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[Vol. 95 
southern populations seem more likely to be monogynous than 
northern populations (Herbers, 1986a). Several other factors influ- 
ence the pattern of polygyny, such as the scarcity of available nest 
sites (Herbers, 1986b). Neighboring populations, therefore, may 
differ in the frequency of polygynous colonies, as was shown, e.g., in 
L. curvispinosus. In one population 75 percent of the colonies con- 
tained several females, but in a population 7 km away only 38.8 
percent were polygynous (Stuart, 1987). 
The facultatively polygynous and functionally monogynous spe- 
cies of the subgenus Leptothorax s. str. usually live in boreal or 
alpine coniferous habitats. Of all North American ants, L. “musco- 
rum ”, comprising several species like Leptothorax spec. A, B, and 
C, is the species best able to survive in extreme arctic and alpine 
conditions (Brown, 1955). With colonies found in north Alaska 
(Nielsen, 1987) and near the tree line in Nouveau Quebec (Fran- 
coeur, 1983), both L. “muscorum” and L. acervorum are among the 
few species of Formicidae that are found so far north. 
Species of the subgenus Myrafant, on the other hand, are abun- 
dant in areas with mild conditions in winter, such as the Mediterra- 
nean. Of the numerous species of this subgenus, only five reach 
Scandinavia, including Denmark (Collingwood, 1979), and among 
those are the facultatively polygynous L. tuberum and L. interrup- 
tus (Buschinger, 1968a; 1974a) and L. nylanderi, of which polygy- 
nous colonies have occasionally been found in the field (Chauvin, 
1947; Plateaux, 1970). Populations of Myrafant in alpine areas, 
such as L. tuberum in the Alps, tend to be facultatively polygynous 
as well (Buschinger, 1968a), and facultatively polygynous L. longi- 
spinosus and L. ambiguus are the only Myrafant to be found in 
Quebec or Ontario (Creighton, 1950). Some populations of L. ruga- 
tulus found at higher elevations in the Rocky Mountains apparently 
are facultatively polygynous, too (S. Cover, pers. comm.). 
As Bolton (1986) has pointed out, polygyny and colony fission in 
certain African and Levantine species of the Monomorium salomo- 
nis group might be an adaptation to hot and dry summers, which 
eventually has led to the evolution of apterous or workerlike queens. 
Colony structure and intermorphic females in the ant tribe Lepto- 
thoracini might be an analogous adaptation to extremely cold cli- 
mates. In areas with long and severe winters a young female perhaps 
will have more success in raising offspring if she hibernates in a 
