Snakes ‘N’ Adders Intermediate Series
Episode 30 : Common & Central American Boas
(Boa imperator and Boa sigma)
A closer look.
Common and central American boas were once considered part of a monotypic genus and considered subspecies of the Red Tailed Boa (Boa constrictor constrictor). They were classified for a long time as Boa constrictor imperator. Some would refer to these snakes as Imperial Boas.
A paper in 2009/2010 suggested that up to a 7% divergence existed in the DNA between the constrictor and imperator populations. This was considered enough to elevate these snakes to species specific status and thus become Boa imperator.
A natural barrier exists in the form of the Andes mountains that separates the two species. Boa constrictor and its remaining subspecies occur to the East of the Andes through the remainder of Colombia, Venezuela, Peru, Guyana, Suriname, French Guiana and Brazil. Other subspecies tend to occur to the south of these regions in Southern Brazil, Bolivia, Paraguay and Argentina (Boa constrictor amarali and Boa constrictor occidentalis). These snakes will be featured in another video looking at the climate changes they experience through their group.
Today we are here to discuss the animals that occur to the West of the Andes from Northern Ecuador through Colombia, Panama, Costa Rica, Nicaragua, El Salvador, Honduras , Belize, Guatemala and Mexico.
This is where the plot now thickens. In 2016 there was another paper published by Daren Card et al where all snakes occurring on the pacific (West Coast) of Mexico up to the Northern most population in Hermosillo were designated Boa sigma. Where this becomes slightly muddy is that this was a previously used name for a proposed Boa subspecies found on the Tres Marias Islands in Mexico. The first time it was used was by Smith in 1943 for this purpose. Part of me thinks it would have been easier to give it a new name altogether but what do I know. Mattison also in one of his text made reference to some people even linking it with Hog Island Boas. This of course makes the matter more confused than it needed to be. Boa borealis would have made more sense (Northern Boa).
Due to the isolation of these North western populaces they have evolved to be far more diminutive than the rest of the mainland animals considered and bear a greater resemblance to some of the insular forms off the coast of Belize, Honduras and Nicaragua.
Using DNA testing the group of scientists from a consortium of US university biology departments decided there was a distinct Northern Race. The only sticking point to this being that there was an area of intergrades between imperator and sigma in Oaxaca State in Mexico. Another conundrum was depending on where you read accurate delineations between imperator and sigma were hard to find. Some sited the Isthmus of Mexico (Tehuantepec) and the hot gates for change but oddly enough a further diminutive isolated populous exists on the Sierra Madre orientalis in the form of the Tarahumera Boa. Despite being exceedingly slight in build like the sigma boas these remained with imperator.
With a distance as the crow flies from Hermosillo, Sonora, Mexico to Manta, Ecuador of 4633km (2878 miles). To put this in perspective a passenger jet flies at roughly 500 mph. It would take 5hrs 45 min to get from one to the other. That is a BIG range.
I will endevour to share some of the data pictures and other pictures in the community section. so please check
chaz x
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