Exploring venom diversity in Mixcoatlus browni and Mixcoatlus barbouri: A comparative analysis of two rare Mexican snake species with crotoxin-like presence.

The genus Mixcoatlus is composed of three species: Mixcoatlus barbouri, M. browni, and M. melanurus, of which the venom composition of M. melanurus, the most common species of the three, has only recently been described. However, very little is known about the natural history of M. barbouri and M. browni, and the venom composition of these two species has remained thus far unexplored. In this study we characterize the proteomic profiles and the main biochemical and toxic activities of these two venoms. Proteomic data obtained by shotgun analysis of whole venom identified 12 protein families for M. barbouri, and 13 for M. browni. The latter venom was further characterized by using a quantitative 'venomics' protocol, which revealed that it is mainly composed of 51.1 % phospholipases A2 (PLA2), 25.5 % snake venom serine proteases (SVSP), 4.6 % l-amino oxidases (LAO), and 3.6 % snake venom metalloproteases (SVMP), with lower percentages other six protein families. Both venoms contained homologs of the basic and acidic subunits of crotoxin. However, due to limitations in M. barbouri venom availability, we could only characterize the crotoxin-like protein of M. browni venom, which we have named Mixcoatlutoxin. It exhibited a lethal potency in mice like that described for classical rattlesnake crotoxins. These findings expand knowledge on the distribution of crotoxin-like heterodimeric proteins in viper snake species. Further investigation of the bioactivities of the venom of M. barbouri, on the other hand, remains necessary.

Phylogenetically diverse diets favor more complex venoms in North American pitvipers

The role of natural selection in the evolution of trait complex-ity can be characterized by testing hypothesized links betweencomplex forms and their functions across species. Predatory ven-oms are composed of multiple proteins that collectively function toincapacitate prey. Venom complexity fluctuates over evolutionarytimescales, with apparent increases and decreases in complexity,and yet the causes of this variation are unclear. We tested alterna-tive hypotheses linking venom complexity and ecological sourcesof selection from diet in the largest clade of front-fanged ven-omous snakes in North America: the rattlesnakes, copperheads,cantils, and cottonmouths. We generated independent transcrip-tomic and proteomic measures of venom complexity and collatedseveral natural history studies to quantify dietary variation. Wethen constructed genome-scale phylogenies for these snakes forcomparative analyses. Strikingly, prey phylogenetic diversity wasmore strongly correlated to venom complexity than was overallprey species diversity, specifically implicating prey species’ diver-gence, rather than the number of lineages alone, in the evolutionof complexity. Prey phylogenetic diversity further predicted tran-scriptomic complexity of three of the four largest gene familiesin viper venom, showing that complexity evolution is a concertedresponse among many independent gene families. We suggest thatthe phylogenetic diversity of prey measures functionally relevantdivergence in the targets of venom, a claim supported by sequencediversity in the coagulation cascade targets of venom. Our resultssupport the general concept that the diversity of species in an eco-logical community is more important than their overall number indetermining evolutionary patterns in predator trait complexity.

Venom characterization of the three species of Ophryacus and proteomic profiling of O. sphenophrys unveils Sphenotoxin, a novel Crotoxin-like heterodimeric ß-neurotoxin.

Venoms of the three species of Ophryacus (O. sphenophrys, O. smaragdinus, and O. undulatus), a viperid genus endemic to Mexico, were analyzed for the first time in the present work. The three venoms lacked procoagulant activity on human plasma, but induced hemorrhage and were highly lethal to mice. These venoms also displayed proteolytic and phospholipase A2 activities in vitro. The venom of O. sphenophrys was the most lethal and caused hind-limb paralysis in mice. Proteomic profiling of O. sphenophrys venom showed a predominance of metalloproteinase (34.9%), phospholipase A2 (24.8%) and serine protease (17.1%) in its composition. Strikingly, within its PLA2 components, 12.9% corresponded to a Crotoxin-like heterodimer, here named Sphenotoxin, which was not found in the other two species of Ophryacus. Sphenotoxin, like Crotoxin, is composed of non-covalently bound A and B subunits. Partial amino acid sequence was obtained for Sphenotoxin B and was similar (78-89%) to other subunits described. The mouse i.v. LD50 of Sphenotoxin at 1:1 M radio was 0.16 µg/g. Also, like Crotoxin, Sphenotoxin induced a potent neuromuscular blockade in the phrenic nerve-diaphragm preparation. Ophryacus is the fifth genus and O. sphenophrys the third non-rattlesnake species shown to contain a novel Crotoxin-like heterodimeric ß-neurotoxin. BIOLOGICAL SIGNIFICANCE: Ophryacus is an endemic genus of semi-arboreal pitvipers from Mexico that includes three species with restricted distributions. Little is known about the natural history of these species and nothing is known about the properties of their venoms. Research on these species' venoms could generate relevant information regarding venom composition of Mexican pitvipers. Additionally, research into the presence of neurotoxic Crotoxin-like molecules outside of rattlesnakes (genera Crotalus and Sistrurus) has identified this molecule in several new genera. Knowing which genera and species possess neurotoxic components is important to fully understand the repercussions of snakebites, the interaction with prey and predators, and the origin, evolution, and phylogenetic distribution of Crotoxin-like molecules during the evolutionary history of pitvipers. Our study expands current knowledge regarding venom's compositions and function from Mexican pitvipers, providing a comparative venom characterization of major activities in the three Ophryacus species. Additionally, the discovery and characterization of a novel Crotoxin-like molecule, here named Sphenotoxin, in O. sphenophrys, and the detailed protein composition of O. sphenophrys venom supports the hypotheses that Crotoxin-like -ß-neurotoxins are more widespread than initially thought.

A rare new treefrog of the genus Sarcohyla (Anura: Hylidae) from Guerrero, Mexico.

Based on morphological data collected from treefrogs related to Sarcohyla hazelae, we describe a new species of the genus Sarcohyla from the cloud forest of the Sierra Madre del Sur of Guerrero, Mexico. We compare physical charactersitics of this new species to its closest relatives within the genus Sarcohyla, including dorsal and ventral coloration, head shape, tympanum distinctiveness, morphometrics and the condition of the tubercles on hands and feet. We analyze accoustic data from the advertisement call of males of the new species. We discuss the relationship of the species described herein with several of its cogeners, plus we resurrect the Sarcohyla hazelae group for these frogs. We describe habitat and distribution species related to Sarcohyla hazelae and also comment on the conservation priorities of these frogs.