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Urosaurus ornatus
Uornatus2018.jpg
Conservation status
Scientific classification
Genus:
Urosaurus
Species:
ornatus
Synonyms
  • Uta ornata
    Baird & Girard, 1852
  • Urosaurus ornatus
    — Mittleman, 1942

Urosaurus ornatus, commonly known as the ornate tree lizard, is a species of lizard in the family Phrynosomatidae. The species is native to the southwestern United States and northwestern Mexico. The species, which formerly was commonly called simply the "tree lizard", has been used to study physiological changes during the fight-or-flight response as related to stress and aggressive competition. Its life history and costs of reproduction have been documented in field populations in New Mexico and Arizona. It has been fairly well studied because it has interesting variation in throat color in males (within a population) that can correlate with different reproductive strategies,

Diet

The ornate tree lizard feeds on mostly insects and their larvae.

Reproduction

A group of U. ornatus, consisting of one male and one or more females, typically inhabits an area containing one or more large trees, shrubs, or boulders. The male copulates with each female, and the females retain eggs about two weeks after mating. In many parts of its range, females may lay more than one clutch of eggs a year.

Territoriality is an important part of reproduction for many males in this species. Males often defend territories by aggressively excluding other males. This aggression can, in part, be enhanced with higher levels of the steroid hormones testosterone and progesterone. Females have home ranges but do not defend territories. When the number of females on a male's territory is experimentally reduced by removing the females, the male is more likely to abandon his territory.

Females also can vary in throat coloration, although this is not as well-studied. When gravid with eggs, females tend to be orange or red. Recent experiments also suggest females have association, and perhaps mating preferences for different male types, and that this female preference varies with the throat color of the female herself, and with the colors of the two males that she was presented.

Appearance and throat color variation

The ornate tree lizard may grow to a snout-to-vent length (SVL) of up to 59 mm (2.3 inches). As adults, all males have paired turquoise patches of skin on the abdomen; females lack this abdominal coloration. Male ornate tree lizards are found in a variety of colors. While not all populations contain more than one or two colors, 9 color types have been documented within U. ornatus. A population documented in Verde River, Arizona, has two types of coloration patterns among male tree lizards that account for 45% of all males. The first is characterized by a blue spot in the center of a larger orange patch on the throat fan ("dewlap"). The second has a solid orange throat fan ("dewlap"). The orange-blue males are more aggressive and defend territories that can include up to four females. The orange males have longer, leaner body types and are much less aggressive. Orange males can be nomadic during dry years, and during rainy years tend to occupy small territories.

Some, such as Stanford professor and biologist Joan Roughgarden, have suggested multiple male genders in this species. Among differently colored male tree lizards, there are different hormonal profiles. On the day a male tree lizard hatches, researchers think that high blood levels of progesterone and then later, as a juvenile, higher testosterone levels will cause him to develop into an orange-blue type; low progesterone and later lower testosterone levels, as a juvenile, may lead the male to develop into an orange type. During dry weather conditions, orange-type males' corticosterone levels increase, which causes testosterone to decrease, leading them to be more likely to leave their territory and become nomadic. Orange-blue males do not have this hormonal response to the weather, and remain in their territories regardless of climatic conditions.

Subspecies

Ten subspecies are recognized as being valid, including the nominotypical subspecies.

  • U. o. ornatus (Baird & Girard, 1852) – Texas tree lizard
  • U. o. caeruleus (H.M. Smith, 1935)
  • U. o. chiricahuae (Mittleman, 1941)
  • U. o. lateralis (Boulenger, 1883)
  • U. o. levis (Stejneger, 1890) – smooth tree lizard
  • U. o. linearis (Baird, 1859) – lined tree lizard
  • U. o. schmidti (Mittleman, 1940) – Big Bend tree lizard
  • U. o. schottii (Baird, 1858) – Schott's tree lizard
  • U. o. symmetricus (Baird, 1858) – Colorado River tree lizard
  • U. o. wrighti (Schmidt, 1921) – northern tree lizard

Nota bene: A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than Urosaurus.

Etymologies

The subspecific name, schmidti, is in honor of American herpetologist Karl P. Schmidt.

The subspecific name, schottii, is in honor of German-American naturalist Arthur Carl Victor Schott.

The subspecific name, wrighti, is in honor of American herpetologist Albert Hazen Wright.

Geographic range

United States: California, Nevada, Utah, Colorado, Wyoming, Arizona, New Mexico, and Texas.
Mexico: Sonora, Sinaloa, Chihuahua, and Coahuila.

  • Baird SF, Girard C (1852). "Characteristics of some New Reptiles in the Museum of the Smithsonian Institution. Second part". Proc. Acad. Nat. Sci. Philadelphia 6: 125-129. (Uta ornata, new species, p. 126).
  • Behler JL, King FW (1979). The Audubon Society Field Guide to North American Reptiles and Amphibians. New York: Alfred A. Knopf. 743 pp. ISBN: 0-394-50824-6. (Urosaurus ornatus, pp. 535–536 + Plate 369).
  • Conant R (1975). A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Second Edition. Boston: Houghton Mifflin Company. xviii + 429 pp. + Plates 1-48. (Urosaurus ornatus, pp. 108–109 + Plate 16 + Map 61).
  • Powell R, Conant R, Collins JT (2016). Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America, Fourth Edition. Boston and New York: Houghton Mifflin Harcourt. xiv + 494 pp. ISBN: 978-0-544-12997-9. (Urosaurus ornatus, pp. 299–300 + Plate 28).
  • Smith HM, Brodie ED Jr (1982). Reptiles of North America: A Guide to Field Identification. New York: Golden Press. 240 pp. ISBN: 0-307-13666-3. (Urosaurus ornatus, pp. 112–113).
  • Stebbins RC (2003). A Field Guide to Western Reptiles and Amphibians, Third Edition. The Peterson Field Guide Series ®. Boston and New York: Houghton Mifflin Company. xiii + 533 pp. ISBN: 978-0-395-98272-3. (Urosaurus ornatus, pp. 296–297 + Plate 32 + Map 96).
  • Zim HS, Smith HM (1956). Reptiles and Amphibians: A Guide to Familiar American Species: A Golden Nature Guide. New York: Simon and Schuster. 160 pp. (Urosaurus ornatus, pp. 54, 155).
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