Desert grassland whiptail lizard
|Desert Grassland Whiptail|
(Wright & Lowe, 1965)
Cnemidophorus uniparens Wright & Lowe, 1965
The desert grassland whiptail lizard (Aspidoscelis uniparens) is an all-female species of reptiles. It was formerly placed in the genus Cnemidophorus. A. uniparens have limited social stimuli, having only two basic needs: finding food and avoiding predators. A common predator of the whiptail lizard is the leopard lizard, that prey on A. uniparens by using ambush and stalk haunting tactics. These reptiles reproduce by parthenogenesis. In this process, eggs undergo a chromosome doubling after meiosis, developing into lizards without being fertilized. However, ovulation is enhanced by female-female courtship and "mating" (pseudo-copulation) rituals that resemble the behavior of closely related species that reproduce sexually.
The desert grassland whiptail lizard is a relatively small reptile, whose size ranges from 2¾ inches (69 mm) to 5¼ inches (137 mm). Desert grassland whiptails are very long and slim, with a thin tail that is longer than their body length. Their distinct identifying feature are the six yellowish lines that run the length of their body. The majority of the whiptail's body tends to be an olive or brown colour that fades to a faint blue or gray on their tail. Comparatively, an adolescent's tail is a very bright and vibrant blue. Their bodies are lined with small coarse scales, which gradually get larger as they approach the tail. The scales on their bellies are much larger in size and are much smoother as well.
The taxonomy of the genus was unknown until the 1950s to early '60's. A 1958 report confirmed that no male lizards had been discovered in a collection of specimens of C. tesselatus. That very year, parthenogenesis was confirmed in the genus Lacerta of the family Lacertidae. Soon after, researchers discovered that there were also no males in C. exsanguis, C. neomexicanus, or C. velox. Rather than subsume all cnemidophorine species into a single large genus, Lowe and Wright proposed a split that placed the North American "Cnemidophorus" clade in the monophyletic genus Aspidoscelis. Under this arrangement, South American taxa remain in the genus Cnemidophorus.
The desert grassland whiptail is mostly found in the deserts of southern to central Arizona and along the Rio Grande river in New Mexico. It is also found in the deserts of northern Mexico. A. uniparens is commonly found in low valleys, grasslands, and slight slopes. Some have argued that the species' range is expanding due to overgrazing. A. uniparens are scarce in developed areas, especially where homeowners keep livestock.
Hybridization and reproduction
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All desert grassland whiptail lizards are female. Their reproduction process does not need male fertilization, although researchers observed pseudo-copulation that promotes fertilization during ovulation. This process involves the alternation between male-typical and female-typical sexual behaviors, driven by progesterone, in both lizards; corresponding to the state of their partner. The lizards reproduce by parthenogenesis, but offspring do not necessarily have the same chromosomes as their mother. This is because the lizards start off with twice the amount of chromosomes as would be found in sexually reproducing individuals. This diversity is maintained by combining sister chromatids instead of pairing homologous chromosomes, thus allowing a recombination and genetic diversity. Current studies suggest that the lizards may be able to distinguish between homologous chromosomes and sister chromatids. The lizard is a triploid unisexual species that reproduce asexually. The lizards were a result from a cross breed of two bisexual species, A. inornata and A. burti. This then produced a diploid unisexual, which backcrossed to inornata and produced triploid uniparens.
For the most part, the lizards eat spiders, termites, antlions, beetles, and short-horned grasshoppers. Their dominant foods vary little over time. Research suggests that this may be because "sexual variation was more evident; it may act to reduce intraspecific competition for food resources and may be associated with secondary sexual size dimorphism."
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- Harmon Katherine (2010) No Sex Needed: All-Female Lizard Species Cross Their Chromosomes to Make Babies. www.scientificamerican.com/article/asexual-lizards/
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Mayer, Greg. (2010). Hybridization and Parthenogenesis in Whiptail Lizards. whyevolutionistrue.wordpress.com. Web 23 Oct 2014.
Harmon Katherine (2010) No Sex Needed: All-Female Lizard Species Cross Their Chromosomes to Make Babies. www.scientificamerican.com/article/asexual-lizards/ Tue 21 Oct 2014.
S. C. Woolley, J. T. Sakata D. Crews(2004) Tracing the Evolution of Brain and Behavior Using Two Related Species of Whiptail Lizards: Cnemidophorus uniparens and Cnemidophorus inornatus ilarjournal.oxfordjournals.org/content/45/1/46.full Tue 21 Oct 2014.
Maryanne E. Tocidlowski, Christine L. Merrill, Michael R. Loomis, and James F. Wright 2001 TERATOMA IN DESERT GRASSLAND WHIPTAIL LIZARDS (CNEMIDOPHORUS UNIPARENS). www.bioone.org/doi/pdf/10.1638/1042-7260(2001)032%5B0257:TIDGWL%5D2.0.CO%3B2 Tue 21 Oct 2014