It is generally believed that physical heterogeneity in common resource or evolutionary restraint can sufficiently prevent direct conflict between host and symbionts in mutualism systems. Our data on fig/fig wasp reciprocal mutualism(Ficus racemosa), however, show that structural barriers of female flowers or genetic constraints of pollinators previously hypothesized exist, but cannot sufficiently maintain the mutualism stability. The results show that a positive relationship between seed and wasp production could be maintained in warm season, which might be because of density dependence restraint among foundresses and their low oviposition and pollination efficiency, keeping common resource(female flowers) utilization unsaturated. Whilst, a negative correlation between wasp offspring and viable seed production was also observed in cold season, which might be that the increased oviposition and pollination efficiency maximized the common resource utilization. The fitness trade-off between fig and pollinator wasps is greatly affected by environmental or ecological variations. The local stability might result from temporal low exploitation efficiency of pollinators together with interference competition among pollinators. We suggest that host repression through the active regulation of bract closure, which can create interference competition among the foundresses and prevent extra more foundresses sequential entry in fruit cavities, would help the figs avoiding the cost of over-exploitation. This essentially takes the same role as sanctioning of cheating or competitive behaviors.
WANG RuiWuWEN XiaoLanCHEN ChunSHI LeiCOMPTON Stephen G.
Co-evolutionary theory assumes co-adapted characteristics are a positive response to counter those of another species,whereby co-evolved species reach an evolutionarily stable interaction through bilateral adaptation.However,evidence from the fig-fig wasp mutualistic system implies very different co-evolutionary selection mechanisms,due to the inherent conflict among interacted partners.Fig plants appear to have discriminatively enforced fig wasps to evolve"adaptation characteristics"that provide greater benefit to the fig,and fig wasps appear to have diversified their evolutionary strategies in response to discriminative enforcement by figs and competition among different fig wasp species.In what appears to be an asymmetric interaction,the prosperity of cooperative pollinating wasps should inevitably lead to population increases of parasitic individuals,thus resulting in localized extinctions of pollinating wasps.In response,the sanctioning of parasitic wasps by the fig should lead to a reduction in the parasitic wasp population.The meta-populations created by such asymmetric interactions may result in each population of coevolved species chaotically oscillated,temporally or evolutionarily.
Classical theories explaining the evolution of cooperation often rely on the assumption that the involved players are symmetrically interacted.However,in reality almost all well-documented cooperation systems show that cooperative players are in fact asymmetrically interacted and that this dynamic may greatly affect the cooperative behavior of the involved players.Here,we developed several models based on the most well known spatial game of the Hawk-Dove game,while also considering the effects of asymmetric interaction.Such asymmetric games possess four kinds of strategies:cooperation or defection of strong player and cooperation or defection of weak player.Computer simulations showed that the probability of defection of the strong player decreases with decreasing the benefit to cost ratio,and that all kinds of strategy will be substituted by cooperation on behalf of the strong player if the benefit to cost ratio is sufficiently small.Moreover,weak players find it difficult to survive and the surviving weak players are mostly defectors,similar to the Boxed Pigs game.Interestingly,the patterns of kinds of strategies are chaotic or oscillate in some conditions with the related factors.
