Media Credit: Tino Mauricio Brian Dias, a neuroscience graduate student working in the Crews' laboratory, holds a female Whiptail lizard. In nature, all 15 species of Whiptail are female.

In a room within the musky, dimly-lit basement of the J.T. Patterson Laboratories Building, rows of cages containing female Desert Grassland Whiptails line the walls. No males are present, because no males exist.

Former conceptions of societal norms have already been broken by the prevalence of single-parent families. Now, these revolutionary reptiles are redefining gender roles by removing males from the reproductive process entirely.

The Whiptail lizard, Cnemidophorus uniparens, is an all-female species that reproduces through a process called parthenogenesis, which results in offspring genetically identical to the mother.


Unisexual, all-female clones

The idea of females sustaining life and producing new generations without any males may seem impossible, but parthenogenesis makes it a reality for the Whiptail.

Each Whiptail lizard has an ovarian cycle of 21 to 28 days. When two are placed in a cage together, they synchronize their cycles so they are opposite. For 10 to 14 days, one of the females will act male, which means she mounts the other. The remaining Whiptail takes the female role by receiving; then they switch roles.

This process of mounting and receiving is common for reptiles; what is uncommon is that neither Whiptail is ever really male, said Brian Dias, a neuroscience graduate student working in the Crews Laboratory.

UT biology professor David Crews said Whiptails have a bisexual brain.

"I study the neurochemistry of male and female typical behavior," he said. "These show both to stimulate each other."

Because this species reproduces by cloning itself, each member of the species is genetically identical, Crews said.

"They are unisexual, all-female clones," said Crews, who has studied the Grassland Whiptail since 1978. He said only 15 unisexual lizard species exist in nature.

Crews' lab also experiments with lizards collected from the field. Every May, Crews and researchers spend three weeks in the deserts of Arizona and New Mexico collecting 200 Whiptails, which are native to Mexico, New Mexico and Arizona.



Interspecies 'love child'

Though Whiptail lizards are not indigenous to Texas, their female ancestor, the Cnemidophorus inornatus, is. Whiptails are a hybrid of the inornatus and the Cnemidophorus burti, which are sexual species containing both males and females. The Whiptail is the interspecies "love child" of these two lizards. All 15 species of Cnemidophorus that are solely female are a result of hybridization.

Crews said it is still disputed by some whether the inornatus is the female ancestor of the Whiptail. The lab has male and female inornatus lizards to compare their behavior with that of the Whiptails, Dias said, as well as Whiptails of various ages. The Whiptail's lifespan remains unknown, but Crews' lab has several 2-year-old Whiptail lizards.

Dias reached into a cage and grabbed one of the two Whiptails as she tried to scurry away. He held the 2-inch lizard between his fingers, the lizard's face sticking out and her tail, which is longer than the rest of her body, hanging down behind her. Yellow and white stripes run down her back, breaking up her reddish-black coloring.

"These are the babies," Dias said, referring to the Whiptails hatched in the lab this past fall.

Media Credit: Tino Mauricio Two Desert Grassland Whiptail lizards engaged in pseudocopulation.

When lizards are born in a lab, researchers can track their sexual experiences, which may affect the lizards' sexual behavior later in life, Dias said. The lab can also study how a Whiptail reacts when introduced to another lizard if she has or hasn't seen another female or male lizard in the past.

Gripping the neck of a Whiptail lizard firmly between his thumb and forefinger, Dias held her still. The lizard's ovaries had been removed and a testosterone implant was surgically inserted, all part of an experiment to test the effects of testosterone on Whiptails. Dias said the implant had caused her to be more aggressive. If placed in the cage with an intact female - one that still has her ovaries - the implanted female will assume the role of the male and mount the receptive intact female, Dias said.

Crews' lab has also been able to produce male Whiptail lizards by manipulating Whiptail eggs.

The process places an inhibitor on an enzyme called aromatase on the egg. The aromatase

inhibitor lowers the level of the estrogen by causing the conversion of estrogen to testosterone, which prevents the lizard from becoming female, Dias said. This results in the birth of a male Whiptail lizard.

These genetically altered male lizards, called "virago lizards," are unable to mate with female Whiptails because they are triploid animals, which means they have three times the chromosome number of basic animals. This makes mating impossible between the two, Crews said. Though a female Whiptail can mate with a male from a different species, the sperm will not fertilize.



'Parthenogenic turkeys'

Parthenogenesis also occurs in some insects, such as bees and ants, and has been induced experimentally in frogs and turkeys, Crews said.

"The Department of Agriculture spent millions of dollars trying to create parthenogenic turkeys," he said. "Seven parthenogenic turkeys were produced but they were all male so they couldn't reproduce. And that was the end of that research."

Though the creation of parthenogenic turkeys failed, some people believe that parthenogenesis may one day be possible in humans, thanks to advances in technology.

Thomas Savage, an animal sciences professor at Oregon State University, said human parthenogenesis is possible, but unlikely.

"With our technology of biological engineering nothing is impossible," Savage said. "It just will take years to develop."

Savage said that though the study of parthenogenesis began in the mid-1960s, few labs study the process because it went out of favor, because of a question of its practical implications.

"Every few decades some scientists become interested in it and study another aspect of it," Savage said.

But Crews believes the only place this would be possible is in science-fiction books.

According to Crews, his lab is the only lab doing research on this species.

Crews said despite the progress researchers have made, there are still many unanswered questions about the Desert Grassland Whiptail.

"I've been working with this animal for 26 years and they are constantly producing new information," Crews said.

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