And on vertebrate taxonomy in general, I come down on the side of the lumpers, with caveats.
I agree with revisions of the Collared Lizards in the genus Crotaphytus which resulted in elevating many previous subspecies to the species level. Those lizards display physiological differences as well as DNA evidence supporting their status as species rather than subspecies of C. collaris.
What I see in entomology is a long-standing effort by some authors to describe species and subspecies based on color morphs and geographical location. In many cases, all populations express the so-called "characters" that are claimed as diagnostic for a given proposed subspecies. I suspect that many of these proposed subspecies are nothing more than regional variants or individual expressions of genetic potential. Upon review by subsequent authors, many hastily described subspecies are relegated to the status of "form", which is more appropriate.
My feeling, pending more substantive investigation, is that the so-called subspecies of Masticophis (or Coluber) flagellum are actually individual phenotypes or at best population trends, as all color phases occur in all populations and there appear to be no reproductive isolating factors other than distance, and that only between the far edges of the collective range. Thus, there seems to be ample opportunity for free flow of genetic material throughout the range of M. flagellum. Still, the practice of identifying organisms as "forms" is not widely used in vertebrate taxonomy but that is how I perceive the various color phases of Western Coachwhips. I recall that at one time, it was thought that the color phases of Lampropeltis alterna were distinct species.
I do think there is still room to wonder regarding one aspect of color in Western Coachwhips, that being the striking pink animals found in Texas and other parts of the range, as contrasted with the red or brick-colored animals also found throughout the range of the species. It seems to me that there is a different quality to the pink suffusion of certain animals as opposed to the more pigment-like color of red animals such as the one in the photos in this post. I agree with Sighthunter that this pink-flush color is at least partly attributable to diet, as I have induced the onset of pink color in two of my Western Coachwhips by feeding them prey which had more beta carotene in its diet than previously, and also by feeding them grocery store chicken, which has been fed the color enhancer Canthaxanthin to give it it's characteristic pinkish color. The carotene in the diet of my feeder mice and the Canthaxanthin in the chicken was passed on to my pink-tending coachwhips and did enhance their color. I do not think that coachwhips which do not express the tendency to flush pink will respond to these dietary supplements, and brown coachwhips will likely remain brown, brick red coachwhips will likely remain as red as ever and no more, etc. It's the ones with the individual tendency to flush pink that respond most dramatically to dietary supplements. Further, if pink-tending coachwhips are fed carotene deficient diets, they fade to pale pink or light tan over time. If this bears out, then would a pink coachwhip which was previously placed in a subspecies based on its color be reclassified after it faded over the course of its captivity?
Do I think about this stuff too much?
