POPULATION-STRUCTURE OF LEPTOTHORAX-AMBIGUUS, A FACULTATIVELY POLYGYNOUS AND POLYDOMOUS ANT SPECIES

We examined the genetic and spatial structure of Leptothorax ambiguus in a Vermont site. Nests of this tiny ant species have variable queen number and comprise larger polydomous colonies, as do their closest re latives in North America. Nests are patchily distributed in the forest , and sometimes occur in local abundance. We collected 121 nests in fo ur years from plots in which all nests were mapped; furthermore, we su bjected nests collected in two separate years to starch gel electropho resis and estimated relatedness according to the Queller-Goodnight (19 89) algorithm. Queens that share a nest site also share 33% of their a lleles on average, and relatedness among worker nestmates is about 0.5 . The existence of diploid males and nonzero F-values demonstrate inbr eeding in this species, an unusual phenomenon for social insects in ge neral. Mapping data showed that nests with like genotypes tended to cl uster in space, forming polydomous colonies. Colonies consisted of 1-6 nest subunits, and about half of all colonies were polygynous. We com pare these features of L. ambiguus to its close relative L. longispino sus and a European congener L. acervorum. These comparisons allow us t o conclude that an interplay between ecological and genetic factors pr oduces the observed pattern of multiple queening and nest spatial dist ribution in this species.