Abstract Detail

Systematics

Dong, Yibo [1], LI, JIANHUA [2], Soltis, Douglas [3], Wong, Gane Ka-Shu [4], Soltis, Pamela  S. [5], Xiang, Qiu-Yun (Jenny) [1].

Patterns of morphological and molecular divergence of species pairs between eastern Asia and eastern North America inferred from transcriptome data.

Organisms at different taxonomic levels (e.g., family and genus) can be distributed in different continents forming intercontinental disjunctions. In flowering plants, there are 65 genera with species distributed in eastern Asia (EA) and eastern North America (ENA), a well-known disjunct distribution since the early days of botanical research in the 18^th century. Closely related species of these genera are largely restricted to the Tertiary relic mesophytic forests in eastern Asia and eastern North America now situated at similar latitudes. The ecological similarity of the forests predicts slow and similar changes of the species counterparts in morphology and molecules. Although there have been extensive molecular phylogenetic studies during the past 15 years to understand the origin of the disjunct pattern, no studies have systematically examined the patterns of morphological and molecular divergence among the disjunct species pairs. Here we compare 21 species pairs across a diverse array of lineages of seed plants. We sequenced the trascriptomes of these species pairs and compared substitution rates of the orthologous genes among genera. We also compiled a morphological matrix identifying features differing between the species counterparts and compare these among the genera. Our results showed that some genera displayed divergence mainly in vegetative structure (e.g., leaves) while other showed striking divergence in reproductive structures (flowers and fruits). However, overall there are more differentiations across the species pairs in reproductive than vegetative traits, suggesting that biologically factors relating to reproduction may have played the most important role in the divergence of species pairs between eastern Asia and eastern North America. The frequency distribution of synonymous substitution rates (Ks) of putative orthologous genes exhibit a peak in all genera. The peak values spanned a range from 0.001–0.055 across the 21 genera. A majority of the putative orthologous genes in each species pair are found to be under strong purifying selection, while a very small number was found to be neutral (Ka/Ks = 1) or under strong positive selection (Ka/Ks >2). The relative proportion of genes under different selection regimes as determined by Ka/Ks values appear to be remarkably similar among genera. Preliminary gene annotation of the genes under strong positive selection showed that a high portion of genes were the integral component of cell membrane in all species pairs and some chloroplast genes exhibited divergence in species pairs with differences in leaf morphology.

1 - North Carolina State University, Department of Plant and Microbial Biology, Gardner Hall 2115, Raleigh, NC, 27695-7612, United States
2 - Hope College, ARNOLD ARBORETUM, 35 E 12th Street, Holland, MI, 49423, USA
3 - University of Florida, Dept. of Biology, 1659 Museum Road, Gainesville, Florida, 32611, United States
4 - University of Alberta, Department of Biological Sciences, CW405, Biological Sciences Bldg. , Edmonton, AB, AB T6G 2E9, Canada
5 - University Of Florida, Florida Museum Of Natural History, 1659 Museum Rd., Gainesville, FL, 32611, USA

Keywords:
comparative transcriptome
eastern Asian-eastern North American Disjunction
Morphological divergence
Molecular evolution
biogeographic pattern.

Presentation Type: Oral Paper
Session: 31, Cooley Awards II
Location: 201/Savannah International Trade and Convention Center
Date: Tuesday, August 2nd, 2016
Time: 5:00 PM
Number: 31014
Abstract ID:864
Candidate for Awards:George R. Cooley Award