*Article* **Individual Variability in** *Bothrops atrox* **Snakes Collected from Different Habitats in the Brazilian Amazon: New Findings on Venom Composition and Functionality**

**Leijane F. Sousa 1, Matthew L. Holding 2, Tiago H. M. Del-Rei 1, Marisa M. T. Rocha 3, Rosa H. V. Mourão 4, Hipócrates M. Chalkidis 5, Benedito Prezoto 6, H. Lisle Gibbs 7 and Ana M. Moura-da-Silva 1,\***

**Abstract:** Differences in snake venom composition occur across all taxonomic levels and it has been argued that this variation represents an adaptation that has evolved to facilitate the capture and digestion of prey and evasion of predators. *Bothrops atrox* is a terrestrial pitviper that is distributed across the Amazon region, where it occupies different habitats. Using statistical analyses and functional assays that incorporate individual variation, we analyzed the individual venom variability in *B. atrox* snakes from four different habitats (forest, pasture, degraded area, and floodplain) in and around the Amazon River in Brazil. We observed venom differentiation between spatially distinct *B. atrox* individuals from the different habitats, with venom variation due to both common (high abundance) and rare (low abundance) proteins. Moreover, differences in the composition of the venoms resulted in individual variability in functionality and heterogeneity in the lethality to mammals and birds, particularly among the floodplain snakes. Taken together, the data obtained from individual venoms of *B. atrox* snakes, captured in different habitats from the Brazilian Amazon, support the hypothesis that the differential distribution of protein isoforms results in functional distinctiveness and the ability of snakes with different venoms to have variable toxic effects on different prey.

**Keywords:** *Bothrops atrox*; individual variability; venom heterogeneity

**Key Contribution:** This study provides new and important insights about functional differences in venom, which could influence the expression of the snake venom phenotypes in specimens inhabiting different habitats, including nearby geographic regions.