title: Phenotypic integration in the feeding system of the eastern diamondback rattlesnake (Crotalus adamanteus).
abstract: Selection can vary geographically across environments and temporally over the lifetime of an individual. Unlike geographic contexts, where different selective regimes can act on different alleles, age-specific selection is constrained to act on the same genome by altering age-specific expression. Snake venoms are exceptional traits for studying ontogeny because toxin expression variation directly changes the phenotype; relative amounts of venom components determine, in part, venom efficacy. Phenotypic integration is the dependent relationship between different traits that collectively produce a complex phenotype and, in venomous snakes, may include traits as diverse as venom, head shape and fang length. We examined the feeding system of the eastern diamondback rattlesnake (Crotalus adamanteus) across environments and over the lifetime of individuals and used a genotype-phenotype map approach, protein expression data and morphological data to demonstrate that: (i) ontogenetic effects explained more of the variation in toxin expression variation than geographic effects, (ii) both juveniles and adults varied geographically, (iii) toxin expression variation was a result of directional selection and (iv) different venom phenotypes covaried with morphological traits also associated with feeding in temporal (ontogenetic) and geographic (functional) contexts. These data are the first to demonstrate, to our knowledge, phenotypic integration between multiple morphological characters and a biochemical phenotype across populations and age classes. We identified copy number variation as the mechanism driving the difference in the venom phenotype associated with these morphological differences, and the parallel mitochondrial, venom and morphological divergence between northern and southern clades suggests that each clade may warrant classification as a separate evolutionarily significant unit.
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, Tallahassee, FL, 32306, USA.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Margres
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, Tallahassee, FL, 32306, USA.
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Wray
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, Tallahassee, FL, 32306, USA.
authors.forename: Margaret
authors.initials: M
authors.lastname: Seavy
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, Tallahassee, FL, 32306, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: McGivern
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, Tallahassee, FL, 32306, USA.
authors.forename: Dragana
authors.initials: D
authors.lastname: Sanader
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, Tallahassee, FL, 32306, USA.
authors.forename: Darin R
authors.initials: DR
authors.lastname: Rokyta
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003435:Crotalid Venoms / Q000737:chemistry*; D017839:Crotalus / Q000033:anatomy & histology / Q000235:genetics*; D056915:DNA Copy Number Variations; D004272:DNA, Mitochondrial / Q000235:genetics; D005431:Florida; D005843:Geography; D005845:Georgia; D010641:Phenotype; D010802:Phylogeny; D040901:Proteomics; D030162:Reptilian Proteins / Q000737:chemistry; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA
chemical_list: D003435:Crotalid Venoms; D004272:DNA, Mitochondrial; D030162:Reptilian Proteins; C013144:myotoxic component of rattlesnake venom
keywords: gene copy number; gene expression; ontogeny; phenotypic integration; snake venom