A massive tsunami promoted gene flow and increased genetic diversity in a near threatened plant species

Kako Ohbayashi,Yoshikuni Hodoki,Natsuko I Kondo,Masakazu Shimada,Hidenobu Kunii

doi:10.1038/s41598-017-11270-5

Abstract

The magnitude and frequency of disturbances affect species diversity and spatial distributions, but the direct effects of large-scale disturbances on genetic diversity are poorly understood. On March 11, 2011, the Great Tohoku Earthquake in Japan caused a massive tsunami that resulted in substantial alteration of community compositions. Populations of a near-threatened tidal marsh Carex rugulosa inhabiting brackish sandbars was also affected. We found four out of six remnant C. rugulosa populations along the Pacific Ocean had become completely extinct. Newly emergent post-tsunami populations, however, had higher allelic numbers than pre-tsunami populations, indicating higher genetic diversity after the tsunami. In addition, genetic differentiation (Fst) between post-tsunami populations was significantly lower than that of pre-tsunami populations. We therefore conclude that the tsunami enhanced gene flow. Seeds of many Carex species persist for long periods in soil, which suggests that seed banks are important genetic resources for post-disturbance recovery of genetic diversity. When its brackish sandbar habitat is no longer subject to disturbance and changes to the land, C. rugulosa is outcompeted by terrestrial plant competitors and eliminated. Disturbance is a driving force for the recovery and maintenance of populations of species such as C. rugulosa—even after near-complete eradication.

Highlights

The magnitude and frequency of disturbances affect species diversity and spatial distributions[1]
There have been controversies surrounding the issue of why clonal plants have maintained both vegetative and seed reproduction, despite their fitness being increased by vegetative reproduction[14]
We have an operational hypothesis that the genetic diversity of soil seed banks before a disturbance, of a near-threatened C. rugulosa in Japan, is higher than that of the present above-ground population because the seed banks of previously above-ground extinct populations would have had high genetic diversity

Summary

Introduction

The magnitude and frequency of disturbances affect species diversity and spatial distributions[1]. Both stress-tolerant (S) and ruderal (R) strategies being classified as an SR strategy following Grim[12, 13] This species maintains its populations by both sexual (seed) and asexual (clonal) reproduction (new shoots budding from rhizomes). We have an operational hypothesis that the genetic diversity of soil seed banks before a disturbance, of a near-threatened C. rugulosa in Japan, is higher than that of the present above-ground population because the seed banks of previously above-ground extinct populations would have had high genetic diversity Intensive disturbance, such as massive tsunamis, may play an important role in increasing genetic diversity available from the soil seed bank. Newly emergent local populations established following a disturbance such as a massive tsunami would, to a great extent, have high genetic diversity and low genetic differentiation because new populations would be established by floating rhizomes and/or seeds through tsunami waves. We investigated all these six populations in 2013 or 2014 (hereafter, post-tsunami)

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Results

Conclusion