Friday, October 30, 2015

An addition to the herpetofauna of Tobago, Anolis tigrinus

Anolis cf tigrinus from Tobago. JCM

Since the 17th century the island of Tobago has been explored by a variety of naturalists including many people who examined the herpetofauna by actually doing field work , others who examined museum specimens, and some that did both. The island is relatively small (~ 300 sq km) but has the oldest protected mature forest in the western hemisphere.

One of the biogeographic puzzles surrounding Tobago is that it has no native members of the genus Anolis. It does have the Giant Crown Anole (Anolis richardii) which is thought to have been introduced from Grenada and it does have Anolis aeneus which appears to be a very recent introduction (probably in the last 20 years). Both of these species are associated with disturbed habitats. We should add that Little Tobago Island (97 ha) is also missing a native anole.

Trinidad, while it is a larger island (~4780 sq km), has only a single known species of native anole, Anolis planiceps (formerly known as Anolis chrysolepis planiceps). However it too has introduced anoles, (A. aeneus, A. trinitatis, A. wattsi, A. extremus, and probably at least another two or three species which we will discuss in a future post).

During the 2015 Tobago Bioblitz (October 24-25) we discovered a small anole, with a body length of about 34 mm, and a mossy green-grey, lichen-like dorsal pattern. Our preliminary results suggest this is Anolis tigrinus Peters. The coloration, body form (slender with short arms and legs) and the scale counts we did all suggest that this is A. tigrinus or something closely related to it.

Anoles come in ecomorphs depending on what microhabitats they exploit, there are trunk-crown ecomorphs (largest body size), trunk-ground ecomorphs (slightly smaller than the previous morph), twig morphs (smaller yet), and the grass-bush morph which is the smallest known morph.

The habitat and distribution of Anolis tigrinus given by Ugetto et al. (2009) was  premontane and montane forest from central Falcón and Yaracuy through Aragua, Distrito Federal, Vargas and Miranda to northern Anzoátegui and southwestern Sucre. Our Tobago record expands the range about 280 km to the northeast.

Anolis tigrinus is a small anole and usually consider a twig morph with males reaching a maximum body length of about 55 mm and females being slightly larger at about 58 mm. Twig anoles use the tips of branches in the crowns of trees, the smallest of perches. This allows them to feed where other, heavier bodied anoles cannot go and gives them a better chance at avoiding their vine snake predators (Oxybelis aeneus and Imantodes cenchoa).

The head is elongate and has relatively large, smooth scales. The supraocular area has a few enlarged scales surround by many smaller, more granular scales. The supraorbital semicircle scales on both sides usually make contact, but may occasionally be separated by one scale; interparietal and supraorbital semicircle scales usually make contact. Dorsal scales small and smooth and from two rows of slightly enlarged scales along the middorsal line.

The most recent review of Anolis tigrinus was done by Ugetto et al. (2009) and they describe its habitat as humid and very humid premontane forests between 980 and 2087 m in Venezuela. It occurs along forest edges and invades the forest for short distances and they are often about three meters off the ground. The individual we found was on the ground in an edge situation and was likely blown off the tree by the wind or fell when it was being chased by a predator. The highest point on Tobago is about 550 m and this specimen was taken at about 400 m ASL. Thus, the Tobago population differs in inhabiting a lower elevation than other clade members.

Ugetto et al. (2009) also reported that male tigrinus have an unspotted dewlap, which is decidedly larger than that of females, and that males are easily recognized by the presence of large, postanal scales and the base of the tail is distinctly wider. While the Tobago specimen has a spotted dewlap, it also displays a hemipenal bulge suggesting it is an adult male. Its stomach contained small wasps.

Del Rosario Castañeda and De Queiroz (2013) found Anolis tigrinus in a clade of nine species (A. lamari, A. menta, A. nasofrontalis, A. paravertebralis, A. pseudotigrinus, A. ruizii, A. solitarius, A. tigrinus, and A. umbrivagus). They share a small body size (40-60 mm adult male body size) large smooth head scales, a large interparietal scale bordered by large scales and usually in contact with the supraorbital semicircle scales, and smooth ventral scales that are larger than dorsal scales. Species in the tigrinus series are distributed at high elevations of the Sierra Nevada de Santa Marta (Colombia), the Andes of Colombia (Eastern Cordillera) and Venezuela, and the Atlantic forest of southeastern Brazil. They considered that the tigrinus series may be nested within the punctatus series representing a twig ecomorph subgroup of the punctatus series which also contains trunk-crown anoles. Del Rosario Castañeda and De Queiroz consider A. tigrinus and its relatives part of the punctatus series rather than a separate tigrinus series, but note that a clade containing A. tigrinus and all species closer to it than to A. punctatus could be recognized as a sub-series or a species group within the punctatus series.

The presence of Anolis tigrinus on Tobago supports the faunistic relationship between the Caribbean Plate island and the Coastal Ranges of Venezuela.

We collected tissue for molecular work and will soon know if it is identical to A. tigrinus or if it is a  relative. We also have evidence that Anolis tigrinus or something similar to it is present on Trinidad.

Literature cited

Del Rosario Castañeda, M., & De Queiroz, K. (2013). Phylogeny of the Dactyloa clade of Anolis lizards: new insights from combining morphological and molecular data. Bulletin of the Museum of Comparative Zoology, 160: 345-398.

Ugueto, G. N., Rivas, G., Barros, T., & Smith, E. N. (2009). A revision of the Venezuelan anoles II: redescription of Anolis squamulatus Peters 1863 and Anolis tigrinus Peters 1863 (Reptilia: Polychrotidae). Caribbean Journal of Science, 45: 30-51.

Authors: Tom Anton, Renoir Auguste, Alvin Braswell, John C. Murphy, Mike G. Rutherford

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