PS 33-47
Of willows and arthropods: Host plant genotype affects arthropod community assemblage and structure
Community genetics seeks to decipher the connections from intraspecific genetic variation to interspecific interactions to community and ecosystem level dynamics. Research from this genes-to-ecosystems perspective has accomplished much in the last two decades, and greatly enhanced our understanding of fundamental biological processes. In this study, we contribute evidence that intraspecific plant genetic variation does influence arthropod communities. Implementing a common garden experiment, we asked: Does the genotype of a host plant (the coastal willow, Salix hookeriana) affect arthropod community composition and structure? We also assessed the effects of plant genotype on phenotype (sex, biomass, and several leaf traits), and how these plant traits affect arthropods.
In spring 2009, we planted 25 stem cuttings (replicates) from 27 willow trees (genotypes; 13 male, 14 female) in a fully-randomized common garden design at our study site on the Humboldt Bay National Wildlife Refuge (northwestern California). In summer 2010, we surveyed arthropods and herbivory levels on the willow plants (26 genotypes, 12 replicates each). All aboveground arthropods, including leaf rolls and galls, were censused, sorted to morphospecies, and identified to family or species level. We also measured aboveground plant biomass, specific leaf area (SLA), leaf toughness, foliar chlorophyll content, and foliar carbon:nitrogen ratio (C:N).
Results/Conclusions
We found 12,965 individual arthropods, representing 189 taxa from 80 families. Plant genotype affected arthropod abundance, richness, evenness, diversity, and community composition. Aboveground plant biomass and SLA also affected arthropod abundance, richness, and community composition. Meanwhile, plant sex, leaf toughness, chlorophyll content, and C:N did not affect the arthropod community, in terms of the aforementioned metrics and composition.
Plant genotype and phenotype also affected different trophic levels when analyzed separately. Plant genotype affected both herbivores and predators/parasitoids (in terms of abundance, richness, evenness, and diversity), whereas plant traits affected the two trophic levels in similar but slightly different ways. Herbivores (abundance, richness, and diversity) were affected by plant biomass, SLA, and chlorophyll. Predators and parasitoids (abundance, richness, and diversity) were affected by plant biomass and SLA only.
This study contributes to the growing field of community genetics, thus enhancing our understanding of ecological interactions, by demonstrating that within-species genetic variation does indeed influence multi-species dynamics, including community composition and structure. Our study site is also a important contribution, as it offers much potential for future research, with many replicates allowing for more experimental treatments.