Extinction, migration, and speciation - a post-glacial history of the population structure, phylogeography, and biodiversity of Liriodendron tulipifera L. (Magnoliaceae)

Fetter, Karl Christian

Extinction, migration, and speciation - a post-glacial history of the population structure, phylogeography, and biodiversity of Liriodendron tulipifera L. (Magnoliaceae) Public Deposited

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March 19, 2019

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Fetter, Karl Christian
- Affiliation: College of Arts and Sciences, Department of Biology

Abstract

Liriodendron tulipifera (Magnoliaceae L.) is a widespread tree in eastern North American deciduous forests that has considerable population structure. Populations in the southern United States have widely divergent cpDNA haplotypes and allozyme alleles when compared to northern populations, and a geographically isolated group of populations in the Florida Peninsula have magnitudes of genotypic, phenotypic, and ecological differences that, when compared to continental populations, suggest these populations may represent a new species. This study tests the hypothesis that genotypically and phenotypically divergent populations of L. tulipifera in the Florida Peninsula and coastal plain should be treated taxonomically as a separate species and sub-species, respectively, as suggested by the results of previous cpDNA and allozyme studies. Population demography and phylogeography are investigated from 137 samples from 55 populations with cpDNA sequences from three molecular markers (psbA-trnH, trnL intron-trnF, trnK5'-matK). Two fundamentally different approaches to species delimitation are used: a traditional phylogenetic approach and the recently popular species discovery plus validation approach. To discover species, Bayesian clustering is implemented in the program Structure and neighbor-joining trees of pairwise Fst are constructed. Various hypotheses of the number of species and the composition of those species are validated by analysis of molecular variance (AMOVA) and the likelihood-based methods in the program spedeSTEM. All of the clustering methods sub-divide L. tulipifera into clusters located in continental North America and the Florida Peninsula, but are incongruent in their recovery of a distinct coastal plain cluster. Validation analyses support the presence of an unrecognized species of Liriodendron in the Florida Peninsula.

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