The Union of Ecology and Evolution: Extended Phenotypes and Community Genetics

Abstract

Community genetics relies on genes with extended phenotypes and on community heritability. An extended phenotype (Dawkins 1982) is a genetically based consequence that extends beyond the physical boundaries of the organism bearing the gene. For example, a cross between Populus fremontii and P. angustifolia exhibits genetic variation at one locus that increases the level of condensed tannin tenfold. Tannin, a chemical plant defense, influences the behavior of herbivorous insects and the rate at which leaves decompose. Thus, a cottonwood’s extended phenotype includes herbivore density and diversity and the rate of nutrient cycling in decomposing leaves. The principle of community heritability is attributed to Goodnight (1990), who wrote, “If the interactions among the members of the community are passed intact from the ‘parent’ community to the ‘offspring’ community, the interaction will be heritable at the community level.” The basis of community genetics is intraspecific genetic variation with major effects that trigger a cascade of interactions with other species in the community. Other fields of genetics focus on indivduals or make use of neutral genetic variation to study systematics, to infer historic events, or to measure gene flow. Because the genetic variation underlying the extended phenotype conforms to normal patterns of inheritance, the extended phenotypes—the interactions with other species—are heritable.