Genetic Diversity Increases Insect Herbivory on Oak Saplings

Abstract

A growing body of evidence from community genetics studies suggests that ecosystem functions supported by plant species richness can also be provided by genetic diversity within plant species. This is not yet true for the diversity-resistance relationship as it is still unclear whether damage by insect herbivores responds to genetic diversity in host plant populations. We developed a manipulative field experiment based on a synthetic community approach, with 15 mixtures of one to four oak (Quercus robur) half-sib families. We quantified genetic diversity at the plot level by genotyping all oak saplings and assessed overall damage caused by ectophagous and endophagous herbivores along a gradient of increasing genetic diversity. Damage due to ectophagous herbivores increased with the genetic diversity in oak sapling populations as a result of higher levels of damage in mixtures than in monocultures for all families (complementarity effect) rather than because of the presence of more susceptible oak genotypes in mixtures (selection effect). Assemblages of different oak genotypes would benefit polyphagous herbivores via improved host patch location, spill over among neighbouring saplings and diet mixing. By contrast, genetic diversity was a poor predictor of the abundance of endophagous herbivores, which increased with individual sapling apparency. Plant genetic diversity may not provide sufficient functional contrast to prevent tree sapling colonization by specialist herbivores while enhancing the foraging of generalist herbivores. Long term studies are nevertheless required to test whether the effect of genetic diversity on herbivory change with the ontogeny of trees and local adaptation of specialist herbivores.

Oak canopy arthropod communities: which factors shape its structure?

“…Similar results were reported by Castagneyrol et al (2012), who found that the genetic attributes of the host plant (genetic diversity, kinship, and genetic identity) had no significant effect on the community of phytophagous insects (endophagous and ectophagous) associated with the canopy of Q. robur in France. The absence of a response by the canopy communities associated with Q. robur in Europe is probably due to the lower levels of genetic diversity of European species (whose populations were affected by glaciations) compared to the diversity reported for Mexican oak species (i.e., Magri et al 2007;Marsico et al 2009).…”

Plant diversity effects on insect herbivores and their natural enemies: current thinking, recent findings, and future directions

“…Other traits such as herbivore mobility [13,34,35] and feeding mode [36] are also thought to be important predictors of plant diversity effects on herbivores but have received comparatively less attention. In an insightful review, Bommarco and Banks [35] reported that highly mobile herbivores responded more strongly to plant diversity than sedentary herbivores because they can disperse more readily and choose among plant patches of varying diversity.…”

“…In an insightful review, Bommarco and Banks [35] reported that highly mobile herbivores responded more strongly to plant diversity than sedentary herbivores because they can disperse more readily and choose among plant patches of varying diversity. In addition, a recent study by Castagneyrol et al [36] emphasizes the importance of feeding mode as they found that plant intra-specific diversity in oak sapling populations increased the abundance of ectophagous herbivores, but was a poor predictor of the abundance of endophagous herbivores.…”

“…For example, in a meta-analysis, Jactel and Brockerhoff [33] found that increased tree diversity reduced herbivory by specialist species, whereas the response of generalist herbivores was variable. These predictions are supported by recent studies in both tropical [9 ] and temperate [31 ] forest systems.Other traits such as herbivore mobility [13,34,35] and feeding mode [36] are also thought to be important predictors of plant diversity effects on herbivores but have received comparatively less attention. In an insightful review, Bommarco and Banks [35] reported that highly mobile herbivores responded more strongly to plant diversity than sedentary herbivores because they can disperse more readily and choose among plant patches of varying diversity.…”

Evolutionary community ecology of plant‐associated arthropods in terrestrial ecosystems

“…Next, I highlight effects of diversity of plant genotypes and phenotypes within a population on arthropod community structure. Several recent studies have addressed how plant genetic diversity influences trophic interactions and community structure of plant-associated arthropods (Crutsinger et al 2006;Johnson et al 2006;Crawford et al 2007;Cook-Patton et al 2011;Tack and Roslin 2011;Utsumi et al 2011;Castagneyrol et al 2012). Ecological mechanisms of the influence of genetic diversity are additive and nonadditive mechanisms.…”