Convergent evolution of pain-inducing defensive venom components in spitting cobras.

Convergent evolution provides insights into the selective drivers underlying evolutionary change. Snake venoms, with a direct genetic basis and clearly defined functional phenotype, provide a model system for exploring the repeated evolution of adaptations. While snakes use venom primarily for predation, and venom composition often reflects diet specificity, three lineages of cobras have independently evolved the ability to spit venom at adversaries. Using gene, protein, and functional analyses, we show that the three spitting lineages possess venoms characterized by an up-regulation of phospholipase A2 (PLA2) toxins, which potentiate the action of preexisting venom cytotoxins to activate mammalian sensory neurons and cause enhanced pain. These repeated independent changes provide a fascinating example of convergent evolution across multiple phenotypic levels driven by selection for defense.

Venom Complexity in a Pitviper Produced by Facultative Parthenogenesis.

Facultative parthenogenesis (FP) is asexual reproduction in plant and animal species that would otherwise reproduce sexually. This process in vertebrates typically results from automictic development (likely terminal fusion) and is phylogenetically widespread. In squamate reptiles and chondrichthyan fishes, FP has been reported to occur in nature and can result in the production of reproductively viable offspring; suggesting that it is of ecological and evolutionary significance. However, terminal fusion automixis is believed to result in near genome-wide reductions in heterozygosity; thus, FP seems likely to affect key phenotypic characters, yet this remains almost completely unstudied. Snake venom is a complex phenotypic character primarily used to subjugate prey and is thus tightly linked to individual fitness. Surprisingly, the composition and function of venom produced by a parthenogenetic pitviper exhibits a high degree of similarity to that of its mother and conspecifics from the same population. Therefore, the apparent loss of allelic diversity caused by FP appears unlikely to have a significant impact on the prey-capturing ability of this snake. Accordingly, the pitviper offspring produced by FP retained complex phenotypic characteristics associated with fitness. This result reinforces the potential ecological and evolutionary importance of FP and questions our understanding of the inheritance of venom-associated genes.

Production and assessment of ovine antisera for the manufacture of a veterinary adder antivenom.

Medically important venomous snakes in Western Europe are Vipera ammodytes, Vipera aspis, Vipera berus and Vipera latastei. Envenomation of dogs and other animals by these snakes receives limited attention despite the relative frequency and potential mortality and morbidity. This reflects, in part, the lack of a dedicated veterinary antivenom. Successful antivenoms are derived from antisera containing high levels of specific polyclonal antibodies that bind to, and neutralise, all the toxins present. This requires a careful choice of immunogen, animals and immunisation schedule. We detected proteomic variation in the venoms of V ammodytes, V aspis, V berus and V latastei by SDS-PAGE (sodium dodecyl sulphate-polyacrylamide gel electrophoresis) gel electrophoresis. Consequently, we used a mixture containing equal amounts of venom from these species to immunise a flock of sheep. We demonstrate that immunisation resulted in antisera containing high levels of specific antibodies directed against the majority of toxic components found in all four snake venoms using immunoblotting, ELISA and small-scale affinity chromatography assays. The latter shows that all 25 sheep responded quickly and maintained high levels of specific antibodies throughout the two-year period of study. This ensures a consistent starting material for the manufacture of a reproducible veterinary antivenom, ViperaVet. Our next objectives are to purify the antibodies from our antisera and demonstrate their preclinical neutralising efficacy in murine animal studies prior to undertaking a clinical trial in envenomed patients.