Population Genetic Structures of Two Sister Tulip Tree Species: Implications for the Diversity Anomaly Between Eastern Asia and North America
Dr. Jianhua Li
It has become increasingly evident that biodiversity in the world has been decreasing. In order to face this problem head on we need to understand the underlying mechanisms for the formation of the patterns of biodiversity. A well-known pattern of biodiversity comes from the intercontinental disjunction of plant genera between eastern Asia and North America with unequal species richness. One hypothesis explaining the greater species diversity in eastern Asia than in North America states that faster speciation occurred on the eastern Asian side of the intercontinental disjunction than on the North American side. If this is true, we expect a greater genetic diversity across populations of eastern Asian species than the sister species in North America. In this study, we used tulip tree Liriodendron as our model system to test the hypothesis. Thirty individuals representing nine populations of the North American species (L. tulipifera) and 17 trees from three populations of the eastern Asia species (L. chinense) were included in the study. Sequences of the plastid rpl32-trnL intergenic spacer were obtained from all trees. Phylogenetic analyses using Magnolia species as the outgroup supported the sister relationship of the two species. Both the average number of differences between populations and the number of haplotypes per population were higher in the eastern Asian species than in the North American counterpart. Nonetheless, the short sequences of the rpl32-trnL region (ca. 1400 bp) provided limited information of genetic variation. Therefore, we obtained the entire plastid genome from one tree of the populations sampled, which resulted in over 97,000 bp. This study represents the first comparative genetic analyses of sister species between eastern Asia and North America to gain insights into the formation of the patterns of the species diversity between the two continents.
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