Conservation Genetics

, Volume 13, Issue 2, pp 475–498 | Cite as

Widespread inbreeding and unexpected geographic patterns of genetic variation in eastern hemlock (Tsuga canadensis), an imperiled North American conifer

  • Kevin M. PotterEmail author
  • Robert M. Jetton
  • William S. Dvorak
  • Valerie D. Hipkins
  • Rusty Rhea
  • W. Andrew Whittier
Research article


Eastern hemlock (Tsuga canadensis [L.] Carr.) is an ecologically important tree species experiencing severe mortality across much of its eastern North American distribution, caused by infestation of the exotic hemlock woolly adelgid (Adelges tsugae Annand). To guide gene conservation strategies for this imperiled conifer, we conducted a range-wide genetic variation study for eastern hemlock, amplifying 13 highly polymorphic nuclear microsatellite loci in 1,180 trees across 60 populations. The results demonstrate that eastern hemlock exhibits moderate inbreeding, possibly a signature of a prehistoric decline associated with a widespread insect outbreak. Contrary to expectations, populations in formerly glaciated regions are not less genetically diverse than in the putative southern refugial region. As expected, peripheral disjunct populations are less genetically diverse than main-range populations, but some are highly genetically differentiated or contain unique alleles. Spatially explicit Bayesian clustering analyses suggest that three or four Pleistocene glacial refuges may have existed in the Southeastern United States, with a main post-glacial movement into the Northeast and the Great Lakes region. Efforts to conserve eastern hemlock genetic material should emphasize the capture of broad adaptability that occurs across the geographic range of the species, as well as genetic variability within regions with the highest allelic richness and heterozygosity, such as the Southern Appalachians and New England, and within disjunct populations that are genetically distinct. Much genetic variation exists in areas both infested and uninfested by the adelgid.


Phylogeography Pleistocene Migration Population genetics Microsatellite Bottleneck 



We thank Sedley Josserand for her advice in optimizing microsatellite PCRs; Joe Nairn and Brian Shamblin for providing eastern hemlock microsatellite primer sequences; John Frampton and Dana Nelson for assistance in initiating this project; Ricardo Hernandez and Jennifer DeWoody for laboratory assistance; and Craig Echt, Alistair Jump and two anonymous reviewers for thoughtful comments on the manuscript. We are very grateful to a long list of government organizations listed in Table 1 and their natural resource professionals who assisted with the identification and collection of hemlock samples. This work was supported by in part through Grant Agreements 05-DG-11083150-210 and 08-DG-11083150-014 and Participating Agreement 06-PA-11083150-002 between the U.S. Department of Agriculture, Forest Service, Forest Health Protection and Camcore, North Carolina State University; and through Cooperative Agreement 05-CA-11330126-210 and Research Joint Venture Agreements 08-JV-11330146-078 and 10-JV-11330146-049 between the U.S. Department of Agriculture, Forest Service, Southern Research Station, and North Carolina State University.

Supplementary material

10592_2011_301_MOESM1_ESM.xls (94 kb)
Online Resource 1: Population pairwise chord genetic distance (D C ) for 60 eastern hemlock populations, based on 13 polymorphic nuclear microsatellites (XLS 94 kb)
10592_2011_301_MOESM2_ESM.xls (96 kb)
Online Resource 2: Population pairwise differentiation values (F ST ) for 60 eastern hemlock populations, based on 13 polymorphic nuclear microsatellites (XLS 96 kb)


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© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Kevin M. Potter
    • 1
    Email author
  • Robert M. Jetton
    • 2
  • William S. Dvorak
    • 2
  • Valerie D. Hipkins
    • 3
  • Rusty Rhea
    • 4
  • W. Andrew Whittier
    • 2
  1. 1.Department of Forestry and Environmental ResourcesNorth Carolina State UniversityResearch Triangle ParkUSA
  2. 2.Camcore, Department of Forestry and Environmental ResourcesNorth Carolina State UniversityRaleighUSA
  3. 3.National Forest Genetics Laboratory, USDA Forest ServicePlacervilleUSA
  4. 4.Forest Health Protection, USDA Forest ServiceAshevilleUSA

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