Water availability drives signatures of local adaptation in whitebark pine (Pinus albicaulis Engelm.) across fine spatial scales of the Lake Tahoe Basin, USA.
Patterns of local adaptation at fine spatial scales are central to understanding how evolution proceeds, and are essential to the effective management of economically and ecologically important forest tree species. Here, we employ single and multilocus analyses of genetic data (n = 116 231 SNPs) to describe signatures of fine-scale adaptation within eight whitebark pine (Pinus albicaulis Engelm.) populations across the local extent of the environmentally heterogeneous Lake Tahoe Basin, USA. We show that despite highly shared genetic variation (FST= 0.0069), there is strong evidence for adaptation to the rain shadow experienced across the eastern Sierra Nevada. Specifically, we build upon evidence from a common garden study and find that allele frequencies of loci associated with four phenotypes (mean = 236 SNPs), 18 environmental variables (mean = 99 SNPs), and those detected through genetic differentiation (n = 110 SNPs) exhibit significantly higher signals of selection (covariance of allele frequencies) than could be expected to arise, given the data. We also provide evidence that this covariance tracks environmental measures related to soil water availability through subtle allele frequency shifts across populations. Our results replicate empirical support for theoretical expectations of local adaptation for populations exhibiting strong gene flow and high selective pressures and suggest that ongoing adaptation of many P. albicaulis populations within the Lake Tahoe Basin will not be constrained by the lack of genetic variation. Even so, some populations exhibit low levels of heritability for the traits presumed to be related to fitness. These instances could be used to prioritize management to maintain adaptive potential. Overall, we suggest that established practices regarding whitebark pine conservation be maintained, with the additional context of fine-scale adaptation.
Integrative Life Sciences Program, Virginia Commonwealth University, Richmond, VA, 23284, USA.
Brandon M
http://orcid.org/0000-0002-8560-5417
BM
Lind
Department of Biology, Virginia Commonwealth University, Richmond, VA, 23284, USA.
Christopher J
CJ
Friedline
Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, 06269, USA.
Jill L
JL
Wegrzyn
Department of Plant Pathology and Tahoe Environmental Research Center, University of California, Davis, CA, 95616, USA.
Patricia E
PE
Maloney
USDA, Forest Service, Pacific Southwest Research Station, Institute of Forest Genetics, 2480 Carson Road, Placerville, CA, 95667, USA.
Detlev R
DR
Vogler
Department of Plant Sciences, University of California, Davis, CA, 95616, USA.
David B
DB
Neale
Department of Biology, Virginia Commonwealth University, Richmond, VA, 23284, USA.
Andrew J
AJ
Eckert
D000222:Adaptation, Physiological / Q000235:genetics*; D004777:Environment; D005787:Gene Frequency; D060106:Lakes; D009505:Nevada; D028223:Pinus / Q000235:genetics* / Q000502:physiology*; D020641:Polymorphism, Single Nucleotide; D062206:Spatial Analysis; D014197:Trees; D014867:Water
D014867:Water

Pinus albicaulis
; Sierra Nevada; linkage disequilibrium; local adaptation; water availability