Difference in queen size distribution and monogyny/polygyny frequencies between two sibling ant species of Leptothorax (Hymenoptera : Formicidae)

The queen size distribution and within-colony number of queens were investi gated at the seasons of pre- and post-queen dispersal in Leptothorax sp. 9 Kinomura. To demonstrate the difference in social structure with reference to queen dispersal strategy between this species and one of its sibling spe cies, L. spinosior, we compared our results on Leptothorax sp. 9 with those published by the preceding studies on L. spinosior Forel. Queens in Leptot horax sp. 9 and their body size distribution was not significantly differen t between monogynous and polygynous colonies. This contrasts with L. spinos ior in which queens are dimorphic and large queens are predominantly found in monogynous colonies rather than in polygynous colonies. Furthermore, in Leptothorax sp. 9, there was no remarkable increase in queen number per col ony after the queen dispersal season, as is in L. spinosior. Throughout the seasons, the frequency of monogynous colonies in Leptothorax sp. 9 was low er than that in the polygynous population of L. spinosior. These results su ggest that, in Leptothorax sp. 9, queen dispersal is more biased to polygyn ous ways, ie. joining existing nests, rather than solitary colony founding, compared with L. spinosior. The lower availability of nest sites for Lepto thorax sp. 9 seems to account for this difference.