title: Exploring Climate Niches of Ponderosa Pine (Pinus ponderosa Douglas ex Lawson) Haplotypes in the Western United States: Implications for Evolutionary History and Conservation.
abstract: Ponderosa pine (Pinus ponderosa Douglas ex Lawson) occupies montane environments throughout western North America, where it is both an ecologically and economically important tree species. A recent study using mitochondrial DNA analysis demonstrated substantial genetic variation among ponderosa pine populations in the western U.S., identifying 10 haplotypes with unique evolutionary lineages that generally correspond spatially with distributions of the Pacific (P. p. var. ponderosa) and Rocky Mountain (P. p. var. scopulorum) varieties. To elucidate the role of climate in shaping the phylogeographic history of ponderosa pine, we used nonparametric multiplicative regression to develop predictive climate niche models for two varieties and 10 haplotypes and to hindcast potential distribution of the varieties during the last glacial maximum (LGM), ~22,000 yr BP. Our climate niche models performed well for the varieties, but haplotype models were constrained in some cases by small datasets and unmeasured microclimate influences. The models suggest strong relationships between genetic lineages and climate. Particularly evident was the role of seasonal precipitation balance in most models, with winter- and summer-dominated precipitation regimes strongly associated with P. p. vars. ponderosa and scopulorum, respectively. Indeed, where present-day climate niches overlap between the varieties, introgression of two haplotypes also occurs along a steep clinal divide in western Montana. Reconstructed climate niches for the LGM suggest potentially suitable climate existed for the Pacific variety in the California Floristic province, the Great Basin, and Arizona highlands, while suitable climate for the Rocky Mountain variety may have existed across the southwestern interior highlands. These findings underscore potentially unique phylogeographic origins of modern ponderosa pine evolutionary lineages, including potential adaptations to Pleistocene climates associated with discrete temporary glacial refugia. Our predictive climate niche models may inform strategies for further genetic research (e.g., sampling design) and conservation that promotes haplotype compatibility with projected changes in future climate.
authors.affiliation: U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Boise, Idaho, United States of America.
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Shinneman
authors.affiliation: Bureau of Land Management Wyoming, Cheyenne, Wyoming, United States of America.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Means
authors.affiliation: Department of Forestry and Environmental Resources, North Carolina State University, Research Triangle Park, North Carolina, United States of America.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Potter
authors.affiliation: National Forest Genetics Laboratory, USDA Forest Service, Placerville, California, United States of America.
authors.forename: Valerie D
authors.initials: VD
authors.lastname: Hipkins
mesh_terms: D005075:Biological Evolution; D002980:Climate; D003247:Conservation of Natural Resources; D004272:DNA, Mitochondrial; D017753:Ecosystem; D004777:Environment; D014644:Genetic Variation; D006239:Haplotypes; D008962:Models, Theoretical; D058974:Phylogeography; D041604:Pinus ponderosa / Q000235:genetics*; D014481:United States
chemical_list: D004272:DNA, Mitochondrial