Resistance of Hybrid Plants to Herbivores: Genes, Environment, or Both?

Analyses of resistance of hybrid plants to herbivores in natural populations have revealed a diversity of patterns, including hybrid susceptibility, hybrid dominance, and hybrid intermediacy. But because many of these studies are conducted on unknown genotypes of hybrid plants in natural habitats, the genetic and environmental causes of the patterns cannot be distinguished. Predicted patterns and models of underlying genetic and environmental causes of these patterns are presented for F1, F2, and BC hybrid genotypes. It is argued that progress in resolving the causal relationships in hybrid plant–herbivore interactions will require experimentation that compares known hybrid genotypes in a combination of common garden and reciprocal transplant experiments. Such experiments will also permit tests of genotype-by-environment interactions in hybrid resistance that parallel hypotheses of hybrid plant fitness in hybrid zones.