Host density drives the postglacial migration of the tree parasite, Epifagus virginiana - PubMed (original) (raw)

Host density drives the postglacial migration of the tree parasite, Epifagus virginiana

Yi-Hsin Erica Tsai et al. Proc Natl Acad Sci U S A. 2010.

Abstract

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 a 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 y. 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. Furthermore, these results confirm predictions of disease ecological models regarding the role of host density in the spread of pathogens. Due to host density constraints, highly specialized species may have low migration capacities and long lag times before colonization of new areas.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Genetic structure of Epifagus virginiana. (A) Range map with competing migration route hypotheses based on host fossil pollen (H p) or host cpDNA (H m). Regions (shaded) were defined by the distribution of host fossil pollen at 13, 9, and 6 kyBP. (B) Distribution of cpDNA haplotypes and haplotype network (Inset). Numbers are the parsimony and likelihood bootstraps and Bayesian posterior probability values. (C) Distribution of microsatellite clusters and cluster phenogram (Inset). (D) Areas of high genetic differentiation. Colors correspond to the average number of genetic breaks found at that location over 1,000 cross-validation subsamples. Color assignments were based on the 50th–90th percentiles: red, 90+%; yellow, 80–89%; green, 70–79%; blue, 60–69%; purple, 50–59%. LGM, ice margin at the last glacial maximum. Maps were drawn in Google Earth (copyright 2010 Google).

Fig. 2.

Fig. 2.

Genetic and fossil map layers of Epifagus virginiana and Fagus grandifolia. (A) Geographic range of both species. Outline shows extent of interpolated data layers. (B) Genetic distance maps for E. virginiana (EV) and F. grandifolia (F.gen). F. grandifolia genetic data are redrawn from McLachlan et al. (5). (C) Fossil pollen layers for F. grandifolia from 21 kyBP (F21) to present (F0) in 1,000-y increments. A pollen layer for 500 ybp (F0.5) is also shown. Pollen layers are redrawn from Williams et al. (6). (D) Summary pollen layers (F.age, F.avgP, and F.varP) of F. grandifolia as described in text. Warmer colors correspond with higher values in all maps. Maps were visualized using a 10-quantile color ramp.

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