The effect of population density on gene flow between adult trees and the seedling bank in Abies alba Mill.

J Paluch,M Kempf,M Zarek

doi:10.1007/s10342-019-01162-w

Abstract

Populations of smaller effective sizes or subjected to strong environmental filtering have a higher risk of stochastic changes in their genetic properties. This study tested the hypothesis that reducing the density of parent trees combined with environmental filtering during the stage of regeneration establishment affects gene flow between the parent and offspring populations of Abies alba Mill. The genetic variation and spatial genetic structure of parent trees and seedlings were compared in the Western Carpathians (southern Poland) in 27 stands with varying adult tree and regeneration densities. The analysis comprised 1592 individuals and was based on five nuclear microsatellite markers. The proportion of stands with significant spatial genetic structure in the adult tree and seedling cohorts increased as the density of adult trees decreased. The genetic differentiation between adult trees and seedlings expressed by the fixation index FST was between 0.005 and 0.021 and increased as the density of adult trees decreased but was not correlated with the seedling abundance. At the within-stand level, the analysis revealed shifts in the average number of alleles per locus (between − 15% and + 28%), the observed heterozygosity (between − 25% and + 20%) and expected heterozygosity (between − 8% and + 11%) between the populations of adult trees and seedlings. It was concluded that in mixed stands with densities of A. alba trees about 50 adult individuals per ha, there may be some risk of reduced effective population size and disturbed vertical gene flow, but significant shifts in the level of genetic variation are less likely.

Highlights

Natural regeneration is commonly considered the best strategy for maintaining genetic diversity and evolutionary potential in most forest tree species with large populations (Finkeldey and Ziehe 2004; Geburek and Müller 2005)
50% of the alleles occurred at a frequency of less than 5%, and in the individual stands the percentage of rare alleles varied between 40 and 62%
There was no evidence that regeneration abundance had any influence on intergenerational gene flow, suggesting that in the stands studied the availability of seeds and the environmental filtering were randomly linked in time and space

Summary

Introduction

Natural regeneration is commonly considered the best strategy for maintaining genetic diversity and evolutionary potential in most forest tree species with large populations (Finkeldey and Ziehe 2004; Geburek and Müller 2005). Populations of smaller effective sizes have a higher risk of stochastic changes in their genetic properties which could result from a number of factors, including a bottleneck in the census size or a large variance in reproductive output (Wang 2005). Reproductive isolation causes shifts in the mating system from outcrossing to selfing (Restoux et al 2008), reduces the diversity of the local pollen pool and increases the relatedness in the generation leading to mating between closely related individuals and inbreeding in subsequent generations

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Discussion

Conclusion