The Mechanism On Discriminative Sanctions To Non-pollinating Fig Wasps And The Sex Ratio Adjustment Of Pollinating Fig Wasp On Ficus Racemosa

Stable and long-term cooperation exist widely in nature.How the long-term reciprocal cooperation occur and maintain in the cooperative system is an important research topic in life sciences.Fig tree(Ficus spp.)and their pollinating wasp form a well-known obligate mutualism.The pollinating fig wasps enter the enclosed fig to pollinate and lay their eggs in the ovules of the female flowers.The highly specialized inflorescences(figs)of the fig tree can only be pollinated by the pollinating fig wasps,and pollinating fig wasps only survive and reproduce within the figs life history of the fig tree and the pollinating fig wasps are tightly interdependent,forming the symbiotic system with the closest relationship in nature.In addition to the pollinating fig wasps,there is a community of non-pollinating fig wasp species that parasitize the figs of fig tree.As pollinating fig wasps,non-pollinating fig wasps can only rely on the figs of the fig trees to survive and reproduce.However,the non-pollinating fig wasps do not provide any services to the fig tree.The fig tree-fig pollinating wasp mutualism and the non-pollinating fig wasp community constitute a classic model system that studies how the stability of the symbiotic system can produce and remain their long-term stability.Recently researchers found that the fig tree can abort the unpollinated figs and reduce the development ratio of less pollinated figs.That is to say,fig tree maintains the stability of the cooperation of the mutualism through sanctions to the uncooperative pollinating fig wasps.Non-pollinating fig wasps do not provide any services to the fig tree,thus fig tree must sanction those non-pollinating fig wasp species as well.The knowledge we have about the ecological functions of non-pollinating wasps and the role of non-pollinating wasps in maintaining this symbiotic system are very limited and the conclusions we got are full of contradictions.Because of the huge differences in trophic status and ecological functions among different non-pollinating wasp species,the effects of different non-pollinating wasp species on symbiotic systems are different.However,nobody has studied the sanctions to the non-pollinating fig wasps.In this study,by introducing a normal pollinating fig wasp into the fig,and additionally introducing pollinating fig wasps whose ovipositor had been removed,we achieved artificially increasing the pollination of the pollinating fig wasp.We found that when the amount of pollination of the pollinating fig wasp was insufficient for the fig,additional pollen spreading could increase the development ratio of the pollinating fig wasps.This result is an important supplement to previous research on the sanction mechanism of pollinating fig wasp without pollen.The two results have shown that under the condition of insufficient pollination,the fig tree can adjust the development ratio of pollinating fig wasp according to the status of pollination in the fig.The result also lays the foundation for discussion of the subsequent research on non-pollination sanction mechanisms.In this study,we studied the effects of an early galling non-pollinating wasp species(Sycophaga testaciea)hosted by Ficus racemosa on the symbiosis of Ficus racemosa and its pollinating wasp through field control experiments.When there were early gallers,the production of seeds reduced significantly,but the offspring number of the pollinating fig wasp was not affected.Sycophaga testaciea oviposit in the figs when they were very young and tiny,which could cause serious physical damage to the figs.We found that most of the figs that were oviposited by the early galling non-pollinating fig wasps were abortion.Only very few figs that were parasitized by the early galling non-pollinating fig wasp species could survive,and the survived figs were abnormally developed and had very low development ratio.It turns out that the fig tree would impose very strong punishment on the early galling non-pollinating fig wasp species.If the figs parasitized by Sycophaga testaciea got pollination and oviposition by the pollinating fig wasp,the growth of figs was significantly improved,and the development ratio of pollinated fig wasp was not significantly affected.Parasitic wasps of pollinating fig wasp(parasitoid)live on the larvae of the pollinating fig wasp.The parasitic wasps oviposit after the figs have fully developed during the interfloral period,and the physical damage to the figs through their oviposition is much less than that of the early galling non-pollinating fig wasps.The oviposition of parasitic wasps will reduce the fitness of pollinating fig wasps and indirectly reduce the fitness of fig trees,thus posing a threat to the stability of fig tree-fig pollinating fig wasp mutualism.Their effects on the host are usually measured only by the number of adult parasitic wasps that are bred.However,sometimes the oviposition attempts by parasitic wasps may result in host death,and sometimes host and parasitic wasps die simultaneously during larval development.Therefore,determining the effects of parasitic wasps on host populations requires estimating the total effect of parasitic wasps on the host and its own reproduction.The symbiotic system of Ficus and its specialized wasp community has become a model system for studying the nutrition flow of this network.In general,each female flower in the fig can only produce a single pollinator or a single wasp,providing a simple way to measure costs.However,some female wasps that lay eggs do not produce pollinating wasp or parasitic wasp offspring,i.e.,empty galls are formed.Our control experiments found that in the absence of parasitic wasps,approximately one-quarter of the galls of pollinator failed to produce the offspring of the pollinating wasps.In the presence of parasitic wasps,the number of empty galls will increase significantly.On average,1.9 pollinating pollinator larvae were killed for each parasitic wasp.Thus,host mortality caused by parasitic wasps is much greater than the actual reproductive success rate of parasitic wasps.At the same time,we found that the development ratio of the galls in the figs was significantly negatively related to the offspring number of parasitic wasps.The abortion rate of figs treated with parasitoid was not significantly different from that treated without parasitic bees,and the growth status was normal,but the development ratio was reduced.It can be seen that the punishment of the fig tree to the parasitoid was relatively weak,but it will gradually increase with the increase of the number of parasitoids.At the same time,because the pollinating fig wasps can only breed offspring in a single fig,coupled with the sex haploid determination mechanism of its offspring,the pollinating fig wasp is an ideal experimental model for studying the sex allocation and sex ratio adjustment of the offspring.At the end of this study,we used the pollinating fig wasp(foundress)on Ficus racemosa(Ceratosolen fuscicpes)as experimental material to study the effect of laying-male-eggs-first pattern on sex ratio adjustment of pollinating fig wasp,and reported our newly discovered sex ratio regulation mechanism The role of this mechanism in maintaining the stability of the fig tree-fig pollinating fig wasp mutualism was also discussed.In this experiment,we introduced a single Ceratosolen fuscicpes foundress into a fig and controlled the ovipositing time of each foundress from zero to five hours,thereby variably reducing their egg load,and then introduced the foundress to a second fig.The sex ratio of the offspring in the second fig is negative correlated to the egg load,and male offspring are produced even in very small clutch size.C.fusciceps mainly lay their male eggs at first,followed by large amount of female eggs.Our results indicate that the foundresses entering the fig do produce a small number of male eggs at the beginning of the oviposition,but the number is not fixed.The oviposit strategy will be reset to zero when they enter the second fig.As the clutch size decreases,the proportion of empty flowers increases,which may be due to a corresponding decrease in the amount of pollen.Therefore,through this study,we have reached the following conclusions.The C.fusciceps foundresses of Ficus racemosa first lays a certain number of unfertilized male eggs,and then the fertilization vesicles(or tubes)are opened,and a large number of female eggs can be laid.The C.fusciceps foundresses also use their own egg-load to adjust the sex ratio of their offspring.If the oviposition in the first fig is interrupted and they enter a new fig,they will start to lay male eggs again.In addition to mating with female offspring,the male offspring also bite a hole in the fig to let the female pollinating fig wasps to release from the fig.Without the male wasps,the female fig wasps cannot leave the figs.Therefore,the resetting mechanism of oviposition can ensure that male offspring are produced in any figs,thereby ensuring that the female pollinating fig wasps can mate and safely leave the figs for reproduction and pollination,which is very important for the stability and maintenance of this obligate mutualism.