Allozyme variation and recent evolutionary history of eastern hemlock (Tsuga canadensis) in the southeastern United States

Abstract

Eastern hemlock (Tsuga canadensis [L.] Carr.) is a widespread and ecologically important conifer species of eastern North America that is threatened by the hemlock woolly adelgid (Adelges tsugae Annand), a pest introduced into the United States from Asia in the 1920s. Information about the genetic composition of eastern hemlock is necessary to guide ex situ conservation efforts in the southeastern United States, where the species is expected to harbor relatively high amounts of genetic variation in areas of Pleistocene glacial refuge. Nineteen allozyme markers were used to quantify the genetic variation present in 20 eastern hemlock populations in the southeastern United States. Results indicate that the species has low levels of genetic diversity in the region compared to most other conifers, but greater population differentiation (F ST = 0.126). Populations along the eastern periphery and in the Appalachian interior exhibited higher levels of diversity than those along the western periphery of its geographic range. The results suggest that the glacial refuge area for eastern hemlock was likely located east of the southern Appalachian Mountains, and indicate that ex situ conservation seed collections should be concentrated in these areas of higher diversity.

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

“…An analysis of highly conserved chloroplast DNA polymorphisms primarily among disjunct populations identified little differentiation (Wang et al 1997), while Zabinski (1992) detected little allozyme variation within eastern hemlock in a study that was focused in the Midwestern portion of the eastern hemlock range. In a study that sampled 20 populations from the Southeastern portion of the range, Potter et al (2008) also found low allozyme diversity in hemlock but reasonably high population differentiation. A range-wide analysis using seven haploid chloroplast DNA loci (Lemieux et al 2011) also detected low among-population differentiation and, consistent with Potter et al (2008), greater differentiation and relatively high allelic richness among southeastern Appalachian populations.…”

“…In a study that sampled 20 populations from the Southeastern portion of the range, Potter et al (2008) also found low allozyme diversity in hemlock but reasonably high population differentiation. A range-wide analysis using seven haploid chloroplast DNA loci (Lemieux et al 2011) also detected low among-population differentiation and, consistent with Potter et al (2008), greater differentiation and relatively high allelic richness among southeastern Appalachian populations. These results led both sets of authors to conclude that the majority of eastern hemlock genetic diversity may have originated from a Pleistocene glacial refuge in this region.…”

Ecological and genetic factors that define the natural distribution of Carolina hemlock in the southeastern United States and their role in ex situ conservation

“…Despite its restricted occurrence, our results indicate that Carolina hemlock exhibits a moderate amount of genetic variation (Camcore, 2006). At the same time, eastern hemlock, which is found throughout eastern North America, appears to have relatively low genetic variation in the southeastern states (Potter et al, 2008).…”

Prioritizing conservation seed banking locations for imperiled hemlock species using multi-attribute frontier mapping

“…Low genetic diversity in eastern hemlock (Potter et al 2008(Potter et al , 2012 and Carolina hemlock (Campbell 2014), coupled with generally high levels of inbreeding across both species, highlight the need for quick and decisive action to assess the genetic diversity of previously undersampled areas and to fully protect the genetic composition of each species.…”