Sonora episcopa ( Kennicott 1859 )

Cox, Christian L., Davis Rabosky, Alison R., Holmes, Iris A., Reyes-Velasco, Jacobo, Roelke, Corey E., Smith, Eric N., Flores-Villela, Oscar, McGuire, Jimmy A. & Campbell, Jonathan A., 2018, Synopsis and taxonomic revision of three genera in the snake tribe Sonorini, Journal of Natural History 52 (13 - 16), pp. 945-988 : 967-968

Sonora episcopa ( Kennicott 1859)

Lamprosomum epsiscopum Kennicott 1859:22. Holotype: The syntypes are in the US National Museum (USNM) 2042 and 2045, specimen 2042 was designated the lectotype by Stickel (1938). Type locality: The type locality is listed as ‘Eagle Pass’, Maverick County, Texas. However, Stickel (1943) speculates that this may have been only an intermediate shipping locality, rather the collection locality.

Contia episcopa episcopa Cope 1880:21

Contia episcopa torquata Cope 1880: 21 Holotype: Syntypes are in the Academy of Natural Sciences in Philadephia 10995 and 10996. Type locality: ‘North-western Texas’.

Contia torquatus Boulenger 1894 ;265

Chionactis episcopus Cope 1900:937

Chionactis episcopus episcopus Cope 1900:938

Chionactis episcopus torquatus Cope 1900:939

Contia nuchalis Schenkel 1901:162

Sonora episcopa van Denburgh and Slevin 1913b:412

Sonora episcopa Stickel 1938:184

Sonora episcopa episcopa Stickel 1943:121

Sonora semiannulata episcopa Frost and VanDevender 1979:6

Sonora semiannulata Frost 1983b :333.1

Diagnosis

This species is distinct from Sonora cincta , S. fasciata , S. straminea , S. aemula , S. annulata , S. occipitalis and S. palarostris by the lack of rostral or caudal adaptations. Sonora episcopa can potentially be confused with S. semiannulata and S. taylori , both of which with it is either sympatric or narrowly allopatric. The S. semiannulata species group has been historically difficult to define using morphological characteristics, and in fact it was this lack of clear colour pattern or meristic characters delimiting species that led Frost and VanDevender (1979) to synonymize S. episcopa with S. semiannulata . However, our genetic data show clear reciprocal monophyly of S. episcopa , S. taylori and S. semiannulata . Perhaps the best way to distinguish S. episcopa from S. taylori and S. semiannulata is by geographic range (see below). Beyond geographic range, the expression of colour pattern in morphs that express black crossbands seems to distinguish S. episcopa and S. semiannulata . Sonora semiannulata generally has rectangular black crossbands, while S. episcopa has oval-shaped saddles. Besides geographic range, Dixon and Werler (2005) suggests that S. episcopa can be distinguished from S. taylori based upon 14 or 15 midbody scale rows (13 in S. taylori ).

Variation

This is one of the most spectacularly variable snakes in North America and is one of the most variable in the genus Sonora. Populations can be polymorphic for the presence or absence of black crossbands, a red, longitudinally oriented dorsal stripe, a single nuchal band, or a black cap on the head. Some individuals have a longitudinal stripe that does not have any red pigment, but lacks maculation that is present on the remaining dorsal scales. Banded individuals can vary greatly in appearance, with bands ranging in expression from complete saddles to broken bands or symmetrical dorsolateral dots. Bands often change in appearance from the head to the tail, becoming broken or absent on the tail and distal surfaces of the body. Ground colour can range from grey, to tan, to brown, to russet or red. The presence of maculations on the scales can vary tremendously, ranging from a barely detectable dot to a large marking that encompasses most of the scale.

Distribution

Sonora episcopa has an extensive geographic range, from the glades of central Missouri and northern Arkansas to the tablelands of Colorado and New Mexico ( Figure 3 ). All of the subgenus Sonora material from Kansas, Colorado, Oklahoma, Missouri, and Arkansas is unequivocally S. episcopa . All populations of the subgenus Sonora in Texas north and west of the Balcones escarpment in Texas are S. episcopa , except for those along the Rio Grande in extreme southern Brewster and Presidio counties and throughout El Paso County (which are S. semiannulata ). Generally, specimens from north-eastern New Mexico are S. episcopa and those from south-western New Mexico are S. semiannulata , but the precise contact zone between these lineages is unknown. Any populations south and east of the Balcones escarpment are S. taylori .

Remarks

The precise range boundaries of S. episcopa , S. taylori and S. semiannulata are not well known, although we have not yet recovered any examples of hybridization or introgression between these lineages. This species is in the subgenus Sonora with S. episcopa and S. taylori .

Figures

Figure 3. Map of the geographic distribution from IUCN and georeferenced occurrence records from GBIF (grey crosses) for the subgenus Sonora, including S. episcopa, S. semiannulata and S. taylori. The top of the map has images of the uniform (a), banded (b), striped (c), and mimetic (d) morphs of Sonora episcopa. The side panel depicts S. taylori without (e) and with (f) a black cap on the head. The bottom panel depicts the uniform (a), banded (b), striped (c), and mimetic (d) morphs of S. semiannulata. Photos by C. L Cox (a–f, h) and A. R. Davis Rabosky (g, i, j). Colours of circular points on the map correspond to the phylogenetic tree in Figures 1 and 2.