Biology 342 Fall 06 Trevor Young
The ontogeny of snake venom
Ontogeny plays a very important role in snake venom variation, which has been shown to vary in both the concentrations of various toxins present in the venom as well as its physiological effects as snakes proceed through development. A recent venom proteome analysis of the Bothrops atrox by Guercio et al (2006) demonstrated differential expression of toxins between the juveniles and adults of this species . The researchers corroborated earlier work showing the enhanced physiological effects of juvenile Bothrops atrox venom, which the researchers hypothesized was due to the higher levels of P-III class Zn-metalloproteinases (involved in degrading the extracellular matrix), berythractivase (involved in coagulation), vascular endothelial growth factors (which enhance vascular permeability and allow for venom distribution throughout the body), and nerve growth factors (which performs an unknown function but has been found in many snake venoms) in juveniles compared to adults. Guercio et al. hypothesize some of this ontogenetic variation has to do with the diet juvenile and adult Bothrops atrox, with the juvenile preferring lizards and amphibians while adults prefer mammalian prey. This differential expression could aid in the development of therapeutic agents from snake venom as venoms from the same species but from different stages of life could be more effective at treating diseases .
Common lancehead (Courtesy of Wikimedia Commons)
Further research correlating changes in venom composition with ontogenetic shifts has been done with northern and southern Pacific rattlesnakes as well as the Midget Faded rattlesnake [3, 4]. As with the Bothrops atrox research, these changes have also been correlated with the shift in diet from ectothermic prey in the juvenile stages to endothermic prey in the adult stages. Further similarities with the Bothrops atrox research include the inverse correlation between body size and venom toxicity, with adult snakes having venom with lesser toxicity but a greater ability to predigest prey. This is especially interesting considering research has shown that venom yields increase exponentially with size in northern and southern Pacific rattlesnakes . However, there are important differences in the ontogenetic shifts between species of rattlesnakes. While maturation causes a fivefold increase in metalloprotease activity in northern and southern Pacific rattlesnakes, it actually decreases in the Midget Faded rattlesnake . Additionally, while phospholipase A2 (which is a neurotoxin) activity decreases with maturation in northern and southern Pacific rattlesnakes, no change is observed in the Midget Faded rattlesnake . This demonstrates a general correlation among snake venoms, that venom can either possess high concentrations of metalloproteases or neurotoxins, but not both .
The Midget Faded Rattlesnake (Courtesy of venomousreptiles.org)
Resources cited in this section:
1. Guercio, R., Shevchenko, A., Shevchenko, A., Lopez-Lozano, J.L., Paba, J., Sousa, M.V., & Ricart, C. Ontogenetic variations in the venom proteome of the amazonian snake Bothrops atrox. Proteome Science 4, 11 (2006).
2. Yuancong, Z. Research and Utilization of Proteins from Snake Venom. http://www.asiabiotech.com/01/english/preserved-docs/0114n15/0339_0343.pdf (1997).
3. Mackessy, S. P. Venom ontogeny in the pacific rattlesnakes Crotalus viridis helleri and C. v. oreganus. Copeia 1, 92-101 (1988).
4. Mackessy, S. P., Williams, K., & Ashton, K.G. Ontogenetic variation in venom composition and diet of Crotalus oreganus concolor: a case of venom paedomorphosis? Copeia 4, 769-782 (2003).