Scolecophis semiannulata, (Baird and Girard 1853)

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 : 968-970

Sonora semiannulata ( Baird and Girard 1853)

Sonora semiannulata Baird and Girard 1853:117 . Holotype: USNM 2109. Type locality: ‘Sonora, Mexico’. The type specimen was collected by John H. Clark during the USA and Mexico Boundary Survey that occurred between 1848 and 1855 ( Goetzmann 1958; James 1969) and described by Spencer F. Baird and Girard (1853). Stickel (1943) assigned the type locality to the Santa Rita mountain range of southern Arizona, based on historical records from the expedition. However, this locality was in the Mexican state of Sonora prior to the Gadsden Purchase in 1854. While Baird and Girard seem to attribute the collection to James D. Graham but the preface specifies that the collector was John H. Clark ( Baird and Girard 1853; Degenhardt et al. 1996). The collection date is unknown ( Frost 1983b), but was likely in 1851 or 1852, the only two years that Graham was present during the survey.

Contia isozona Cope 1866:304 . Holotype: The holotype is in the USNM 11417 . Type locality: Arizona, Ft. Whipple.

Contia episcopa isozona Cope 1880:21

Chionactis episcopus isozonus Cope 1900

Chionactis isozonus Richardson 1915:426

Sonora semiannulata semiannulata Stickel 1938:185

Sonora semiannulata blanchardi Stickel 1938:185. Holotype: University of Michigan Museum of Zoology ( UMMZ) 83122. Type locality: ‘north-eastern slopes of the Chisos Mountains , Brewster County, Texas’.

Sonora semiannulata gloydi Stickel 1938:186. Holotype: University of Michigan Museum

of Zoology (UMMZ) 83754. Type locality: ‘ Bright Angel Trail , Lower Sonoran Level of the

Grand Canyon, Grand Canyon National Park, Arizona’.

Sonora miniata miniata Stickel 1938:187 . Holotype: Chicago Academy of Sciences 5139. Type locality: ‘ 2 miles north-west of Mesa, Arizona’.

Sonora miniata linearis Stickel 1938:189. Holotype: San Diego Museum of Natural History ( SDNHM) 2013. Type locality: ‘ Seeley , Imperial County, California’.

Sonora semiannulata semiannulata Stickel 1943:119

Sonora semiannulata isozona, Stickel 1943:120

Sonora semiannulata linearis, Stickel 1943:121

Sonora semiannulata blanchardi, Stickel 1943:121

Sonora bancroftae Klauber 1943:69 . Holotype: San Diego Museum of Natural History

(SDNHM) 3077. Type locality: ‘ San Jorge, Lower California, Mexico’ .

Sonora semiannulata semiannulata Frost and VanDevender 1979:6

Sonora semiannulata Frost 1983b :333.1

Diagnosis

This species is distinct from S. 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 be potentially confused with S. semiannulata , S. mosaeri , S. mutabilis and S. michoacanensis . 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) and Frost (1983a, 1983b) to synonymize many different species and subspecies into S. semiannulata . However, our genetic data show clear reciprocal monophyly of S. episcopa , S. taylori , S. mosaueri and S. semiannulata . Perhaps the best way to distinguish S. semiannulata from S. episcopa , S. mosaeri , S. mutabilis or S. michoacanensis 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 ovalshaped saddles. There are no other consistent meristic or qualitative characters that seem to separate these species, despite deep evolutionary divergences.

Variation

Along with S. episcopa , S. semiannulata 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. 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. Some individuals that are found in west Texas have distinctively grey crossbands, rather than the normal black crossbands.

Distribution

Sonora semiannulata has an extensive geographic range, from Oregon and California in the west to Texas and New Mexico in the east ( Figure 3 ). All of the Sonora subgenus material from Idaho, Oregon, California, Utah, Nevada and Arizona in the USA and both Chihuahua and Sonora in Mexico is unequivocally S . semiannulata. The only records of S . semiannulata in Texas are from along the Rio Grande in extreme southern Brewster and Presidio counties and throughout El Paso County . The situation in New Mexico is more complex, with populations in the north-east of the state assignable to S . episcopa and those in the south and west to S. semiannulata , but the precise contact zone is unknown. Populations of S . semiannulata species group material in extreme northern Baja California in Mexico are also likely S . semiannulata, although we have no genetic information for these populations.

Remarks

Despite the similarity in appearance and proximity of geographic ranges, we have not uncovered any evidence of sympatry or hybridization among S. semiannulata or S. episcopa . 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.