Many asexually-reproducing Unisexual (all-lesbian) anole lizard species frequently copulate anyway. (Gender Showcase, 9-12)

Confused?

If the entire species is one sex, how can there be lesbian? Doesn’t there have to be something else? Here, “lesbian” is used to refer to how their behavior is based on progesterone cycles but the entire species is one sex; if it were based on testosterone cycles, I assume authors would have referred to it as gay asexual lizards.

If they’re asexual, why are they having sex? Here, “asexual” means they’re able to reproduce without having sex. Some humans identify as asexual, but this is different from the term “asexual reproduction” as it is traditionally used in biology.

Some parthenogenic unisexual species include:

• Cnemidophorus inornatus (Arizona whiptail lizard)

• Cnemidophorus velox (Colorado whiptail lizard)

• Cnemidophorus tesselatus (Colorado whiptail lizard)

• Aspidoscelis tesselatus (Common checkered whiptail lizard)

Book Excerpt

Courtship in an asexual species is almost exactly the same [as in sexual species of American whiptail lizards].(EN3) One of the females copies the male role down to the last detail. One mounting female was even seen everting her cloacal region to contact the cloacal area of the mounted female. Courtship between female whiptail lizards is not a sloppy parody of male-female courtship left over from its sexual ancestry, but an intricate and finely honed sexual ritual.

When two females are housed together, they quickly wind up with alternating hormonal cycles. (EN4) As one female cycles into high estradiol, her eggs mature and she assumes the female role in courtship. At the same time, the other cycles into high progesterone (not testosterone) and assumes the male role. Then they switch roles a few weeks later as their hormone cycles switch. (Roughgarden 129)

Why do asexual females bother with courtship?

Because they lay twice the number of eggs!

In nature, asexual females lay an average of 2.3 batches of eggs each season. If a female is housed alone, she lays only about 0.9 batches. If housed with a female whose hormonal state leads to male behavior, she lays 2.6 batches during the season. (Roughgarden 130)

New Mexico’s Environthon reports:

“The New Mexico Whiptail, as well as several other all-female species of whiptail lizard, does reproduce, and all of its offspring are female. Moreover, it reproduces by parthenogenesis -- its eggs require no fertilization, and its offspring are exact and complete genetic duplicates of the mother. Scientists understand only partially how this reproductive mode developed, and it raises many questions. One of the most intriguing is how this cloning affects the lizard's ability to adapt to environmental changes. Since there is no genetic variation except that which occurs through mutation, the New Mexico Whiptail cannot evolve as other species do.”

National Geographic Magazine (Nov 2016 issue) reports on the Baumann team’s research:

“The lizards are all female and parthenogenetic, meaning their eggs develop into embryos without fertilization. But before the eggs form, Baumann’s team discovered, the females’ cells gain twice the usual number of chromosomes—so the eggs get a full chromosome count and genetic variety and breadth (known as heterozygosity) rivaling that of a sexually reproducing lizard.

Why does this occur?

Because long ago, Baumann says, lizards of the genus Aspidoscelis had “a hybridization event”—that is, females of one species broke form and mated with males of another species. Those outlier liaisons gave whiptails robust heterozygosity, which has been preserved by the identical replication—essentially, cloning—that occurs in asexual reproduction. It’s a genetic-diversity advantage that today’s females still enjoy and propagate.”

Crews, D. (1987) Courtship in Unisexual Lizards: A Model for Brain Evolution. Scientific American Vol. 257, No. 6 (December 1987), pp. 116-121. writes:

“The females produce by parthenogenesis, that is, reproduction without fertilization, and therefore copulation between its members is not directly related to the production of offspring. Nevertheless, the females in this species actively engage in courtship rituals that are virtually identical with those observed between male and female whiptail lizards.”

Book Citations: Roughgarden, J. (2013) Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press, Berkeley. pp. 129-131.

Related Citations

1. D. Crews and K. Fitzgerald, 1980, "Sexual" behavior in parthenogenetic lizards (Cnemidophorus), Proc. Nat. Acad. Sci. (USA) 77:499-502

2. D. Crews, 1987, Courtship in unisexual lizards: A model for brain evolution, Scientific American 257 (6): 116-21.

3. L. Young and D. Crews, 1995, Comparative neuroendocrinology of steroid gene expression and regulation: Relationship to physiology and behavior, Trends in Endocrinology and Metabolism 6: 317-23.

4. D. Crews, M. Grassman, and J. Lindzey, 1986, Behavioral facilitation of reproduction in sexual and unisexual whiptail lizards, Proc. Nat. Acad. Sci. (USA) 83:9547-50.

5. C. Cole and C. Townsend, 1983, Sexual behaviour in unisexual lizards, Anim. Behav. 31:724-28.

6. D. Crews and L. Young, 1991, Pseudocopulation in nature in a unisexual whiptail lizard, Anim. Behav. 42:512-14.

7. B. Leuck, 1982, Comparative burrow use and activity patterns of parthenogenetic and bisexual whiptail lizards (Cnemidophorus: Teiidae), Copeia 416-25.

8. B. Leuck, 1985, Comparative social behavior of bisexual and unisexual whiptail lizards (Cnemidophorus), J. Herpetology 19:492-506.

9. Y. Werner, 1980, Apparent homosexual behavior in an all-female population of a lizard, Lepidodactylus lugubris, and its probable interpretation, Tierpsychol. 52:144-50.

10. M.J. McCoid and R.A. Hensley, 1991, Pseudocopulation in Lepidodactylus lugubris, Herpetological Review 22:8-9.

11. Dias, B. G., & Crews, D. (2006). Serotonergic modulation of male-like pseudocopulatory behavior in the parthenogenetic whiptail lizard, Cnemidophorus uniparens. Hormones and behavior, 50(3), 401–409. https://doi.org/10.1016/j.yhbeh.2006.05.001

12. Paulissen, M., & Walker, J. (1989). Pseudocopulation in the Parthenogenetic Whiptail Lizard Cnemidophorus laredoensis (Teiidae). The Southwestern Naturalist, 34(2), 296-298. doi:10.2307/3671747

The sex-changing Australian goby species have 2 sexes: all-female or part-male-part-female. (Gender Showcase, 9-12)

Image credit: Yellowfin Goby, Acanthogobius flavimanus, in Jawbone Marine Sanctuary, Williamstown, Port Phillip, Victoria, February 2018. Source: Wayne Martin / iNaturalist.org. License: CC By Attribution-NonCommercial.

Edit (6/23/21): The book excerpt uses “gender” when it talks about morphology (body plan) in the Barlow study. Thanks to reader Breanna H. for asking about a previous draft of this post that repeated the book’s wording. I learned recently how much K-6 material leans on gender norms to explain biological things. Models are always imperfect, and Breanna refers to a teaching approach that avoids applying the human concept of gender to animals, and a discussion about the risks in conflating sex and gender in animal model studies. (-RXS)

Edit (6/8/23): Thanks to Wayne, adding this: Editor’s note: The term "hermaphrodite" is appropriate for referring to non-human animals with sex characteristics that do not fit typical binary notions of male or female bodies. For humans, “intersex” is the appropriate term—learn more here!(-RXS)

A species of goby from Lizard Island on Australia’s Great Barrier Reef [is the Australian goby].(EN12) In the Australian goby, all the juveniles mature into females, with some later becoming males. The males, however, can change back into females. In fact, the meaning of male is ambiguous here. The investigators defined a male to be any fish with at least some sperm production. All males, however, contain early-stage oocytes—cells that develop into eggs—in their gonads. So all the males remain part female. The species therefore consists of two genders at any one time: all-female fish and part-male-part-female fish.

(EN12 G. Barlow (2000) The Cichlid Fishes: Nature’s Grand Experiment in Evolution. Perseus.)

Citation: Roughgarden, J. (2013) Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press, Berkeley. pp. 137-38.

All bighorn rams that mate with ewes participate in gay courting & copulation most of the year. (Gender Showcase, 9-12)

Bighorn Sheep

1. Males (rams) & females (ewes) live separately except during breeding season.

2. Females are only sexually active 3 days of the year! They refuse all other approaches the rest of the time.

Book excerpt:

The males (rams), with large thick horns that curl back from above the eye to behind the ear, weigh up to 300 pounds. Their macho appearance has become a symbol for many male athletic teams. The females (ewes) live separately from the males. The sexes associate only during the breeding season, called the rutting season, which extends from mid fall to early winter. A female is receptive for about three days, and will not allow herself to be mounted outside of these three days. (EN29)

(EN29 ) V. Geist (1971) Mountain Sheep: A Study in Behavior and Evolution, University of Chicago Press; J.T. Hogg (1984) Mating in bighorn sheep: Multiple creative male strategies, Science 225: 526-29; J.T. Hogg (1987) Intrasexual competition in and mate choice in rocky mountain bighorn sheep, Ethology 75: 119-44.

All male bighorn sheep that breed with female ewes also participate in homosexual courting & anal copulation.

Book excerpt:

The males have been described as “homosexual societies.” Almost all males participate in homosexual courting and copulation. Male-male courtship begins with a stylized approach, followed by genital licking and nuzzling, and often leads to anal intercourse in which one male, usually the larger, rears up on his hind legs and mounts the other. The mounted male arches his back, a posture known as lordosis, which is identical to how a female arches her back during heterosexual mating. The mounting male has an erect penis, makes anal penetration, and performs pelvic thrusts leading to ejaculation.

Source: Roughgarden, J. (2013) Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press, Berkeley. pp. 137-38.

article excerpt:

Four behavioral phenotypes have been described in domestic rams raised in all-male groups: female-oriented, male-oriented, bisexual, and asexual. To make behavioral assignments, rams are first given sexual performance tests, also known as serving capacity tests, to determine whether or not they are attracted to females and to get a measure of their sexual performance.

Source: Roselli, C. E., Reddy, R. C., & Kaufman, K. R. (2011). The development of male-oriented behavior in rams. Frontiers in neuroendocrinology, 32(2), 164–169. https://doi.org/10.1016/j.yfrne.2010.12.007.

Bighorn Sheep have 3 behavior-based genders & 2 body types:

1. Female-body ewes live separately from gay male rams and only accept mounting 3 days of the year.

2. Male-body rams live together separately from females and copulate anally with other male-body sheep most of the year.

3. Male-body rams that live with female-body ewes most of the year and refuse mounting by other male-body rams.

Book excerpt:

The few males who do not participate in homosexual activity…are identical in appearance to other males but behave quite differently. (EN30) They differ from [so-called] “normal males” by living with the ewes rather than joining all-male groups. These males do not dominate females, are less aggressive overall, and adopt a crouched, female urination posture. These males refuse mounting by other males. In physical appearance, including body size and horn development, these males are indistinguishable from other males.

(EN30) J. Berger. (1985) Instances of female-like behaviour in a male ungulate, Anim. Behav. 33:333-35.

Citation: Roughgarden, J. (2013) Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press, Berkeley. pp. 137-38.

Species: Ovis canadiensis (wiki)

Range: North American (Rocky Mountains, Sierra Nevada, southwestern US, Mexico)