Western mexico whiptail
Aspidoscelis costatus, also known as the western Mexico whiptail, is a species of whiptail lizard endemic to Mexico, including Guerreto, 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. 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 18 mph (29 kph), 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. 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.
The subspecific name, zweifeli, is in honor of American herpetologist Richard G. Zweifel.
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.
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.
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.
Western Mexico whiptail are striped lizards, which tend to be active foragers, constantly moving around than lizards with cryptic patterns. 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 37 and 40 °C (99 and 104 °F)
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 18 mph (29 kph), and appear to keep theirs tail behind the body in a straight line. They do not whip their tails when they run.
About one third of whiptail lizards are parthenogenic, which is asexual reproduction by development from an ovum without fertilization, essentially cloning, but with strategies to create diversities. This is not the case with Western Mexico Whiptail lizard, which is a bisexual species. They have sexual and dioecious (having the male and female reproductive organs in separate individuals) reproduction. Aspidoscelis costatus males, like the majority of other lizards, reproduce through cloaca, which is an orifice, sort of semicircular-shaped, located in the ventral side (underside) of the tail base of the lizard, just distal to its hindlegs. Digestive wastes like urine and feces are eliminated through cloaca. And the male reproductive organs, called hemipenes, which come in a bilateral pair, are held inverted within the cloaca when not in use. During copulation, the pair of hemipenes becomes evert, and sperm are ejaculated. Usually only one hemipenis is used at a time. Female also use cloaca for elimination of digestive waste and for reproduction. For female lizards, the cloaca is the external genital opening for the genital canal, equivalent to vagina in mammals. Copulation is performed through cloacal kiss, in which the male and female press their cloacas together as the male discharges sperm. Unlike Cnemidophorus males, Aspidoscelis costatus males do not have anal spurs, or pelvic spurs, which are vestigal limbs used by males to stimulate and position females during mating.
Female reproductive cycle was markedly seasonal, recorded from April (end of the dry season) through August (middle of the rainy season). And this is in regardless of climate. Same timing of female reproduction period is reported for populations inhabiting different climate zones, including semi-humid warm climate to temperate-zone, to higher-elevation. Reproduction is associated with day length rather than with temperature.
Aspidoscelis costata lizards exhibit associated reproductive cycles (also called synchronic reproductive cycles), in which males and females reach the maximum sperm production, mating, and ovulation activities during the same period. However, male A. costatus reaches reproduction maturity at a smaller SVL length than female (about 2 inches for male versus 2.5 inches for female).
In 2007, Aspidoscelis costatus are listed as “Least Concern”, following IUCN criteria.
According to Wilson et al. (2013), A. costatus scores a medium environmental vulnerability score principally due to its restricted distribution, and threats from intensive agriculture or human settlements., considerable habitat clearance and environmental disturbance in localized areas for human-modified habitats.
