KROCHMAL, A.R.; GARDNER, C.E.; Whitman College, Walla Walla, WA, USA; Whitman College, Walla Walla, WA, USA: Potent poison or Liquid Lysol: On the evolutionary origins of snake venom

Snakes have been generally classified as being either venomous or non venomous, a dogma that has been recently challenged by the widespread occurrence of medically significant bites from �non venomous� snakes. Empirical investigations have shown that many snakes typically considered �non venomous� possess toxic salivary secretions which closely resemble true venoms at both the biochemical and genetic levels. Behavioral studies have failed to show a role of such secretions in either defense or predation, leaving their utility unknown. The ophidian feeding habits, which often include scavenging, dictate that snakes often encounter a high microbial load when feeding; this load is further exacerbated by the ectothermic physiology of snakes. We hypothesized that the toxic salivary secretions of �non venomous� snakes serve as antimicrobial agents and that snake venom initially arose as an antimicrobial agent and was subsequently exapted for prey capture. To test these hypotheses, we assayed the antimicrobial activity of the toxic salivary secretions of snakes within a phylogenetic context. We used venom and secretions from snakes representing a variety of feeding habits and phylogenetic positions and investigated the ability of these secretions to impede the growth of common bacteria. Salivary secretions from both �venomous� and �non venomous� snakes strongly inhibited the growth of all bacteria tested. This ability did not differ among snakes (venomous or non venomous) and was significantly higher than that of control solutions. Our results demonstrate that the toxic salivary secretions of snakes have antimicrobial properties and they support the idea that snake venom might have initially evolved as an antimicrobial agent.