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Reduced Gene Flow from Mainland Populations of Liriodendron tulipifera into the Florida Peninsula Promotes Diversification

2019; University of Chicago Press; Volume: 180; Issue: 3 Linguagem: Inglês

10.1086/702267

1537-5315

Karl C. Fetter, Alan S. Weakley,

Plant and animal studies

Premise of research. Glacial cycles during the last circa 5 Myr altered the distribution of genetic variance observed today. During periods of unfavorable climate, populations survive glacial maxima in refugial microclimates where growth and reproduction are possible. Peninsulas provide refuge but may alter demographic processes in comparison with mainland populations. The Florida peninsula is an important refugium for plant populations, and its unique geologic history created environments that differ from those of nearby mainland sites. Peninsular demographic effects and adaptation may contribute to genetic diversity. We investigate the genetic divergence of tulip trees (Liriodendron tulipifera L.) across much of their range and interpret our results in the context of eastern North American phylogeography, detectable signals of population expansion during recolonization, and peninsular demographic effects. We also test the hypothesis that peninsular populations represent a new species or subspecies within L. tulipifera.Methodology. Population structure was evaluated in a sample of 141 individuals from 56 populations at one nuclear DNA region (LFY) and three cpDNA intergenic regions (psbA-trnH, trnL intron-trnF, trnK 5′-matK). We use population genetic methods to identify clusters, test their significance, and estimate coalescent parameters. Phylogenetic trees and population trees were built to observe relationships between groups.Pivotal results. Genetic clusters determined with population genetic and phylogenetic methods are regionally coherent. We observe a secondary contact zone in the Gulf Coast near the Apalachicola River basin. Florida peninsula populations both are genetically diverse and experience low migration from mainland populations.Conclusions. We detect patterns of phylogeographic clustering using population genetic and phylogenetic methods. Analysis of genetic diversity and gene flow indicates range expansion has influenced their patterns. A demographic peninsular effect appears to have altered patterns of genetic diversity, linkage disequilibrium, and gene flow between peninsular and mainland populations. We interpret these results to indicate that a subspecies of L. tulipifera from the Florida peninsula exists.