J Integr Plant Biol. ›› 2019, Vol. 61 ›› Issue (4): 433-448.DOI: 10.1111/jipb.12718

• Molecular Ecology and Evolution • Previous Articles     Next Articles

Incomplete reproductive isolation between Rhododendron taxa enables hybrid formation and persistence

Li-Jun Yan1,2,3,4†, Kevin S. Burgess5†, Wei Zheng1,3, Zhi-Bin Tao1,3, De-Zhu Li1,2,3* and Lian-Ming Gao1*   

  1. 1Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
    2Germplasm Bank of Wild Species, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650201, China
    3Kunming College of Life Science, University of the Chinese Academy of Sciences, Kunming 650201, China
    4College of Vocational and Technical Education, Yunnan Normal University, Kunming 650092, China
    5Department of Biology, College of Letters & Sciences, Columbus State University, University System of Georgia, 31907-5645 Columbus, GA, USA

    These authors contributed equally to this work.
    Email: Lian-Ming Gao (gaolm@mail.kib.ac.cn, Dr. Gao is fully responsible for the distribution of all materials associated with this article); De-Zhu Li (dzl@mail.kib.ac.cn)
  • Received:2018-08-18 Accepted:2018-09-06 Online:2018-09-07 Published:2019-04-01

Abstract: The evolutionary consequences of hybridization ultimately depend on the magnitude of reproductive isolation between hybrids and their parents. We evaluated the relative contributions of pre- and post-zygotic barriers to reproduction for hybrid formation, hybrid persistence and potential for reproductive isolation of hybrids formed between two Rhododendron species, R. spiciferum and R. spinuliferum. Our study established that incomplete reproductive isolation promotes hybrid formation and persistence and delays hybrid speciation. All pre-zygotic barriers to reproduction leading to hybrid formation are incomplete: parental species have overlapping flowering; they share the same pollinators; reciprocal assessments of pollen tube germination and growth do not differ among parents. The absence of post-zygotic barriers between parental taxa indicates that the persistence of hybrids is likely. Reproductive isolation was incomplete between hybrids and parents in all cases studied, although asymmetric differences in reproductive fitness were prevalent and possibly explain the genetic structure of natural hybrid swarms where hybridization is known to be bidirectional but asymmetric. Introgression, rather than speciation, is a probable evolutionary outcome of hybridization between the two Rhododendron taxa. Our study provides insights into understanding the evolutionary implications of natural hybridization in woody plants.

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