Originally published as Genetics Published Articles Ahead of Print on November 16, 2009.

Genetics, Vol. 184, 381-392, February 2010, Copyright © 2010
doi:10.1534/genetics.109.110130

Mating-System Variation, Demographic History and Patterns of Nucleotide Diversity in the Tristylous Plant Eichhornia paniculata

Rob W. Ness1, Stephen I. Wright and Spencer C. H. Barrett

Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario M5S 3B2, Canada

1 Corresponding author: Department of Ecology and Evolutionary Biology, 25 Willcocks St., University of Toronto, Toronto, ON M5S 3B2, Canada.
E-mail: rob.ness{at}utoronto.ca

Inbreeding in highly selfing populations reduces effective size and, combined with demographic conditions associated with selfing, this can erode genetic diversity and increase population differentiation. Here we investigate the role that variation in mating patterns and demographic history play in shaping the distribution of nucleotide variation within and among populations of the annual neotropical colonizing plant Eichhornia paniculata, a species with wide variation in selfing rates. We sequenced 10 EST-derived nuclear loci in 225 individuals from 25 populations sampled from much of the geographic range and used coalescent simulations to investigate demographic history. Highly selfing populations exhibited moderate reductions in diversity but there was no significant difference in variation between outcrossing and mixed mating populations. Population size interacted strongly with mating system and explained more of the variation in diversity within populations. Bayesian structure analysis revealed strong regional clustering and selfing populations were highly differentiated on the basis of an analysis of Fst. There was no evidence for a significant loss of within-locus linkage disequilibrium within populations, but regional samples revealed greater breakdown in Brazil than in selfing populations from the Caribbean. Coalescent simulations indicate a moderate bottleneck associated with colonization of the Caribbean from Brazil ~125,000 years before the present. Our results suggest that the recent multiple origins of selfing in E. paniculata from diverse outcrossing populations result in higher diversity than expected under long-term equilibrium.