Snake population venomics and antivenomics of Bothrops atrox: Paedomorphism along its transamazonian dispersal and implications of geographic venom variability on snakebite management.

We describe two geographically differentiated venom phenotypes across the wide distribution range of Bothrops atrox, from the Colombian Magdalena Medio Valley through Puerto Ayacucho and El Paují, in the Venezuelan States of Amazonas and Orinoquia, respectively, and São Bento in the Brazilian State of Maranhão. Colombian and Venezuelan venoms show an ontogenetic toxin profile phenotype whereas Brazilian venoms exhibit paedomorphic phenotypes. Venoms from each of the 16 localities sampled contain both population-specific toxins and proteins shared by neighboring B. atrox populations. Mapping the molecular similarity between conspecific populations onto a physical map of B. atrox range provides clues for tracing dispersal routes that account for the current biogeographic distribution of the species. The proteomic pattern is consistent with a model of southeast and southwest dispersal and allopatric fragmentation northern of the Amazon Basin, and trans-Amazonian expansion through the Andean Corridor and across the Amazon river between Monte Alegre and Santarém. An antivenomic approach applied to assess the efficacy towards B. atrox venoms of two antivenoms raised in Costa Rica and Brazil using Bothrops venoms different than B. atrox in the immunization mixtures showed that both antivenoms immunodepleted very efficiently the major toxins (PIII-SVMPs, serine proteinases, CRISP, LAO) of paedomorphic venoms from Puerto Ayacucho (Venezuelan Amazonia) through São Bento, but had impaired reactivity towards PLA(2) and P-I SVMP molecules abundantly present in ontogenetic venoms. The degree of immunodepletion achieved suggests that each of these antivenoms may be effective against envenomations by paedomorphic, and some ontogenetic, B. atrox venoms.

Snake population venomics and antivenomics of Bothropsatrox: Paedomorphism along its transamazonian dispersaland implications of geographic venom variability on snakebite management

We describe two geographically differentiated venomphenotypes across the wide distributionrange of Bothrops atrox, fromthe ColombianMagdalena Medio Valley through Puerto Ayacuchoand El Paují, in the Venezuelan States ofAmazonas and Orinoquia, respectively, and São Bentoin the Brazilian State of Maranhão. Colombian and Venezuelan venoms show an ontogenetictoxin profile phenotype whereas Brazilian venoms exhibit paedomorphic phenotypes.Venoms from each of the 16 localities sampled contain both population-specific toxins andproteins shared by neighboring B. atrox populations.Mapping themolecular similarity betweenconspecific populations onto a physical map of B. atrox range provides clues for tracingdispersal routes that account for the current biogeographic distribution of the species. Theproteomic pattern is consistent with a model of southeast and southwest dispersal andallopatric fragmentation northern of the Amazon Basin, and trans-Amazonian expansionthrough the Andean Corridor and across the Amazon river between Monte Alegre andSantarém. An antivenomic approach applied to assess the efficacy towards B. atrox venoms oftwo antivenomsraised in Costa Rica and Brazil using Bothrops venomsdifferent than B. atrox inthe immunization mixtures showed that both antivenoms immunodepleted very efficientlythe major toxins (PIII-SVMPs, serine proteinases, CRISP, LAO) of paedomorphic venoms fromPuerto Ayacucho (Venezuelan Amazonia) through São Bento, but had impaired reactivitytowards PLA2 and P-I SVMP molecules abundantly present in ontogenetic venoms. The degreeofimmunodepletion achieved suggests that each of these antivenomsmay be effective againstenvenomations by paedomorphic, and some ontogenetic, B. atrox venoms.

Intraspecific variation of the crotamine and crotasin genes in Crotalus durissus rattlesnakes.

Crotamine is a small basic myotoxin peptide of Crotalus durissus venom, with beta-defensin scafold and variable concentration in individual venoms. The crotamine gene was mapped to the end of chromosome 2 and the signal intensity differed significantly between the two homologues. In contrast to crotamine, the paralogous crotasin gene is scarcely expressed in the venom glands. In this study, we analyzed the crotamine concentrations in the venoms of a total of 23 rattlesnakes from diverse Brazilian localities by ELISA as well as the copy number of both crotamine and crotasin genes by real-time PCR. Crotamine was found to constitute 5-29% of venom proteins varying greatly among individual animals. The crotamine gene exists from 1 to 32 copies per haploid genome, whereas the crotasin gene is present from 1 to 7 copies. Furthermore, we observed that the crotamine concentration and crotamine gene copy number are positively correlated (r(2)=0.68), implying the variation of crotamine in venom results from the variation of the gene copy number. Sequencing of 50 independent copies of crotamine and crotasin genes from four different rattlesnakes revealed the presence of six crotasin isoforms with a single amino acid difference from the original crotasin sequence, whereas only two additional crotamine isoforms were observed. Taken together, our results suggested that after duplication from a common ancestor gene, crotamine and crotasin may have diverged in such a way that the crotamine gene underwent repetitive duplication to increase its copy number, whereas the crotasin gene diversified its sequence.