COMPLEX COLONY STRUCTURE IN SOCIAL INSECTS .1. ECOLOGICAL DETERMINANTS AND GENETIC CONSEQUENCES

For social insect species, intraspecific variation in colony social st ructure provides an opportunity to relate the evolution of social beha vior to ecological factors. The species Myrmica punctiventris is a cav ity-dwelling forest ant that exhibits very different colony structures in two populations in the northeastern United States. Combined data f rom seasonal censuses, allozyme electrophoresis, and worker hostility tests showed that a population of M. punctiventris in Vermont was stri ctly monogynous and seasonally polydomous. The same procedures showed that a population of M. punctiventris in New York was facultatively po lygynous and predominantly monodomous. Genetic relatedness among colon y-mates was not different from Hamilton's expected values in the Vermo nt population and was consistent with little exchange of ants between colonies and single-mating of queens. In contrast, relatedness was low er in New York, and examination of nest-mate genotypes revealed exchan ge of ants between colonies, high rates of colony loss and replacement of queens, or multiple-mating of queens. The genetic structure of the Vermont population was consistent with no inbreeding, but in New York , the population genetic structure reflected microgeographic subdivisi on and inbreeding. Previous study of the ant communities at these site s implicates nest-site limitation in New York as a primary constraint on social structure.