It's complicated! Ontogenetic variation in venom composition of rattlesnakes
Hayes, William K.
whayes@llu.edu
Fox, Gerad A.
Kelln, Wayne
Department of Earth and Biological Sciences
Loma Linda University
Loma Linda, California USA
Gren, Eric C. K.
University of Montana, Bitterroot College Campus
Bitterroot Community Science Center
Hamilton, Montana USA
Cochran, Chip
Travis, Zachary D.
Department of Earth and Biological Sciences
Loma Linda University
Loma Linda, California USA
Dugan, Eric A.
Dugan Biological Services, LLC
Upland, California USA
Lee, Kyung H.
Neurology Residency
Dartmouth Hitchcock Medical Center
Lebanon, New Hampshire USA
Cardwell, Michael D.
Biology Department
San Diego State University
San Diego, California USA
Goode, Matthew J.
School of Natural Resources
University of Arizona
Tucson, Arizona USA
Morris, Cale
Heritage Academy
Mesa, Arizona USA
Schuett, Gordon W.
Department of Biology ǀ Neuroscience Institute
Georgia State University
Atlanta, Georgia USA
Chiricahua Desert Museum
Rodeo, New Mexico USA
When young, the small size of rattlesnakes severely constrains the prey they can capture and consume. As the snakes grow their larger size and greater venom supply expands their range of prey intake, often from smaller ectothermic prey to larger, endothermic prey. Smaller snakes are also subject to a greater range of predators. We examined ontogenetic changes in venom composition and complexity of seven southwestern North American rattlesnake species to test four hypotheses: that (1) change is greater in species or populations possessing largely proteolytic (type I or type B) rather than largely neurotoxic (type II or type A) venom; (2) change is greater in species that transition from reptile to mammal prey than those which specialize on mammals throughout their life; (3) change occurs continuously as an individual grows, even after attaining reproductive size; and (4) venom complexity is moderate in small individuals, greatest during the period of ontogenetic shift in toxins, and least in adults. We separated venom components of individual venoms using reverse-phase high-pressure liquid chromatography (RP-HPLC), and quantified protein content of individual chromatogram peaks. We identified specific toxins using mass spectrometry. To associate ontogenetic changes in venom with diet, we dissected prey material from the stomachs and/or guts of snakes. Results indicated that ontogenetic change in venom composition exists in all seven species. Moreover, we found support for all but one hypothesis. Hypothesis 2 proved wrong, as the most profound ontogenetic change occurs in C. ruber, which feeds largely on mammals throughout its life. Collectively, our findings demonstrate the remarkably varied patterns of venom ontogeny that exist within a closely related group of vipers, and even within a single species, leading to few, if any, general patterns. They also underscore the likely adaptive importance of venom composition changes coincident with dietary shifts.