Ontogenetic Venom Variation in Black-tailed Rattlesnakes (Crotalus m. molossus, C. molossus oaxacus,

Borja, Miguel

alessandro_53@hotmail.com

Facultad de Ciencias Biológicas

Universidad Juárez del Estado de Durango

Gómez Palacio, Mexico

The Black-tailed Rattlesnake complex includes two species (Crotalus ornatus and C. molossus) and four subspecies (C. m. molossus, C. m. nigrescens, C. m. oaxacus and C. m. estebanensis) distributed across the United States and Mexico. Venom of these taxa has not been well characterized. Recently, we demonstrated that there is intraspecific variation in C. m. nigrescens venom related to the total body length (TBL) of the individual. However, it is unknown if the other subspecies or species also undergo the same ontogenetic change in venom phenotype. To evaluate this, we collected venom from two individuals (one <60 cm TBL and other >70 cm TBL) of C. m. molossus (Texas), C. m. oaxacus (Puebla), and C. ornatus (Texas). We separated components by HPLC and SDS-PAGE and evaluated the proteolytic activity. In addition, we analyzed the toxicity of venoms in a mouse model. Similar to what we found in C. m. nigrescens, juvenile individuals of the three taxa displayed venoms with more crotamine-like myotoxins than adult venoms. In addition, venoms of individuals with a total body length (TBL) of less than 60 cm were less proteolytic than venoms of individuals with a TBL larger than 70 cm. This likely coincides with sexual maturation in these taxa. Variation in proteolytic activity might be related to the observed variation in the amount of metalloproteinases in the venoms. Interestingly, venoms of the same age class were similar in protein profile and proteolytic activity among the three taxa. Our data suggest similar ontogenetic changes for juvenile and adult life stages of the Black-tailed Rattlesnakes, C. molossus and C. ornatus which may be due to similar selection pressures at the different life stages.