J Syst Evol

• Research Article •    

Mechanisms of reproductive isolation between annual and perennial plants of Incarvillea sinensis

Wen‐Juan Lan1†, Fang‐Yuan Wang1†, Spencer C. H. Barrett2, Wen‐Ting Wang3, Yue Ma1, Yang Yang1, Nan Li1, Jun‐Chen Deng1,4,5, and Wei‐Ning Bai1*   

  1. 1 Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, College of Life Sciences, Beijing Normal University, Beijing 100875, China;
    2 Department of Ecology and Evolutionary Biology, University of Toronto, Toronto M5S 3B2, ON, Canada;
    3 School of Mathematics and Computer Science, Northwest Minzu University, Lanzhou 730030, China;
    4 Institute of Environmental Sciences, Faculty of Biology, Jagiellonian University, Gronostajowa 7, Kraków 30-387, Poland;
    5 Doctoral School of Exact and Natural Sciences, Jagiellonian University, Gronostajowa 7, Kraków 30-387, Poland
    Wen-Juan Lan and Fang-Yuan Wang are co-first authors.
    *Author for correspondence. E-mail:baiwn@bnu.edu.cn
  • Received:2023-02-08 Accepted:2023-05-13 Online:2023-07-18

Abstract: Quantifying the relative strength of isolating barriers is a major focus of research on plant speciation. Contrasting life histories and mating systems have the potential to limit gene exchange between closely related populations growing in sympatry. However, few studies have quantified reproductive isolating barriers between conspecific annual and perennial populations and their contributions to total reproductive isolation (RI). Incarvillea sinensis Lam. (Bignoniaceae) is an insect‐pollinated herb with largely allopatric annual and perennial populations that differ in mating systems. The perennial populations are primarily outcrossing whereas annual populations are predominantly selfing. At a rare sympatric site in northern China we estimated prezygotic and postzygotic barriers to gene exchange between annual and perennial plants and found complete RI between the two life histories. Annuals exhibited significantly higher ecogeographic isolation than perennials whereas perennials experienced more isolation through pollen–pistil interactions than annuals. Crosses between annuals and perennials demonstrated that postzygotic barriers influencing fruit and seed formation, F1 germination and survival were negligible for annuals but played a small role for perennials. However, F1 hybrids of crosses between annuals and perennials produced no pollen and their ovules were largely sterile. Our study provides insight into the relative importance of prezygotic and postzygotic isolating barriers between closely related annual and perennial populations of I. sinensis and some of these barriers could have been involved with speciation. Annuals and perennials of I. sinensis represent two biological species and thus deserve to be recognized as distinct taxonomic species.

Key words: asymmetric barriers to gene exchange, Incarvillea sinensis, life history, mating system, reproductive isolation