*5.1. Snakes and Venoms*

Thirty-seven male and female adult specimens of *B. atrox* snakes, with sizes ranging from 71.2 to 124.5 cm, were captured in four environments at Santarem and Oriximiná, in the western region of the state of Pará, Brazil (Supplementary Figure S2) under ICM-Bio/SISBio license 32098-1 and SISGEN number A78BD88: (1) Pasture: ten adult snakes were collected from a pasture area in the municipality of Oriximiná (ATXO 1, 2, 3, 5, 6, 7, 9, 15, 16, 19) on the north shore of the Amazon River. This site was historically Terra Firme forest characterized by large trees that were cleared for pasture ~20 years earlier. (2) Floodplain (ATXV): five adults were collected from a seasonally flooded island in the main course of the Amazon river near Santarem (at Urucurituba: ATXV 5, 7, 8, and 9; at Tapará: ATXV 16) or Oriximiná (ATXV 10, 11, 12, 13). These areas are typical of floodplain habitats subject to periodic flooding by the Amazon River and formed by the deposition of sediments that have led to the formation of many islands. The typical vegetation consists of grasses that grow on highly fertile alluvial soils. (3) Forest: ten snakes were captured at the Floresta Nacional do Tapajós, a protected area located in the municipality of Belterra (ATXF 24, 25, 26, 28, 29, 30, 31, 33, 34, and 35) next to the Tapajos River about 50 km south of the Amazon River. This site also represents the upland Terra Firme forest. (4) Degraded: eight snakes were collected at a recently degraded (ATXD 3, 4, 6, 7, 8, 9, and 10) area contiguous to the forest area at Floresta Nacional do Tapajós, which was cleared for pasture. After capture, the snakes were transferred to the Herpetarium of Laboratório de Pesquisas Zoológicas, Universidade da Amazônia (UNAMA), in Santarém, PA. Venom samples were collected using manual extraction techniques, freeze-dried, and kept at −20 ◦C until use. Animal care and procedures used in the handling of snakes were undertaken according to the guidelines and permits (CEUAIB 1244/14, Instituto Butantan, São Paulo, Brazil).

### *5.2. Chromatographic Analysis*

The *B. atrox* venom samples were individually fractionated by reverse-phase highperformance liquid chromatography (RF-HPLC) in the Vydac C18 column as previously described [15]. The fractions had their toxin composition predicted according to peak shape and retention time comparing to a previous standard chromatography of *B. atrox* venom from snakes collected in the same areas from which components present in each fraction were identified and quantified by free-label mass spectrometry [15].
