How the H-Snake Lost Its Hs: Mendelian Inheritance and Geographic Distribution of the Blonde- phase

Rhoads, Dustin D.

Department of Biology

Texas Christian University

Fort Worth, TX 76129 USA

The Blonde phase of the Trans-Pecos Ratsnake (Bogertophis subocularis) is a naturally occurring color pattern mutation dramatically different from the more common H-patterned type. Yet, although it has been deemed apparently noteworthy enough to be featured in most field guides inclusive of Chihuahuan Desert herpetofauna, nothing has been published in peer-reviewed literature on its genetics, geographic distribution, frequency of occurrence, or any other basics of its natural history. Here, I analyze comparative meristic data along with the outcomes of captive matings involving Blonde and H-patterned B. subocularis in order to infer the nature of color pattern inheritance in this taxon. Color pattern frequencies among 161 offspring were consistent with inheritance of the Blonde pattern as a discrete Mendelian recessive trait. I also analyze the mating outcomes of two other heretofore poorly known pattern phenotypes for this taxon and from these—combined with the aforementioned meristic data—present early evidence that the typical Η-pattern phenotype found throughout the species’ range is possibly composed of two genes—namely, stripes and blotches. Furthermore, as no geographic map has ever been produced for this mutation, I also describe the known distribution of the Blonde phase, and from this data present evidence that Blonde occurrence and coloration appears to coincide with, and closely match in hue, its natural substrate of cream-yellow or yellow-gray cretaceous limestone. This, in turn, informs potential range beyond the biased collecting sites of documented Blonde specimens. Additionally, nothing has been published on the frequency of the Blonde allele in nature, and thus I also use field observation data to conservatively estimate both morph frequency and allele frequency and quantitatively classify the allele not as a rare mutation (typically defined as comprising < 1% of the population) but indeed as a polymorphism (comprising significantly > 1% of the population).