A revised taxonomy of Asian snail-eating snakes Pareas (Squamata, Pareidae): evidence from morphological comparison and molecular phylogeny

Description of a New Species of the Pareas hamptoni Complex from Yunnan, China, with Confirmation of P. hamptoni Sensu Stricto in China (Squamata, Pareidae)

We describe a new species of the genus Pareas, based on three specimens collected from Guanyinshan Provincial Nature Reserve in Yuanyang County, Honghe Prefecture, Yunnan Province, China. The new species is distinguished from its congeners by one preocular, one postocular or postocular fused with subocular, loreal not bordering the orbit, one row enlarged vertebral scales, five rows keeled mid-dorsal scales at the middle of the body, 189-192 ventral scales and 72-89 subcaudal scales. The dorsal surfaces of the head and body are yellowish red or yellowish brown, and the belly and ventral surfaces of the head and tail are pinkish yellow or yellow with more or less small black spots. Phylogenetic analyses of mitochondrial DNA recovered the new species being the sister taxon to P. hamptoni sensu stricto. The genetic divergences between the new species and P. hamptoni sensu stricto were 4.2% in the Cyt b sequences and 5.0% in the ND4 sequences. In addition, based on specimens collected from Honghe and Wenshan prefectures, we confirmed that P. hamptoni sensu stricto is distributed in China.

A New Species of Pareas (Squamata, Pareidae) from Guangxi Province, China

We described a new species of genus Pareas from Baise City, Guangxi Zhuang Autonomous Region, China, based on morphological and molecular evidence. Pareas baiseensis sp. nov. is distinguished from its congeners by the combination of (1) Yellowish-brown body colouration; (2) Frontal subhexagonal to diamond-shaped with its lateral sides converging posteriorly; (3) The anterior pair of chin shields is longer than it is broad; (4) Loreal not in contact with the eye, prefrontal in contact with the eye, two or three suboculars; (5) Rows of 15-15-15 dorsal scales, five rows of mid-dorsal scales keeled at the middle of the body, one vertebral scale row enlarged; (6) 187-191 ventrals, 89-97 subcaudals, all divided, cloacal plate single; (7) Two postocular stripes, the nuchal area forming a dark black four-pointed fork collar with the middle tines shorter than the outside tines. The genetic divergence (uncorrected p-distance) between the new species and other representatives of Pareas ranged from 13.9% to 24.4% for Cytochrome b (Cyt b) and 12.1% to 25.5% for NADH dehydrogenase subunit 4 (ND4). Phylogenetic analyses of mitochondrial DNA gene data recovered the new species from being the sister taxon to (P. boulengeri + P. chinensis) from China.

A New Species of Pareas Wagler, 1830 (Squamata, Pareidae) from Northwestern Yunnan, China

A new species of Pareas Wagler, 1830 is described from Dulongjiang Township, Gongshan County, Yunnan Province, China. Phylogenetically, the new species is most closely related to Pareas kaduri Bhosale, Phansalkar, Sawant, Gowande, Patel and Mirza, 2020; however, the genetic divergence (uncorrected p-distance) of the cyt b gene between the new species and P. kaduri reached 9.4%. Morphologically, the new species can be distinguished from P. kaduri by the absence of preoculars, loreal bordering the orbit, the fusion of subocular and postocular, three rows enlarged vertebral scales, five rows keeled mid-dorsal scales at the middle of the body, having more subcaudals, and having a relatively longer tail. In addition, the new species can be distinguished from all other congeners by a combination of morphological characteristics. Our work brings the total number of recognized species of the genus Pareas to 29, of which 23 occur in China.

DNA barcoding of Chinese snakes reveals hidden diversity and conservation needs

DNA barcoding has greatly facilitated studies of taxonomy, biodiversity, biological conservation, and ecology. Here, we establish a reliable DNA barcoding library for Chinese snakes, unveiling hidden diversity with implications for taxonomy, and provide a standardized tool for conservation management. Our comprehensive study includes 1638 cytochrome c oxidase subunit I (COI) sequences from Chinese snakes that correspond to 17 families, 65 genera, 228 named species (80.6% of named species) and 36 candidate species. A barcode gap analysis reveals gaps, where all nearest neighbour distances exceed maximum intraspecific distances, in 217 named species and all candidate species. Three species-delimitation methods (ABGD, sGMYC, and sPTP) recover 320 operational taxonomic units (OTUs), of which 192 OTUs correspond to named and candidate species. Twenty-eight other named species share OTUs, such as Azemiops feae and A. kharini, Gloydius halys, G. shedaoensis, and G. intermedius, and Bungarus multicinctus and B. candidus, representing inconsistencies most probably caused by imperfect taxonomy, recent and rapid speciation, weak taxonomic signal, introgressive hybridization, and/or inadequate phylogenetic signal. In contrast, 43 species and candidate species assign to two or more OTUs due to having large intraspecific distances. If most OTUs detected in this study reflect valid species, including the 36 candidate species, then 30% more species would exist than are currently recognized. Several OTU divergences associate with known biogeographic barriers, such as the Taiwan Strait. In addition to facilitating future studies, this reliable and relatively comprehensive reference database will play an important role in the future monitoring, conservation, and management of Chinese snakes.

Transcriptome Analysis Reveals Olfactory System Expression Characteristics of Aquatic Snakes

Animal olfactory systems evolved with changes in habitat to detect odor cues from the environment. The aquatic environment, as a unique habitat, poses a formidable challenge for olfactory perception in animals, since the higher density and viscosity of water. The olfactory system in snakes is highly specialized, thus providing the opportunity to explore the adaptive evolution of such systems to unique habitats. To date, however, few studies have explored the changes in gene expression features in the olfactory systems of aquatic snakes. In this study, we carried out RNA sequencing of 26 olfactory tissue samples (vomeronasal organ and olfactory bulb) from two aquatic and two non-aquatic snake species to explore gene expression changes under the aquatic environment. Weighted gene co-expression network analysis showed significant differences in gene expression profiles between aquatic and non-aquatic habitats. The main olfactory systems of the aquatic and non-aquatic snakes were regulated by different genes. Among these genes, RELN may contribute to exploring gene expression changes under the aquatic environment by regulating the formation of inhibitory neurons in the granular cell layer and increasing the separation of neuronal patterns to correctly identify complex chemical information. The high expression of TRPC2 and V2R family genes in the accessory olfactory systems of aquatic snakes should enhance their ability to bind water-soluble odor molecules, and thus obtain more information in hydrophytic habitats. This work provides an important foundation for exploring the olfactory adaptation of snakes in special habitats.

An integrative taxonomic revision of slug-eating snakes (Squamata: Pareidae: Pareineae) reveals unprecedented diversity in Indochina

Slug-eating snakes of the subfamily Pareinae are an insufficiently studied group of snakes specialized in feeding on terrestrial mollusks. Currently Pareinae encompass three genera with 34 species distributed across the Oriental biogeographic region. Despite the recent significant progress in understanding of Pareinae diversity, the subfamily remains taxonomically challenging. Here we present an updated phylogeny of the subfamily with a comprehensive taxon sampling including 30 currently recognized Pareinae species and several previously unknown candidate species and lineages. Phylogenetic analyses of mtDNA and nuDNA data supported the monophyly of the three genera Asthenodipsas, Aplopeltura, and Pareas. Within both Asthenodipsas and Pareas our analyses recovered deep differentiation with each genus being represented by two morphologically diagnosable clades, which we treat as subgenera. We further apply an integrative taxonomic approach, including analyses of molecular and morphological data, along with examination of available type materials, to address the longstanding taxonomic questions of the subgenus Pareas, and reveal the high level of hidden diversity of these snakes in Indochina. We restrict the distribution of P. carinatus to southern Southeast Asia, and recognize two subspecies within it, including one new subspecies proposed for the populations from Thailand and Myanmar. We further revalidate P. berdmorei, synonymize P. menglaensis with P. berdmorei, and recognize three subspecies within this taxon, including the new subspecies erected for the populations from Laos and Vietnam. Furthermore, we describe two new species of Pareas from Vietnam: one belonging to the P. carinatus group from southern Vietnam, and a new member of the P. nuchalis group from the central Vietnam. We provide new data on P. temporalis, and report on a significant range extension for P. nuchalis. Our phylogeny, along with molecular clock and ancestral area analyses, reveal a complex diversification pattern of Pareinae involving a high degree of sympatry of widespread and endemic species. Our analyses support the "upstream" colonization hypothesis and, thus, the Pareinae appears to have originated in Sundaland during the middle Eocene and then colonized mainland Asia in early Oligocene. Sundaland and Eastern Indochina appear to have played the key roles as the centers of Pareinae diversification. Our results reveal that both vicariance and dispersal are responsible for current distribution patterns of Pareinae, with tectonic movements, orogeny and paleoclimatic shifts being the probable drivers of diversification. Our study brings the total number of Pareidae species to 41 and further highlights the importance of comprehensive taxonomic revisions not only for the better understanding of biodiversity and its evolution, but also for the elaboration of adequate conservation actions.

The complete mitochondrial genome of Taiwan slug-eating snake (Pareas formosensis) and phylogenetic analysis

We report the complete mitochondrial genome (mtDNA) of Pareas formosensis (Squamata: Colubridae). This circular mtDNA is 17,703 bp in size and consists of 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs, and 2 non-coding sequence (D-loop). The total of mtDNA was composition of 57.26% A + T and 42.74% G + C (T: 25.21%, C: 28.84%, A: 32.05%, G: 13.90%). The phylogenetic analysis revealed that P. formosensis formed a clade with other species of Pareas. This mtDNA sequence of P. formosensis provides useful data for studying the population genetics and phylogeography of Colubridae.

Range extension of the Common Slug Snake Pareas monticola (Cantor, 1839) (Reptilia: Squamata: Pareidae): a new family record for Nepal

In this paper, we present the first evidence of the snake Pareas monticola in Nepal. An individual snake belonging to the species was recorded in eastern Nepal, about 25 km southwest of Darjeeling in India, where the species is known to occur.  

A new species of the genus Pareas (Squamata, Pareidae) from Yunnan, China

A new species of Pareas is described from Yunnan Province, China, based on morphological comparisons and molecular data. Genetically, the new species is most closely related to the recently-described Pareasgeminatus, for which we present new topotypic findings. The genetic divergence (uncorrected p-distance) of the cytb gene between the new species and congeners ranged from 6.14% to 24.68%. Morphologically, the new species can be distinguished from P.geminatus and all other congeners. Our work brings the total number of species within the genus Pareas to 22.

Eviscerated alive: Novel and macabre feeding strategy in Oligodon fasciolatus (Günther, 1864) eating organs of Duttaphrynus melanostictus (Schneider, 1799) in Thailand

A hitherto unknown feeding mode among snakes is described for the colubrid snake Oligodon fasciolatus in Northeast Thailand. Three cases of O. fasciolatus using enlarged posterior maxillary teeth to cut open the abdomen of a live poisonous toad Duttaphrynus melanostictus and eat its organs are described. The snakes and toads fought vigorously, and the toads secreted toxic white liquid on the dorsum and neck. The snakes inserted their heads into the abdomen of the toads, pulled out some of the organs and swallowed them. The snakes and toads were adults. All three cases were documented by extensive photographic material.

In a fourth case from Central Thailand, an adult O. fasciolatus was observed swallowing an entire semi-adult D. melanostictus.

The majority of all snake species swallow their prey in one piece, but to place our observations in a broader context we review a number of exceptions.