Venoms of snake species inhabiting distinct geographies exhibit significant intraspecific variation. For instance, remarkable biogeographic venom variation has been documented in the venoms of the common cobra (Naja naja) and Russell’s viper (Daboia russelii), two of India’s widely distributed snake species. The distinct ecologies and habitats across their range distribution may determine venom phenotypes and toxin abundances. Moreover, venom variation may also be contributed by inter-and intra-specific competition, distinct sexual ecologies, dietary shifts, varying predator pressures, and ontogenetic shifts in ecology. Here, we assess the ontogenetic variability in the venoms of Naja naja and Daboia russelii. Venoms collected from snakes of these two species across their developmental stages were analysed for their proteomic composition, biochemical activities, and lethality against a variety of prey species. The relative abundances of toxin families in D. russelii venoms significantly varied between the young and adult individuals. While the adult venoms were enriched with higher molecular weight proteases, increased abundances of lower molecular weight toxins, such as phospholipases, were recorded in the venoms of younger individuals. These compositional variations also correlated with the biochemical and pharmacological properties of these venoms. In addition, a light interference-based toxin-receptor binding experiment was also performed to understand the prey-specific neurotoxicity of the adult and juvenile N. naja venoms. The study, for the first time, comprehensively documents the similarities and differences in venoms of two medically important Indian snakes across their developmental stages. These results further augment our knowledge of the toxin repertoire evolution in these lineages.
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