title: Limitations of climatic data for inferring species boundaries: insights from speckled rattlesnakes.
abstract: Phenotypes, DNA, and measures of ecological differences are widely used in species delimitation. Although rarely defined in such studies, ecological divergence is almost always approximated using multivariate climatic data associated with sets of specimens (i.e., the "climatic niche"); the justification for this approach is that species-specific climatic envelopes act as surrogates for physiological tolerances. Using identical statistical procedures, we evaluated the usefulness and validity of the climate-as-proxy assumption by comparing performance of genetic (nDNA SNPs and mitochondrial DNA), phenotypic, and climatic data for objective species delimitation in the speckled rattlesnake (Crotalus mitchellii) complex. Ordination and clustering patterns were largely congruent among intrinsic (heritable) traits (nDNA, mtDNA, phenotype), and discordance is explained by biological processes (e.g., ontogeny, hybridization). In contrast, climatic data did not produce biologically meaningful clusters that were congruent with any intrinsic dataset, but rather corresponded to regional differences in atmospheric circulation and climate, indicating an absence of inherent taxonomic signal in these data. Surrogating climate for physiological tolerances adds artificial weight to evidence of species boundaries, as these data are irrelevant for that purpose. Based on the evidence from congruent clustering of intrinsic datasets, we recommend that three subspecies of C. mitchellii be recognized as species: C. angelensis, C. mitchellii, and C. Pyrrhus.
authors.affiliation: Department of Biological Sciences, Tarleton State University, Stephenville, Texas, United States of America.
authors.forename: Jesse M
authors.initials: JM
authors.lastname: Meik
authors.affiliation: Department of Biology, University of Texas at Arlington, Arlington, Texas, United States of America.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Streicher
authors.affiliation: Department of Ecosystem Science and Management, Texas A&M University, College Station, Texas, United States of America.
authors.forename: A Michelle
authors.initials: AM
authors.lastname: Lawing
authors.affiliation: Museo de Zoología, Facultad de Ciencias, Universidad Nacional Autónoma de México, Distrito Federal, México.
authors.forename: Oscar
authors.initials: O
authors.lastname: Flores-Villela
authors.affiliation: Department of Biology, University of Texas at Arlington, Arlington, Texas, United States of America.
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Fujita
mesh_terms: D000818:Animals; D002980:Climate; D016000:Cluster Analysis; D017839:Crotalus / Q000145:classification* / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D049810:Genetic Speciation; D005843:Geography; D006824:Hybridization, Genetic; D009656:North America; D010641:Phenotype; D010802:Phylogeny; D020641:Polymorphism, Single Nucleotide; D025341:Principal Component Analysis; D013045:Species Specificity
chemical_list: D004272:DNA, Mitochondrial