Trends in Venom Composition in Mexican Rattlesnakes

Mackessy, Stephen P.

School of Biological Sciences

University of Northern Colorado

Greeley, Colorado USA

México is a large country with diverse terrain, currently supporting a diverse assemblage of more than 30 species of rattlesnakes. Although several species have ranges extending into the United States, many are endemic, particularly in montane regions, with several species showing isolated and narrowly circumscribed distributions. Venoms from medically important species, including Crotalus atrox, C. basiliscus, C. molossus, C. scutulatus and C. simus, have been extensively studied, but relatively little is known of montane rattlesnake venoms. Using protein chemistry and proteomic techniques, we analyzed venoms of Crotalus lepidus, C. polystictus, C. pricei, C. scutulatus and C. willardi from various locations within México and the US. Several distinct patterns emerge, but in general, the type I/type II dichotomy in venom composition is observed in all of these species. None of the montane rattlesnakes (from populations sampled) showed the presence of crotoxin/Mojave toxin homologs, a hallmark feature of type II venoms, and compositional patterns in general were rather conserved among all montane species. Among C. lepidus, Mexican populations (C. l. maculosus, C. l. morulus) showed higher levels of venom metalloproteinases, while northern populations (C. l. klauberi, C. l. lepidus) produced venoms more toxic to mice and lizards. Crotalus pricei venoms showed high metalloproteinase levels also, and the venom was quite toxic toward mice and lizards, but no neurotoxins were present. Additional trends will be presented, but overall venom compositional trends followed patterns typical for many other rattlesnake species. This lack of unique diversification of venoms again underscores the observation that rattlesnake venoms, which may show local adaptation and some variation in composition, share a majority of venom toxins.

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