GEOGRAPHIC-VARIATION IN WHOLE VENOM PROFILES FROM THE MOTTLED ROCK RATTLESNAKE (CROTALUS-LEPIDUS-LEPIDUS) IN TEXAS

Venom variation in the mottled rock rattlesnake (Crotalus lepidus lepi dus) was assessed by polyacrylamide gel electrophoresis. Whole venom s amples were stained for general protein, the banding recorded, and the se profiles were used to compare the variation within and between popu lations in Texas. Analyses using agglomerative methods (phenetic clust ering methods and neighbor joining analyses) and ordination from Princ ipal Components analyses provide several geographically correlated gro ups of rattlesnake venom profiles. Evidence is provided for difference s in venom profiles of geographically distinct populations. Venom prof iles of C. lepidus collected along the Rio Grande River, though geogra phically disparate, are generally homogeneous. Thus, the analyses supp ort previously hypothesized dispersal of C. lepidus in Texas along the se Rio Grande canyons. A potential region of population interchange be tween eastern plateau populations and those of the west Texas mountain ranges was identified at the southern end of the Davis Mountains in B rewster Co. Lethality assessments using LD, analyses reveal variation in venom toxicity to range from 2.20-0.72 mg/kg across the geographic range for this subspecies.