POLYGYNY AND FUNCTIONAL MONOGYNY IN 
LEPTOTHORAX ANTS (HYMENOPTERA: FORMICIDAE) 
By J. Heinze 1 and A. Buschinger 2 
The number of queens present in colonies of social insects may 
affect several features of colony structure, such as the relationship 
between workers within the nest. The high degree of relatedness of 
nestmates, which is thought to be one of the fundamental traits in 
the evolution of altruistic behavior in Hymenoptera, can be sus- 
tained only if all the female brood is produced by one single queen 
(monogyny) that has been inseminated by only one male (mono- 
andry). 
During the last two decades numerous studies on queen number 
and colony structure of ants have shown, however, that in about 50 
percent of all species colonies may contain several fully fertile 
queens (Buschinger, 1974a). Some species (e.g., Leptothorax acer- 
vorum or Myrmica ruginodis) are facultatively polygynous; in other 
species (e.g., Plagiolepis pygmaea or Formica exsecta) virtually all 
colonies are polygynous. Colonies of some highly polygynous spe- 
cies, such as Formica polyctena, may contain thousands of queens. 
Polygyny may arise by the cooperative foundation of new colonies 
by several inseminated young females (pleometrosis), by the fusion 
of colonies, or by the adoption of young, inseminated females into a 
colony. 
In some taxonomic groups, polygyny appears to be associated 
with ecological factors, such as patchy distribution of habitats or 
high instability of nesting sites (Holldobler and Wilson, 1977), and 
recently queen number has been interpreted as an ecologically 
responsive trait, explainable by a combination of kin selection and 
ecological elements (Nonacs, 1988). An obvious advantage of poly- 
gyny on the colony level is that the presence of multiple fertile 
'Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, 
USA. 
2 Institut fur Zoologie, TH Darmstadt, Schnittspahnstr. 3 
D6100 Darmstadt, West Germany. 
Manuscript received by the editor November 21, 1988. 
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