Landscape Genetics: The distribution and geographical arrangement of species has long fascinated ecologists. Widespread, morphologically-variable species are of particular interest, as they lend themselves to the pursuit of integrated research that addresses the biology, ecology, evolutionary history, and historical migration patterns of species. Many forest tree species have extensive ranges that occur over a breadth of environments, with these species documented to effectively disperse and remain connected through gene flow across disconnected, distant, and heterogeneous landscapes. These widely-dispersed, wind pollinated species appear to overcome the substantial landscape barriers known to limit gene flow among other plant populations, but the effect of the landscape on dispersal and connectivity has rarely been tested in forest tree species.
Pinus contorta (Douglas Ex. Louden) is one of the most widely distributed trees in North America, playing an ecologically, economically, and historically important role in western forests from Baja California to the Yukon Territory. This species’ broad distribution is divided into four geographically and morphologically distinct subspecies (ssp. latifolia, contorta, murrayana, and bolanderi). Each subspecies inhabits a discrete portion of the species’ range, growing under and hypothesized to be locally adapted to a unique set of environmental and climatic conditions.
We used landscape genetics to explore the influence of spatial patterns and landscape characteristics on population structuring across the four subspecies of Pinus contorta. This analysis of gene flow across the range of Pinus contorta indicated only moderate population differentiation at the continental scale. The three genetic clusters identified in this analysis correspond with North American physiographic regions that are separated by conspicuous geographic barriers and characterized by distinct environmental conditions. The genetic clusters identified here coincide with three of the four subspecies (contorta, latifolia, and murrayana), and the geographic distribution of genetic clustering supports the taxonomic treatment of these three subspecies.
Landscape Genomics: We are collaborating with Dr. Thomas Parchman on genomic sequencing of the samples from our landscape genetics study. The goal of this work is to obtain better resolution of genetic differentiation across this widespread species. Current work involves the use of next-generation sequencing technologies for studies of geographic and adaptive variation across the four subspecies.