al., 2013) was used to check for convergence of the chains and adequate ESSs. Independent runs were combined using LogCombiner (part of the BEAST package), discarding the first 25% of each run as burn-in. The maximum clade credibility tree was summarized with TreeAnnotator (part of the BEAST package) and visualized with Fig-Tree 1.4 (http://tree.bio.ed.ac.uk/software/figtree). GMYC species delimitation was conducted using the “splits” package (Ezard, Fujisawa & Barraclough, 2009) in R (R Development Core Team, 2019) under the single-threshold method.

The genealogical relationships between haplotypes of mtDNA and each nDNA marker were separately assessed with haplotype networks. For the purpose of allele network construction, sequences with more than one heterozygous site were resolved in PHASE 2.1.1 (Stephens, Smith & Donnelly, 2001) for which the input data were prepared in SeqPHASE (Flot, 2010). PHASE was run under default settings except for the probability threshold, which was set to 0.7. Haplotype networks of all analyzed markers were examined and drawn using PopArt (http://popart.otago.ac.nz) and the implemented parsimony network algorithm of TCS (Clement, Posada & Crandall, 2000), with 95% connection limit. Independent networks are considered distinct evolutionarily significant units, following Fraser & Bernatchez (2001), thus this analysis was also used to infer genetic structure within the studied taxa.

Material for morphological analyses and collection of specimens

In total, we examined external morphology of 95 specimens (46 males, 29 females, 20 individuals of unidentified sex) of E. sauromates s. l. from the Crimean Peninsula, Turkey, Armenia, and Azerbaijan (Fig. 1D; Table 2). Only snakes with SVL ≥ 650 mm were used in the analyses of metric characters (75 adult animals in total), while all available specimens with known sex were used in scale count descriptive statistics and comparisons. The material was obtained either directly in the field or from collections of the following institutions: Zoology Department of Ege University, Turkey (ZDEU); Institute of Zoology, Azerbaijan, National Academy of Sciences, Baku, Republic of Azerbaijan (IZANAS); Institute of Zoology, Russian Academy of Sciences, Saint Petersburg, Russia (ZISP); Zoological Department of Tula State Regional Exotarium, Ministry of Culture of Tula Region, Tula, Russia (TuRE).

Table 2:
List of the material used for morphological analyses.
Species Country Locality Locality number N E Elevation (m) No. of adult specimens (males/females/unidentified) No. of juvenile specimens (males/females/unidentified) Museum voucher number
E. sauromates “Crimea” Akmonayi Isthmus, Kerch Peninsula 1 45.31 35.60 17 1/0/0 0/0/0
E. sauromates “Crimea” Albat, Bakhchisarayi 2 44.64 33.91 343 2/2/2 0/0/0
E. sauromates “Crimea” Between Bash-Kirghi and Dzhaga-Setdzhevyut, Kerch Peninsula 3 45.14 35.72 60 0/0/0 0/0/1
E. sauromates “Crimea” Between Cape Opuk and Cape Kyz-Aul, Kerch Peninsula 4 45.06 36.30 7 1/0/0 0/0/0
E. sauromates “Crimea” Between Hafuz and Dzhaga-Setdzhevyut, Kerch Peninsula 5 45.14 35.61 21 1/0/0 0/0/0
E. sauromates “Crimea” Between Kara-Tobe and Nikolaevka 6 45.13 33.62 17 0/0/0 1/1/0
E. sauromates “Crimea” Between Suuk-Su and Kiziltash, Sudak 7 44.93 35.00 167 0/0/0 0/1/0
E. sauromates “Crimea” Cape Chauda, Kerch Peninsula 8 45.01 35.84 21 1/2/1 0/0/4
E. sauromates “Crimea” Cape Kazantip, Kerch Peninsula 9 45.46 35.86 74 2/2/0 0/0/0
E. sauromates “Crimea” captive breeding: female from Azov Sea coast, male from Black Sea coast, Kerch Peninsula 10 ? ? ? 0/0/0 1/0/0
E. sauromates “Crimea” Inkerman, upland Mekenzievy Gory, Sevastopol 11 44.66 33.59 75 0/1/0 0/0/0
E. sauromates “Crimea” Karadag Reserve, Theodosia 12 44.91 35.20 3 1/0/0 0/0/1
E. sauromates “Crimea” Lake Koyashskoe, Kerch Peninsula 13 45.06 36.18 3 0/0/0 0/0/1
E. sauromates “Crimea” Mt. Kalafatlar near Cape Aya, Sevastopol 14 44.47 33.67 401 1/0/0 0/0/0
E. sauromates “Crimea” Mt. Opuk, Kerch Peninsula 15 45.03 36.22 54 2/1/0 0/0/2
E. sauromates “Crimea” Nauchnyi 16 44.73 34.01 549 0/0/0 1/0/0
E. sauromates “Crimea” Orta-Sabla, reservoir Partizanskoe, Simferopol 17 44.82 34.06 304 0/1/0 0/0/0
E. sauromates “Crimea” Peredovoe (Urkusta), Bayidar Valley, Sevastopol 18 44.52 33.81 370 0/1/0 0/0/0
E. sauromates “Crimea” Primorskyi, Akmonayiskyi Isthmus, Theodosia 19 45.13 35.45 33 0/0/1 0/0/0
E. sauromates “Crimea” Sary-Su near Belogorsk (Karasu-Bazar) 20 45.04 34.54 330 0/1/0 0/0/0
E. sauromates “Crimea” Solenoe Ozero railway station, Dzhankoyi 21 45.92 34.49 11 1/1/3 0/0/0
E. sauromates “Crimea” Tatar-Koyi, Mt. Kyz-Kermen, Bakhchisarayi 22 44.70 33.92 210 1/0/0 0/0/0
E. sauromates “Crimea” Tiup-Tarkhan Peninsula, Dzhankoyi 23 44.87 34.67 3 0/0/2 0/0/0
E. sauromates “Crimea” Uppa-Koyi, ruines of aul Uzen-Bash, Sevastopol 24 44.55 33.77 397 1/0/0 0/0/0
E. sauromates Turkey Akçay-Elmalı 25 36.55 29.79 1,477 0/0/0 1/0/0
E. sauromates Turkey Yağmurlusayobası 26 39.25 33.94 1,412 1/0/0 0/0/0
E. sauromates Turkey Çığlıkara-Elmalı 27 36.55 29.88 1,690 1/0/0 0/0/0
E. sauromates Turkey Efes-Selçuk 28 37.94 27.37 15 1/0/0 0/0/0
E. sauromates Turkey Elmalı 29 36.73 29.90 1,086 0/1/0 0/0/0
E. sauromates Turkey Göltarla, Elmalı 30 36.56 29.89 1,690 1/0/0 0/0/0
E. sauromates Turkey Hasköy-Enez 31 40.66 26.34 62 1/0/0 0/0/0
E. sauromates Turkey İhsaniye-Eyüp, İstanbul 32 41.28 28.75 20 1/0/0 0/0/0
E. sauromates Turkey Karamürsel 33 40.68 29.60 21 1/0/0 0/0/0
E. sauromates Turkey Öksüt Village-Develi 34 38.28 35.51 1,685 1/0/0 0/0/0
E. sauromates Turkey Tokmak Village-Karmürsel 35 40.68 29.54 42 0/1/0 0/0/0
E. sauromates Turkey Yağcılı Village-Soma 36 39.33 27.66 348 1/0/0 0/0/0
E. sauromates Ukraine Island Kuyuk-Tuk 37 46.12 34.42 7 0/0/0 0/0/1
E. urartica sp. nov., paratype Armenia Mt. Atis, Kotayikskoe Plateau 38 40.31 44.73 2,345 0/1/0 0/0/0 TuRE ES 0000003303
E. urartica sp. nov., paratype Armenia Mt. Atis, Kotayikskoe Plateau 39 40.36 44.61 1,456 1/0/0 0/0/0 TuRE ES 0000003302
E. urartica sp. nov., paratypes Armenia Mt. Gutanasar, Gegamsky Ridge, near Abovyan 40 40.37 44.69 2,300 1/1/0 3/5/0 TuRE ES 0000003300;
TuRE ES 0000003301
E. urartica sp. nov. Azerbaijan Azerbaijan—locality unknown 41 ? ? ? 2/0/0 0/0/0
E. urartica sp. nov. Azerbaijan Ganja 42 40.68 46.36 430 1/0/0 1/1/0
E. urartica sp. nov. Azerbaijan Ganja, “near Areshsk” 43 40.69 46.37 450 1/0/0 0/0/0
E. urartica sp. nov. Azerbaijan Goytapa 44 39.12 48.60 0 1/0/0 0/0/0
E. urartica sp. nov. Azerbaijan Khazar 45 41.76 48.70 0 0/1/0 0/0/0
E. urartica sp. nov., paratype Azerbaijan Lenkoran 46 38.75 48.85 0 1/0/0 0/0/0 IZANAS 68
E. urartica sp. nov. Azerbaijan Masally 47 39.02 48.67 0 1/0/0 0/0/0
E. urartica sp. nov. Azerbaijan Mughan 48 40.10 48.84 0 1/0/0 0/0/0
E. urartica sp. nov. Azerbaijan Qaraçala 49 39.82 48.95 0 0/1/0 0/0/0
E. urartica sp. nov., paratype Azerbaijan Guzdak, Qobustan 50 40.37 49.68 140 1/0/0 0/0/0 IZANAS T-17
E. urartica sp. nov., paratypes Azerbaijan Şamaxi 51 40.63 48.63 648 1/1/0 0/0/0 IZANAS 69
IZANAS 70
E. urartica sp. nov., paratype Azerbaijan Zivi-Zkaro (Tsivi-Tskaro) 52 41.32 45.27 246 0/1/0 0/0/0 IZANAS 71
E. urartica sp. nov., paratypes Azerbaijan Zaqatala 53 41.63 46.65 511 1/1/0 0/0/0 IZANAS 518
IZANAS 529
E. urartica sp. nov., paratype Turkey Hoşerenler Plateau, Kars 54 40.61 43.09 1,747 1/0/0 0/0/0 ZDEU 114/1970
E. urartica sp. nov., holotype Turkey Kısıklı, Süphan Mts. 55 38.93 42.91 2,394 1/0/0 0/0/0 ZDEU 26/2012
DOI: 10.7717/peerj.6944/table-2

Note:

Specimens of the type series are in bold.

Field permits for this study were issued by the Republic of Turkey Ministry of Forest and Water Affairs (No. B.23.0.DMP.0.15.01–510–38417) and by the Crimean authority under the title “Study of Biodiversity and Landscape Structure of the Southeastern Crimea, monitoring of Biotic and Abiotic Components of the Regional Ecosystems” (FASO: AAA–A16–116022510087–5) and by “Study of the structure and dynamics of land ecosystems in various climatic zones” No. AAAA–A19–119012490044–3). All efforts were made to minimize animal suffering.

Analysis of the external morphology

Body and tail lengths were measured with a ruler to the nearest one mm, while the head and individual skin plates were measured with a caliper with accuracy to the nearest 0.01 mm. For the purpose of obtaining basic information, the head scales of the juvenile snakes from Armenia were measured using their photographs (see Kropachev et al., 2015), but they were not used in further statistical analyses.

In total, we targeted 15 metric and 18 meristic (scale count) characters, however not all measurements or counts were available for each individual (see Sahlean et al., 2016; Table S2 for explanation of the characters). In addition to the measurements and scale counts, we calculated two main morphometric indices: the snout-vent length to tail length (SVL/TL) and the snout-vent length to head length (SVL/HL) ratio.

Prior to morphological analyses, the snakes were split into two groups based on the results of molecular-genetic analyses and their origin: E. sauromates sensu stricto (s. s.; 63 specimens) and a new species that is formally described and named below (32 specimens). All measures were a priori log-transformed and the homoscedasticity (equal variances) was checked by Levene’s test before the comparisons were carried out. We used independent sample t-tests to compare the length (SVL and total) of both snake groups. The tail and head lengths were compared using multivariate analysis of variance with SVL as a co-variate (MANCOVA). The overall head size was further compared with MANCOVA with head length used as a co-variate. The scale counts, which are not dependent on the snake length, were compared with multivariate analysis of variance (MANOVA). In all tests, the sexes were treated separately. We also examined the sexual differences within both groups and employed the same statistical strategy as in the species comparisons. The significance level was set to 0.05 and Bonferroni correction was applied in multiple-comparison analyses. All analyses were performed in SPSS Statistics 17.0.0. (SPSS Inc., Chicago, IL, USA).

The type material note

While the holotype of the newly described species (see below) as well as eight paratypes are deposited in public museums or scientific institutions (see Tables 1 and 2), four paratypes are currently still alive at TuRE (as of March 2019; Tula, Russia). These individuals have been described in detail, photographed, and assigned identification numbers. Upon death, the animals will be fixed and deposited in one of the central zoological museums in Russia (ZISP and/or ZM MSU). While the use of live animals as type material is not recommended by some authors (Dubois & Nemésio, 2007), such practice is not prohibited by International Commission on Zoological Nomenclature (ICZN). We decided to include these specimens (originating from Armenia) among the type series to provide a better representation of the material that was predominantly used as tissue sample source for molecular-genetic analyses.

Nomenclatural note

The electronic version of this article in portable document format will represent a published work according to the ICZN, and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank Life Science Identifiers (LSIDs) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix http://zoobank.org/. The LSID for this publication is: urn:lsid:zoobank.org:pub:F0BF1D63–7BD5–4340–85A0–E044CC56CD5B. The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central and CLOCKSS.

Results

Phylogeography and genetic diversity

The final nucleotide dataset of 4,068 bp comprised sequences of two mtDNA genes: COI (581 bp), ND4 (810 bp), and fragments of four nuclear genes: C-MOS (459 bp), MC1R (650 bp), PRLR (552 bp), and RAG1 (1,016 bp). The phylogenetic trees (ML and BA) of mtDNA concatenated dataset showed the same topologies with very similar, high statistical supports for each node (Fig. 2; Figs. S1 and S2). Therefore, we only present the BA tree here to show the topology and interrelationships among the studied snake lineages.

Phylogenetic relationships of Elaphe quatuorlineata (photo by Daniel Jablonski), E. sauromates (photo by Mark Pestov), and E. urartica sp. nov. (photo by Ilya Korshunov) reconstructed using Bayesian inference of concatenated COI and ND4 sequences.

Figure 2: Phylogenetic relationships of Elaphe quatuorlineata (photo by Daniel Jablonski), E. sauromates (photo by Mark Pestov), and E. urartica sp. nov. (photo by Ilya Korshunov) reconstructed using Bayesian inference of concatenated COI and ND4 sequences.

The numbers above the branches represent Bayesian Posterior Probabilities/Bootstraps showing branch supports. The vertical bars next to the clades illustrate support of three mtDNA species delimitation methods for the three-species arrangement: the Bayesian implementation of the Poisson tree processes model (bPTP), the multi-rate Poisson Tree Processes (mPTP), and the Bayesian implementation of the general mixed yule-coalescent model (GMYC). The full BI and ML and trees that formed the basis for the presented tree can be found in Figs. S1 and S2.

We identified two major, deeply divergent clades within E. sauromates s. l. Together they form a sister clade to that of E. quatuorlineata sequences. Uncorrected p-distances (mtDNA) among the clades ranged between 5.80% (ND4) and 8.24% (COI; Table 3). One of these clades corresponds to E. sauromates s. s., while the other one represents a distinct phylogenetic lineage, which we consider a new, separate species. The clade corresponding to E. sauromates has been detected (based on mtDNA) from western and central Anatolia (Turkey), the Balkans (Bulgaria, Turkey), southern Ukraine, Crimean Peninsula, southern Russia, and western Kazakhstan. Samples from the new species originated from eastern Anatolia (Turkey), Armenia, Azerbaijan, Georgia, and Dagestan (southern Russia). Both species seem to be geographically separated, presumably by the Anatolian Diagonal, and partially, also by the Great Caucasus (Fig. 1).

Table 3:
Uncorrected p-distances (in %) in mtDNA (COI/ND4) and nDNA (CMOS/MC1R/PRLR/RAG1) sequences of E. quatuorlineata, E. sauromates, and E. urartica sp. nov.
E. quatuorlineata E. sauromates E. urartica sp. nov.
E. quatuorlineata 0/0/0.73/0.30 0.15/0.15/0/0.20
E. sauromates 7.71/7.90 0.57/0.42 0.15/0.15/0.73/0.24
E. urartica sp. nov. 8.24/5.80 7.20/6.91 0.52/0.16
DOI: 10.7717/peerj.6944/table-3

Note:

Intraspecific mtDNA (COI/ND4) average p-distance is in diagonal and italics.

All three methods of species delimitation, that is, bPTP, mPTP, and GMYC recognized the three divergent lineages as distinct entities among the analyzed members of Elaphe (Fig. 1): E. quatuorlineata, E. sauromates, and the new species described below that has a sister relationship to E. sauromates (Fig. 2).

The mtDNA diversity is lower in the new species than in E. sauromates s. s. We identified eight haplotypes in both COI and ND4 of E. sauromates s. s., with the following characteristics of DNA polymorphism: Hd = 0.409; π = 0.179%; S = 10; V = 10; Pi = 2 (COI), Hd = 0.726; π = 0.207%; S = 9; V = 9; Pi = 4 (ND4). In the new species, we only detected two (COI) and three haplotypes (ND4), respectively, with lower values describing DNA polymorphism: Hd = 0.173; π = 0.067%; S = 2; V = 2; Pi = 2 (COI), Hd = 0.279; π = 0.036%; S = 2; V = 2; Pi = 1 (ND4). Neither clade shows a clear geographic structure based on the haplotype networks (Figs. 1B and 1C), although E. sauromates s. s. is more diversified. Haplotypes of both E. sauromates s. s. mtDNA genes are more broadly distributed, mainly in the northern Black Sea region. Unique haplotypes of this clade were detected in central and southwestern Anatolia, Bulgaria, and Crimea. In contrary, the new species shows much lower haplotype diversity with unique haplotypes found in Dagestan (COI, ND4), Armenia, and eastern Anatolia (ND4) (Fig. 1).

The network analysis of nuclear genes in all three related clades, which correspond to E. quatuorlineata, E. sauromates s. s., and the new species, indicate incomplete lineage sorting in all loci with the exception of RAG1 (Fig. 3). The new species, E. sauromates s. s., and E. quatuorlineata share C-MOS and PRLR haplotypes, while in MC1R E. sauromates s. s. and E. qutuorlineata have one haplotype in common. A very low haplotype diversity was detected in both C-MOS and MC1R. On the other hand, PRLR was more variable, with three haplotypes found in E. sauromates s. s., one of which was shared with both E. quatuorlineata and the new species. The largest diversity was observed in RAG1, in which we recovered six haplotypes. Three of them correspond with E. sauromates s. s., one with E. quatuorlineata, and two with the new species. DNA polymorphism values of all four analyzed nuclear markers are as follows: C-MOS (h = 2; Hd = 0.143; π = 0.031%; S = 1; V = 1; Pi = 0), MC1R (h = 2; Hd = 0.351; π = 0.054%; S = 1; V = 1; Pi = 1), PRLR (h = 3; Hd = 0.599; π = 0.60%; S = 7; V = 7; Pi = 7), RAG1 (h = 6; Hd = 0.610; π = 0.13%; S = 6; V = 6; Pi = 6).

Nuclear allele network of the phased sequences of RAG1 (A), PRLR (B), C-MOS (C), and MC1R (D) of Elaphe quatuorlineata (gray), E. sauromates (yellow), and E. urartica sp. nov. (red).

Figure 3: Nuclear allele network of the phased sequences of RAG1 (A), PRLR (B), C-MOS (C), and MC1R (D) of Elaphe quatuorlineata (gray), E. sauromates (yellow), and E. urartica sp. nov. (red).

The species are identified based on their mtDNA haplotypes. Circle sizes are proportional to the number of specimens. Small black circles indicate missing or hypothetical haplotypes (alleles). Different alleles of a single heterozygous specimen are coded as a and b variants, while an asterisk indicates an allele of a homozygous specimen. The code numbers are same as used in Table 1.

Morphology

Comparison of Elaphe sauromates s. s. and the new species

For all morphological analyses, we split the snakes into two taxonomic groups corresponding to E. sauromates s. s. (abbreviated as ES in this and the following section) and the new species (EU; see Methods; Tables 1 and 2), and males and females were treated separately for the purpose of both descriptive statistics (Tables 4 and 5; Tables S3 and S4) and comparisons (Table S5).

Table 4:
Morphometrics of Elaphe sauromates and E. urartica sp. nov.
Character (in mm except SVL/TL and SVL/HL) Elaphe sauromates Elaphe urartica sp. n.
Males Females Males Females
N Range Mean ± SD N Range Mean ± SD N Range Mean ± SD N Range Mean ± SD
Snout-vent length (SVL) 23 714–1,250 937±152 14 710–1,187 929 ± 160 15 650–970 795 ± 80 7 700–970 861 ± 97
Tail length (TL) 20 166–323 235 ± 42 13 135–253 196 ± 36 15 146–245 201 ± 27 7 150–235 182 ± 31
Total length 20 892–1,503 1,164 ± 191 13 845–1,439 1,115 ± 196 15 796–1,193 996 ± 104 7 850–1,205 1,043 ± 123
SVL/TL 20 3.43–5.29 3.98 ± 0.48 13 4.13–5.31 4.72 ± 0.40 15 3.46–4.45 3.99 ± 0.29 7 4.13–5.65 4.79 ± 0.20
Head length (HL) 10 24.1–34.6 29.3 ± 2.9 10 24.5–33.0 28.6 ± 3.0 7 25.4–31.0 27.9 ± 2.0 5 26.3–31.5 29.3 ± 2.4
SVL/HL 10 28.52–40.06 31.74 ± 3.18 10 28.41–36.38 32.43 ± 2.87 7 27.30–37.80 29.06 ± 3.87 5 22.30–33.92 29.61 ± 4.61
Head width (inter-ocular) 10 9.8–13.9 12.2 ± 1.2 10 10.5–15.0 12.1 ± 1.5 7 11.0–13.4 12.1 ± 1.0 5 11.0–13.1 12.1 ± 1.0
Pileus length 19 20.0–31.9 25.6 ± 3.4 12 21.0–31.6 24.0 ± 3.2 9 21.1–27.1 24.4 ± 2.0 5 23.4–27.1 25.3 ± 1.7
Pileus width 13 12.9–20.1 15.9 ± 2.1 5 12.1–17.5 13.9 ± 2.3 9 12.3–16.2 4.0 ± 1.4 5 12.5–14.8 13.5 ± 0.9
Rostrum height 13 4.0–6.9 5.6 ± 0.9 5 4.1–6.8 5.0 ± 1.1 9 3.6–6.1 4.5 ± 0.8 5 4.1–4.4 4.3 ± 0.1
Rostrum width 13 6.4–10.2 7.8 ± 1.1 5 6.1–9.4 7.3 ± 1.2 9 5.7–7.8 6.9 ± 0.8 5 6.1–8.0 7.2 ± 1.0
Inter-nostril width 13 6.3–10.5 8.3 ± 1.3 5 7.0–10.0 8.0 ± 1.2 9 5.6–8.9 7.1 ± 1.1 5 6.5–8.3 7.5 ± 0.8
Eye diameter 13 4.3–6.5 5.5 ± 0.7 5 4.7–6.1 5.4 ± 0.6 9 4.2–6.6 4.9 ± 0.7 5 4.8–5.5 4.9 ± 0.3
Supraocular plate width 13 3.6–6.9 5.0 ± 1.0 5 4.0–6.1 4.9 ± 0.8 9 3.8–5.1 4.2 ± 0.4 5 4.3–4.7 4.5 ± 0.2
Frontal plate length 13 8.1–12.5 9.2 ± 1.1 5 7.3–10.5 8.2 ± 1.3 9 6.2–8.5 7.5 ± 0.9 5 6.9–8.3 7.6 ± 0.5
Frontal plate width 13 5.6–8.6 6.8 ± 0.8 5 5.5–7.4 6.5 ± 0.7 9 5.7–6.7 6.2 ± 0.4 5 5.2–6.5 5.8 ± 0.5
Anterior inframaxillar scute length 13 7.6–14.1 10.0 ± 1.9 5 7.8–11.6 9.1 ± 1.5 9 6.7–9.7 8.0 ± 1.0 5 6.8–7.8 7.5 ± 0.4
Posterior inframaxillar scute length 13 6.5–12.5 8.8 ± 2.0 5 6.3–10.2 8.1 ± 1.7 9 5.2–8.5 6.8 ± 1.2 5 5.4–6.8 5.7 ± 0.6
DOI: 10.7717/peerj.6944/table-4

Note:

Plates on the left side were measured.

Table 5:
Scale counts in E. sauromates and E. urartica sp. nov.
Character Elaphe sauromates Elaphe urartica sp. n.
Males Females Males Females
N Range Mean ± SD N Range Mean ± SD N Range Mean ± SD N Range Mean ± SD
Ventrals 22 199–214 205 ± 4 11 206–222 212 ± 5 12 154–206 196 ± 14 10 194–211 204 ± 6
Subcaudal scale pairs 23 64–79 75 ± 3 15 61–72 66 ± 3 19 65–74 70 ± 3 13 60–72 64 ± 4
Dorsals and temporals touching parietals 20 9–20 13 ± 3 9 11–15 13 ± 1 12 9–14 11 ± 2 10 10–15 11 ± 1
Rows of keeled scales 10 0–19 11 ± 6 6 9–20 14 ± 4 7 18–21 19 ± 1 5 19–20 20 ± 1
Preventrals 22 0–3 11 1–2 12 1–2 10 0–3
Rows of dorsals one head length posterior to the head 17 21–25 6 21–27 12 23–25 10 25
Rows of dorsals at midbody 26 23–25 16 24–25 19 23–25 13 24–25
Rows of dorsals one head length posterior to the cloaca 17 18–19 6 19–21 12 19 10 18–19
Preoculars 23 1–3 13 1–2 19 1–3 13 1–2
Loreals (tip of) 19 1–3 9 1–3 12 1–2 10 1–2
Postoculars 21 1–2 11 2 19 1–2 13 2–3
Temporals 23 1–3 15 2–3 19 2 13 2–3
Posttemporals 23 2–5 15 2–5 19 2–4 13 3–4
Labials 26 7–9 16 8–10 18 8 13 8–9
Sublabials 26 9–12 15 9–12 15 10–13 11 10–12
Gulars between posterior labials 15 10–16 6 13–15 12 13–16 10 11–16
Gulars between anterior intermaxillars 20 0–2 10 1 12 1–2 10 1–2
Gulars between posterior intermaxillars 20 0–4 10 1–4 12 2–4 10 2–5
DOI: 10.7717/peerj.6944/table-5

First, we asked whether both species differ in their lengths. Indeed, we found the difference between males EU and ES (SVL: t(36) = 3.359, p = 0.002, n(ES) = 23, n(EU) = 15; total length: t(33) = 3.082, p = 0.004, n(ES) = 20, n(EU) = 15), with ES males (937 ± 152 mm on average) being longer than EU males (795 ± 80 mm; Table 4) on average. Although EU females seem to be generally shorter (861 ± 97 mm) than ES females (929 ± 160 mm; Table 4), the differences are not statistically significant (SVL: t(19) = 0.932, p = 0.363, n(ES) = 14, n(EU) = 7; total length: t(18) = 0.794, p = 0.438, n(ES) = 13, n(EU) = 7). Next, we asked whether species differ in the relative lengths of their tails and heads. We found no significant differences between the species when the straight head length (Males: F(2,11) = 1.506, p = 0.264, Wilks’ Λ = 0.785, n(ES) = 8, n(EU) = 7; Females: F(2,10) = 1.536, p = 0.262, Wilks’ Λ = 0.765, n(ES) = 9, n(EU) = 5) or pileus length (Males: F(2,12) = 1.512, p = 0.260, Wilks’ Λ = 0.799, n(ES) = 9, n(EU) = 7; Females: F(2,10) = 3.188, p = 0.078, Wilks’ Λ = 0.653, n(ES) = 11, n(EU) = 5) was used as a proxy of the total head length. The between-subject effects indicated that neither tail length nor head length differed between the two species. We then analyzed the relative head size and proportions by comparing several other head dimensions with head length used as a co-variate (see Table 4; Table S2). While the full models were not significant in either sex (Males: F(8,1) = 2.717, p = 0.439, Wilks’ Λ = 0.044, n(ES) = 4, n(EU) = 7; Females: F(5,1) = 1.035, p = 0.629, Wilks’ Λ = 0.162, n(ES) = 3, n(EU) = 5), the between-subject comparisons showed that several head dimensions differed between the species (Bonferroni correction alpha = 0.0042). In males these were pileus length, rostrum height, frontal plate length, anterior inframaxillar scute length, while females only differed in pileus length. EU has relatively longer pileus, but the scutes are relatively longer in ES than in EU (see Table 4). Next, we compared counts of selected scales on the head and body. We found a difference between EU and ES males (F(1,23) = 3.235, p = 0.030, Wilks’ Λ = 0.207, n(ES) = 13, n(EU) = 12), but not between females (F(1,12) = 2.658, p = 0.449, Wilks’ Λ = 0.030, n(ES) = 4, n(EU) = 10). The between-subject comparison showed that significant differences in males were in the numbers of subcaudal scale pairs (75 ± 3 in ES; 64 ± 4 in EU) and loreal (1–3 in ES; 1–2 in EU) scales. Though not significant after Bonferroni correction, the analyses indicated possible additional differences in ventral, temporal, and gular (between the anterior intermaxillars) scales in males and ventral, loreal, and gular scales in females (Table 5). Morphological data originating from the type material of the new species can be found in Table 6 and data on a few juvenile specimens originating from Armenia in Table S4. Due to very low numbers, these were not subjected to statistical comparisons.

Table 6:
Morphological characters of holotype and paratypes of E. urartica sp. nov. from Turkey (TR), Armenia (AR), and Azerbaijan (AZ).
Measure/Count Holotype Male 1 Male 2 Male 3 Male 4 Male 5 Male 6 Male 7 Female 1 Female 2 Female 3 Female 4 Female 5
TR ZDEU 26/2012 TR ZDEU 114/1970 AR TuRE ES 0000003301 AR TuRE ES 0000003302 AZ IZANAS T-17 AZ IZANAS 70 AZ IZANAS 68 AZ IZANAS 518 AR TuRE ES 0000003300 AR TuRE ES 0000003303 AZ IZANAS 69 AZ IZANAS 71 AZ IZANAS 529
Snout-vent length 803 812 750 701 860 792 848 790 872 892 951 700 880
Tail length 210 229 176 177 221 213 245 202 168 158 203 150 200
Total length 1,013 1,041 926 878 108 1,005 1,093 992 1,040 1,050 1,154 850 1,080
Pileus length 24.9 26.8 22.6 21.1 24.6 25.4 27.1 24.4 23.7 23.4 25.8 27.1 26.8
Pileus width 16.2 13.9 12.6 12.3 14.6 14.9 15.7 13.0 12.9 12.5 13.3 14.1 14.8
Rostrum height 5.3 6.1 4.4 4.4 3.6 4.4 4.8 4.00 4.4 4.4 4.4 4.4 4.1
Rostrum width 6.6 7.8 5.9 5.7 6.9 7.7 7.6 7.0 6.2 6.1 8.0 8.0 8.0
Inter-nostril width 8.5 5.6 6.3 6.2 6.6 8.1 8.9 6.5 6.8 6.5 8.2 8.3 7.7
Eye diameter 4.8 4.9 4.7 4.7 4.9 6.6 5.4 4.2 4.8 4.8 4.8 5.5 4.9
Frontal plate length 8.5 8.4 6.4 6.2 8.2 7.6 8.3 6.8 7.2 6.9 7.8 7.5 8.3
Frontal plate width 6.6 6.7 5.9 5.7 6.5 6.6 6.5 5.8 5.3 5.2 6.0 5.8 6.5
Anterior inframaxillar length 8.5 7.9 8.1 7.1 8.4 9.7 9.1 7.8 7.8 5.4 7.7 7.7 7.6
Posterior inframaxillar length 6.9 6.5 6.5 5.2 8.5 7.8 8.2 6.9 6.8 5.4 5.7 5.4 6.8
Ventrals 202 195 205 204 202 199 197 154 211 206 209 194 209
Subcaudal scale pairs 72 73 67 65 68 74 70 69 60 60 70 60 63
Dorsals and temporals touching parietals 9 13 12 11 10 9 14 10 10 11 12 11 12
Preventrals 1 1 1 1 1 1 1 1 1 2 1 1 1
Rows of dorsals one head length posterior to the head 25 25 25 25 23 24 25 24 25 25 25 25 25
Rows of dorsals at midbody 23 25 25 25 23 25 23 23 25 25 25 25 25
Preoculars (left/right) 2/2 2/2 2/1 2/2 3/3 2/3 2/2 2/2 1/1 2/2 2/2 2/2 2/2
Loreals (left/right) 1/1 1/1 1/1 2/2 1/1 1/1 1/1 1/1 1/1 1/1 1/1 2/1 1/1
Postoculars (left/right) 2/2 2/2 1/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 2/2 3/3
Temporals (left/right) 2/2 2/2 2/3 2/2 2/2 2/2 2/2 2/2 2/2 2/2 3/3 2/2 3/3
Posttemporals (left/right) 4/4 2/3 4/3 4/4 4/4 4/4 4/4 4/3 4/4 4/4 3/4 3/3 4/3
Labials (left/right) 8/8 8/8 8/8 8/8 8/8 8/8 8/8 8/8 8/8 8/8 8/8 8/8 8/8
Sublabials (left/right) 11/11 12/12 13/11 10/10 11/11 10/9 11/11 11/10 11/12 11/11 10/11 11/11 10/10
Gulars between posterior labials 15 15 16 13 13 13 13 13 14 11 15 13 14
DOI: 10.7717/peerj.6944/table-6

Sexual dimorphism

We found no differences in the length between males and females of ES (SVL: t(35) = 0.190, p = 0.850 n(M = Males) = 23, n(F = Females) = 14; total length: t(31) = 0.745, p = 0.462, n(M) = 20, n(F) = 13) and EU (SVL: t(20) = 1.626, p = 0.120, n(M) = 15, n(F) = 7; total length: t(20) = 0.898, p = 0.380, n(M) = 15, n(F) = 7), however, the sexes of both taxa differed in the relative tail lengths (ES: F(2,23) = 21.107, p = 0.000, Wilks’ Λ = 0.353, n(M) = 16, n(F) = 11; EU: F(2,10) = 43.678, p = 0.000, Wilks’ Λ = 0.103, n(M) = 9, n(F) = 5; pileus length was used as the total head length proxy in MANCOVA, SVL as a co-variate). The tails were longer in males than in females, which is also illustrated by the SVL/tail length indices–in males the tail length forms about 25% of the SVL, while it is around 21% in females (Table 4).

We also did not find overall differences in the relative head size (ES: F(4,1) = 1.406, p = 0.554, Wilks’ Λ = 0.151, n(M) = 4, n(F) = 3; EU: F(9,1) = 5.492, p = 0.320, Wilks’ Λ = 0.020, n(M) = 7, n(F) = 5), although the between-subject comparisons indicate that some differences may exist in pileus size (length and width) and eye diameter (Table 4).

There are also no sexual differences in scalation in ES (F(1,15) = 2.575, p = 0.237, Wilks’ Λ = 0.082, n(M) = 13, n(F) = 4), but according to the between-subject comparisons some differences may exist in numbers of ventral and subcaudal scales. However, model showed differences in scalation between males and females of EU (F(1,20) = 3.995, p = 0.036, Wilks’ Λ = 0.111, n(M) = 12, n(F) = 10), which was mainly driven by differences in numbers of subcaudal scale pairs (70 ± 3 in males, 64 ± 4 in females) and preocular (1–3 in males, 1–2 in females) scales. More thorough morphological comparison of larger and more complete datasets will be necessary to obtain a more robust picture of both interspecific and intersexual differences in both species.

Systematic account

Our findings indicate that the taxon E. sauromates s. l. (type locality of E. sauromates: Pre-Sivash area of the Crimean peninsula, the Perekop Isthmus and adjacent territories of the Lower Dnieper region; related sample nos. 1,178 and 1,179 in this study; see Table 1) is composed of two clearly genetically differentiated allopatric populations. The populations from Transcaucasia and eastern Anatolia, which are also morphologically differentiated from E. sauromates s. s., represent a cryptic phylogenetic lineage. In accordance with the definition of the genetic species concept (i.e., genetic species is a group of genetically compatible interbreeding natural populations that is genetically isolated from other such groups; Baker & Bradley, 2006) and evolutionary species concept (i.e., populations with a long independent evolutionary history, represents a lineage of ancestral descendent populations, and maintains its identity from other lineages both on genetic (mtDNA and nDNA) and morphological level; Simpson, 1951; Wiley, 1978), we describe this lineage as a new species:

  • Family Colubridae

  • Genus: Elaphe Fitzinger in Wagler, 1833

  • Elaphe urartica Jablonski, Kukushkin, Avcı, Bunyatova, Ilgaz, Tuniyev et Jandzik sp. nov.

  • urn:lsid:zoobank.org:act:A8F964EB–FD8E–4EAB–9549–DECD0648075C

Coluber sp. (No. 15)—Hohenacker, 1831: 374; Coluber sp. (No. 18)—Hohenacker, 1831: 375; C. cereus—Dwigubsky, 1832: 27, (nomen dubium); C. fulvus—Dwigubsky, 1832: 28, (nomen dubium); C. taeniothys Fischer von Waldheim, (nomen dubium), 1832: 575; Hohenacker, 1837: 145; Tropidonotus sauromates Eichwald, 1841: 140; Elaphis sauromates Duméril, 1853: 453 (part.); Strauch, 1873: 92 (part.); C. quatuorlineata sauromates Boulenger, 1894: 47 (part.); C. dione var. sauromates Nikolsky, 1905: 257 (part.); C. quatuorlineata var. sauromates Schreiber, 1912: 698 (part.); E. quatuorlineata Nikolsky, 1916: 133 (part.); Alekperov, 1978: 128; E. quatuorlineata sauromates Lindholm, 1929: 80 (part.); Sobolevssky, 1929; Szczerbak, 1966: 200 (part.); Muskhelishvili, 1970: 163; Schulz, 1996: 224 (part.); Sindaco et al., 2000: 473 (part.); E. sauromates Lenk, Joger & Wink, 2001: 329 (part.); Utiger et al., 2002: 105 (part.); Tuniyev et al., 2009: 80 (part.); Arakelyan et al., 2011: 88; Kornilios et al., 2014: 149 (part.); Wallach, Williams & Boundy, 2014: 263 (part.); Safaei-Mahroo et al., 2015: 279. For further details on nomenclature, see the Supplementary Information.

Holotype. (Fig. 4). ZDEU 26/2012 (tissue sample no. 1,124), adult male from Bitlis Province, Turkey (Kısıklı Village, Süphan Mts.; 38.93°N, 42.91°E, 2,394 m a. s. l.; Fig. 5), collected by Sako B. Tuniyev; July 16, 2012 (see also Tuniyev et al., 2014).

Holotype (ZDEU 26/2012) of Elaphe urartica sp. nov. from eastern Turkey.
Figure 4: Holotype (ZDEU 26/2012) of Elaphe urartica sp. nov. from eastern Turkey.
(A) Dorsal view, (B) ventral view, (C) dorsal view of the head, (D) lateral view, (E) ventral view (photos by Aziz Avcı), (F) the holotype while alive (photo by Çetin Ilgaz), (G) Sako B. Tuniyev with freshly caught holotype of E. urartica sp. nov. (photo by Boris Tuniyev).
Habitat at the type locality (Kısıklı, Süphan Mts., Turkey) of Elaphe urartica sp. nov. in south-eastern Turkey (photo by Boris Tuniyev).
Figure 5: Habitat at the type locality (Kısıklı, Süphan Mts., Turkey) of Elaphe urartica sp. nov. in south-eastern Turkey (photo by Boris Tuniyev).

Paratypes. (Fig. 6; Table 6). 12 specimens (seven males, five females; eight fixed specimens and four alive).

Paratypes of Elaphe urartica sp. nov. from Armenia ((A and B) photo by Ilya Korshunov and Konstantin Shiryaev) and Azerbaijan ((C) photo by Sabina Bunyatova) showing the habitus and details of the head.
Figure 6: Paratypes of Elaphe urartica sp. nov. from Armenia ((A and B) photo by Ilya Korshunov and Konstantin Shiryaev) and Azerbaijan ((C) photo by Sabina Bunyatova) showing the habitus and details of the head.
For the locality details, see Table 1.
Head coloration of juvenile Elaphe urartica sp. nov. from Armenia.
Figure 7: Head coloration of juvenile Elaphe urartica sp. nov. from Armenia.
(A) Males, (B) females (photos by Ilya Korshunov and Konstantin Shiryaev).

ZDEU 114/1970, adult male from Kars Province (Hoşerenler Plate), Turkey, 40.61°N, 43.09°E; IZANAS T-17, (tissue sample 3,655) adult male from surroundings of Guzdak, Qobustan, Azerbaijan, 40.37°N, 49.68°E (Fig. 6C); IZANAS 518, adult male from surroundings of Zaqatala, Azerbaijan, 41.63°N, 46.65°E; IZANAS 529, adult female from surroundings of Zaqatala, Azerbaijan, 41.63°N, 46.65°E; IZANAS 68, adult male from surroundings of Lenkoran, Azerbaijan, 38.75°N, 48.85°E; IZANAS 71, adult female from Zivi-Zkaro (=Tsivi-Tskaro; now Soyuqbulaq), Azerbaijan, 41.32°N, 45.27°E; IZANAS 70, adult male from surroundings of Şamaxi, Azerbaijan, 40.63°N, 48.63°E; IZANAS 69, adult female from Şamaxi, Azerbaijan; TuRE ES 0000003300 (tissue sample 3,196), live adult female from Mt. Gutanasar, Gegamsky Ridge (=Ahmangan), near Abovyan, Armenia, 40.37°N, 44.69°E (Fig. 6A); TuRE ES 0000003301 (tissue sample 3,195), live adult male from Mt. Gutanasar, Gegamsky Ridge (=Ahmangan), near Abovyan, Armenia, 40.37°N, 44.69°E (Fig. 6B); TuRE ES 0000003302 (tissue sample 3,450), live adult male from surroundings of Mt. Atis, Kotayikskoe Plateau, Armenia, 40.36°N, 44.61°E; TuRE ES 0000003303 (tissue sample 3,449), live adult female from NW slope of the Mt. Atis, Kotayikskoe Plateau, Armenia, 40.31°N, 44.73°E.

Etymology. The specific epithet is a feminine adjective derived from the name of the ancient kingdom of Urartu that flourished in the Armenian Highlands and around lake Van, an area of recent distribution of E. urartica sp. nov., in the 9th–6th century BCE (Asher & Asher, 2009). We are choosing this name out of respect for Peter Simon Pallas, who proposed the name for E. sauromates, now the sister species of E. urartica, which most likely refers to Sarmatians (Sauromatae; Σαυρομαται in Greek), a confederation of nomadic peoples inhabiting vast portions of the recent range of E. sauromates between the 5th century BCE and 4th century CE.

Diagnosis. A new species of western Palearctic genus Elaphe, very similar to E. sauromates (Pallas, 1814), characterized by the combination of the following characters: total length usually does not exceed 1,200 mm (796–1,205 mm), snout-vent (SVL) length usually less than 1,000 mm (650–970 mm), tail length less than 250 mm (146–245 mm) (see Tables 4 and 6). Tail forms about 25% of the SVL in males and about 21% in females. Head relatively large, distinguished from the body. Snout in prefrontal and internasal area is conspicuously convex which usually forms a hook-nosed head profile. Pileus length on average 1.8–1.9 times larger than its width. Frontal plate 1.2–1.3 times longer than wide. Anterior inframaxillar scute relatively large and wide, 1.2–1.3 times longer than the narrow posterior inframaxillar scute. One or two preocular scales, one loreal, two postoculars, two temporals, three or four posttemporals, eight labials, 10–11 sublabials on each side of the head. Eye in contact with fourth and fifth labials (Table 5; Table S3). Variation in head scale counts is relatively low (see Table S3). Usually two gulars located the anterior inframaxillars. The total number of gulars between inframaxillars and first preventral scale exceeds 12. Number of ventrals is 154–211 (154–206 in males, 194–211 in females), 60–74 subcaudal pairs (65–74 in males, 60–72 in females). 23–25 longitudinal rows of scales are around the midbody, with well-developed keels on 18–21 rows of body scales. The background of dorsal surfaces of the body and lateral surfaces of the head are yellowish or whitish, or seldomly bright yellow. The pattern of the dorsal surface of the body is composed of 50–65 rounded brown or black large ellipsoid spots, which may have whitish edges. Spots can be extended transversely in the posterior part of the body. Pileus is dark, often almost black, slightly lighter on the tip of the snout. Upper preoculars and temporals are dark forming a postocular stripe extending toward the mouth corner. This stripe blends with the dark dorsolateral head coloration anterior to the eye. Pale spots on the labials, only barely visible or lacking on sublabials. Ventral side of the body is whitish to pale yellow, sometimes with pinkish tint. There are marbled patterns of numerous small irregular dark brown and light gray spots with reddish contours that are more pronounced on the lateral sides of ventral plates. Throat is light, with numerous reddish-orange or brownish speckles on the lower jaws and anterior ventral plates. Iris is dark brown or almost black with a thin light rim around the pupil.

Differential diagnosis. Elaphe urartica sp. nov. is closely related to E. sauromates and E. quatuorlineata. The genetic distance between E. urartica sp. nov. and E. sauromates is 7.20% and 6.91% in COI and ND4, respectively, and 0.15%, 0.15%, 0.73%, and 0.24%, in C-MOS, MC1R, PRLR, and RAG1, respectively. The genetic distance between E. urartica sp. nov. and E. quatuorlineata is 8.24% and 5.80% in COI and ND4, respectively, and 0.15%, 0.15%, and 0.20%, in C-MOS, MC1R, and RAG1, respectively. E. urartica sp. nov. is also morphologically very similar to E. sauromates. E. urartica sp. nov. attains shorter lengths than E. sauromates (795 ± 80 mm vs. 937 ± 152 mm in E. sauromates males, 861 ± 97 mm vs. 929 ± 160 mm in E. sauromates females; though E. sauromates from other parts of the range, for example, the Balkans, can be even larger than specimens in our dataset, see Sahlean et al., 2016). Both taxa also differ in some relative head dimensions. E. urartica sp. nov males have relatively (in comparison to the head length) longer pileus, higher rostrum, but shorter frontal plate and anterior inframaxillary scute. Females only differ in the pileus length (Table 4). The upper surface of the head is more convex near orbits, prefrontals, and internasals and the rostrum is more anteriorly pronounced in E. urartica sp. nov. than in E. sauromates. Males of both species also slightly differ in their scalation: E. urartica sp. nov. males have fewer subcaudal pairs (64 ± 4 vs. 75 ± 3 in E. sauromates) and loreal scales (1–2 vs. 1–3 in E. sauromates). Other differences in metric and meristic characters were not found statistically significant. The coloration of E. urartica sp. nov. is generally darker than that of E. sauromates (Figs. 4 and 610). The dorsal side of the head is very dark, sometimes almost black and without the whitish area separating two blotches just posterior to the head as seen in E. sauromates (Figs. 4 and 610). On the lateral side of the head the dark stripe running from behind the eye toward the corner of the mouth is also less distinguished in E. urartica sp. nov. compared to E. sauromates, in which it is clearly separated by lighter color from the darker head coloration. E. urartica sp. nov. has more conspicuous dorsal body spots that are more rounded than in E. sauromates, in which transverse elongation of the spots is common. These dorsal spots are typically lined with whitish color in E. urartica sp. nov. rather than yellow or yellowish as in E. sauromates.

Color and pattern variation in Elaphe urartica sp. nov.
Figure 8: Color and pattern variation in Elaphe urartica sp. nov.
(A–D) Kaputan, Armenia; (E) Didi Shiraki, Georgia; (F) Ersi, Dagestan, Russian Federation (photos by Boris Tuniyev).
Coloration and pattern of adult (A) and subadult (B) males of Elaphe sauromates from south-western Turkey (photos by Aziz Avcı).
Figure 9: Coloration and pattern of adult (A) and subadult (B) males of Elaphe sauromates from south-western Turkey (photos by Aziz Avcı).
For the locality details, see Table 1.

Description of the holotype. Adult male (ZDEU 26/2012; Fig. 4). Body cylindrical, snout-vent length 803 mm, tail length 210.00 mm. Head big and clearly distinct from the neck, pileus length 24.90 mm, width 16.20 mm. Head and body scales keeled. Rostral slightly curved toward the top of the head, indistinctly wedged between the internasals. Rostrum height 5.3 mm and width 6.6 mm, in contact with two labials, two nasals, and two internasals. Nostrils located within the nasal scales, inter-nostril width is 8.5 mm. Loreal on either side of the head in contact with second and third labials. Two preocular and postocular plates on each side of the head. Eyes circular with circular pupil of 4.8 mm diameter. Length of the narrow frontal 8.5 mm, width 6.6 mm. Eight labials, with fourth and fifth in contact with the eyes on each side. A total of 11 sublabials on each side, five sublabials in contact with the anterior chin shields on each side. Two temporals and two posttemporals on each side. Nine dorsal and temporal scales surrounding the posterior margin of the parietals. Two gular scales in contact with the anterior chin shield. A total of 23 dorsal scale rows at midbody, 25 at the level of one head length posterior to the head, and 19 at one head length anterior to the cloaca level. One preventral, 202 ventral plates, two anal plates, and 72 and 73 subcaudals on each side, respectively (Table 4).

The dorsal side of the body is yellowish with round black spots. Flanks with two rows of dark blotches. Dorsal and lateral spots form striped pattern on the tail. The top of the head is black. Temporal stripe distinct, blending with the dark dorsolateral head coloration anterior to the eye. The ventral side of the body is yellowish white, with black markings (Fig. 4).

Variation. Details on variation among the type specimens of E. urartica sp. nov. are presented in Table 6. The coloration of the paratypes is very similar to that of the holotype.

Distribution and habitat. The geographic range of E. urartica sp. nov. is bordered by the Armenian Plateau, south-eastern foothills of the Great Caucasus, Alazan Valley, Kur-Aras, Lenkoran Lowlands, and the area of Qobustan. The species is distributed in Turkey, Georgia, Armenia, Azerbaijan, Nagorno-Karabakh, Iran, and Russia. In Turkey, it can be found east of the Anatolian Diagonal with reliable records from Kars, Bitlis, Diyarbakır, and Van Provinces, presumably also in Erzurum, Iğdır, and Ağrı Provinces (Baran et al., 2012). In eastern Transcaucasia E. urartica sp. nov. is distributed from south-eastern Georgia to the Zalka Plateau or to Suramskyi Ridge in Southern Ossetia in the West, throughout most of the Armenian territory, Nagorno-Karabakh, and Azerbaijan with the exception of the Abşeron Peninsula. The eastern part of the range lies in northern Iran to the Golestan Province to the East, and Kermanshah and Semnan Provinces to the South (Alekperov & Loginov, 1953; Muskhelishvili, 1970; Flärdh, 1983; Schulz, 1996; Sindaco et al., 2000; Arakelyan et al., 2011; Bunyatova, Akhmedov & Dzhafarov, 2012; Bunyatova, 2013; Najafov, Hashimov & Isgenderov, 2013; Safaei-Mahroo et al., 2015). In the Russian Federation, E. urartica sp. nov. occurs in Samur-Devichi Lowlands of southern Dagestan and probably in the Dagestan Intermontane Region as well (Ananjeva et al., 2006; Mazanaeva & Askenderov, 2014). The species could also occur in the extreme northern regions of Iraq (Sindaco, Venchi & Grieco, 2013).

The snake occurs in a wide range of altitudes—from ca. 25 m below sea level in the Lenkoran foredeep to about 2,600 m a.s.l. in the Shirak Province in Armenia (Arakelyan et al., 2011). It is an eurytopic species inhabiting a wide variety of landscapes: mountain and lowland semi deserts, different types of the steppe, semi subtropical savannah-like forest-steppes with oreoxerophytes, sparse juniper forests, montane broad-leaved forests, and alpine meadows (Fig. 5). The climate within the E. urartica sp. nov. range varies from the subtropical in Lenkoran and piedmont area of eastern Transcaucasia to cold mountain climate in Armenia and north-eastern Anatolia. Humidity varies from highly arid (with annual precipitation of less than 200 mm) to moderately humid (1,400–1,600 mm per year; Clark & Clark, 1973; Arakelyan et al., 2011; Bunyatova, Akhmedov & Dzhafarov, 2012; Şensoy et al., 2016).

Elaphe urartica sp. nov. is sympatric with E. dione in Dagestan, central-eastern Azerbaijan, eastern Georgia, and presumably in north-eastern Turkey, southern Armenia, and northern Iran. All other species of the genus Elaphe have allopatric distribution relative to E. urartica sp. nov. Since the species occurs in a region of southern Russia (Dagestan), north of the Caucasus, that is geographically and politically considered a part of Europe (Sillero et al., 2014), E. urartica sp. nov. is considered another member of the European herpetofauna.

Conservation status. Elaphe sauromates is a species with declining population numbers and is listed (as E. quatuorlineata) in the Red Data Books of: Ukraine (1994)—category 3, Kazakhstan (1996)—category 4—a little-known species, and Turkmenistan (1999)—category 3—a rare species on the periphery of the distribution range. It is also listed among the taxa recommended to be included in the new edition of the Red Data Book of the Russian Federation as vulnerable species (requiring priority of protection measures—III) (Ananjeva et al., 2006; Iljashenko et al., 2018). The current global IUCN Red List status for E. sauromates s.l. is of Least Concern (Aghasyan et al., 2017). Since E. urartica sp. nov. occurs in the parts of the territory from which the data for these lists was derived, similar conservation concerns might apply for it as well. However, the consequence of splitting E. sauromates s. l. into two separate species is that the ranges of both species have significantly decreased, and this should be considered in future conservation measures as well.

Proposal of common names. We propose the English name “Urartian Rat Snake” for E. urartica sp. nov. Along with the name “Blotched rat snake”, we also suggest using the name “Sarmatian Rat Snake” for E. sauromates, instead of the older “Eastern Four-lined Rat Snake” derived as a subspecific name from the common name of E. quatuorlineata. The newly proposed name would decrease confusion and also better reflects the scientific name of E. sauromates.

Discussion

Systematics of Elaphe sauromates and Elaphe urartica sp. nov

Since the publication of Boulenger’s Catalogue of the snakes in the British Museum (1894) E. sauromates had been considered an eastern subspecies of E. quatuorlineata. Based solely on genetic distances between the two taxa, Helfenberger (2001) and Lenk, Joger & Wink (2001) proposed their split into two sister species, which has been largely accepted. The distribution of both species is parapatric (Sindaco, Venchi & Grieco, 2013; Kornilios et al., 2014). While E. quatuorlineata and E. sauromates are clearly and easily distinguishable, mainly based on adult pattern and coloration (Böhme & Ščerbak, 1993; Schulz, 1996), E. urartica sp. nov. represents a cryptic species, only moderately phenotypically differentiated from E. sauromates. Based on the available evidence, both species currently have allopatric ranges, presumably separated by the Anatolian Diagonal and the Great Caucasus (Fig. 1; see Schulz, 1996; Sindaco et al., 2000). Phylogenetically E. urartica sp. nov. and E. sauromates represent sister lineages, and together they form a lineage sister to E. quatuorlineata (Fig. 2). Relatively little is known about intraspecific variation of E. urartica sp. nov. but haplotype diversity indicates that it is much lower than in E. sauromates (Figs. 1 and 3; Table 3, Results). The species occurs in a relatively small range (Fig. 1), however, in the region known as a radiation and speciation center (Tuniyev, 1995). While it does not seem likely that E. urartica sp. nov. is further differentiated into the subspecies in eastern Anatolia or Transcaucasia, the Caucasian montane part of the range of E. sauromates s. l. has yet to be genetically analyzed, and thus it remains unclear what species inhabits this region. Using phenotypic identification (i.e., without genetic analysis), it seems that both species come into possible parapatry in Dagestan—with E. sauromates in northern plains and E. urartica sp. nov. in more southerly located montane habitats (B.S. Tuniyev, 2018, personal observation). E. sauromates has been found relatively close to the southern ranges of the Anatolian Diagonal (Kayseri Province, Turkey, sample 2,892, see Table 1; Fig. 1A). On the other hand, the Anatolian Diagonal has formed a natural barrier to this species’ ability for dispersal southward from western and central Anatolia (Davis, 1971; Nilson, Andrén & Flärdh, 1990; Jandzik et al., 2018), so it is more likely that the Levantine populations actually belong to E. urartica sp. nov. Given the commonly observed biogeographic pattern in this region (Jandzik, Avcı & Gvoždík, 2013; Jandzik et al., 2018; Stümpel et al., 2016; Tamar et al., 2016; Kornilios, 2017), it is also possible that these, likely, isolated populations have diverged from one of these species (or their common ancestor) and represent a yet undiscovered taxon (Zinner, 1972).

Differentiation of E. sauromates and E. urartica sp. nov

Elaphe urartica sp. nov. is clearly genetically differentiated from E. sauromates and both taxa form statistically highly supported lineages (Fig. 2) in mtDNA trees. The uncorrected p-distances between both lineages in mtDNA sequences reach values around 7% (Table 3), which is very similar to distances observed in many other closely related snake species, for example, E. dione and E. bimaculata (~9%), E. quadrivirgata and E. carinata (~8.6%), E. quadrivirgata and E. schrenckii (~8.2%), Z. persicus Werner, 1913 and Z. longissimus (Laurenti, 1768) (~8%), Vipera ursinii (Bonaparte, 1835), V. graeca Nilson & Andrén, 1988, and V. renardi (Christoph, 1861) (~4.5%), Rhynchocalamus melanocephalus (Jan, 1862) and R. dayanae Tamar, Šmíd, Göçmen, Meiri, Carranza, 2016 (4–10.2%) (Utiger et al., 2002; Gvoždík et al., 2012; Huang et al., 2012; Tamar et al., 2016; Mizsei et al., 2017). Two out of four nuclear genes (MC1R and RAG1) are also clearly differentiated, though closely related between E. urartica sp. nov. and E. sauromates, while the remaining two (C-MOS and PRLR) show signs of incomplete lineage sorting. Interestingly, E. sauromates and E. quatuorlineata share alleles in three of the analyzed genes, and only haplotypes of RAG1 are mutually exclusive for each of them (Fig. 3). Such pattern of differences between mtDNA and nDNA has been observed among other closely related reptile species as well (see above or Gvoždík et al., 2010; Tamar et al., 2016; Mizsei et al., 2017) and it is to be expected as the autosomal loci have fourfold slower rate of lineage sorting (Avise, 2000).

Elaphe urartica sp. nov. represents a cryptic taxon within E. sauromates s. l. While we found some phenotypic differences, mainly being relatively smaller in size, having a moderate differences in the shape of the head, some head scalation dimensions, and rather different adult coloration, both species are still morphologically very similar (see Figs. 4 and 68 for E. urartica sp. nov. and 9, 10 for E. sauromates), especially when compared to their sister taxon E. quatuorlineata. However, this is also not unusual among closely related snake species, even within the genus ElapheE. dione, E. bimaculata, and E. zoigeensis Huang, Ding, Burbrink, Yang, Huang, Ling, Chen & Zhang, 2012 are virtually indistinguishable based on external morphology (Schulz, 1996; Huang et al., 2012). This similarity could be the result of similar environmental conditions and, consequently, the absence of selective pressure toward other type of coloration, size, or proportions (Fišer, Robinson & Malard, 2018). Though none of the morphological characters seem to be species-specific, using their combination will allow for confident specific identification. More robust sampling for morphological analyses will shed additional light on the levels of differentiation between both species.

Color and pattern variation in Elaphe sauromates.

Figure 10: Color and pattern variation in Elaphe sauromates.

(A) Gelendzhik, Krasnodar Territory, Russian Federation (photo by Boris Tuniyev); (B) Chauda Cape, Crimea (photo by Egor Kalmykov & Oleg Kukushkin); (C) Solenoe Ozero, Crimea (photo by Anton Nadolnyi); (D) Göltarla, Antalya, Turkey (ZDEU 298/2013); (E) Iskenderun, Turkey (photo by Daniel Jablonski), (F) Ustyurt, Kazakhstan (photo by Mark Pestov).

Historical biogeography

The fossil record indicates that the ancestors of modern E. sauromates s. l. were present in the region of the recent range since at least Late Pliocene. Snake remnants identified as either E. quatuorlineata or E. cf. quatuorlineata, presumably belonging to E. sauromates s. l., are known from the Early-Middle Pleistocene of the Balkans, Transcaucasia, and central Anatolia (Szyndlar, 1984, 1991; Venczel & Şen, 1994; Venczel, 2000; Venczel & Várdai, 2000; Kornilios et al., 2014; Wallach, Williams & Boundy, 2014; Blain et al., 2014; Blain, 2016). In addition, Elaphe aff. quatuorlineata fossils were also described from the Middle Pliocene of Moldova (Redcozubov, 1991, 2005), indicating that parts of the range were probably inhabited even earlier.

Molecular-phylogenetic analyses suggest that E. sauromates s. l. and E. quatuorlineata split from their last common ancestor sometime in the Late Miocene (7.3–8.3 Mya), presumably during the formation of the mid-Aegean Trench that separated the Balkans from Asia Minor (Lymberakis & Poulakakis, 2010; Kornilios et al., 2014). Further evolution of E. sauromates s. l. is mainly associated with Anatolia and adjacent areas of the southern Caucasus. The mtDNA genetic distances between E. sauromates s. s. and E. urartica sp. nov. (Table 3) place the split between these two lineages at the Miocene-Pliocene boundary (five to eight Mya; see Kornilios et al., 2014), so they presumably separated from each other not very long after their ancestors separated from E. quatuorlineata. Although our estimation is only approximate, it coincides with the splits among other snake and lizard taxa from the same region, most notably the montane vipers of Montivipera xanthina complex—M. xanthina clade from western Anatolia and M. bornmuelleri clade from the east and south of the Anatolian Diagonal separated around five to six Mya (Stümpel et al., 2016). However, these authors propose that the valley of Göksu River south-west of the Anatolian Diagonal formed the natural barrier for the vipers adapted to the life in high altitudes, which was probably not true for the eurytopic rat snakes. Nevertheless, similar patterns of the east-west Anatolian split have been described in numerous other reptilian taxa (see Fritz et al., 2008; Kyriazi et al., 2008; Kornilios et al., 2012; Ahmadzadeh et al., 2013; Jandzik, Avcı & Gvoždík, 2013; Jandzik et al., 2018; Kapli et al., 2013; Skourtanioti et al., 2016).

Elaphe sauromates s. s. then presumably survived the Pleistocene climatic oscillations in refugia located mainly in Anatolia, Crimea, and/or the southern Balkans, where the highest haplotype diversity was recorded (see Figs. 1B and 1C). Subsequently in the Late Pleistocene, E. sauromates s. s. reoccupied the territories of eastern Europe concomitant with dispersing north of the steppe and semi-desert habitats and the Black Sea regression (Ratnikov, 2014), similarly as proposed for the snake Dolichophis caspius (Nagy et al., 2010) and lizards Lacerta viridis (Marzahn et al., 2016), Pseudopus apodus (Jandzik et al., 2018), and Podarcis tauricus (Psonis et al., 2018). Before the terminal phase of the last Pleistocene glaciation, E. sauromates already lived in the Crimean Mountains as confirmed by the fossil record (Ratnikov, 2015), although remnants of E. quatuorlineata–sauromates from the Pleistocene and Holocene are not known from the East European Plain (Ratnikov, 2002). Interestingly, Mazanaeva & Tuniyev (2011) proposed that E. sauromates and other Mediterranean faunal elements might have colonized the Great Caucasus from the North through the Kuma–Manych Strait during the last phases of the Pleistocene. Our lack of samples from the south-eastern parts of E. sauromates s. s. range does not allow us to confirm or reject this scenario. Colonization of the Transcaspia and Central Asia is probably very recent as the region is inhabited by the common northern E. sauromates s. s. haplotypes (Figs. 1A1C) and might have coincided with the Late Pleistocene or even the Early Holocene regression of the Caspian Sea (see Krijgsman et al., 2018).

The significantly lower genetic diversity of E. urartica sp. nov. (only two haplotypes in COI, three in ND4, one to three in the nDNA genes; Figs. 1 and 3) does not provide enough information for drawing viable biogeographic scenarios. The species probably survived the Pleistocene glaciations in one, or a few, Transcaucasian or east-Anatolian refugia (Kahle et al., 2011; Kornilios et al., 2011; Jandzik et al., 2018) and spread relatively fast to the north-eastern Caucasus and southern Anatolia. A very similar situation with low genetic variation in the same region was observed in an anguid lizard Pseudopus apodus (Jandzik et al., 2018). Additional samples from Iran, central Anatolia, and the Levant will be necessary to learn more about the history of this species. In particular, one might expect surprises from the Levantine region given that it hosts many endemic taxa and lineages, and several Anatolian species have their subspecies or sister species located in the region, for example, Natrix tessellata complex (Guicking, Joger & Wink, 2009), the L. trilineata complex (Ahmadzadeh et al., 2013), Z. hohenackeri (Jandzik, Avcı & Gvoždík, 2013), the Ablepharus kitaibelii complex (Skourtanioti et al., 2016), Xerotyphlops vermicularis (Kornilios, 2017), and the Mediodactylus kotschyi complex (Kotsakiozi et al., 2018).

Conclusions

Here we studied the biogeography of the rat snake E. sauromates from the Balkans, Anatolia, Caucasus, and Ponto-Caspian region using both molecular and morphological data. We found that the taxon is, in fact, comprised of two distinct evolutionary lineages and the cryptic lineage represents a new species that we name E. urartica sp. nov. Both species split from their common ancestor around the Miocene-Pliocene boundary and their recent genetic structure was mainly influenced by Pleistocene climatic oscillations.

Supplemental Information

Supplementary Information.

DOI: 10.7717/peerj.6944/supp-1

Phylogenetic relationships of Elaphe quatuorlineata, E. sauromates, and E. urartica sp. nov. reconstructed using Bayesian inference of concatenated COI and ND4 sequences.

The numbers above the branches represent Bayesian Posterior probabilities showing the branch support.

DOI: 10.7717/peerj.6944/supp-2

Phylogenetic relationships of Elaphe quatuorlineata, E. sauromates, and E. urartica sp. nov. reconstructed using Maximum Likelihood tree analysis of concatenated COI and ND4 sequences.

The numbers above the branches represent bootstraps showing the branch support.

DOI: 10.7717/peerj.6944/supp-3

Alignments of mitochondrial and nuclear sequences used in this study.

DOI: 10.7717/peerj.6944/supp-4