Synthesis of fossils and genetics reveals host controls on the post-glacial migration of a parasitic plant

To survive changes in climate, successful species shift their geographic ranges to remain in suitable habitats. For parasites and other highly specialized species, distributional changes not only are dictated by climate but can also be engineered by their hosts. The extent of host control on parasite range expansion is revealed through comparisons of host and parasite migration and demographic histories. However, understanding the codistributional history of entire forest communities is complicated by challenges in synthesizing datasets from multiple interacting species of differing datatypes. Here, we integrate genetic and fossil pollen datasets from an eastern North American host-parasite pair; specifically, the population structure of the parasitic plant (Epifagus virginiana) was compared with both its host (Fagus grandifolia) genetic patterns and abundance data from the paleopollen record of the last 21,000 yrs. Through tests of phylogeographic structure and spatial linear regression models we find, surprisingly, host range changes had little effect on the parasite's range expansion and instead host density is the main driver of parasite spread. Unlike other symbionts that have been used as proxies to track their host's movements, this parasite's migration routes are incongruent with the host and instead reflect the greater importance of host density in this community's assembly. Because host density largely defines the suitability of an area for the parasite, habitat cost maps based on host density were developed in order to locate the migration corridors for the parasite. Based on these results, we believe the presented spatial linear model framework is a promising method for synthesizing disparate datasets, and that this provides a flexible statistical methodology for comparing multiple species' phylogeographic patterns.

Speaker: Erica Tsai, Ph.D, Louisiana State University

Room 2040