Genetic architecture of susceptibility to herbivores in hybrid willows

Abstract

We performed a common garden experiment using parental, F1, F2, and backcross willow hybrids to test the hypothesis that hybrid willows experience breakdown of resistance to herbivores. After exposing plants to herbivores in the field, we measured the densities/damage caused by 13 insect herbivores and one herbivorous mite. Using joint‐scaling tests, we determined the contribution of additive, dominance, and epistasis to variation in susceptibility to herbivores (measured either as density or damage level) among the six genetic classes. We found the genetic architecture of susceptibility/resistance in the parental species to be complex, involving additive, dominance, and epistasis for each herbivore species. Although genic interactions altered plant susceptibility for each of the 14 herbivores, three distinct patterns of response of herbivores to hybrids were expressed. One pattern, observed in four herbivore species, supported the hypothesis of breakdown of resistance genes in recombinant hybrids. A second pattern, shown by six other herbivore species, supported the hypothesis of hybrid breakdown of host recognition genes. In other words, epistatic interactions for host recognition traits (probably oviposition/feeding stimulants or attractants) appeared to be important in determining herbivore abundance for those six species. The final patterns supported a structure of dominance, either for host recognition traits (in the case of three herbivore species) or for host resistance traits (for one herbivore species). The combination of differing responses of herbivore species, including members of the same genus and tribe, and the ubiquitous importance of epistasis suggests that many genes affect herbivore resistance in this hybrid willow system.

Development of an Insect Herbivore and its Pupal Parasitoid Reflect Differences in Direct Plant Defense

“…In addition to the wild B. oleracea populations, genetic variation in the expression of allelochemicals has been studied extensively in only a few species of wild plants, including both forbs and trees (Fritz et al 2003;Lawrence et al 2003;Ode et al 2004;Zangerl and Berenbaum 2005;Loney et al 2006). Interpopulation differences in the expression of allelochemicals may be driven by the intensity of selection from herbivores, particularly if natural enemies are scarce or absent (Ode et al 2004;Zangerl and Berenbaum 2005).…”

Genetic architecture of resistance to aphids and mites in a willow hybrid system

“…An opposite pattern was observed for mite resistance -F 2 hybrids were more resistant than predicted from a purely additive model of resistance (Figure 3). Perhaps a disruption of gene interactions has occurred within the S. eriocephala genome that affect traits used by mites to locate suitable host plants (Fritz et al, 2003). Alternatively, favourable interactions that confer resistance to mites may be expressed in these F 2 hybrids.…”

“…: Aphididae) and a mite (Aculops tetanothrix: Eriophyidae). The current study differs from Fritz et al (2003) in that the plants were kept free of herbivores other than the two species studied, and thus interspecific interactions with other herbivore species could not potentially affect resistance measurements (ie, aphid survival, aphid reproduction, and total number of mite galls). We document the potential of herbivores to affect plant evolution, such that selection by herbivores can lead to the creation of gene interactions that influence plant resistance traits or host recognition traits used by herbivores.…”

“…Using a Salix eriocephala-S. sericea hybrid system, Fritz et al (2003) examined the genetic architecture of plant resistance to arthropods that existed within a community and found that additive and nonadditive genetic effects were important to explain the difference in resistance between the two species. Here, we examined the relative importance of additive and nonadditive genetic effects on differences between S. eriocephala and S. sericea in resistance to two arthropods, a willow leaf aphid (Chaitophorus sp.…”

Genetic structure of a foundation species: scaling community phenotypes from the individual to the region

“…We first examine the genetic scaling in the Populus hybrid complex using line cross analysis (Lynch and Walsh, 1998;Fritz et al, 2003) of three traits: stem and root fractal architecture, and condensed tannin concentrations. This analysis determines whether traits from parental lineages and their hybrid cross types show recognizable patterns of phenotypic expression in progeny that are consistent with additive and/or dominance effects.…”