FM 170 is easily one of the
most scenic roads in the United States with outstanding
views into Northern Chihuahua, Mexico. A pilgrimage to
this area generally turns into an awakening for alterna enthusiasts
and serves to tie together the alterna experience in a way that can
never happen perusing snakes in deli cups at reptile
expositions. Simply put, for many, the place gets into
the blood like a fever that never quite goes away. Along
this long stretch of highway are several well know
collecting spots but alterna
can appear at just about anywhere along its length if
there is adequate roadside habitat. At Vivid Reptiles we
have narrowed our focus over the years to animals
originating from the "Big Hill" area - an impressive
desert mountain located about 12 miles west of the town
of Lajitas. Because of the scarcity of accessible
collecting spots, the sampling of alterna from all
River Road collecting spots is heavily biased and
undoubtedly many "surprises" lurk in the more
inaccessible areas to the north of the River Road.
To those unfamiliar with the species, alterna from the
River Road can appear so radically different from the
eastern types that they can be forgiven for making the
assumption that they are not one and the same species.
Indeed, regarding both pattern and color morphology -
quite literally, anything goes. The clean, neatly laid
out patterns of the eastern morphs can be rare here and
although you can find light blair's phase animals
here they are more often than not the exception. In
River Road captive collections, blair's phase animals
are not well represented
because of collector bias rather than such animals being
rarities. The River Road animals feature several,
readily identifiable pattern types and the locality
appears to be the geographic loci for the more
flamboyant patterns involving speckling,
multi-alternates, pin-banding and so forth. It is with
much angst and frustration that we look south across the
Rio Grande from the Big Hill and wonder what alterna variations
lurk in the vast, unsampled desert expanses of Northern
Mexico. Indeed, the true geographic origins for the
aforementioned pattern types may well lie to the south
of the Rio Grande.
Identifying River Road alterna by pattern/color is somewhat
easier than identifying alterna from localities that lie to
the immediate east and north. That said, exceptions do
occur with enough regularity to keep one cautious. River
Road signature features are readily identifiable in
these proximal alterna
localities and it would appear that the historic
direction of gene
flow has been from the River Road area outward to Black
Gap to the east, the Christmas and Davis Mountains to
the north and ultimately to the Guadalupe and Heuco
Mountains to the northwest. Most of this gene flow
likely occurred during the Pleistocene when migration
barriers were much less reduced or altogether absent.
One is left to ponder why so much variation and
plasticity evolved in this species. Whatever the
evolutionary forces were/are driving the evolution of
this reptile, we have been presented with a
treasure chest bursting with
ophidian wonders. This is surely one of the most
beautiful and varied colubrids on the planet.
For a compilation of significant features of River Road
alterna please
use the following button:
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