Mating system evolution and genetic structure of diploid sexual populations of Cyrtomium falcatum in Japan

Ryosuke Imai,Ryo Ootsuki,Yoshiaki Tsuda,Yasuyuki Watano,Ayumi Tezuka,Atsushi Ebihara,Atsushi J Nagano,Sadamu Matsumoto

doi:10.1038/s41598-021-82731-1

Abstract

Evolution of mating systems has become one of the most important research areas in evolutionary biology. Cyrtomium falcatum is a homosporous fern species native to eastern Asia. Two subspecies belonging to a sexual diploid race of C. falcatum are recognized: subsp. littorale and subsp. australe. Subspecies littorale shows intermediate selfing rates, while subsp. australe is an obligate outcrosser. We aimed to evaluate the process of mating system evolution and divergence for the two subspecies using restriction site associated DNA sequencing (RAD-seq). The results showed that subsp. littorale had lower genetic diversity and stronger genetic drift than subsp. australe. Fluctuations in the effective population size over time were evaluated by extended Bayesian skyline plot and Stairway plot analyses, both of which revealed a severe population bottleneck about 20,000 years ago in subsp. littorale. This bottleneck and the subsequent range expansion after the LGM appear to have played an important role in the divergence of the two subspecies and the evolution of selfing in subsp. littorale. These results shed new light on the relationship between mating system evolution and past demographic change in fern species.

Highlights

Evolution of mating systems has become one of the most important research areas in evolutionary biology
To deepen our understanding of the relationship between selfing evolution and demographic history, in this study we focused on a homosporous fern species, Cyrtomium falcatum (L.f.) C.Presl
We addressed two questions by means of these analyses: (1) Are separate type (S-type) populations in subsp. littorale more closely related to subsp. australe than mixed type (M-type) ones? (2) Are there any associations between demographic events, lineage divergence and the evolution of selfing? By answering these questions, we aimed to clarify the process of mating system evolution in the two subspecies of diploid sexual C. falcatum

Summary

Introduction

Evolution of mating systems has become one of the most important research areas in evolutionary biology. This bottleneck and the subsequent range expansion after the LGM appear to have played an important role in the divergence of the two subspecies and the evolution of selfing in subsp. To deepen our understanding of the relationship between selfing evolution and demographic history (e.g. the occurrence of population bottlenecks), in this study we focused on a homosporous fern species, Cyrtomium falcatum (L.f.) C.Presl. The variation in the mating systems of the derived subspecies and the predominance of outcrossing in its ancestral subspecies constitute an evolutionary pattern that makes C. falcatum a useful model for studying mating system evolution in homosporous ferns

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