Differential role of a persistent seed bank for genetic variation in early vs. late successional stages.

Benjamin Schulz,Jiří Danihelka,Walter Durka,Rolf Lutz Eckstein,Craig Eliot Coleman

doi:10.1371/journal.pone.0209840

Abstract

Persistent seed banks are predicted to have an important impact on population genetic processes by increasing effective population size and storing past genetic diversity. Accordingly, persistent seed banks may buffer genetic effects of disturbance, fragmentation and/or selection. However, empirical studies surveying the relationship between aboveground and seed bank genetics under changing environments are scarce. Here, we compared genetic variation of aboveground and seed bank cohorts in 15 populations of the partially cleistogamous Viola elatior in two contrasting early and late successional habitats characterized by strong differences in light-availability and declining population size. Using AFLP markers, we found significantly higher aboveground than seed bank genetic diversity in early successional meadow but not in late successional woodland habitats. Moreover, individually, three of eight woodland populations even showed higher seed bank than aboveground diversity. Genetic differentiation among populations was very strong (фST = 0.8), but overall no significant differentiation could be detected between above ground and seed bank cohorts. Small scale spatial genetic structure was generally pronounced but was much stronger in meadow (Sp-statistic: aboveground: 0.60, seed bank: 0.32) than in woodland habitats (aboveground: 0.11; seed bank: 0.03). Our findings indicate that relative seed bank diversity (i.e. compared to aboveground diversity) increases with ongoing succession and despite decreasing population size. As corroborated by markedly lower small-scale genetic structure in late successional habitats, we suggest that the observed changes in relative seed bank diversity are driven by an increase of outcrossing rates. Persistent seed banks in Viola elatior hence will counteract effects of drift and selection, and assure a higher chance for the species’ long term persistence, particularly maintaining genetic variation in declining populations of late successional habitats and thus enhancing success rates of population recovery after disturbance events.

Highlights

Instead of relying solely on the spatial dispersal of their seeds, many plant species have developed the ability to disperse their offspring in time by accumulating long-lived, dormant seeds of several years in the soil or in aerial reservoirs
For private band richness (PBr) (LMM, chi2 = 4.40, df = 1, p = 0.036) and proportion of unique genotypes (Pu) (LMM, chi2 = 15.77, df = 1, p
The latter was corroborated by the comparison of log response ratios, indicating for band richness (Br), PBr and Pu significantly higher values for aboveground cohorts in meadow but not in woodland habitats (Fig 2)

Summary

Introduction

Instead of relying solely on the spatial dispersal of their seeds, many plant species have developed the ability to disperse their offspring in time by accumulating long-lived, dormant seeds of several years in the soil or in aerial reservoirs Such persistent seed banks are a common feature of plants to counteract the consequences of environmental or demographic stochasticity that can be found across a wide range of life history types, habitats and climate zones [1,2]. Persistent seed banks may increase effective population size [7,8] and store even more genetic diversity than present in the aboveground populations [5]. Seed banks may enable gene flow from past generations stored in the soil, maintain genes in populations through periods in which they are selected against [6], and slow down adaptation processes and damp out directional selection in response to environmental fluctuations

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Discussion

Conclusion