Disentangling the effects of isolation-by-distance and isolation-by-environment on genetic differentiation among Rhododendron lineages in the subgenus Tsutsusi

Chun Lin Huang, Jui Hung Chen, Chung Te Chang, Jeng Der Chung, Pei Chun Liao, Jenn Che Wang, Shih Ying Hwang

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5 Citations (Scopus)


Ecological speciation has long been noted as a central topic in the field of evolutionary biology, and investigation into the relative importance of ecological and geographical factors is becoming increasingly emphasized. We surveyed genetic variation of 277 samples from 25 populations of nine Rhododendron species within Tsutsusi subgenus in Taiwan using simple sequence repeats of expressed sequence tags. Bayesian clustering revealed four genetic lineages: (1) the Rhododendron simsii, Rhododendron kanehirai, and Rhododendron nakaharae lineage (lineage 1); (2) the Rhododendron longiperulatum, Rhododendron breviperulatum, and Rhododendron noriakianum lineage (lineage 2); (3) the Rhododendron rubropilosum lineage (lineage 3); and (4) the Rhododendron oldhamii lineage (lineage 4). Asymmetric introgressions were found from lineage 3 into lineages 1 and 2 (introgressed lineages). Genetic admixture of non-R. oldhamii species was also revealed by a neighbor-joining tree. Variation partitioning showed that environment explained much larger portions of genetic variation than geography between non-introgressed lineages (i.e., between R. oldhamii and other lineages). However, the Mantel and partial Mantel tests and the multiple matrix regression with randomization found that isolation-by-distance played a more important role than isolation-by-environment (IBE) in contributing to genetic variation in most between lineage comparisons. Nevertheless, strong IBE was found when compared between non-introgressed lineages of R. oldhamii and R. rubropilosum, suggesting post-speciation ecological divergence. Several environmental variables, including annual mean temperature, aspect, isothermality, seasonal precipitation, slope, and soil pH, could be important ecological drivers involved in reproductive isolation between R. oldhamii and non-R. oldhamii species within the Tsutsusi subgenus.

Original languageEnglish
Article number53
JournalTree Genetics and Genomes
Issue number3
Publication statusPublished - 2016 Jan 1



  • Asymmetric introgression
  • Closely related plant species
  • Post-speciation ecological divergence
  • Reproductive isolation

ASJC Scopus subject areas

  • Forestry
  • Molecular Biology
  • Genetics
  • Horticulture

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