Temporal changes in the relationship between observed and expected sex-investment frequencies, social structure and intraspecific parasitism in Leptothorax tuberum (Formicidae)

The proportional investment in females (IF0) was observed in three Dorset (UK) populations (Portland, Holworth and St Alban's Head) of the ant Leptothorax tuberum during 1993 and 1994. The workers' optimum investment in females predicted by kin selection theory (IF_E) was calculated for these populations from relatedness values estimated from an isozyme polymorphism. Although a previous study at Portland in 1992 found IF_o and IF_E not to differ, in 1993 IF_o and IFE were significandy different from each other at Portland and St Alban's Head. In 1994 the difference was significant at Portland only. IF_o was lower than IF_E at all three sites in both years. The differences between 1992 and 1993 and 1994 were consistent with either an unresolved conflict between workers and queens for control of the IF or change in an environmental factor that affected all sites. Relatedness values showed that at Portland most nests were founded by one singly-mated queen. However, at St Alban's Head relatedness values were consistent with some serial polygyny in 1993 but not 1994, while at Holworth there was some egg-dumping by queens unrelated to the colony queen. The differences in nest structure between sites may have been related to habitat differences. In 1993 there was evidence of a split sex ratio. However, unlike 1992, the female biased nests did not have a higher relatedness asymmetry than the male biased nests.