New record and range expansion of Masticophis lateralis ( Hallowell , 1853 ) ( Squamata , Colubridae ) into western Baja California Sur , Mexico

A specimen of Masticophis lateralis (Hallowell, 1853) was found and photographed in the outskirts of San Juanico Bay, Baja California Sur, Mexico. This record fills in a gap of the distribution of this species along both coasts of Baja California Sur.


Introduction
Masticophis (Baird & Girard, 1853) is a relatively small genus (11 species) of harmless colubrid snakes (Colu bridae, Colubrinae), whose distribution ranges from the southern United States to northern South America (Pow ell et al. 2016).Distinctive characteristics of the genus include a slender long body, a bellshaped elongate fron tal scale, and dorsal scales arranged in 13 rows (Wil son 1996).The California Whipsnake or Striped Racer, Masticophis lateralis (Hallowell, 1853), is a fairly com mon, fastmoving, mediumsized diurnal species with a total length of 90-152 cm (Wilson 1996, Uetz 2012).This species has contiguous distribution from Trinity County, California, west of the Sierra Nevada Moun tains to northwestern Baja, at altitudes between 0-2250 m (Bogert 1930, Jennings 1983, Grismer and Marhdt 1996, Wilson 1996, Grismer 2002).Habitat preferences for this species varies considerably, including along the California coast and in the foothills, the chaparral of northern Baja, mixed deciduous and pine forests of the Sierra de Juárez, and deserts and canyons of Sierra San Pedro (Grismer and Marhdt 1996, Grismer and McGuire 1993, Wilson 1996, Grismer 2002).Masticophis aurigu lus (Cope, 1861), M. fulginosis, andM. barbouri (Van Denburgh &Slevin, 1921) are sympatric in some regions of Baja California Sur (Uetz 2012).Although this species is also found within isolated populations south of Cañon de los Reyes to the north of La Paz (Jennings 1983, Gris mer 2002), we report a new record of this species extend ing to the western side of the peninsula.

Methods
While exploring the foothills east of San Juanico Bay, Baja California Sur, Mexico (Fig. 1) during a 10day long field course hosted by the Islands and Seas Field Station, a single individual of M. lateralis was found climbing through the branches of a Colubrina viridis (M.E.Jones) M.C.Johnst.(family Rhamnaceae) within a ravine per pendicular to a cliff face.The specimen was captured by hand and made no attempts to bite when handled.The snake appeared to be in good overall condition although its tail was quite blunt, which indicates a previous loss of the tail tip.The specimen was not collected because there was no collection permit.However, the external anatomy and insitu environment of this specimen were documented with photographs and the snake was identi fied unambiguously (Figs 2, 3).The specimen was released after identification.This region has previously been sur veyed during 2016 and 2017 and only Masticophis fulgi nosis (Cope, 1895) was observed during those trips.Identification.The specimen was identified as M. later al is based on the following diagnostic characters: having 8 supralabial scales; 17 dorsal midbody scale rows; a dark olivegrey dorsum; a single white/cream lateral lon gitudinal stripe 2 scales in width on scale rows 3 and 4 counting from the venter; and a mottled greywhite pat tern along the supralabials anterior to the eye (Figs 2, 3).This specimen had an additional mottled stripe from the supraocular to the prenasal, wrapping around the rostral scales, and a pink venter which faded to white anteriorly (Figs 2, 3).

Masticophis
The Species identification was initially based on information by Grismer (2002), with additional infor mation by Riemer (1953), Grismer (1990), andWilson (1996).This specimen was differentiated from M. aurig ulus and M. barbouri in having the roughly square loreal scale, a faint temporal spot was present, presence of mot tling as previously described, and primary middorsal stripes on the third and fourth scale rows terminating at the tail (Grismer 1990).Masticophis aurigulus and M. fuliginosis possess a loreal scale which is twice as high as it is long, a prominent temporal spot, no ventral mot tling, a clear white line along the preocular, prenasal, postnasal and rostral scales, and the middorsal stripe along the third and fourth dorsal scale rows terminates twothirds down the body (Grismer 1990).Masticophis lateralis is differentiated from M. fuliginosis by obvi ous color differences in which M. fuliginosis has a light brown and black mottled dorsum becoming darker at the head with no prominent lateral stripe.

Discussion
Studies have demonstrated considerable flexibility in thermoregulatory behavior in M. lateralis as well as distinct species complexes within Masticophis due to vicariance events and barriers of isolation within North America (Hammerson 1979, O'Connell et al. 2017).This new record expands the range of M. lateralis into the westward plain desert of Baja California Sur; this is a new isolated environment compared to former records.Even though individuals of M. lateralis have been collected near La Paz (Fig. 1), our finding fills the distributional gap of this species from the Sarcocaulescent shrubland lateralis (Hallowell, 1853) New records.(Fig. 1.) Mexico: Baja California Sur: ca 15 km E of San Juanico Bay (26°19.187ʹN, 112°23.904ʹW; WGS84; alt.295 m), observed by Aaron Goodman, Lau ren Esposito, W. Brian Simison, Eric Stiner, Perla Ponce, Ashley Sauer & Sara Ruane, 29 June 2018 (09:45 h).

Figure 2 .
Figure 2. Masticophis lateralis from San Juanico Bay, Baja California Sur, Mexico.A. Right lateral head view.B. Left lateral head view.C. Ventral head view.D. Lateral body view.Photographs by S. Ruane.

Figure 3 .
Figure 3. Masticophis lateralis individual from San Juanico Bay, Baja California Sur, Mexico.A. Ventral body view B. Dorsal body view.C. Closeup of ventral head and body.D-F.Locality and habitat where individual was found.Photographs by S. Ruane and W.B. Simison.