Evolution, 59(10), 2005, pp. 2185±2199 BREEDING SYSTEM, COLONY STRUCTURE, AND GENETIC DIFFERENTIATION IN THE CAMPONOTUS FESTINATUS SPECIES COMPLEX OF CARPENTER ANTS MICHAEL A. D. GOODISMAN1,2,3,4 AND DANIEL A. HAHN1,5,6 1Center for Insect Science, University of Arizona, Tucson, Arizona 85721 2Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, Arizona 85721 3School of Biology, The Georgia Institute of Technology, Atlanta, Georgia 30332 4E-mail:
[email protected] 5Interdisciplinary Graduate Program in Insect Science, University of Arizona, Tucson, Arizona 85721 6Department of Entomology and Nematology, University of Florida, Gainesville, Florida 32608 Abstract. All social insects live in highly organized societies. However, different social insect species display striking variation in social structure. This variation can signi®cantly affect the genetic structure within populations and, consequently, the divergence between species. The purpose of this study was to determine if variation in social structure was associated with species diversi®cation in the Camponotus festinatus desert carpenter ant species complex. We used polymorphic DNA microsatellite markers to dissect the breeding system of these ants and to determine if distinct C. festinatus forms hybridized in their natural range. Our analysis of single-queen colonies established in the laboratory revealed that queens typically mated with only a single male. The genotypes of workers sampled from a ®eld population suggested that multiple, related queens occasionally reproduced within colonies and that colonies inhabited multiple nests. Camponotus festinatus workers derived from colonies of the same form originating at different locales were strongly differentiated, suggesting that gene ¯ow was geographically restricted. Overall, our data indicate that C.