Morphological Variation In A Population Of The Snake Tantilla Gracilis Baird And Girard PDF Download

"Examination of numerous characters (primarily of head coloration, hemipenes, scutellation, and size and proportions) of more than 750 specimens suggests that Tantilla planiceps, as recognized by Tanner (1966), actually represents four distinct species: Tantilla planiceps (Blainville, 1835), of southern California and Baja California; Tantilla yaquia Smith, 1942, of southeastern Arizona and northwestern Mexico; Tantilla atriceps (Günther, 1895), of southern Texas and northeastern Mexico; and Tantilla hobartsmithi Taylor, '1936' (1937), which is broadly distributed in the southwestern United States and northern Mexico and usually has been considered synonymous with T. atriceps. Synonymies, diagnoses, descriptions, illustrations, range maps, and ecological notes are presented for each of these species. Tantilla atriceps and T. hobartsmithi are sibling species with strikingly different hemipenes. They also are the only species of the complex for which sympatry (in Coahuila) has been documented. Future collecting may well demonstrate sympatry at the periphery of the ranges of T. planiceps and T. hobartsmithi and of T. yaquia and T. hobartsmithi. Analysis of variation indicates that some classical taxonomic characters used previously (e.g., number of ventral scales) are not particularly reliable for distinguishing among species of Tantilla. The best specific characters we found are in anatomy of the hemipenes. Variation in hemipenial features usually is correlated with variation in head coloration. Because T. atriceps and T. hobartsmithi are sibling species, now known to differ consistently only in hemipenial characters, and because they exhibit sympatry at the periphery of their ranges, specific identification of females is a problem that requires additional investigation. Once it appeared that male copulatory organs would provide important, diagnostic characters for the four species formerly assigned to T. planiceps, we examined hemipenes on as many specimens (258) as were reasonably available. These included pertinent type-specimens and outgroup comparisons with T. gracilis, T. nigriceps, and T. wilcoxi; hemipenes of these species are distinctive also, and examples of all are described and illustrated (excepting T. wilcoxi). One problem that remains under investigation is the specific relationship between T. atriceps and southern populations of T. nigriceps. No such problem exists between T. hobartsmithi and T. nigriceps, however, as they differ rather consistently in hemipenes and head coloration, and they are sympatric in the western part of the range of T. nigriceps. We also examined maxillary bones, sex ratio, and karyotypes (including that of T. coronata) in addition to the characters mentioned above. Most of these data are not taxonomically useful, due either to lack of significant variation or lack of comparative data from congeners. A preferred cladogram of phylogenetic relationships of T. wilcoxi, T. planiceps, T. yaquia, T. nigriceps, T. atriceps, T. hobartsmithi, and T. gracilis is presented, as is a key to all species of Tantilla known to occur in the western United States and northern Mexico. The most useful characters for distinguishing species of Tantilla, particularly in North America, appear to be in the hemipenes and head coloration. Hereafter, all taxonomic studies within Tantilla routinely should include examination of hemipenes of the specimens examined. When possible, males should be selected as type-specimens"--P. 203.