|Ornate tree lizard|
Baird & Girard, 1852
The tree lizard or ornate tree lizard (Urosaurus ornatus) is a species of lizard native to the southwestern United States and northern Mexico. The species has been used to research the physiological changes in the body during the fight-or-flight response as related to stress and aggressive competition. Also, its life history and costs of reproduction have been documented in field populations in New Mexico.
The tree lizard feeds on mostly insects and their larvae.
A group consisting of one male and one or more females typically inhabit an area containing one or more large trees or shrubs. The male copulates with each female and the female retain eggs (vivipary) about two weeks after mating. In many parts of the its range, females may deliver more than one clutch of juveniles a year.
Male 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 spot on the chin, a throat fan that is orange by the body and blue at the tip, and a blue stomach. The second is orange in color; the chin is solid orange, as is the throat fan and the stomach. 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 not 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, an abundance of progesterone will cause him to develop into an orange-blue type. Low progesterone will lead to the male developing into an orange type. During dry weather conditions, orange-type males' corticosterone levels increase, which causes testosterone to decrease, which leads to their instinct to become nomadic. Likewise, orange-blue types do not have this hormonal response to the weather, and remain in their territories regardless of climatic conditions.
- Texas tree lizard, U. o. ornatus (Baird & Girard, 1852)
- U. o. caeruleus (Smith, 1935)
- U. o. chiricahuae (Mittleman, 1941)
- U. o. lateralis (Boulenger, 1883)
- Smooth tree lizard, U. o. levis (Stejneger, 1890)
- Lined tree lizard, U. o. linearis (Baird, 1859)
- Big Bend tree lizard, U. o. schmidti (Mittleman, 1940)
- Schott's tree lizard, U. o. schottii (Baird, 1858)
- Colorado River tree lizard, U. o. symmetricus (Baird, 1858)
- Northern tree lizard, U. o. wrighti (Schmidt, 1921)
- * Global Reptile Assessment Coordinating Team (2007). "Urosaurus ornatus". IUCN Red List of Threatened Species. Version 2009.1. International Union for Conservation of Nature. Retrieved 10 July 2009. Database entry includes justification for why this species is of least concern.
- Matt, K. S.; M. C. Moore; R. Knapp; I. T. Moore (1997). "Sympathetic mediation of stress and aggressive competition: plasma catecholamines in free-living male tree lizards". Physiology and Behavior 61 (5): 639–647. doi:10.1016/S0031-9384(96)00500-8. PMID 9145930.
- Landwer, Allan J. (December 1994). "Manipulation of egg production reveals costs of reproduction in the tree lizard (Urosaurus ornatus)". Oecologia 100 (3): 243–9. doi:10.1007/BF00316951.
- Roughgarden, Joan (2004). Evolution's Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press. pp. 87–8. ISBN 0-520-24073-1.
- Roughgarden, Joan (2004). Evolution's Rainbow: Diversity, Gender, and Sexuality in Nature and People. University of California Press. p. 88. ISBN 0-520-24073-1.
- Herpedia: The Reptiles and Amphibians of Wyoming