Evolutionary genetics of Mojave toxin among selected rattlesnake species (Squamata: Crotalinae)

Randy L Powell, University of Texas at El Paso


Mojave toxin is a powerful neurotoxin found in the venom of various crotalids in the United States and Mexico. The toxin is composed of two peptides, an acidic subunit and a phospholipase A2 (PLA2) basic subunit. Both sequences must be present to effect this toxin, which makes the venom much more toxic if present than if absent. One hundred thirty-five specimens representing ten species were tested for the presence of the Mojave toxin subunit A and subunit B using PCR and DNA sequencing. The Mojave toxin subunit A and subunit B primer pairs using temperature stringent PCR parameters produced successful amplifications corresponding to the second and fourth exons of their respective subunits. When compared to the published Mojave toxin A and B subunits, all of the amplifications in the various Crotalus species tested produced greater than 86% sequence identity for both the A and B subunits. The results of the venom testing for Mojave toxin using the anti-Mojave toxin antibody (CSS12) produced results in accord with the PCR analysis. Venom was available from 66 of 135 (48%) individuals and was tested for CSS12 antibody reactivity. The two methods (PCR and CSS12 antibodies) produced results that were 100% congruent in all individuals that were tested by both methods. Outside the scutulatus/viridis/oreganus and mitchellii/tigris clades the Mojave toxin subunits were considerably less common and infrequent. However, both subunits were present either as the B alone independent of the A subunit or A in conjunction with the B subunit, in more than one species within the remaining Crotalus species (i.e., C. adamanteus, C. horridus, and C. lepidus ). The results indicate that the Mojave toxin B subunit is widespread and occurs in populations at high and low frequencies in various rattlesnake species (C. adamanteus, C. mitchellii, C. oreganus, C. scutulatus, and C. viridis) independent of the A subunit. In contrast the Mojave toxin A subunit is limited to individuals in populations that are also positive for the B subunit. It was found only in conjunction with subunit B in individuals, thereby producing snakes with active Mojave toxin. The results suggest that high toxicity in Crotalus and numerous other viperid snakes will be transitory in population's dependant on historical biogeography and related ecological adaptations. Hypotheses on those factors are discussed. (Abstract shortened by UMI.)

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Recommended Citation

Powell, Randy L, "Evolutionary genetics of Mojave toxin among selected rattlesnake species (Squamata: Crotalinae)" (2003). ETD Collection for University of Texas, El Paso. AAI3118653.