New Records for Reptiles from Chihuahua, Mexico, with Comments on Sympatry between two Species of Cnemidophorus

Abstract

NEW RECORDS FOR REPTILES FROM CHIHUAHUA, MEXICO, WITH COMMENTS ON SYMPATRY BETWEEN TWO SPECIES OF CNEMIDOPHORUS.-The species mentioned below were collected during a brief collecting trip in the Mexican state of Chihuahua in July, 1962. Numbers refer to specimens in the collection of Ralph W. Axtell (RWA) or Robert G. Webb (RGW). We thank Hobart M. Smith for information concerning Tantilla atriceps. Cnemidophorus exsanguis Lowe and Cnemidophorus septemvittatus scalaris Cope.-Duellman and Zweifel (Bull. Amer. Mus. Nat. Hist., 123: 198, 1962) wrote that and west of Chihuahua City (the exact areas of contact remain to be discovered) C. s. scalaris is replaced by C. On a previous page, however, (op. cit.: 186) they mentioned the possibility of intergradation between C. exsanguis and C. septemvittatus on the Mexican Plateau. We found the two species sympatric at three localities-12 road mi. NW Cd. Chihuahua (2 scalaris, 2 exsanguis), 12 road mi. NW Est. Bachimba (27 road mi. NW of Meoqui, 7 scalaris, 3 exsanguis), and 10 road mi. NW Est. Bachimba (2 scalaris, 1 exsanguis). The four lizards from the first-mentioned locality are not included in the discussion below because the two exsanguis, presumably gravid, are being kept alive. Lizards from the last two localities are lumped for comparison between the two species. Duellman and Zweifel (op. cit.: 199) mentioned that several specimens of scalaris from near Meoqui, Chihuahua, resembled exsanguis, and, in the field, we initially identified several specimens of scalaris as exsanguis. Our four female exsanguis (RGW 2753-54; RWA 1084, 1086) range from 76 to 86 mm. in snout-vent length and closely resemble some scalaris of corresponding size in having whitish ventral surfaces and dorsal patterns of longitudinal stripes with spots in the dark fields. However, such individuals of exsanguis were distinguished from scalaris in having (1) the pale longitudinal stripes dim and obscure on the neck, often a uniform grayisholive (striping bright and prominent on neck in scalaris), (2) the stripes on back obscure, so that the pale spotting was most prominent (striping as prominent as spotting on back in scalaris), and (3) smudges of dark pigment on the lateralmost row of ventrals (scales whitish in scalaris). In regard to the last-mentioned character, only one of nine scalaris (RWA 1080) resembled exsanguis. Duellman and Zweifel (op. cit.:198) reported an average of 86.5 (82-92) granules at midbody for six specimens of scalaris from Cd. Chihuahua-a number which corresponds to an average of 89.3 (78-99) for seven of our nine scalaris. However, the remaining two scalaris (RGW 2752, RWA 1080) had low counts of 70 and 72, which correspond to those of our exsanguis, averaging 73.0 (72-75). The above-mentioned facts suggest the possibility of gene exchange (perhaps via male scalaris, as no male exsanguis are known) between these two species which we found to overlap approximately 33 airline miles. No differences in habitat preference between the two species were noted. Lizards of both species were collected between elevations of 5000 and 5300 feet in hilly to low mountainous terrain, usually on alluvial outwash fans, but several specimens were collected on steep, talus and boulder-strewn slopes. Vegetative cover was widely spaced and principally mesquite, several species of acacia, creosote bush, and patches of grasses and herbs. Motts of scrub oak occurred only at the locality of highest elevation north of Cd. Chihuahua. Bufo punctatus, Holbrookia texana, Phry-