Geographical variation in Crotalus scutulatus scutulatus (Mojave rattlesnake) venom properties

Individual venom samples were analyzed from 12 specimens of Crotalus scutulatus scutulatus, from north of Tucson to the extreme southeastern region of Arizona. Six of the specimens, from north of Tucson, produced venom lethal toxicity (i.p. ld 50) values in mice of 2.0 – 6.0 mg/kg. These coincided with the values previously reported for C. s. scutulatus in the Phoenix, Arizona, region and designated as type B venom ( Glenn and Straight, 1978). In contrast, the venom ld 50 of six individuals from extreme southeastern Arizona, including one individual near Tucson, ranged from 0.22 – 0.46 mg/kg. This corresponds to the values for C. s. scutulatus venom previously reported and designated as type A venom ( Glenn and Straight, 1978). Specimens with type A venom have been collected in California, Nevada, Utah and regions of Arizona. In addition to differences in lethal toxicity, the type B venom consistently exhibits a different protein profile, greater proteolytic activity, greater hemorrhagic activity and contains little or none of the major lethal toxin, Mojave toxin, compared to the type A venom. No external morphological characteristic could be found differentiating the type A venom specimens from the type B venom specimens. These findings further confirm the geographical variation of C. s. scutulatus venom in Arizona.