Document: JAS-3-41-3

Holocene migration patterns of eastern North American trees: Evidence from molecular markers.

MCLACHLAN, J.S.*, P.S.MANOS and J.S.CLARK

Duke University, Durham, NC 27708 ¹

Abstract:
The rate and pattern of spread of North American trees in the early Holocene provides an opportunity to examine forest response to rapid climate change. Migration rates are hard to estimate from fossil evidence, however, due to the difficulty of determining a taxon's local arrival at a fossil site and the scarcity of sites south of the ice margin. Maternally inherited molecular markers provide a complementary record of migration history that does not suffer from the same limitations. We sequenced portions of the chloroplast genome from numerous individuals throughout the ranges of Acer rubrum and Fagus grandifolia in order to identify glacial refugia and routes of postglacial expansion. We expected that the North American record of postglacial migration would contrast with that of Europe, where chloroplast DNA (cpDNA) studies have shown continental-scale migrations from southern refugia isolated by east-west oriented mountain ranges. We also expected that the two species would have different migration histories based on their different life histories. The distribution of cpDNA variants (haplotypes) in Fagus indicates Holocene migration routes both to the east and to the west of the Appalachians. In contrast to European records, haplotype diversity in Fagus does not have a strong latitudinal gradient, suggesting the absence of large southern glacial refugia. Most Acer rubrum haplotype diversity, on the other hand, occurs south of 37^o N, and a geographically distinct south-coastal haplotype suggests a southern glacial refugium for this species. Differences in postglacial history between our two study species and between the North American and European record show that there is much to learn about forest response to climate change and that the molecular record can contribute to this process.

Keywords: cpDNA, plant migration, Holocene, Acer rubrum, Fagus grandifolia

This abstract is being presented at: 10:30 AM in session:
PALEOECOLOGY