title: Incipient speciation with biased gene flow between two lineages of the Western Diamondback Rattlesnake (Crotalus atrox).
abstract: We used mitochondrial DNA sequence data from 151 individuals to estimate population genetic structure across the range of the Western Diamondback Rattlesnake (Crotalus atrox), a widely distributed North American pit viper. We also tested hypotheses of population structure using double-digest restriction site associated DNA (ddRADseq) data, incorporating thousands of nuclear genome-wide SNPs from 42 individuals. We found strong mitochondrial support for a deep divergence between eastern and western C. atrox populations, and subsequent intermixing of these populations in the Inter-Pecos region of the United States and Mexico. Our nuclear RADseq data also identify these two distinct lineages of C. atrox, and provide evidence for nuclear admixture of eastern and western alleles across a broad geographic region. We identified contrasting patterns of mitochondrial and nuclear genetic variation across this genetic fusion zone that indicate partially restricted patterns of gene flow, which may be due to either pre- or post-zygotic isolating mechanisms. The failure of these two lineages to maintain complete genetic isolation, and evidence for partially-restricted gene flow, imply that these lineages were in the early stages of speciation prior to secondary contact.
authors.affiliation: Department of Biology & Amphibian and Reptile Diversity Research Center, 501 S. Nedderman Drive, University of Texas at Arlington, Arlington, TX 76019, USA.
authors.forename: Drew R
authors.initials: DR
authors.lastname: Schield
authors.affiliation: Department of Biology & Amphibian and Reptile Diversity Research Center, 501 S. Nedderman Drive, University of Texas at Arlington, Arlington, TX 76019, USA.
authors.forename: Daren C
authors.initials: DC
authors.lastname: Card
authors.affiliation: Department of Biology & Amphibian and Reptile Diversity Research Center, 501 S. Nedderman Drive, University of Texas at Arlington, Arlington, TX 76019, USA.
authors.forename: Richard H
authors.initials: RH
authors.lastname: Adams
authors.affiliation: School of Life Sciences, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154, USA.
authors.forename: Tereza
authors.initials: T
authors.lastname: Jezkova
authors.affiliation: Department of Biology & Amphibian and Reptile Diversity Research Center, 501 S. Nedderman Drive, University of Texas at Arlington, Arlington, TX 76019, USA.
authors.forename: Jacobo
authors.initials: J
authors.lastname: Reyes-Velasco
authors.affiliation: Department of Biology & Amphibian and Reptile Diversity Research Center, 501 S. Nedderman Drive, University of Texas at Arlington, Arlington, TX 76019, USA.
authors.forename: F Nicole
authors.initials: FN
authors.lastname: Proctor
authors.affiliation: Museum of Vertebrate Zoology, 3101 Valley Life Sciences Building, University of California, Berkeley, CA 94720, USA.
authors.forename: Carol L
authors.initials: CL
authors.lastname: Spencer
authors.affiliation: School of Natural Resources and the Environment, 1041 E Lowell Street, University of Arizona, Tuscon, AZ 85721, USA.
authors.forename: Hans-Werner
authors.initials: HW
authors.lastname: Herrmann
authors.affiliation: School of Biological Sciences, 501 20(th) Street, University of Northern Colorado, Greeley, CO 80639, USA.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Mackessy
authors.affiliation: Department of Biology & Amphibian and Reptile Diversity Research Center, 501 S. Nedderman Drive, University of Texas at Arlington, Arlington, TX 76019, USA. Electronic address: todd.castoe@uta.edu.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Castoe
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics; D017839:Crotalus / Q000145:classification* / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D051456:Gene Flow; D049810:Genetic Speciation; D005828:Genetics, Population; D006239:Haplotypes; D008800:Mexico; D008957:Models, Genetic; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide; D011156:Population Density; D060047:Reproductive Isolation; D017422:Sequence Analysis, DNA; D014481:United States
chemical_list: D004272:DNA, Mitochondrial
keywords: Introgression; Population genomics; Population structure; RADseq; Speciation continuum; Viperidae