Anolis gorgonae BARBOUR 1905

Submitted by Fernando Racimo 05 Dec
Scientific name:  Anolis gorgonae BARBOUR 1905
Common names
Common names:  Blue Anole [en]
Common names:  Anole Azul [es]
Overview: 

Anolis gorgonae is one of the only lizard species in the world that is blue in coloration. It is found only on Isla Gorgona, a small tropical island 56 km off the Pacific coast of Colombia. It feeds on insects and spends most of the time high in the branches of the trees. Little is known about this anole, and its conservation status is presently uncertain.

Associations
Associations: 

Known natural predators of Anolis gorgonae include the larger lizard Basiliscus galeritus and the snake Boa constrictor.

Behaviour
Behaviour: 

Although Anolis gorgonae is typically found many meters up on tree trunks and branches, it may descend to the lower trunk in the morning where it will typically sit perched with its head facing down. This lizard is extremly wary and will rapidly ascend into the canopy if disturbed by humans. In the afternoon, it returns to the tree tops, where it remains during the night (von Prahl et al. 1979).

The male displays its large white dewlap to attract females and to signal to other males. Also during visual communication, the male may also erect a small, fleshy nuchal crest.

Conservation status
Conservation Status: 

Von Prahl et al. speculated that logging on Gorgona Island may have caused Anolis gorgonae populations to decrease in number (von Prahl et al. 1979). In 1985 the island was designated as a national park (covering an area of 120,000 acres), and destructive land use effectively ceased at that point. Although some have suggested that Anolis gorgonae is at risk of extinction (Butler and Butler 2007), recent investigators have found the species to be relatively abundant, accounting for the difficulty of observing these animals high in the tree tops (D. L. Mahler, pers. obs.).

As of December 2010, the conservation status of this species has not yet been reviewed by the International Union for Conservation of Nature (IUCN), and no quantitative data are presently available to indicate whether the abundance of this species has changed over time on Gorgona Island.

Diagnostic description
Diagnostic Description: 

Upon describing Anolis gorgonae, Barbour (1905) noted that it differs from Anolis gemmosus (previously known as A. andianus) in having five rows of loreal scales, no tricarinate supraoculars and six labials below the center of the eye. Its hind limbs are also longer than those of A. gemmosus. Anole specialists generally regard Anolis gorgonae as most closely related to A. chloris, an arboreal green anole found in the Pacific lowland and mid-elevation forests of Panama, Colombia, and Ecuador. Anolis chloris and Anolis gorgonae are nearly indistinguishable in body dimensions and scale characteristics, but differ strikingly in coloration - A. chloris is bright green while A. gorgonae is bright blue.

Distribution
Distribution: 

Anolis gorgonae can only be found on Gorgona Island, in the Pacific Ocean (56 km off the coast of Colombia).

Evolution
Evolution: 

Anolis gorgonae is almost identical in morphology to Anolis chloris (Boulenger's Green Anole), which inhabits mainland Colombia, Ecuador, and Panama, but it is colored blue instead of green. This has led some to suspect that A. gorgonae evolved its characteristic blue coloration by losing the ability to express yellow skin pigments (D. L. Mahler, pers. comm.), but this hypothesis has yet to be tested. Also of relevance to the evolution of color in A. gorgonae is the fact that this species has a blue iris in addition to blue skin. 

Habitat
Habitat: 

Anolis gorgonae is often found in large trees (typically 40 cm in trunk diameter or greater). They are located from 1 meter above the ground to more than 10 meters high in the canopy. These anoles prefer to stay on the side of the tree that is not in direct sunlight and are rarely observed basking (von Prahl et al. 1979). Typically, only one male may be observed on a single tree at a time, although occasionally, multiple males have been observed displaying or fighting.

Management
Management: 

As the entire population of Anolis gorgonae occurs within a national park (Gorgona Island National Park), the entire range of this species is protected by the government of Colombia.

The removal of individuals of Anolis gorgonae from Gorgona Island is prohibited by law.

Morphology
Morphology: 

Anolis gorgonae is blue in all dorsal coloration, and its ventral surfaces are lighter and buffish. The dewlap of this anole, which is only present in males, is large and whitish, with lilac-colored lines and dots at the base. There are no color differences between males and females, except for the bright, white dewlap found in males. The body of A. gorgonae is very slightly dorsoventrally compressed. Its ventral scales are small and imbricate, but are considerably larger than the dorsal scales, which are very fine. The tail is slightly laterally compressed, and is covered with large, equal-sized, strongly keeled scales. The adhesive toe pads under the digits are considerably dilated. There are 16 sticky lamellae under phalanges II and III of the fourth toe. Anolis gorgonae has a medium-sized round ear opening. The lower surfaces of the thighs are buff with indistinct wavy bands of pale lilac (Barbour 1905).

Physical description
Size: 

Measurements from Barbour (1905):

Head: 16 mm

Width of head: 9 mm

Body: 51 mm

Fore limb: 33 mm

Hind limb: 60 mm

Tibia: 14 mm

Trophic strategy
Trophic strategy: 

Anolis gorgonae feeds on insects it obtains from surfaces of the trees in which it lives (von Prahl et al. 1979).

References
References: 
Barbour, T. in: Bangs, O., Brown, W.W., Thayer, J.E., Barbour, T. (1905) The Vertebrata of Gorgona Island, Colombia. Bull. Mus. Comp. Zool. Harvard 46(5): 99-100.
Butler, T. & Butler, R. One of world's only pure blue lizards at risk of extinction. 7 Mar. 2007. URL: http://news.mongabay.com/2007/0307-blue_anole.html [Accessed 30 Apr. 2010]
Reptiles Database - J. Craig Venter Institute. URL: http://jcvi.org/reptiles/species.php?genus=Anolis&species=gorgonae [Accessed 30 Apr. 2010]
von Prahl, H., Guhl, F. & Grogl, M. (1979) Gorgona. Grupo Futura Editorial: Universidad de los Andes, Bogotá.
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Attribution
Rights holder:  Fernando Racimo
Author(s):  Fernando Racimo
Editor(s):  D. Luke Mahler

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