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Sexy Sundays: Happy Times for Lesbian Lizards

Posted by Richard Conniff on February 7, 2009

Equal opportunity sex

Equal opportunity sex

Did you ever wonder why men play such a small part in the perpetuation of life, and spend so much time fighting, bragging, and leaving the toilet seat up? Did you ever wonder why they exist at all? Maybe you thought there should be some other way to accomplish their small reproductive task. Or maybe you thought the pleasure of being part of a sexual species was worth the hassle.

If you thought any of those things, your idea was not original. A Southwestern whiptail lizard species, Cnemidophorus uniparens, has cut out all the expense of sexual reproduction, but— unlike other asexual species— kept the fun part. These whiptails have an entirely female population, but continue to engage in sexual behavior called pseudocopulation.

During their erotic encounters whiptail lizards will assume “male” or “female” roles depending on the stages of their ovulation cycles. A lizard approaching ovulation will have high levels of estrogen, dictating a submissive female behavior, while a lizard recently finished with ovulation will have high levels of progesterone, dictating dominant male behavior. As their cycles progress a half turn the lizards will switch roles and do it again.

The whiptails’ pseudocopulation appears to be just as kinky as any other animal sexual ritual—including mounting and biting— but it does not involve any exchange of genetic material or bodily fluids. The offspring which may be generated inside of the “female” will all be clones. The risqué behavior does benefit the participants however.

The progesterone crazed “male” lizard stimulates serotonin through their sexual act. Serotonin makes you feel good—so basically, the lizards playing the male role do it just for fun.

The receptive “female” will bear a greater number of offspring after being mounted by another whiptail than she would if she had spent her time in abstemious  solitude. And then, after the ovulation has passed, her progesterone levels will rise and she will become the man for a time.

There is a downside to all of this—in case it had started to seem to be too good to be true. Clones lack the genetic variation necessary to evolve defense mechanisms against parasites and disease. As time passes, the perpetual generations of clones accumulate deleterious mutations and fail to develop disease resistance. Small pathogenic organisms and viruses are bound to eventually out-compete Cnemidophorus uniparens in the genetic arms race.

To read more about the hormonal cues dictating the lizard’s behavior, read “Regulation of pseudosexual behavior in the parthenogenetic whiptail lizard, Cnemidophorus uniparens” by Brian George Dias and David Crews. Published in Endocrinology, 2008; 149(9): 4622-4631

or  “Serotonergic modulation of male-like pseudocopulatory behavior in the parthenogenetic whiptail lizard” by the same authors and found at http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2394198

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