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Signature Features


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Black Gap Alterna Overview

For aficionados of locality alterna, the Black Gap Wildlife Management Area is a magical place. Neophyte hobbyists may find the animals from this area confusing, even frustrating, when viewed through the lens of the current reptile market. Calling the entire 103,000 acres where the Sierranias del Burro and Sierra del Carmen Mountain Ranges do their best to enter into Texas the "locality" is a bit misleading as virtually all animals ever collected here come from only a very small section along the tiny ribbon of FM 2627 which terminates at the Mexico border at the La Linda river crossing. The usual problematic process of naming localities based on road numbers has oddly been defied in this case in favor of going to the other extreme and naming the locality after an area that has had only a tiny region sampled for alterna. Indeed, the habitat along FM 2627 looks mostly less than spectacular and this can be confirmed by examining the satellite imagery. Something unique happened in the Black Gap area, probably during the last glacial retreat or one of the mini wet periods that followed during the last 10 thousand years, that introduced some strange genetic material into the existing local population. The proximity of the Sierra del Carmen and Sierranias del Burro Mountain Ranges are suspect as points of origin. These are very unique mountain ranges with unique rainfall patterns, unique flora and elevational/temperature extremes. Alterna from these mountains have not been sampled. Though totally speculative without specimens for comparison, this "injection" of uniqueness could very well have originated from these ranges. It is possible that alterna with the signature Black Gap features evolved in situ. This would be quite a tricky accomplishment considering that the eastern and western forms were already in place and contributing specimens to the area. Giving a nod to the fact that the Black Gap region is vastly under sampled from an alterna collecting point of view, it is very intriguing to speculate on what other variations one might encounter in other parts of the management area, especially those with more typical alterna habitat in close proximity to the Rio Grande.

Even for hardcore alterna fans, Black Gap is mind boggling in its diversity of pattern and color combinations. This is truly the area where eastern alterna phenotypes collide with western alterna phenotypes. Besides having a very unique and identifiable set of unique pattern/color morphs (signature features), Black Gap animals can represent typical specimens from just about any other locality in Texas. It is not at all unusual to collect an alterna on this road that is a dead ringer for an average blairs phase from the Devils River drainage and then proceed to collect another specimen a few feet away that looks like it was caught in a paint fight between Jackson Pollack and Picasso. There is quite obviously a rather heavy River Road locality influence in the Black Gap population as can be seen in the speckled and busily patterned individuals.
Identifying Black Gap animals can be very easy to impossible - depending on the pattern and color morphology. For our purposes I will address the Black Gap "signature" features unique to the locality. Both Blair's and alterna phases are well represented with every conceivable intermediate form. It is very odd that such a mixing "train wreck" of morphologies can occur here while the unique Black Gap signature phenotypes remain reliably consistent. It is possible that we may be watching the process of clade influx and development as it is occurring in real time. The River Road pattern types, coming from the west with slight modifications, is very much in evidence as are the eastern blairs pattern types.

If you wish to explore Black Gap alterna in more detail please use the "Signature Features" button in the button cluster in the upper left of this page.

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