It's a Femininomenon: All-female lizards

it's giving polycule

A New Mexico whiptail (lizard) | Photo source: Wikipedia

Let’s imagine you’re on a sunny herpetology walk through the desert of central Arizona when you notice two female whiptail lizards performing a mating ritual. That’s not what they taught you in high school science class!¹ Remembering that your walk is a sex-positive space, you call the guide over and ask about what you saw. Could it be true?

*clutches pearls* how could this happen??!?

Some species of whiptail lizards, including the one you observed mid-coitus, are comprised only of females. These whiptails reproduce asexually through a process called parthenogenesis. In short, this method of reproduction only requires an unfertilized egg. Therefore, male sperm contribution is obsolete in this species.

In sexually reproductive species, unfertilized eggs contain only half of the organism’s chromosomes. The process that generates eggs (or sperm) with half of the number of chromosomes is called meiosis. In sexually reproducing species, fertilization is required for both half-sets of chromosomes to be present in the new zygote.

In parthenogenetic whiptail lizards, meiosis occurs normally - leading to the production of four unfertilized eggs. However, these unfertilized eggs fuse to make two cells with the complete chromosomal composition of the species (termed automixis). With the proper number of chromosomes, these unfertilized eggs can begin embryogenesis, thus creating two new whiptails without the need for a male or his sperm.

Of course, this chromosomal explanation does not address the sexual behavior you observed on the herpetology walk. Scientists refer to the sex between female whiptails as “pseudocopulatory” because the mechanics are the same as in sexual whiptail species but do not result in egg fertilization.²

In sexually reproducing lizards, males court and mount ovulating females to deposit sperm. If a female is not ovulating (or if the male is not a quality partner), she rejects the male’s advances. In sex between female whiptail lizards, all females participate in both sets of behaviors (reception and mounting) at different phases of their ovulation cycle.

Specifically, during ovulation parthenogenetic whiptails are receptive to mounting by female conspecifics (other members of the same species). Individual females display mounting during the period after ovulation, driven by high levels of progesterone. (In fact, some males in sexually reproducing whiptail species also display mounting in response to progesterone.) You can watch these mating behaviors between two female whiptails in this clip from a 2010 BBC documentary. (If you want to avoid the male gaze of the narrator, listen without sound.)

Additionally, sex between female parthenogenetic whiptails benefits the species at large. Progesterone induces mounting in female whiptails through the same brain pathways (including the feel-good neurotransmitter dopamine) that drive mounting in males of related whiptail species that reproduce sexually. Further, cooperative sex between female whiptails promotes the overall fecundity of the population by shortening the time between ovulation cycles. This ensures that the species maintains a robust population size.

*whispers* is the brain “bisexual”?

All-female whiptails also helped shift scientists’ understanding of how sexual behavior manifests in the brain. Many scientists believed (and some still believe) that there are innate biological differences between males and females. This argument is the core of much scientific queerphobia and can even be found on the pages of The New York Times (as QSL has covered previously).

In neuroscience, the (false) assumption of sex-specific biological differences manifests in theories of sexual behavior. Adherents to this school of thought believe that heteronormative sexual behaviors are hard-wired into the brain due by sex-specific chromosomal differences. However, this opinion was not unanimous, and other scientists put forward an idea that the brain was “bisexual” - meaning that the brain could drive a wide variety of sexual behaviors and that an individual’s specific behaviors are determined by a combination of genetics, environment, and experience.³

Sex between female whiptails is strong evidence for a “bisexual” brain because these lizards reject the heteronormative assumptions about sex held by the scientific establishment. The brain circuitry that drives mounting is intact in these female lizards. If sexual behaviors were hard-wired in the brain based on chromosomal sex, then these female lizards would never mount.

Thus, the whiptail brain is plastic with respect to sexual behaviors. Parthenogenetic whiptails capitalized on the preexisting sensitivity to progesterone within the brain circuitry that coordinates mounting. This sensitivity helped produce a variation on whiptail sexual behavior that has measurable positive impacts on the longevity of the species.

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Whiptails are not the only species that reproduces by parthenogenesis. In fact, many species do. Evolution naturally produces variations in sex and reproduction, and no single set of sexual behaviors is more “natural” than another. These false hierarchical taxonomies are the product of human assumptions about the world mixed with the omnipresent political dimension of science. Given that academic science has historically been male-dominated, politics has relied on science to reinforce a patriarchal and heteronormative worldview about sex. To those still peddling this misinformation, I say:

Dude, can you play a song with a fucking beat?

1. Or at least in the high school science classes at my Catholic high school.

2. They also use the word “pseudosexual” to describe these behaviors. I prefer "pseudocopulatory” because it avoids unintended negative implications for non-heteronormative sex in humans.

3. I use “bisexual” in quotes here to mark that the use of the word is not equivalent to bisexual as a descriptor of human sexual orientation. Interestingly, there is a version of the “bisexual brain” argument that excludes human bisexuality by suggesting that at some point in the life of an organism, its brain settles on one set of sexual behaviors from the gendered binary. We can easily reject this corollary given the lived experiences of queer folks.