Black Gap Alterna Overview
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.