ABSTRACT
Pseudechis (black snakes) is an Australasian elapid snake genus that inhabits much of mainland Australia, with two representatives confined to Papua New Guinea. The present study is the first to analyse the venom of all 9 described Pseudechis species (plus one undescribed species) to investigate the evolution of venom composition and functional activity. Proteomic results demonstrated that the typical Pseudechis venom profile is dominated by phospholipase A2 toxins. Strong cytotoxicity was the dominant function for most species. P. porphyriacus, the most basal member of the genus, also exhibited the most divergent venom composition, being the only species with appreciable amounts of procoagulant toxins. The relatively high presence of factor Xa recovered in P. porphyriacus venom may be related to a predominantly amphibian diet. Results of this study provide important insights to guide future ecological and toxinological investigations.
Subject(s)
Elapid Venoms/metabolism , Hydrophiidae/physiology , Models, Molecular , Reptilian Proteins/metabolism , Animals , Australia , Coagulants/chemistry , Coagulants/metabolism , Coagulants/toxicity , Databases, Protein , Elapid Venoms/chemistry , Elapid Venoms/genetics , Elapid Venoms/toxicity , Electrophoresis, Polyacrylamide Gel , Evolution, Molecular , Hydrophiidae/growth & development , Molecular Conformation , New Guinea , Phospholipases A2/chemistry , Phospholipases A2/genetics , Phospholipases A2/metabolism , Phospholipases A2/toxicity , Phylogeny , Proteomics/methods , Reptilian Proteins/chemistry , Reptilian Proteins/genetics , Reptilian Proteins/toxicity , Species Specificity , Two-Dimensional Difference Gel ElectrophoresisABSTRACT
Venom is a key evolutionary trait, as evidenced by its widespread convergent evolution across the animal kingdom. In an escalating prey-predator arms race, venoms evolve rapidly to guarantee predatory or defensive success. Variation in venom composition is ubiquitous among snakes. Here, we tested variation in venom activity on substrates relevant to blood coagulation among Pseudonaja (brown snake) species, Australian elapids responsible for the majority of medically important human envenomations in Australia. A functional approach was employed to elucidate interspecific variation in venom activity in all nine currently recognised species of Pseudonaja. Fluorometric enzymatic activity assays were performed to test variation in whole venom procoagulant activity among species. Analyses confirmed the previously documented ontogenetic shift from non-coagulopathic venom in juveniles to coagulopathic venom as adults, except for the case of P. modesta, which retains non-coagulopathic venom as an adult. These shifts in venom activity correlate with documented ontogenetic shifts in diet among brown snakes from specialisation on reptilian prey as juveniles (and throughout the life cycle of P. modesta), to a more generalised diet in adults that includes mammals. The results of this study bring to light findings relevant to both clinical and evolutionary toxinology.
Subject(s)
Animal Nutritional Physiological Phenomena , Coagulants/pharmacology , Elapid Venoms/pharmacology , Elapidae/physiology , Phylogeny , Animals , Australia , Factor VII/metabolism , Factor Xa/metabolism , Humans , Least-Squares Analysis , Predatory Behavior , Prothrombin/metabolism , Species SpecificityABSTRACT
Australia is the stronghold of the front-fanged venomous snake family Elapidae. The Australasian elapid snake radiation, which includes approximately 100 terrestrial species in Australia, as well as Melanesian species and all the world's sea snakes, is less than 12 million years old. The incredible phenotypic and ecological diversity of the clade is matched by considerable diversity in venom composition. The clade's evolutionary youth and dynamic evolution should make it of particular interest to toxinologists, however, the majority of species, which are small, typically inoffensive, and seldom encountered by non-herpetologists, have been almost completely neglected by researchers. The present study investigates the venom composition of 28 species proteomically, revealing several interesting trends in venom composition, and reports, for the first time in elapid snakes, the existence of an ontogenetic shift in the venom composition and activity of brown snakes (Pseudonaja sp.). Trends in venom composition are compared to the snakes' feeding ecology and the paper concludes with an extended discussion of the selection pressures shaping the evolution of snake venom.
