The Effects of Hybridization on Divergent Venom Phenotypes: Characterization of Venom From Crotalus

Smith, Cara

Mackessy, Stephen P.

School of Biological Sciences

University of Northern Colorado

Greeley, CO 80639 USA

Hybridization between divergent species can be analyzed to elucidate expression patterns of distinct parental characteristics, as well as to provide information about the extent of reproductive isolation between species. A known hybrid cross between two rattlesnakes with highly divergent venom phenotypes provided the opportunity to examine occurrence of parental venom characteristics in the F1 hybrids as well as ontogenetic shifts in the expression of these characters as the hybrids aged. Although venom phenotypes of adult rattlesnake venoms are known for many species, the effect of hybridization on phenotype inheritance is not well understood, and effects of hybridization on venom ontogeny have not yet been investigated. In this study we investigated both phenomena resulting from the hybridization of a male snake with type I venom, Crotalus oreganus helleri (Southern Pacific Rattlesnake), and a female snake with type II venom, C. scutulatus scutulatus (Mojave Rattlesnake). SDS-PAGE, enzymology, Western blot and reversed phase HPLC (RP-HPLC) were used to characterize the venom of the C. o. helleri male, the C. s. scutulatus female and their two hybrid offspring as they aged. In general, Crotalus o. helleri  × C. s. scutulatus hybrid venoms appeared to exhibit overlapping parental venom profiles, and several different enzyme activity patterns. The C. s. scutulatus  × C. o. helleri hybrid male's venom profile provided the strongest evidence that type I and type II venom characteristics are expressed simultaneously in hybrid venoms, as this snake contained distinctive characteristics of both parental species. However, the possibility of sex-influenced development of metalloprotease activity, as seen in the ontogenetic shifts of the hybrid female, may influence the levels of expression of both type I and type II characteristics in hybrid venoms.