Those speedy, little lizards you see are spotted whiptails

Look closely at the dark background between the light-colored stripes and you can see the spots that give this lizard its name: Texas Spotted Whiptail. The pink throat and a white belly indicate that this specimen is a female. These lizards are common in South Texas. (Photo by Robert Benson)

have been seeing fast little lizards in my yard all summer. I could see that they were striped, but I could never get close enough to tell much more about them. 

If I approached one closer than three feet, the lizard would run off, but not very far. After it had gained a lead on me of about ten feet, it would stop, turn, and eyeball me. I felt it was checking to see if it needed to keep running. Because of their longitudinal stripes and speediness, I decided these lizards were six-lined racerunners. 

However, when I consulted my field guide, Texas Lizards (2015) by Troy D. and Toby J. Hibbitts, I learned that ‘stripes and speed’ were insufficient to identify lizards to species. Swift, striped lizards are known as the whiptails (or racerunners), and nine species can be found in Texas. 

To ensure my identification, I needed to count the stripes and scales and look at the belly’s color. In other words, I needed to have a lizard in hand. 

The Hibbitts brothers say, “Lizards can often be collected by hand, provided one has good hand-eye coordination.” Oops. They say that when the lizard is in range, “quickly and adroitly reach out and snatch the lizard.” 

Easy for them to say! Even the Hibbitts brothers note that “capture is greatly assisted by working with a partner.” 

Troy and Toby have been catching lizards together since they were little boys, and I didn’t stand a chance of getting one by myself. 

Fortunately, there is a tool you can make to help you catch those particularly wary lizards. It is called a lizard noose. You construct a sliding noose out of a monofilament line and attach it to the end of a telescoping fishing pole. Then you approach the lizard with the rod extended and slip the loop around the lizard’s neck. Jerk the rod upwards sharply. 

While the lizard dangles in mid-air, you extract the lizard from the noose. The Hibbitts said this technique works well for big-headed lizards. However, they said that the narrow-headed lizards (like racerunners and whiptails) could wiggle out of the noose unless you have a “partner” ready to grab it. I gave up on the noose idea. 

As it turned out, I did catch one of these speedy lizards, after all. And I did have a partner. My dog had cornered something next to the chicken coop wall, and I went to see what she had, and there it was: a racerunner. 

I quickly and adroitly snatched the lizard before it could run away. (I think it was exhausted.) With the lizard in hand, I counted seven light stripes on a dark background, and there were light-colored spots between the stripes. It was not a Six-lined Racerunner but a Texas Spotted Whiptail. They both belong to the same genus: Aspidoscelis. They are very closely related species, and both can be found here, although Aspidoscelis gularis, the whiptail, is much more common in this part of Texas.

The Texas Spotted Whiptail and the Six-lined Racerunner can hybridize where their ranges overlap. The cross is viable (much like a horse and donkey cross produces a mule). The trouble comes when the hybrid lizard (again like a mule) tries to breed. 

Because the chromosome pairs in the hybrid’s gamete-making cells (ovaries and testes) don’t quite match up, viable eggs and sperm rarely form. The hybrid lizard is doomed to a life without reproduction. Or is it? 

Recent studies have shown that some female hybrid lizards are capable of parthenogenesis, meaning their eggs develop into embryos without fertilization. During egg formation (meiosis), the lizard’s gamete-making cells gain twice the usual number of chromosomes. 

Thus, the eggs develop a complete chromosome count. The resulting embryos are all female but with the genetic variety (known as heterozygosity) rivaling that of sexually reproducing lizards. When these females also undergo parthenogenesis, their offspring is a line of all-female lizards. This lineage is referred to as an “all-female species” with typical distinguishing characteristics of a species (except for having no males). 

There are at least four all-female species of whiptails in Texas. Two of them, the Chihuahuan spotted whiptail and the Laredo striped whiptail, have the Texas spotted whiptail as one of their parents. DNA studies have shown that the Laredo striped whiptail came about through the hybridization of a Texas spotted whiptail and a six-lined racerunner. 

Even though the eggs develop without fertilization, the lizards in these all-female species still need courtship behavior and pseudo-copulation to initiate the development. Scientists have observed that these lizards “engage in behaviors quite similar to those seen in sexually reproducing species.” 

The lizards in any population undergo hormonal cycling. So a lizard with a high estrogen level will act as a female while a low-estrogen individual behaves like a male. 

A male-acting lizard will bite the female-acting lizard just in front of the hips and curl “his” body around the other lizard so that their vents meet. Somehow this behavior stimulates the eggs to begin dividing and developing in the female-acting lizard. After she lays her eggs, her estrogen levels drop, becoming a male-acting individual. 

These lizards “alternate between male-like and female-like roles throughout the reproductive season.” Pretty crazy, right? 

I again examined my captive whiptail. It was a female; there was no blue color on the belly. But she didn’t have any of the markings of one of the all-female species. She was just a healthy specimen of a Texas Spotted Whiptail. When I let her go, she turned around and blinked at me. It was as if she was asking, “What was that all about?”

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