Contributions of historical and contemporary geographic and environmental factors to phylogeographic structure in a Tertiary relict species, Emmenopterys henryi (Rubiaceae).

Yong-Hua Zhang,Ying-Xiong Qiu,Hans Peter Comes,Hua Peng,Ian J Wang

doi:10.1038/srep24041

Abstract

Examining how historical and contemporary geographic and environmental factors contribute to genetic divergence at different evolutionary scales is a central yet largely unexplored question in ecology and evolution. Here, we examine this key question by investigating how environmental and geographic factors across different epochs have driven genetic divergence at deeper (phylogeographic) and shallower (landscape genetic) evolutionary scales in the Chinese Tertiary relict tree Emmenopterys henryi. We found that geography played a predominant role at all levels – phylogeographic clades are broadly geographically structured, the deepest levels of divergence are associated with major geological or pre-Quaternary climatic events, and isolation by distance (IBD) primarily explained population genetic structure. However, environmental factors are clearly also important – climatic fluctuations since the Last Interglacial (LIG) have likely contributed to phylogeographic structure, and the population genetic structure (in our AFLP dataset) was partly explained by isolation by environment (IBE), which may have resulted from natural selection in environments with divergent climates. Thus, historical and contemporary geography and historical and contemporary environments have all shaped patterns of genetic structure in E. henryi, and, in fact, changes in the landscape through time have also been critical factors.

Highlights

Examining how historical and contemporary geographic and environmental factors contribute to genetic divergence at different evolutionary scales is a central yet largely unexplored question in ecology and evolution
The three chloroplast DNA (cpDNA)-intergenic spacer (IGS) regions surveyed across the 443 individuals of E. henryi were aligned along a total length of 2163 bp with 26 single-site mutations, 18 length polymorphisms (2–78 bp) and one inversion (27 bp) observed (Table S5)
In the cpDNA phylogeography, we found two major lineages corresponding to the Northern and Southern populations

Summary

Introduction

Examining how historical and contemporary geographic and environmental factors contribute to genetic divergence at different evolutionary scales is a central yet largely unexplored question in ecology and evolution. The flora of subtropical (Central-Southeast) China presents some excellent systems for such studies, including several genera of Tertiary relict trees that have inhabited topographically and ecologically heterogeneous environments (in terms of climate, soil, etc.) for millions of years[23,24,25,26] These genera (e.g. Cathaya, Ginkgo, Metasequoia, Davidia, Emmenopterys) are thought to represent remnants of the so-called ‘boreotropical flora’ that likely formed a belt of vegetation around the Northern Hemisphere during the Early Tertiary/ Eocene[27,28,29]. We examine this key question by investigating how environmental and geographic factors across different epochs have driven genetic divergence at deeper (phylogeographic) and shallower (landscape genetic) evolutionary scales in the Chinese flowering tree Emmenopterys henryi Oliv. We examine this key question by investigating how environmental and geographic factors across different epochs have driven genetic divergence at deeper (phylogeographic) and shallower (landscape genetic) evolutionary scales in the Chinese flowering tree Emmenopterys henryi Oliv. (Rubiaceae)

Methods

Results

Conclusion