Mating ecology of the nonpollinating fig wasps of Ficus ingens

The males of many fig wasps fight fatally for mating opportunities. The con centration of females in space has been proposed as one factor selecting fo r their aggressive behaviour. We studied the temporal distribution of recep tive females to obtain a clearer impression of the operational sex ratio in figs. Females of nonpollinating species emerged from figs over a protracte d period of time and this resulted in an extremely male-biased operational sex ratio, conducive to extreme fighting. Since there were so few receptive females at any one time, a male could defend an eclosing female. Consequen tly, the largest Otitesella longicauda male in a fig had a much higher mati ng success than smaller males. This suggests that larger males have a large r fitness advantage than larger females and a Trivers-Willard effect could have important implications for sex allocation. Apterous and seemingly nond ispersing males routinely left their figs. Such dispersal can affect both ( 1) sex allocation by reducing the degree of local mate competition between brothers and (2) male dimorphism by reducing the mating opportunities of ma les with a dispersing morphology. We show that the wingless digitata males of the Otitesella digitata species group disperse on to leaves close to the ir natal fig. An extremely male-biased sex ratio resulted in almost all O. longicauda females being mated. These findings suggest that the classical c oncept of the fig wasp mating system is too simplistic and that important a ssumptions of sex allocation models are violated. (C) 1999 The Association for the Study of Animal Behaviour.