08/21/2015 These Lizards Don’t Lounge Around

Lizard head

This close-up of the Texas Spotted Whiptail shows its pinkish throat. A pink throat and a white belly indicate that this specimen is a female. Robert Benson Photo.

 

08/21/2015 – These Lizards Don’t Lounge Around

I had been seeing these 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 had the feeling it was checking to see if it really needed to keep running.

Because of their longitudinal stripes, and speediness, I decided these lizards were Six-lined Racerunners. Looking them up in my new field guide, Texas Lizards (2015) by Troy D. and Toby J. Hibbitts, I learned that ‘stripes and speed’ were not enough to identify lizards to species. There is a whole group of swift, lined lizards known as the whiptails and racerunners. To be sure of my identification, I needed to count the stripes and scales and to look at the color of the belly. In other words, I needed to have a lizard in hand.

For me, catching a racerunner was out of the question. The Hibbitts brothers say that “Lizards can often be collected by hand, provided one has good hand-eye coordination.” Oops. They go on to 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. 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 monofilament line and attach it to the end of a telescoping fishing pole. Then you approach the lizard with the pole extended and slip the loop around the lizard’s neck. Jerk the pole upward so the lizard is dangling in mid-air, and then quickly extract the lizard from the noose. The Hibbitts said this technique works well for big-headed lizards. However, they went on to say that the narrow-headed lizards (like racerunners and whiptails) can wiggle out of the noose, unless you have a “partner” ready to grab it.   I gave up on the noose idea.

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. Also notice its long orange-colored tail. These lizards are common in South Texas. Robert Benson Photo.

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. Also notice its long orange-colored tail. These lizards are common in South Texas. Robert Benson Photo.

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 wall of the chicken coop. 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 could see it had seven light stripes and in the dark background between the stripes there were light-colored spots. 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.

Where their ranges overlap, the Texas Spotted Whiptail and the Six-lined Racerunner can hybridize. Apparently, 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 of the female hybrid lizards are capable of parthenogenesis. That is, their eggs can develop without fertilization. The eggs develop into females that are genetic clones of their mother. If these females also reproduce by parthenogenesis, then a line of all-female lizards is produced. 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 hybridization of a Texas Spotted Whiptail and a Six-lined Racerunner.

Even though the eggs develop without fertilization, it seems that the lizards in these all-female species still need to have courtship behavior and pseudo-copulation in order 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, and then she becomes 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 nice 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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