Research Article |
Corresponding author: Uri Omar García-Vázquez ( urigarcia@gmail.com ) Academic editor: Robert Jadin
© 2018 Uri Omar García-Vázquez, Carlos J. Pavón-Vázquez, Jean Cristian Blancas-Hernández, Epifanio Blancas-Calva, Eric Centenero-Alcalá.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
García-Vázquez UO, Pavón-Vázquez CJ, Blancas-Hernández JC, Blancas-Calva E, Centenero-Alcalá E (2018) A new rare species of the Rhadinaea decorata group from the Sierra Madre del Sur of Guerrero, Mexico (Squamata, Colubridae). ZooKeys 780: 137-154. https://doi.org/10.3897/zookeys.780.25593
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A new species of the Rhadinaea decorata group is described based on two specimens from the Sierra Madre del Sur, Guerrero, Mexico. The new species differs from all other members of the genus Rhadinaea by having: eight supralabials; 149–151 (male) ventrals; 63–77 (male) subcaudals; two large pale nuchal blotches, forming an incomplete collar that occupies two scales laterally and is bissected along the dorsal midline; a postocular pale marking consisting of a well-defined, narrow line beginning behind the upper posterior margin of the eye and extending posteriorly nearly horizontally until connecting with the nuchal blotches; and the dark ground color of the flanks extending to the lateral portion of the ventrals. The large nuchal blotches distinguish the new species from the other members of the R. decorata group, except for R. cuneata and some individuals of R. hesperia (pale nuchal marking one-scale wide in R. marcellae, absent in the other species). The condition of the postocular pale marking distinguishes it from R. cuneata and R. hesperia (postocular pale marking wedge-shaped in R. cuneata, not connected with the pale post-cephalic markings in R. hesperia). Furthermore, the number of subcaudals and the coloration of the lateral portion of the ventrals distinguish it from R. omiltemana and R. taeniata, the remaining congeners found in Guerrero (85–90 in males of R. omiltemana and 91–121 in R. taeniata; dark color of the flanks not reaching ventrals in the former species, occasionally and faintly in R. taeniata). Additionally, a new combination for R. stadelmani is proposed. The new species is the first described in the genus Rhadinaea in more than 40 years.
Description, reptile, snake, systematics, taxonomy
Snakes of the genus Rhadinaea Cope, 1863 (Colubridae: Dipsadinae) are distributed throughout Mesoamerica, ranging from the Sierra Madre Occidental of southern Sinaloa and Sierra Madre Oriental of northern Nuevo León in Mexico to northwestern Ecuador in South America, with an isolated species, R. flavilata (Cope, 1871), in the southeastern USA (
The Rhadinaea decorata group is characterized by the following combination of traits (
The Rhadinaea decorata group is the most diverse assemblage within the genus. Members of the group collectively range from the Mexican states of Tamaulipas and Sinaloa south and east to northwestern Ecuador, where they are mainly found in high mountains. All the species occur in Mexico and only R. decorata (Günther, 1858) is not endemic to the country (
During fieldwork conducted in the Sierra Madre del Sur, Guerrero, between 2006 and 2008 we collected an unusual individual of Rhadinaea in the vicinity of El Molote. In eleven trips to the locality we were unable to locate another specimen. Eight years after concluding our fieldwork another specimen with similar characteristics was collected ca. 3 km NW (in straight line) of where the first specimen was found. The snakes show a unique combination of characters and are apparently allopatric with respect to closely related species of Rhadinaea (see comparison section). These two individuals possess a unique combination of characteristics leading us to conclude they represent a new species that we describe below.
Acronyms for herpetological collections follow
We follow
Our review of the literature revealed the need to update the binomial name of Rhadinaea stadelmani Stuart & Bailey, 1941. The species was placed in the synonymy of Rhadinaea hempsteadae Stuart & Bailey, 1941 (= Rhadinella hempsteadae) by
Morphological examination of the specimens from El Molote supported their inclusion in the genus Rhadinaea (sensu
Holotype. MZFC-HE 22161, (original field number JCBH 015) an adult male, from 0.36 km SE of El Molote, municipality of Atoyac de Álvarez, Guerrero, México (17.4167°N; 100.1672°W), ca. 1720 m elevation, collected by J.C. Blancas-Hernández on July 19, 2006. Paratype. MZFC-HE 34958, (original field number CIG 1078) an adult male, from El Molote, municipality of Atoyac de Álvarez, Guerrero, México (17.4376°N; 100.1891°W), ca. 1680 m elevation, collected by Christoph I. Grünwald, Héctor Franz-Chávez, and Karen I. Morales-Flores on September 11, 2016.
A colubrid snake of the Rhadinaea decorata group (sensu
Rhadinaea nuchalis sp. n. may be distinguished from all other members of the genus Rhadinaea (except R. cuneata and some individuals of R. hesperia and R. omiltemana Günther, 1894) by the presence of two large pale nuchal blotches forming an incomplete collar that occupies two scales laterally and is bissected along the dorsal midline (pale nuchal marking one-scale long in R. laureata (Günther, 1868) and R. marcellae, absent in the other species). Rhadinaea nuchalis can be further distinguished from the members of the R. flavilata group by the presence of eight supralabials (usually seven in the R. flavilata group). Additionally, it differs from R. calligaster (Cope, 1875), R. forbesi, R. hesperia, R. marcellae, R. macdougalli, and R. montana by the presence of a well-defined, pale postocular line beginning anteriorly behind the upper posterior margin of the eye and extending nearly horizontally posteriorly until connecting with the nuchal blotches (pale postocular line oblique in R. calligaster [if present], R. forbesi, R. macdougalli, and R. marcellae; not connected with the pale post-cephalic markings in the other species [except for one side in one specimen of R. montana]).
Furthermore, Rhadinaea nuchalis can be distinguished from members of the R. vermiculaticeps group by having more ventrals in males (149–151 vs. 117–124 ventrals in males of the R. vermiculaticeps group). Rhadinaea nuchalis differs from R. cuneata by having less subcaudals in males (63–77 vs. 106–115) and by having a narrow postocular pale marking in the form of a nearly horizontal line (postocular pale marking wedge-shaped in R. cuneata). Specifically, R. nuchalis differs from other congeners that inhabit Guerrero except R. myersi by having fewer subcaudals in males (63–77 vs. 110–137 in R. hesperia; 85–90 in R. omiltemana; 91–121 in R. taeniata Peters, 1863). Additionally, it differs from R. myersi, R. omiltemana, and R. taeniata by having the dark ground color of the flanks extending to the lateral portion of the ventrals (dark ground color of the flanks not reaching ventrals in R. omiltemana, occasionally and faintly so in R. myersi and R. taeniata).
(Figs
Transverse dorsal scale rows 17-17-17, smooth; apical pits absent; ventrals 151; cloacal scute divided; paired subcaudals 63.
Color (in life; Figs
Nuchal blotches brownish orange; separated dorsally by median dark line; one dorsal scale long dorsally, widening laterally to two dorsal scales; nearly immaculate dorsally, with abundant dark speckling at level of supralabials; connected to pale ventral coloration. First and second transverse dorsal scale rows posterior to nuchal blotches reddish brown, slightly darker than rest of body.
Coloration of rest of body and tail: median dark line dark brown, with darker spots on tip of each dorsal scale in vertebral row; extending to third mid-dorsal scale posterior to parietals anteriorly, to tip of tail posteriorly; narrower anteriorly and posteriorly (confined to vertebral dorsal scale row near head and to medial edges of innermost dorsal scale rows in tail), wider at midbody (occupying vertebral dorsal scale row entirely and dorsal edges of adjacent dorsal scale rows). Dorsolateral stripe ochre; failing to contact nuchal blotches anteriorly by two scales, extending to tip of tail posteriorly; extending between upper portion of fifth and lower portion of eighth longitudinal dorsal scale rows at level of mid-body, between upper portion of second and lower portion of third longitudinal dorsal scale rows at level of mid-tail. Scales on fifth longitudinal dorsal scale row at level of mid-body and second at level of mid-tail exhibiting prominent orange spots. Lateral dark line bordering dorsolateral stripe ventrally; contacting nuchal blotches anteriorly, extending to tip of tail posteriorly; occupying three longitudinal dorsal scale rows just posteriorly to head, upper portion of fourth and lower edge of fifth longitudinal dorsal scale rows at level of mid-body, upper edge of first and lower edge of second longitudinal dorsal scale rows at level of tail. Flanks dark ochre, slightly darker than dorsolateral stripes, presenting abundant dark speckling. Ground color of flanks extending ventrally onto lateral portions of ventrals and subcaudals. Lateral portion of ventrals with black spots posteriorly at level of ventral edge of color of flanks. Conspicuous dark line passing along lateral edge of subcaudals. Remaining surface of ventrals and subcaudals white, suffused lightly with bright pink from head to level of mid-body, with sparse tiny dark dots.
Hemipenes (Figure
The paratype differs from the holotype by having the upper posterior temporal divided into two small scales on the right side, 10/9 infralabials, the posterior chinshields separated from first ventral by two rows of small scales, 149 ventrals, and 77 subcaudals. No remarkable differences in color pattern are present in the paratype with respect to the holotype.
The specific name nuchalis comes from the Latin nucha, meaning nape. It makes reference to the large nuchal blotches present in the new species.
Rhadinaea nuchalis sp. n. is known only at intermediate elevations from the vicinity of El Molote in the western portion of the Sierra Madre del Sur of Guerrero. The species appears to be allopatric with the other species of the R. decorata group. The closest Rhadinaea record to R. nuchalis is that of R. omiltemana from El Tambor, Coyuca de Benítez, Guerrero, approximately 8 km E in straight line from the type locality of R. nuchalis (
The region of El Molote is characterized by rugged topography and the presence of numerous permanent streams that flow into the Atoyac and Coyuca rivers, whose basins belong to the Costa Grande hydrologic region (
An identification key to the species of Rhadinaea was included in
40 | Pair of large pale nuchal blotches, forming a collar broken on the dorsal midline | R. nuchalis sp. n. |
– | Post-cephalic pale markings not significantly enlarged, not as described above | 41 |
Former number 40, a bracket including R. bogertorum and R. myersi, would become number 41.
Color pattern has been considered one of the most informative characters for distinguishing between species and species groups within Rhadinaea: “…once some idea has been gained of intraspecific variation, color pattern offers the most generally reliable method of identifying species because no two forms have identical patterns…” (
DNA sequences of Rhadinaea have been included in studies looking at phylogenetic relationships above the generic level (e.g.,
The presence of a continuous median dark line, the extension of the dark ground color of the flanks onto the ventrals, the darker coloration of the flanks with respect to the stripes surrounding the median dark line, the relative length of the capitulum and sulcus spermaticus, and the high number of hemipenial spines suggest that Rhadinaea nuchalis may be closely related to R. hesperia (
The congeners geographically closest to Rhadinaea nuchalis outside the R. decorata group are R. omiltemana and R. taeniata, members of the R. taeniata group. They differ from R. nuchalis by having more subcaudals in males; the dark ground color of the flanks usually not reaching the ventrals, except for some individuals of R. taeniata in which case the color is faint (see Comparison); a broad (involving at least five dorsal scale rows) dorsal stripe darker than the flanks (median dark line flanked by two stripes paler than the flanks and occupying only the vertebral row and the innermost portions of adjacent scale rows in R. nuchalis); and a relatively small capitulum, comprising between two-sevenths and two-fifths of the length of the sulcate side of the hemipenis (capitulum comprising approximately half of length of the sulcate side in R. nuchalis).
The Sierra Madre del Sur of Guerrero has received scant attention from herpetologists and most expeditions have focused on the central region of the state, particularly in the Chilpancingo region (i.e.
Support for fieldwork in which comparative material was collected was provided by a grant from the Dirección General de Apoyo al Personal Académico, Universidad Nacional Autónoma de México (PAPIIT-IN 221016) to Uri O. García-Vázquez. We thank Herp.mx and Biodiversa A.C. for assistance in the field and for donating the paratype, Ian G. Brennan for reviewing our manuscript for proper use of English, Jonathan A. Campbell and Robert C. Jadin for commenting on preliminary versions of this manuscript, and Luis Canseco Márquez and Ricardo Palacios Aguilar for sharing relevant literature. Fieldwork was conducted under a collecting permit issued to Uri O. García-Vázquez by the Secretaría de Medio Ambiente y Recursos Naturales (permit number FAUT-0243).
Specimens examined