Journal Article

Extrafloral Nectaries in Aspen (<i>Populus tremuloides</i>): Heritable Genetic Variation and Herbivore-induced Expression

Stuart C. Wooley, Jack R. Donaldson, Adam C. Gusse, Richard L. Lindroth and Michael T. Stevens

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 100, issue 6, pages 1337-1346
Published in print November 2007 | ISSN: 0305-7364
Published online November 2007 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcm220
Extrafloral Nectaries in Aspen (Populus tremuloides): Heritable Genetic Variation and Herbivore-induced Expression

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

A wide variety of plants produce extrafloral nectaries (EFNs) that are visited by predatory arthropods. But very few studies have investigated the relationship between plant genetic variation and EFNs. The presence of foliar EFNs is highly variable among different aspen (Populus tremuloides) genotypes and the EFNs are visited by parasitic wasps and predatory flies. The aim here was to determine the heritability of EFNs among aspen genotypes and age classes, possible trade-offs between direct and indirect defences, EFN induction following herbivory, and the relationship between EFNs and predatory insects.

Methods

EFN density was quantified among aspen genotypes in Wisconsin on trees of different ages and broad-sense heritability from common garden trees was calculated. EFNs were also quantified in natural aspen stands in Utah. From the common garden trees foliar defensive chemical levels were quantified to evaluate their relationship with EFN density. A defoliation experiment was performed to determine if EFNs can be induced in response to herbivory. Finally, predatory arthropod abundance among aspen trees was quantified to determine the relationship between arthropod abundance and EFNs.

Key Results

Broad-sense heritability for expression (0·74–0·82) and induction (0·85) of EFNs was high. One-year-old trees had 20% greater EFN density than 4-year-old trees and more than 50% greater EFN density than ≥10-year-old trees. No trade-offs were found between foliar chemical concentrations and EFN density. Predatory fly abundance varied among aspen genotypes, but predatory arthropod abundance and average EFN density were not related.

Conclusions

Aspen extrafloral nectaries are strongly genetically determined and have the potential to respond rapidly to evolutionary forces. The pattern of EFN expression among different age classes of trees appears to follow predictions of optimal defence theory. The relationship between EFNs and predators likely varies in relation to multiple temporal and environmental factors.

Keywords: Aspen; extrafloral nectaries; herbivory; indirect defence; induction; mutualism; optimal defence; Populus tremuloides; heritability; genetic variation

Journal Article.  6642 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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