Snake Venomics of the Arboreal Talamancan Palm-Pitviper, Bothriechis nubestris, Provides Clues on the Origin of a Phenotypic Dichotomy between Type‑I and Type-II Venoms

We report the biochemical and proteomic characterization of the venom of the arboreal Talamancan palm-pitviper, Bothriechis nubestris, a species endemic to north and central parts of the Costa Rican Cordillera de Talamanca, at 2100 to 3000 m above sea level. The Talamancan palm-pitviper venom arsenal comprised the translated products of 26 unique transcripts into 10 toxin classes, where metalloproteinases PIIa and PIII represent the dominant components. In vitro, the venom proteolyzed azocasein and gelatin but showed no phospholipase A2 or human plasma coagulant activities. In vivo, B. nubestris venom exhibited an intravenous median lethal dose (LD50) of 21.5 (95% confidence interval: 15.6–29.5) μg/mouse, and a minimum hemorrhagic dose (MHD) of 1.85 μg. PoliVal-ICP antivenom neutralized the venom’s lethal activity with a potency of 9.7 mg of venom/g of antivenom and significantly reduced the hemorrhagic effect. Comparison of venom gland transcriptomes and venom proteomes of B. nubestris and its closest congeneric relative, B. nigroviridis, revealed that highly conserved venom gland transcriptomes are differentially processed by each species to produce divergent (type-I vs type-II, respectively) venoms. This phenomenon contributes to the remarkable venom phenotypic variability found across the palm-pitviper phylogeny. A possible mechanism for the occurrence of type-I/type-II venom phenotypic dichotomy is discussed.