To Maintain The Mechanism Of The Chemical Ecology Of The Banyan Tree And Pollinating Fig Wasp Obligate Symbiotic Relationship

Almost each of the known 750 fig species (Ficus, Moraceae) forms obligate pollination mutualism with its species-specific fig wasp (Agaonidae, Chalcidoidea, Hymenoptera). A fig species is pollinated exclusively by a corresponding fig wasp species only and supply reproduction sites as reward to the pollinator. In this system, the encounter of the two partners is a crucial phase for each of them. Previous studies have shown that fig emits specific volatile to attract its pollinator when it is receptive. Based on the chemical analysis and biological assays, this paper investigated the changes of composition and emission rhythm of fig volatiles and tested the wasps'behavioural responses to those changes, in order to explore the chemical mechanisms which maintain the stability of the mutualism. In this paper, three parts as following were focused on:(1) The specificity of fig volatiles and the host locating ability of pollinating fig wasps to their hostsThe volatiles of receptive fig of four common species in Xishuangbanna were analyzed, including three dioecious species, i.e. F. tinctoria, F. hispida and F. semicordata, and one monoecious species, i.e. F. racemosa. There were significant differences of volatile quantities and compositions among those four species. The volatile specificity of F. tinctoria, F. hispida and F. racemosa was achieved by some general compounds constituted at a specific ratio, i.e. by the path of"gerneralization"; while the volatile specificity of F. semicordata was achieved by one specific compound named p-methyl anisole which had a 99% of relative amount in the volatile, i.e. by the path of"specialization". The results also indicated that the quantity of fig volatile emitted was not significantly correlated with the fig physical characters, such as the fig diameter and the number of female flowers.In the bioassays, the volatile of receptive fig of F. hispida had significant attractive effect to its pollinating wasps, Ceratosolen solmsi marchali. However, the non-host receptive figs were not attractive and even repellent to C. solmsi marchali. If the tested volatile was more different from the volatile of receptive fig of F. hispida, there would be less number of C. solmsi marchali attracted by it in the Y tube.(2) The changes of volatiles before and after pollination and their influences on pollinators'behaviour With the changes of pollination status, the quantity and composition of fig volatile had dynamic changes. The quantity of volatile emitted by receptive fig was significantly higher than that by figs in other floral stages. However, the changes of volatiles of F. hispida and F. semicordata had two different rhythms. Compared with the receptive stage, the quantity of fig volatile of F. hispida decreased to half and the composition of it did not significant change in one day after pollination. While the volatile composition of fig of F. semicordata changed significantly in one day after pollination because p-methyl anisole almost disappeared completely.In the bioassays, C. solmsi marchali showed significant preference to both volatiles of host receptive figs and inter-floral figs in the no-choice tests; however, when they faced both of the two volatiles in the two-choice tests, they almost always chose the volatile of host receptive figs. While pollinating wasps of F. semicordata, C. gravelyi, only showed significant preference to volatile of host receptive figs and showed significant avoidance to volatile of host inter-floral figs. The pollinating wasps of F. altissima, Eupristina altissima, also showed significant avoidance to volatile of host inter-floral figs. And they showed no significant responses to volatile of host figs in male flower stage. The bioassays on four monoterpenes in volatile of receptive fig of F. hispida, i.e. linalool,α-terpineol,β-pinene and limonene, showed that linalool, one of the main components of volatile of receptive fig of F. hispida, had a significant attractive effect to C. solmsi marchali. The behaviour of pollinating fig wasp is adjusted by both the quality and quantity of fig volatile, mostly by quality.(3) The reason why the pollinating wasps have no preference between two genders of host receptive figs in dioecious speciesThere is no significant difference between compositions of volatiles emitted by two genders of receptive figs of F. hispida, although there is significant higher quantity in volatile emission of female receptive fig of F. hispida. The bioassay results indicated that C. solmsi marchali had no preference to volatiles of two genders of receptive fig of F. hispida. These results proved the view of"inter-sexual volatile mimicry".