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The genetics underlying adaptive trait evolution describes the intersection between the probability that particular types of mutation are beneficial and the rates they arise. Snake venoms can vary in a directly meaningful manner through coding mutations and regulatory mutations. The amounts of different components determine venom efficacy, but point mutations in coding sequences can also change efficacy and function. The Timber Rattlesnake (Crotalus horridus) has populations that have evolved neurotoxic venom from the typical hemorrhagic rattlesnake venom present throughout most of its range. We identified only a handful of nonsynonymous differences in just five loci between animals with each venom type, and these differences affected lower-abundance toxins. Expression of at least 18 loci encoding hemorrhagic toxins was severely reduced in the production of neurotoxic venom. The entire phospholipase A2 toxin family was completely replaced in the neurotoxic venom, possibly through intergeneric hybridization. Venom paedomorphosis could, at best, explain only some of the loss of expression of hemorrhagic toxins. The number of potential mechanisms for altering venom composition and the patterns observed for C. horridus suggest that rapid venom evolution should occur primarily through changes in venom composition, rather than point mutations affecting coding sequences., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Snake venom plays a critical role in food acquisition, digestion, and defense. Venoms are known to change throughout the life of some snake species, but nothing is known about the venom composition of hatchling/neonate snakes prior to and just after their first shedding cycle, despite this being a critical time in the life of the snake. Using a cohort of Crotalus horridus and two cohorts of Crotalus adamanteus, we showed for the first time that snakes undergo significant changes in venom composition after the postnatal shedding event. The number of changes among cohorts ranged widely and there was wide variation in the direction of protein regulation, which appeared to be on a locus-specific level rather than protein-family level. These significant venom composition changes that take place in the first few weeks of life most likely play critical roles in venom economy and resource conservation and may partially explain the rare, post-birth maternal care found in some venomous species., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Despite causing considerable human mortality and morbidity, animal toxins represent a valuable source of pharmacologically active macromolecules, a unique system for studying molecular adaptation, and a powerful framework for examining structure-function relationships in proteins. Snake venoms are particularly useful in the latter regard as they consist primarily of a moderate number of proteins and peptides that have been found to belong to just a handful of protein families. As these proteins and peptides are produced in dedicated glands, transcriptome sequencing has proven to be an effective approach to identifying the expressed toxin genes. We generated a venom-gland transcriptome for the Eastern Diamondback Rattlesnake (Crotalus adamanteus) using Roche 454 sequencing technology. In the current work, we focus on transcripts encoding toxins. We identified 40 unique toxin transcripts, 30 of which have full-length coding sequences, and 10 have only partial coding sequences. These toxins account for 24% of the total sequencing reads. We found toxins from 11 previously described families of snake-venom toxins and have discovered two putative, previously undescribed toxin classes. The most diverse and highly expressed toxin classes in the C. adamanteus venom-gland transcriptome are the serine proteinases, metalloproteinases, and C-type lectins. The serine proteinases are the most abundant class, accounting for 35% of the toxin sequencing reads. Metalloproteinases are the most diverse; 11 different forms have been identified. Using our sequences and those available in public databases, we detected positive selection in seven of the eight toxin families for which sufficient sequences were available for the analysis. We find that the vast majority of the genes that contribute directly to this vertebrate trait show evidence for a role for positive selection in their evolutionary history., (Copyright © 2011 Elsevier Ltd. All rights reserved.)