Heterozygous Trees Rebound the Fastest after Felling by Beavers to Positively Affect Arthropod Community Diversity

Faith M Walker,Thomas G Whitham,Stephen M Shuster,Rachel Durben,Richard L Lindroth

doi:10.3390/f12060694

Faith M Walker, Thomas G Whitham + Show 3 more

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https://doi.org/10.3390/f12060694

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Abstract

Although genetic diversity within stands of trees is known to have community-level consequences, whether such effects are present at an even finer genetic scale is unknown. We examined the hypothesis that genetic variability (heterozygosity) within an individual plant would affect its dependent community, which adds a new dimension to the importance of genetic diversity. Our study contrasted foliar arthropod community diversity and microsatellite marker-derived measures of genetic diversity of cottonwood (Populus fremontii) trees that had been felled by beavers (Castor canadensis) and were resprouting, relative to adjacent standing, unfelled trees. Three patterns emerged: 1. Productivity (specific leaf area), phytochemical defenses (salicortin), and arthropod community richness, abundance, and diversity were positively correlated with the heterozygosity of individual felled trees, but not with that of unfelled trees; 2. These relationships were not explained by population substructure, genetic relatedness of the trees, or hybridization; 3. The underlying mechanism appears to be that beaver herbivory stimulates increased productivity (i.e., 2× increase from the most homozygous to the most heterozygous tree) that is the greatest in more heterozygous trees. Salicortin defenses in twigs were also expressed at higher concentrations in more heterozygous trees (i.e., 3× increase from the most homozygous to the most heterozygous tree), which suggests that this compound may dissuade further herbivory by beavers, as has been found for other mammalian herbivores. We suggest that high stress to trees as a consequence of felling reveals a heterozygosity–productivity linkage, which in turn is attractive to arthropods. Although experiments are required to demonstrate causality, these results link the genetic diversity of individual trees to community diversity, supporting the hypothesis that interactions among foundation species (beavers and trees) have community-level effects, and underscores the importance of genetic diversity for biodiversity, conservation, and restoration.

Highlights

IntroductionA growing number of reviews show that dominant or foundation species can have extended genetic effects that impact associated communities, ecosystem processes, and evolution [1,2,3,4,5,6,7,8]
7 of 16 the arIn agreement with our hypothesis that individual tree heterozygosity affects thropod community, we found that a felled tree’s Individual multilocus heterozygosity (IMH) was positively correlated with its arthropod community diversity
In agreement with our hypothesis that interactions among foundation species have community-level effects, we found that genetic diversity (IMH) of individual resprouting beaver-felled trees was positively correlated with productivity, a phenolic glycoside, and arthropod community richness, diversity, and abundance, whereas these correlations were absent for trees not felled by beavers

Summary

Introduction

A growing number of reviews show that dominant or foundation species can have extended genetic effects that impact associated communities, ecosystem processes, and evolution [1,2,3,4,5,6,7,8]. The broadest levels of genetic effects involve a number of unique individuals (genotypes) within a population, which can consist of genotypes within species or, more loosely, hybrid genotypes of closely related sympatric species. Such genetic variation is most accurately referred to as genotypic diversity [9]. The finest level of genetic diversity is measured within the genotype itself as individual heterozygosity (the proportion of heterozygous loci sampled in an individual)

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Conclusion