title: History matters more when explaining genetic diversity within the context of the core-periphery hypothesis.
abstract: The core-periphery hypothesis (CPH) predicts that populations located at the periphery of a species' range should have lower levels of genetic variation than those at the centre of the range. However, most of the research on the CPH focuses on geographic distance and not on ecological distance, or uses categorical definitions of core and periphery to explain the distribution of genetic diversity. We use current climate data and historical climate data from the last glacial maxima to develop quantitative estimates of contemporary and historical ecological suitability using ecological niche models. We analysed genetic diversity using 12 polymorphic microsatellites to estimate changes in heterozygosity, allelic richness and population differentiation in 31 populations of the wood frog (Lithobates sylvaticus) spanning the species' entire eastern clade (33(o) to 45(o) latitude) from Alabama, USA, to Nova Scotia, Canada. Our data support predictions based on the CPH. Populations showed significant differences in genetic diversity across the range, with lower levels of genetic variation at the geographic range edge and in areas with lower levels of historical and contemporary ecological suitability. However, history and geography (not current ecological suitability) best explain the patterns. This study highlights the importance of examining more than just geography when assessing the CPH, and the importance of historical ecological suitability in the maintenance of genetic diversity and population differentiation.
authors.affiliation: Department of Biological Sciences, The University of Alabama, 500 Hackberry Lane, Box 870345, Tuscaloosa, AL, 35487, USA.
authors.forename: Sarah I
authors.initials: SI
authors.lastname: Duncan
authors.affiliation: School of Biological Sciences, Washington State University, PO Box 644236, Pullman, WA, 99164, USA.
authors.forename: Erica J
authors.initials: EJ
authors.lastname: Crespi
authors.affiliation: Department of Biological Sciences, The University of Alabama, 500 Hackberry Lane, Box 870345, Tuscaloosa, AL, 35487, USA.
authors.forename: Nichole M
authors.initials: NM
authors.lastname: Mattheus
authors.affiliation: Department of Biological Sciences, The University of Alabama, 500 Hackberry Lane, Box 870345, Tuscaloosa, AL, 35487, USA.|Division of Environmental Biology, National Science Foundation, 4201 Wilson Blvd, Arlington, VA, 22230, USA.
authors.forename: Leslie J
authors.initials: LJ
authors.lastname: Rissler
mesh_terms: D000818:Animals; D002980:Climate; D017753:Ecosystem; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D018895:Microsatellite Repeats; D008954:Models, Biological; D009656:North America; D011898:Ranidae / Q000235:genetics*; D017422:Sequence Analysis, DNA
keywords: Lithobates sylvaticus; Rana sylvatica; biogeography; ecological niche models; microsatellites; species’ distributions