J Syst Evol

• Research Articles •    

Stable persistence of relict populations involved evolutionary shifts of reproductive characters in the genus Tanakaea (Saxifragaceae)

Daiki Takahashi1*, Yuji Isagi2, Pan Li3, Ying-Xiong Qiu3, Hiroaki Setoguchi4, Yoshihisa Suyama1, Ayumi Matsuo1, Yoshihiro Tsunamoto5, Shota Sakaguchi4   

  1. 1Kawatabi Field Science Centre, Graduated School of Agricultural Science, Tohoku University, Osaki, Miyagi, Japan

    2Graduate School of Agriculture, Kyoto University, Kyoto, Japan

    3Systematic and Evolutionary Botany and Biodiversity Group, MOE Laboratory of Biosystem Homeostasis and Protection, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China

    4Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan

    5Research Institute of Energy, Environment and Geology, Hokkaido Research Organization, Sapporo, Hokkaido, Japan

  • Received:2021-12-27 Accepted:2022-03-17 Online:2022-03-21

Abstract:

Tertiary relicts often show evolutionary stasis in morphology and ecology and have been hypothesized to retain stable population sizes in refugia. However, recent studies have reported that some relicts evolutionarily shifted their physiology, ecology, and morphology and experienced various patterns of demography. To understand the historical survival of relict plants, a multidimensional study investigating the evolution of ecological and morphological traits as well as population demographic history is needed. The genus Tanakaea (Saxifragaceae) comprises two species in China and Japan. These species share most vegetative characteristics and are sometimes treated as a single species. The distribution pattern is relictual, as the populations are confined to small areas in mesic warm temperate forests less influenced by Quaternary glacial climates. Focusing on the relictual plant group, this study tested the hypotheses of evolutionary stasis and population stability in long-term refugia. Genetic analyses using plastome sequences and genome-wide single-nucleotide polymorphisms revealed divergence of the two species approximately 6.8 million years ago and strong genetic differentiation of the regional populations. Demographic analysis revealed that almost all populations retained stable population sizes during glacial–interglacial climate changes, supporting the traditional view. However, morphological assessments revealed a simultaneous shift in breeding systems (from hermaphrodite to dioecy/non-clonal to clonal reproduction) in Japanese species and intraspecific differentiation of leaf traits. Therefore, the relict species do not show evolutionary stasis in every aspect. Changes in reproductive characteristics may have contributed to their long-term in situ survival.

Key words: Tertiary relict plants, Phylogeography, East Asia, Evolutionary stasis hypothesis, mating system evolution, Tanakaea, Saxifragaceae