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 (IFO) was observed in three Dor set (UK) populations (Portland, Holworth and St Alban's Head) of the a nt Leptothorax tuberum during 1993 and 1994. The workers' optimum inve stment in females predicted by kin selection theory (IFE) was calculat ed for these populations from relatedness values estimated from an iso zyme polymorphism. Although a previous study at Portland in 1992 found IFO and IFE not to differ, in 1993 IFO and IFE were significantly dif ferent from each other at Portland and St Alban's Head. In 1994 the di fference was significant at Portland only. IFO was lower than IFE at a ll three sites in both years. The differences between 1992 and 1993 an d 1994 were consistent with either an unresolved conflict between work ers and queens for control of the IF or change in an environmental fac tor that affected all sites. Relatedness values showed that at Portlan d most nests were founded by one singly-mated queen. However, at St Al ban's Head relatedness values were consistent with some serial polygyn y in 1993 but not 1994, while at Holworth there was some egg-dumping b y queens unrelated to the colony queen. The differences in nest struct ure between sites may have been related to habitat differences. In 199 3 there was evidence of a split sex ratio. However, unlike 1992, the f emale biased nests did not have a higher relatedness asymmetry than th e male biased nests. (C) 1997 The Linnean Society of London.