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Plant Species pairs between eastern Asia and North America

Project Full Title:

Patterns of morphological and genetic differentiation between species pairs in eastern Asia and eastern North America

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Project Description:

Organisms at different taxonomic levels (e.g., family and genus) can be distributed in different continents forming intercontinental disjunction. Phylogenetic analyses have identified and verified dozens of species pairs between EAS and ENA. but detailed morphological studies have rarely been done. For sister species with common evolutionary history and similar ecological niches, we expect each species of the pair to be experiencing similar selective pressures after their divergence. Consequently, their morphological differences are expected to be present randomly in stem, leaf, flower, fruit, or seed. Species pairs in different families may have diverged at different times. However, floristic similarity and continual exchanges between EAS and ENA since the early Tertiary suggest similar changes of the various lineages in the two regions. Our cursory survey of a few detailed morphological studies of species pairs between EAS and ENA suggested that there wre more differentiations in reproductive structures than in vegetative traits. Additional disjunct species pairs are needed to examine whether this is the general pattern of morphological divergence between EAS and ENA. Along with changes of reproductive structures and/or vegetative traits, we expect to see changes in genes that are directly involved in the development of the traits. Next-generation sequencing of transcriptomes provides data of thousands of expressed genes and a new way to examine whether species pairs has enabled the genome-wide comparison of genes under selection. The objective of the study, hence, is to test the hypothesis that similar morphological differentiation may have occurred across diverse disjunct lineages between EAS and ENA, and similarly, the number of genes under positive selection is also expected to be similar across the disjunct lineages.

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