Venom Composition of Neglected Bothropoid Snakes from the Amazon Rainforest: Ecological and Toxinological Implications
Snake venoms have evolved in a few families of Caenophidae, and their toxins have been fine-tuned over the evolutive process into highly effective biochemical weapons with a particular role as a trophic adaptation. However, there are many outstanding questions on how venom contributes to the success of venomous species and their adaptation to different environments. Here we analyze the venoms from sympatric and generalist specimens of B. hyoprora, B. taeniatus, B. b. smaragdinus, B. brazili, and B. atrox collected in the wild of Alto Jurua region at the Amazon Forest aiming to understand whether the venom composition could be a driver or influence the arboreal habitats of B. taeniatus and B. b. smaragdinus, or the successful dispersion of B. atrox across the Amazon Forest. Venom composition and the primary sequences of toxin isoforms were characterized by venom gland transcriptomics followed by proteomics. The venom composition of the five species conserved the same protein families present in venoms of Bothropoid snakes but with remarkable differences in the chromatographic profiles and in the relative amount of each toxin group: CTLs were the most abundant in the venoms of B. taeniatus (31.6%), B. b. smaragdinus (33.0%), and B. atrox (32.0%) and SVMPs and PLA2s dominated in venoms of B. hyoprora (23.7% and 20.2%) and B. brazili (20.2% and 20.4%). Some peculiarities were also observed: B. hyoprora venom was the least complex, conserving important isoforms shared with B. atrox venom; the presence of one cluster of SVSPs exclusive to B. brazili venom isoforms; and the presence of the K49-PLA2 homologs only in B. b. smaragdinus and particularly in B. brazili venoms. The SVMP, SVSP, and PLA2 enzyme activities were consistent with the abundance and type of isoforms present in the venoms. B. hyoprora, B. taeniatus, B. b. smaragdinus, and B. atrox venoms presented low lethality to small rodents, while B. brazili venom was the most lethal. Concluding, differences were evidenced between the venoms of B. taeniatus and B. b. smaragdinus arboreal species, while B. b. smaragdinus shared a venom with a similar composition to B. atrox venom, mostly terrestrial. Considering the role of venom toxicity in species' success for adaptation in different areas, B. atrox is the most adapted in the whole Amazonian territory and presented the least lethal venom, while the venom of B. brazili was the most lethal despite its small distribution in the same area. Therefore, our data suggest that the selection of venom composition may not influence the success or behavior of snake species. In this way, other biotic or abiotic factors influence their foraging status or their dispersal in different ecological niches.