Abstract

Southwest China is a biodiversity hotspot characterized by complex topography, heterogeneous regional climates and rich flora. The processes and driving factors underlying this hotspot remain to be explicitly tested across taxa to gain a general understanding of the evolution of biodiversity and speciation in the region. In this study, we examined the role played by historically neutral processes, geography and environment in producing the current genetic diversity of the subtropical pine Pinus yunnanensis. We used genetic and ecological methods to investigate the patterns of genetic differentiation and ecological niche divergence across the distribution range of this species. We found both continuous genetic differentiation over the majority of its range, and discrete isolated local clusters. The discrete differentiation between two genetic groups in the west and east peripheries is consistent with niche divergence and geographical isolation of these groups. In the central area of the species’ range, population structure was shaped mainly by neutral processes and geography rather than by ecological selection. These results show that geographical and environmental factors together created stronger and more discrete genetic differentiation than isolation by distance alone, and illustrate the importance of ecological factors in forming or maintaining genetic divergence across a complex landscape. Our findings differ from other phylogenetic studies that identified the historical drainage system in the region as the primary factor shaping population structure, and highlight the heterogeneous contributions that geography and environment have made to genetic diversity among taxa in southwest China.

Highlights

  • Genetic differentiation is strongly influenced by neutral processes and ecological selection

  • Network analysis showed that the 13 mitotypes were distinctly separated from those of P. tabuliformis (M1–M10), which was used as an outgroup, and all neighboring mitotypes differed by only one mutational step (Fig. 1a)

  • A marked geographic pattern of mitotype distribution was observed in P. yunnanensis

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Summary

Introduction

Genetic differentiation is strongly influenced by neutral processes and ecological selection. The combination of informative molecular markers, spatial statistics and high resolution geographic information system (GIS) data has made it more feasible to carry out explicit evaluation of environmental influences on the distribution of genetic variation [8,9,10]. This approach offers the opportunity of assessing how specific landscape and environmental features have shaped gene flow between populations and the extent of local adaptation [11]. Such information is important for understanding the neutral and selective processes driving divergence and, speciation

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