Genotype-environment interaction occurs when a genotype that has a superior phenotype in one environment loses its relative advantage in some other environment. Such interactions are of particular interest to evolutionary ecologists when the "environment" is another species in the community. Interspecies interactions of this sort differ from other genotype-environment interactions because the environment for one species is itself an evolving entity, that is, another species. When selection acts only at the level of the individual, these interspecies interactions normally cannot contribute to a response to selection. When selection is acting at the community level, however, interspecies interactions can contribute to a response to community selection. Variation that is expressed as environmental variation at the individual level becomes heritable variation at the community level. In the experiment reported here simple communities consisting of two species of flour beetles, Tribolium castaneum and Tribolium confusum, were studied. I measured the general intermixing ability of strains of each species and the specific intermixing ability of pairs of strains of both species in the communities, using a diallel experiment similar to that used to measure general and specific combining ability of individuals. The results indicate that there is significant general intermixing ability for traits measured in both species, and significant specific intermixing ability for one trait (adult population size) measured in T. confusum. These results are discussed in relation to community selection.
