FSD 2010 - Hamrick

5th International Symposium-Workshop on Frugivores and Seed Dispersal (1985-2010)

James L. Hamrick

Department of Plant Biology, University of Georgia, Athens, GA 30602 USA. Email : hamrick@plantbio.uga.edu

Activities

My long-standing interest in the genetic structure of plant populations has resulted in studies of pollen and seed dispersal in natural populations of several plant species. More recently, I’ve become interested in using landscape genetic approaches together with parentage analyses to examine the maintenance of genetic connectivity in highly disturbed tropical landscapes. One goal for these studies is to develop management strategies for these landscapes, so that natural levels of genetic diversity can be maintained.

Abstract

Using population genetic analyses to understand patterns of seed dispersal.

Neutral genetic markers can be employed to better understand patterns and levels of seed dispersal in natural landscapes. The use of biparentally and maternally inherited genetic markers to estimate levels of genetic differentiation among spatially separated populations makes it possible to determine the relative effectiveness of historical pollen and seed flow. Direct estimates of contemporary seed dispersal rates and distances can be obtained by using parentage analysis procedures to identify the parents of dispersed fruits, seeds, or seedlings. With standard parent-pair analyses on seeds or seedlings, problems can arise in distinguishing maternal and paternal parents. The more recent use of maternally derived DNA from dispersed fruits or seed coats allows the direct identification of maternal individuals and, as a consequence, the distance and patterns of seed dispersal and deposition can be described. From such studies, we can better understand the role that seed dispersal plays in the maintenance of genetic connectivity between populations in natural and highly disturbed landscapes. Finally, studies that utilize estimates of genetic relatedness among plants in relatively recently colonized populations can provide insights into the role of seed dispersal in population colonization and growth. High levels of genetic relatedness within such populations would indicate that the site was originally colonized by few individuals and that increases in population size are largely due to the establishment of progeny of the original colonists. In contrast, low levels of relatedness would result if population growth resulted from continuous long-distance seed dispersal from multiple sources. Case studies are reviewed that illustrate each of these approaches.

References

Trapnell, D.W. and J.L. Hamrick. 2004. Partitioning nuclear and chloroplast variation at multiple spatial scales in the neotropical epiphytic orchid, Laelia rubescens. Molecular Ecology 13: 2655-2666.

Grace, S.L., J.L. Hamrick, and W.J. Platt. 2004. Estimation of seed dispersal in an old-growth population of longleaf pine (Pinus palustris) using maternity exclusion analysis. Castanea 69: 207-215.

Pardini, E.A. and J.L. Hamrick. 2008. Inferring recruitment history from spatial genetic structure within populations of the colonizing tree, Albizia julibrissin (Fabaceae). Molecular Ecology 17: 2865-2879.

Gonzales, E., J.L. Hamrick, P.E. Smouse, D.W. Trapnell, and R. Peakall. 2010. The impact of landscape disturbance on spatial genetic structure in the Guanacaste tree, Enterolobium cyclocarpum (Fabaceae). Journal of Heredity, in press. (photo : Fruit and seedlings of the Guanacaste tree, a dominant tree in Central American dry forests. J.L. Hamrick).

Former FSD presentations

Hamrick, J. L. and M. D. Loveless. 1986. The influence of seed dispersal mechanisms on the genetic structure of plant populations. Pages 211-223 in A. Estrada and T. H. Fleming, editors. Frugivores and seed dispersal. Dr. W. Junk Publishers, Dordrecht.

Hamrick, J. L., D. A. Murawski, and J. D. Nason. 1993. The influence of seed dispersal mechanisms on the genetic structure of tropical tree populations. Vegetatio 107/108:281-297.