Aspidoscelis costatus, also known as the western Mexico whiptail, is a species of whiptail lizard endemic to Mexico, including Guerrero, Morelos, and Puebla in southern Mexico, as well as other Mexican states. Its range spans both temperate and tropical habitats, and even densely populated urban areas.Maslin, T.P., and D.M. Secoy. 1986. A checklist of the lizard genus Cnemidophorus (Teiidae). University of Colorado Museum, Contributions in Zoology 1:1–60 Its common name, the Western Mexico Whiptail, can easily be confused with the Western Whiptail, which refers to a different lizard, Aspidoscelis tigris.
A small lizard, up to only 4 inches SVL (snout to vent length), this striped lizard has a pointed snout, a slender body, a pair of long hind legs, and an extremely long tail. Its whip-like, tapering tail, if not recently shortened from caudal autotomy (self-amputation of the tail), may be more than two times its SVL. Therefore, although this dwarf lizard has a short SVL length, it can reach a total length of close to 1 foot, tail included, giving the false impression that it's a long lizard. When the lizards fight to maintain territory or compete for mates, they whip their long tails around, therefore its common name is the whiptail lizard. They are often found under low desert scrubs, rocks, or nosing around leaf litter. Whiptails are diurnal but mostly solitary creatures, except during the breeding season, when males start accompanying females around.
Aspidoscelis are not sit-and-wait ambush predators. Instead, they are non-territorial, active "widely foraging" lizards. They move quite frequently, and almost incessantly, in short gaits and at a frenetic pace. Foraging is their primary activity throughout the day. They are aseen busy probing with their snouts under leaf-litter, in crevices, scratching in the ground, or digging furiously through piles of accumulated debris. When they are on the move under plants or through leaf-litter, their jerky bouts of start-stop movement create unique crunching sounds from disturbed dry leaves. When Aspidoscelis must run away from threats, they run fast at top speeds of , and appear to keep their tails behind the body in a straight line similar to a galloping crocodile, running across barren open areas to reach the cover of dense shrubs.
There are limited reports about Aspidoscelis costatus, simply because the nomenclatural changes for the genus Aspidoscelis was recommended by T.W. Reeder et al. as recent as 2002.REEDER, T.W.; CHARLES J. COLE AND HERBERT C. DESSAUER 2002. Phylogenetic Relationships of Whiptail Lizards of the Genus Cnemidophorus (Squamata: Teiidae): A Test of Monophyly, Reevaluation of Karyotypic Evolution, and Review of Hybrid Origins. American Museum Novitates 3365: 1-64 Prior to that, this species was under the genus Cnemidophorus, in the family Teiidae. As a matter of fact, the seminal documentations of this species, particularly of some of its subspecies, go back to as early as 1959, albeit under different taxa.
Aspidoscelis costatus has 8 subspecies, all of which are endemic to Mexico.
Taxonomy, history, and etymology There are several genus of whiptail lizards in the family Teiidae. The genus of Aspidoscelis lizard was originally under the genus Cnemidophorus until 2002, when Reeder proposed that there are significant divergent characters, including morphological and genetic differences, for many species that warrant regrouping.
Morphological deviations between Cnemidophorus and Aspidoscelis are detailed in the Physical Description section.
Nomenclatural changes of genus unavoidably causes confusion and difficulties for researchers.Aldo Gómez-Benitez, et al. (2020) Color Pattern and Body Size Variation in live Aspidoscelis costatus costatus (Squamata: teiidae) From a Protected enclave in Southern mexico. Herpetological Conservation and Biology 15(2):335–349. To illustrate this dramatic change, the subspecies Aspidoscelis costata zweifeli was named Cnemidophorus sacki zweifeli when it was first reported by Duellman et al. in 1960.Duellman, W. E. 1960. A new subspecies of lizard, Cnemidophorus sacki, from Michoacan, México. Univ. Kansas Publ. Mus. Nat. Hist. 10: 587-598. In this seminal 1960 publication, Duellman states "In recognition of the important contributions to the systematics of the genus Cnemidophorus made by Dr. Richard G. Zweifel, I propose that the subspecies of Cnemidophorus sacki in the Tepalcatepec Valley be named as follows: Cnemidophorus sacki zweifeli, a new subspecies."
That subspecies is the nowadays Aspidoscelis costata zweifeli. The subspecies name of "zweifeli" is still kept to in honor of Dr. Zweifel, an American herpetologist, who contributed immensely to the documentation of the nowadays Aspidoscelis costata species. Out of the eight costata subspecies, Dr. Zweifel reported/named five of them.Zweifel, Richard G. 1959. Variation in and distribution of lizards of western Mexico related to Cnemidophorus sacki. Bull. Amer. Mus. Nat. Hist. 117 (2): 57-116Cope, E.D. 1878. Tenth contribution to the herpetology of Tropical America. Proc. Amer. Philos. Soc. 17: 85-98 Gadow, H. 1906. A contribution to the study of evolution based upon the Mexican species of Cnemidophorus. Proc. Zool. Soc. London 1906: 277-375 (+ maps)
Physical description Western Mexico Whiptails have scaly skin with stripes, bowed legs, and pointed snout. It does not have any vertebral crests (spines).
Western Mexico Whiptails are striped lizards. They have multiple straight dorsal stripes with varying color patterns on grey, brown, or black ground, often mixed with pale-hued spots, or bar-like pattern. Ventrally, the lizard has abdominal, and pelvic regions that are either cream colored, or sometimes light to medium blue, sometimes even red in the pelvic region. The gular (throat) region can have increased intensity of coloration that ranges from pink to red. These colors and pattens are subject to individual variation, ontogenetic (juvenile, adult) variation, sexual (male, female) dimorphism, and even seasonal changes.Sexual dimorphism and natural history of the Western Mexico Whiptail, Aspidoscelis costata (Squamata: Teiidae), from Isla Isabel, Nayarit, Mexico Raciel Cruz-Elizalde, Aurelio Ramirez-Bautista, Uriel Hernandez-Salinas, Cynthia Sosa-Vargas, Jerry D. Johnson and Vicente Mata-Silva
Males progressed through stages of dorsal pattern changes from pale stripes, dark intervening fields, no spots to spots, and diverse pale configurations set in a black ground color. Females in this population (females representing all stages of color patterns) showed similar changes but did not lose striping as they grew. Ontogenetic changes in ventral color patterns were also apparent, with males becoming more colorful than females.
Morphological deviations between Cnemidophorus and Aspidoscelis refer to the fact that Aspidoscelis has (1) forked tongue structure posteriorly (2) no basal tongue sheath that lots of lizards have (3) smooth ventral scutes (enlarged scales in the belly) (4) eight rows of ventral scutes at midbody (5) no anal spurs in males (anal spurs are used by males to stimulate and position females during mating) (6) mesoptychial scales (scales in the gular/throat region of the lizard) abruptly enlarged (7) three parietal scales (enlarged scales on the crown, as often seen in snakes), and three or four supraocular scales (enlarged scales above the eyes) on each side.
Like crocodiles, Western Mexico Whiptail have nictitating membrane eyelids, also called the third eyelids, which is a translucent membrane that, when the lizard blinks, is drawn from the inner corner of the eyes across the eyeball surface, while its upper and lower eyelids remain open. This allows moistening, protection of eye surface, and a certain degree of vision while blinking.
Distribution and habitat
Most species of whiptail lizards prefer dry climates and seek out habitats in deserts. Therefore, many species of whiptail lizards are found throughout Sonoran Desert, spanning northwestern Mexico and southern California, a region with sparse vegetation, such as sagebrush, low desert scrubs, grasslands, woodlands and pine forests.
Similarly, Aspidoscelis costatus prefers natural habitats such as savanna, and shrubland in brushy, broken country. But they also extend their habits into open areas of tropical low deciduous forest and thorn forest, low spiny sub-evergreen forest and medium sub-deciduous forest. spanning both temperate and tropical climates in western and southwestern Mexico. Since considerable habitat clearance has taken place for intensive agriculture or human settlements, we are starting to see urban population of Aspidoscelis costatus, even in densely populated cities, at least for Aspidoscelis costatus costatus, which is a subspecies of Western Mexico Whiptail lizard, commonly named Balsas Basin Whiptail.
One research paper suggested that global warming has affected the habitats of Western Mexico Whiptail lizard. Some climatic groups of Aspidoscelis costatus costatus are exhibiting reductions and others exhibiting expansions in their distribution. Redistribution to higher elevation may potentially occur in response to climate warming.The Impact of Global Warming on the Range Distribution of Different Climatic Groups of Aspidoscelis costata costata December 2012 ZOOLOGICAL SCIENCE 29(12):834-843
Ecology and behavior Western Mexico whiptail are striped lizards, which tend to be active foragers, constantly moving around than lizards with cryptic patterns.Li, S.R., X. Hao, Y. Wang, B.J. Sun, J.H. Bi, Y.P. Zhang, F.J. Janzen, and W.G. Du. 2018. Female lizards choose warm, moist nests that improve embryonic survivorship and offspring fitness. Functional Ecology 32:416–423. It records very high moves per minute or percent time moving values.
All whiptail lizards in the genera Aspidoscelis are active at body temperatures between .
Since they need the sunlight to heat their bodies up for activities, whiptails adjust their activity to take advantage of heat sources. Larger whiptails are present in shaded regions more so that their bodies don't overheat. Smaller whiptails can heat and cool their bodies quickly so they are more comfortable in open areas even in the summer.
Aspidoscelis are not sit-and-wait ambush predators. Instead, they are active foragers. They move quite frequently, and almost constantly, in short gaits and at a frenetic pace. Foraging is their primary activity throughout the day.
When they are on the move under plants or through leaf-litter, their jerky, start-stop movements create unique crunching switch sounds from disturbed dry leaves.
When Whiptails must run away from threats, they run fast at top speeds of , and appear to keep theirs tail behind the body in a straight line. They do not whip their tails when they run.
Predators This species and virtually all Aspidoscelis species are preyed upon by snakes and predaceous birds. The active mode of foraging, constantly moving behavioral pattern of whiptail lizards may subject them to a high frequency of predation attempts by diurnal predators.Vitt, L. J., and R. D. Ohmart. 1977. Ecology and reproduction of lower colorado river lizards: ii. Cnemidophorus tigris (Teiidae), with comparisons. Herpetologica 33:223-234.
Such predators include owls, eagles, hawks, coyotes, foxes, bobcats, virtually all species of snakes large enough to swallow them, and even larger lizards such as collared lizards, long-nose leopard lizards.
Many species of bird of prey take whiptails for diet. It was found that whiptail lizards make up a large percentage of the food items consumed by roadrunners (a largely terrestrial, speedy running bird).