Notes: 2018-09-11

Secrets of the Rarest Venom

A look at North America's rarest pitviper, Ophryacus sphenophrys, reveals the new neurotoxin: Sphenotoxin

Horned Pitvipers
New Neurotoxin

In the summer of 1949, William Burger and his brother Jack were in the mountains of southern México collecting specimens for William's graduate work at the Univeristy of Illinois. On the 22nd of July, on an otherwise unremarkable hill in southern Oaxaca, they unknowingly made the find of a lifetime when they happened upon a horned pitviper.

While superficially similar to Ophryacus undulatus, a handful of differences caught Hobart Smith's trained eye. Like a few other pitviper species in Mexico, this specimen had horn-like projections above the eyes, but these were distinctly wide, wedge-shaped horns. There were also fewer scales between the eyes and on the underside of the tail. With these differences, Smith described Burger’s specimen as the new species: Bothrops sphenophrys and inferred a close relationship to B. undulatus some eleven years after the Burger brothers first picked the snake out of the cloud-forests in Oaxaca.

William Leslie Burger's unique pitviper from Oaxaca

Fast forward to 1971. Without public explanation, W. Leslie Burger placed the species in synonymy with Ophryacus undulatus in his PhD dissertation at the University of Kansas. 18 years later, Campbell and Lamar followed his lead, but this time noting that most of the distinguishing characters for O. sphenophrys fall within the range of known variation for O. undulatus in their book on The Venomous Reptiles of Latin America.

Unbeknownst to all parties, this “variation” was contaminated by a third, undescribed species of horned viper. HERP.MX's chance encounter with that third species in 2010 and a subsequent review of museum specimens resulted in the description of Ophryacus smaragdinus and validated Hobart Smith's half-a-century-old Ophryacus sphenophrys.

Slender Horned Pitviper
(Ophryacus undulatus)
Emerald Horned Pitviper
(Ophryacus smaragdinus)
Broad-horned Pitviper
(Ophryacus sphenophrys)
A Broad-horned Pitviper (Ophryacus sphenophrys) in Habitat
A Broad-horned Pitviper (<i>Ophryacus sphenophrys</i>) in Habitat © Hector Franz / HERP.MX
A Broad-horned Pitviper (Ophryacus sphenophrys) in Habitat

What are they packing?

Among the logical questions following the discovery of two new pitvipers is: "what's up with their venom?". Edgar Neri-Castro from the Instituto de Biotecnología at the UNAM campus in Morelos and Miguel Borja at the Universidad Juárez del Estado de Durango reached out to the HERP.MX Team to secure venom samples for analysis, including a contribution from the rarest pitviper in North America: Ophryacus sphenophrys.

Venom extraction from an Ophryacus smaragdinus
An Ophryacus sphenophrys contributing to science.

Toxic Cocktails: a first look

Edgar and his colleagues: Roberto Ponce, Bruno Lomonte, Melisa Benard-Valle, Alejandro Alagón, Fernando Zamudio, and Mariel Valdés, were the first researchers to analyze venom in the genus Ophryacus. Among their results they found that while all three species produced a venom that was highly toxic to mice, the venom from Ophryacus sphenophrys was the most lethal and induced hind-limb paralysis. A profile of O. sphenophrys venom's proteins revealed a novel neurotoxin related to Crotoxin that Edgar and team named Sphenotoxin. The full results of their anlaysis were recently published in the Journal of Proteomics: Venom characterization of the three species of Ophryacus and proteomic profiling of O. sphenophrys unveils Sphenotoxin, a novel Crotoxin-like heterodimeric β-neurotoxin.

Download the Paper

© 2021 HERP.MX