A Potential Threat to Males Everywhere
While the role of the male in relationships and reproduction has long been assumed a necessity, there is now proof that at least one vertebrate species has learned how to get along fine without males. As discovered by the well-renowned biologist David Crews of the University of Austin, Texas, the whiptail lizard (specifically, C. uniparens) has somehow adapted the ability to reproduce in a population made up entirely of females.
In a packed UAF auditorium last February, Crews revealed the hormonal mechanisms with which the whiptail lizard has developed this remarkable adaptation. Apparently, the females of this species have learned how to take turns acting as males and, along with some special genetic changes, have completely eliminated the male sex from their species. They now possess the ability to lay eggs that hatch and grow into healthy lizards without the need to be fertilized by a male.
Although the exact ancestral lines may never be untangled, there is some genetic evidence that the all-female species of the lizard is the result of a hybrid between two sexually normal species, which somehow created a new species that lost its need for males. To prove this idea, Crews and his team performed hormonal tests on the males of suspected ancestors of these lizards, which indicate that some males of these ancestral species are sexually responsive to the hormone progesterone. Progesterone, while usually considered a female hormone (in fact it has been used to curtail sexual desire in rapists), somehow elicits sexual behavior in the males of these lizards.
Crews thinks that it was a mating between one of these progesterone-sensitive males and a regular female which produced a new female that no longer needed males for reproduction.
While the all-female population is strange enough, the most intriguing discovery that Crews made about these lizards is that they take turns acting male and female. Crews observed two captured females that performed a mating ritual he called a "doughnut." In brief, one female (the male actor) bites the neck of another, more submissive female (the female actor), contorts herself in a loop around her partner so their genitalia contact each other, then disengages. Next, the female (actor) lays her eggs. Then, after only a few weeks, the two lizards switch roles and the other female lays her eggs. This process repeats itself throughout the three-month mating season.
The chemical stimulus of this strange behavior was investigated by Crews, and he found that the different actors have different amounts of two main hormones in their blood during the mating ritual. While the male actor has large amounts of progesterone in her blood, the female actor has large amounts of estradiol (estrogen) in her blood. After a female ovulates, there is an increase in the levels of progesterone in her blood. In turn, this increase leads her to act like a male. Eventually, the ovaries in this female will continue to develop and mature, until her ovaries grow and she has high levels of estradiol in her blood and is ready to lay her eggs. Now, this same female reverses roles and acts female (for another lizard who takes the role of the male), thus completing the cycle.
The recently reported cloning of a sheep has brought up worries that people will someday clone other people and eliminate the need for regular sexual behavior. C. uniparens has already taken steps in this direction by eliminating the males from its species--and this adaptation comes without the aid of intelligence or billion-dollar technologies. If a lowly lizard can eliminate males and propagate itself, perhaps human males should take note and beware!
