Resource allocation: a conflict in the fig/fig wasp mutualism?

Conflicts of interest are omnipresent between mutualist species. In the monoecious fig/pollinator wasp mutualism, each female flower produces either a seed or a pollinator offspring (which has fed on a single seed). Pollen from a syconium (i.e. fig, a closed urn-shaped inflorescence) is only dispersed by female pollinator offspring born in this syconium. Thus the fig tree is selected to produce both seed and pollinator offspring whereas for the pollinator there is no short term advantage in seed production. Using controlled pollination experiments (pollen injection, and foundress introduction), we show that 1) The relative proportion of seeds and pollinator offspring produced (i.e., the effective allocation between female and male function) depends mainly on the number of foundresses that entered the syconium. 2) Many female flowers within every syconium mature neither a seed nor a wasp (from 25% to 33%). 3) All the female flowers within a syconium that are not vacant at maturity have the potential to produce a seed, and at least 80% of them can produce a pollinator. Several hypotheses concerning mechanisms that govern the partitioning between seed and wasp production are discussed, and their evolutionary consequences are considered.     

Endo-β-N-acetylglucosaminidase from fig latex

Commercially available fig latex contains several endo-β-N-acetylglucosaminidases which catalyze the reaction: (Man)_nG1cNAcβ₁→4G1cNAcAsn → (Man)_nG1cNAc + G1cNAcAsn. Using (NH₄)₂SO₄ fractionation followed by chromatography on Sephadex G-100 and DEAE-Sephadex A-50, two distinct types of endo-β-N-acetylglucosaminidases have been partially purified and characterized. One, called F-I, hydrolyzes the di-N-acetylchitobiosyl linkage in the glycopeptide, (Man)₃(G1cNAc)₂Asn prepared from human IgG, much faster than that linkage in the glycopeptides, (Man)₅(G1cNAc)₂Asn and (Man)₆(G1cNAc)₂Asn both from ovalbumin. The other, called F-II, hydrolyzes the same linkage in (Man)₅(G1cNAc)₂-Asn and (Man)₆(G1cNAc)₂Asn, but not that in (Man)₃(G1cNAc)₂Asn.     

Why do fig wasps actively pollinate monoecious figs?

Active pollination, although rare, has been documented in a few pollination mutualisms. Such behaviour can only evolve if it benefits the pollinator in some way. The wasps that pollinate Ficus inflorescences can be active or passive pollinators. They lay their eggs in fig flowers, so that a proportion of flowers will host a wasp larva instead of a seed. We show in an actively pollinated monoecious fig that lack of pollination does not induce fig abortion or affect wasp offspring size but results in smaller numbers of offspring. Hence, conversely to other active pollination systems, seed formation is not obligatory to sustain developing pollinator larvae; however there is a direct fitness cost to active pollinators not to pollinate. We then compared the locations of eggs and fertilised flowers of three actively pollinated Ficus species and one passively pollinated species. We found that more flowers containing wasp eggs were fertilised in the actively pollinated species relative to those of the passively pollinated one. These results along with comparison with similar studies on dioecious figs, support the hypothesis that active pollination has evolved in fig wasps to ensure that more flowers containing wasp eggs are fertilised as this may increase the chances of successful gall development. The stigmatic platform characterising actively pollinated figs is probably an adaptation to increase pollen dispersion within the fig.     

Clutch size: a major sex ratio determinant in fig pollinating wasps?

Under local mate competition, sex ratio theory predicts that increasing numbers of ovipositing females (foundresses) on a site should lead to higher proportions of males in their broods. Fig pollinators have confirmed this prediction. It is also predicted that with decreasing clutch size, solitary foundresses should produce increasing proportions of sons. We show this to be true. Further, when several females compete, brood size decreases. As a result, the proportion of males increases, and this could provide a mechanistic explanation of sex ratio response to numbers of colonizing females. Therefore, sex ratio data on fig wasps need to be reassessed to determine whether females 'count' other foundresses, as is generally accepted, or whether they simply 'count' the number of eggs that they lay.     

Host–parasitoid development and survival strategies in a non-pollinating fig wasp community

In a tritrophic system, parasitoid development and galler host survival strategies have rarely been investigated simultaneously, an approach crucial for a complete understanding of the complexity of host–parasitoid interactions. Strategies in parasitoids to maximize host exploitation and in gallers to reduce predation risk can greatly affect the structure of tritrophic communities. In this study, the developmental strategies of galler hosts and their associated parasitoids in the tritrophic fig–fig wasp system are experimentally investigated for the first time. In this highly co-evolved system, wasp development is intrinsically tied with the phenology of the wasp brood sites that are restricted to the enclosed urn-shaped fig inflorescence called the syconium which can be regarded as a microcosm. Wasp exclusion experiments to determine host specificity, gall dissections and developmental assays were conducted with non-pollinating fig wasps in Ficus racemosa. Our results provide evidence for exceptions to the widely accepted koinobiont–idiobiont parasitoid dichotomy. This is also the first time fig wasps were raised ex situ from non-feeding stages onwards, a technique that enabled us to monitor their development from their pre-pupal to adult stages and record their development time more accurately. Based on variation in development time and host specificity, the possibility of a cryptic parasitoid species is raised. The frequency of different wasp species eclosing from the microcosms of individual syconia is explained using host–parasitoid associations and interactions under the modulating effect of host plant phenology.     

Micropropagation of fig (Ficus carica L.) ‘Roxo de Valinhos’ plants

Summary An in vitro protocol for Ficus carica cv. ‘Roxo de Valinhos’ was optimized. Nodal explants containing two buds were excised from field-grown mature plants, and transferred to different proliferation media consisting of combinations of distinct concentrations of activated charcoal with benzyladenine (BA), kinetin with gibberellic acid (GA₃), and WPM (woody plant medium) with kinetin. The regular strength of WPM in combination with 0.5 mgl⁻¹ kinetin was the best condition for shoot proliferation of Ficus carica ‘Roxo de Valinhos’ plants. The addition of activated charcoal in the medium completely inhibited shoot proliferation. The inclusion of BA in the medium induced excessive callus formation as well as small and vitrified shoots, while GA₃ induced excessive elongation associated with vitrification, chlorosis, and tip-burned shoots.     

Consequences of protecting flowers in a fig: a one-way trip for pollinators?

Abstract. Fig trees ( Ficus ) have closed inflorescences. Closure is an efficient protection of flowers against non-specialist predators and harsh external environmental conditions. Each Ficus species is pollinated by a single insect species, an agaonid wasp, capable of forcing its way through a bract-covered pore, the ostiole, to gain access to the flowers. Figs also provide oviposition sites for the wasps. The fig/pollinator interaction is a classic example of mutualism. It has been widely assumed that, once pollinators have entered a fig, oviposited and pollinated, they die trapped within the fig. In this paper, we present observations under natural conditions and results of field experiments on three very different fig species ( Ficus aurea Nutt., F. carica L. and F. microcarpa L.) showing that some pollinators do exit or try to exit from the fig after pollination and oviposition. Moreover, experimental results demonstrate that in at least one species ( F. carica ), the pollinator is able to oviposit successively in two different figs.
The frequency of re-emergences from figs after pollination varies among species and this may be related to variations in pollination dynamics depending on environmental constraints such as the abundance of trees and tree phenology. Several factors that may favour pollinators that leave figs after pollination and oviposition are discussed. They include competition between pollinators for oviposition sites, and minimising of the risk of vertical transmission of parasites and pathogens.     

Seed dispersal in an African fig tree: birds as high quantity,low quality dispersers?

Abstract. Ficus burtt-davyi is a shrub or small tree found in the south and east of South Africa. Based on studies carried out in an area where the plant grows mainly as a rock-splitter, we first describe the nature and timing of the fruit resources it offers to potential dispersal agents, and then the animals that feed on the fruits. The figs are eaten by a diverse avian disperser assemblage, although just two species comprised about half of the recorded visits to the trees. Germination trials with seeds defecated by the birds found that they germinated more quickly than control seeds. Small terrestrial mammals and ants were also found to have a role in fig seed dispersal which may be disproportionate to the number of seeds they transport.     

Fig choice by the pollinator of a gynodioecious fig: selection to rush,or intersexual mimicry?

Due to selection to maximise the benefits accrued, conflicts of interest exist between mutualists. An extreme conflict occurs between gynodioecious fig trees and their pollinating wasps. Female wasps, which are required for pollination, cannot reproduce in female figs and should be selected to avoid them. We investigate fig choice in Liporrhopalum tentacularis , pollinator of Ficus montana . We show that entry rates are independent of fig sex and diameter, with wasps instead entering the first fig encountered (although significant between-tree differences in entry rates to figs were observed). This suggests that wasps are unable to discriminate between the sexes because of selection for inter-sexual fig mimicry. In conjuction with data on other species pairs, these findings imply that that the resolution of the conflict is ultimately under the tree's control, with the level of mimicry evolving in response to both the propensity of wasps to discriminate and the costs of them doing so.     

First detection of “Candidatus Phytoplasma asteris” - and “Candidatus Phytoplasma solani”-related strains in fig trees

In July 2017, a survey was conducted in a fig collection plot at Locorotondo (south of Italy) to investigate the possible presence of phytoplasmas in plants showing yellowing, deformed leaves, short internodes, mottling and mosaic. Samples were collected from symptomatic plants and tested by nested PCR assays using universal and specific primers to amplify the 16S rDNA of these prokaryotes. PCR results detected the presence of phytoplasma sequences in twenty plant samples that resulted clustering two phylogenetically distinct phytoplasmas, i.e., “Candidatus Phytoplasma asteris” and “Candidatus Phytoplasma solani” affiliated to 16SrI and 16SrXII ribosomal groups, respectively. The presence of phytoplasmas belonging to both ribosomal groups was confirmed with group specific quantitative PCR and RFLP assays on 16S ribosomal amplicons. Results of this study indicate for the first time the occurrence of phytoplasmas in fig; however, more work should be carried out to verify their association with the symptoms observed on diseased fig plants.     

Spatial distribution patterns of three fig wasps on Ficus semicordata: How non-pollinators affect pollinator’s sex ratio

Sex ratio theory is one of the most productive fields in research on evolutionary biology. Pollinating fig wasps, due to their particular natural life history, are considered to be a valuable model for the study of sex ratio evolution. A great deal of research concerning the factors that affect pollinator fig wasp (Agaonidae) progeny sex ratio has been done, and at present three main factors (haplodiploidy, local mate competition and inbreeding) are found to be important at the population level. However, there still exists variation between empirical data and model predictions. Another factor to which little thought has been given before is the effect of non-pollinating fig wasps (NPFWs) which parasitize in the larvae gall of pollinator thus kill pollinators and exploit the fig/fig pollinator mutualistic systems. In this study, we focus on why and how non-pollinating fig wasps distort pollinator fig wasp’s original sex ratio. Through controlling the number of ovipositing foundresses inside a fig, combined with the observation of ovipositing behavior and sequence, we studied three species of wasp in the figs of a dioecious fig Ficus semicordata including the pollinator Ceratosolen gravely and NPFWs Platyneura cunia, Sycoscapter trifemmensis in tropical area of Xishuangbanna from September to December 2009. First, we observed the timing of oviposition of all fig wasps utilizing F. semicordata and found differences when compared to previous studies. Such as P. cunia is the fourth rather then the secondary fig wasps to oviposit on the syconia approximately 10 days after the pollinator. S. trifemmensis oviposits much earlier than previously thought, 14–32 days after the pollinators. We examined the spatial location of male and female progeny of the pollinator. We found foundresses of pollinator prefer to use innermost ovules first. Only at high offspring numbers were the outer ovules used. More male pollinator offspring were developed near the fig cavity, while female pollinator offspring were more evenly distributed among ovule layers. As pollinator offspring numbers increased, this phenomenon became more pronounced. This pattern of segregation of male larvae gall in inner ovules and female larvae gall in outer ovules suggests that female offspring might be more vulnerable to attack by parasitic wasps that oviposit from outside the syconium. Experiments later demonstrated that NPFWs are restricted by their ovipositor length and they prefer to or can only lay their eggs into ovules near the fig wall. Then we examined the spatial location of NPFWs and compared this with the spatial location of male/female progeny of pollinator. NPFWs had a high probability of parasitizing female pollinator larvae. Thus, NPFWs have a substantial effect on the sex ratio of the pollinator, as parasitism risk decreases towards the center of the syconium, where inner ovules provide enemy-free space for most of male pollinator offspring. Partial correlation analyse shows that sex ratio of pollinator progeny has a positive relationship with the number of NPFWs. We suggest that the resulting gradient in offspring viability between male and female contributes to selection on pollinators’ for a less femalebiased sex ratio. When the affect of NPFWs was excluded, the pollinator sex ratio was not in good agreement with local mate competition theory, although it was still female-biased. In addition, the average number of offspring per foundress decreased with increasing foundress number, but pollinator sex ratio was positively related to brood size. Thus, pollinator females do not appear to adjust their sex ratio to foundress density directly, but use brood size and foundress density simultaneously as cues to assess potential LMC.     

Chemical composition of volatiles from the syconia of Ficus microcarpa and host recognition behavior of pollinating fig wasps北大核心CSCD

Aims: Chemical communication plays a key role in host plant recognition of pollinators. There are two recognized types of chemical communication between syconia and their pollinating fig wasps: one is "generalization", of which the wasps respond to the relative ratio of multiple compounds, and the other is "specialization", of which the key signal is a single uncommon, possibly unique, compound. The aims of this study were to identify the chemical composition of volatiles from the syconia of Ficus microcarpa at different developmental phases, and to determine if the signaling between F. microcarpa and its pollinating fig wasp, Eupristina verticillata, is of generalized type, or of specialized type. Methods: The volatiles from syconia of F. microcarpa were extracted using solid-phase micro extraction (SPME) at different developmental phases (pre-female, female (before and after pollination), interfloral, male and postfloral phases) and the chemical compounds were identified by gas chromatography mass spectrometry (GC-MS). We then tested the behavioral responses of E. verticillata to fresh syconia at different developmental phases using two-choice olfactometers. Important findings: There were 21 volatile compounds identified from the syconia at different developmental phases, which were mainly fatty acid derivatives, terpenoids and aromatic compounds. The components of the volatiles apparently differed among the developmental stages. The contents of terpenoids declined, but the contents of fatty acid derivatives increased, from before the pollination to after the pollination. Especially, the characteristic compounds of 2-heptanone and 3-octanone before the pollination disappeared, D-limonene decreased after the pollination, but copanene, cyclohexane and 2-hexenal increased. The results of the two-choice olfactometer experiment showed that the pollinating fig wasps had higher selection ratio to chemicals found in the female phase syconia than those in other phases; whereas the volatile compounds from the male phase syconia had the function pushing the pollinating fig wasps to leave the natal syconia so that there existed the "push-pull" responses by fig wasps to volatiles released by their host syconia. We conclude that there are multiple chemical compounds playing the roles in host recognition of pollinating fig wasp E. verticillata. The mutualistic relationship between F. microcarpa and E. verticillata is maintained by the chemical communication of "generalization" strategy.     

A switch from mutualist to exploiter is reflected in smaller egg loads and increased larval mortalities in a ‘cheater’ fig wasp

The interaction between the hundreds of Ficus species and their specific pollinating fig wasps (Agaonidae) presents a striking example of mutualism. Foundress fig wasps pollinate fig flowers, but also lay their eggs in (and gall) some of them. Only two cases of cheating fig wasps (that fail to pollinate) have been reported, from two continents, suggesting that there is a cost to abandoning pollination. Reasons for the rarity of cheating are a major question in fig biology, because persistence of the mutualism depends on fig wasps continuing to pollinate. A cost in terms of reduced reproductive success among cheaters could be one explanation. Here we compare the behavior and reproduction of an undescribed Eupristina sp., a cheater that coexists with the pollinator Eupristina altissima on Ficus altissima in southern China. Adult females of both species fought with conspecifics when they were seeking entry through the ostiole into receptive figs, but there was no fighting with heterospecifics. Despite a similar body size, female pollinators contained more eggs than female cheaters. Pollinators and cheaters produced similar number of galls, and although almost twice as many flowers were galled in figs entered by two compared to one foundress, larval mortality was greatly increased when two foundresses were present. Larval mortality was also significantly higher for cheaters compared to pollinators, independent of the number of foundresses. Ovules galled by the cheater were thus significantly less likely to result in adult offspring, suggesting that there are significant costs associated with abandoning the mutualism.     

Activity of digestive proteinases and carbohydrases in the alimentary tract of the fig leaf roller,Choreutis nemorana Hübner (Lepidoptera: Choreutidae)

.The fig leaf roller or Fig-tree Skeletoniser, Choreutis nemorana (Lep.: Choreutidae), is a destructive pest of fig trees found in some fig-growing areas of Iran. The larvae feed on the upper level of leaves, near the main vein. In this study, digestive carbohydrases including α-glucosidase, β-glucosidase, α-galactosidase, β-galactosidase and proteinases including trypsin, chymotrypsin and elastase were investigated. The results showed that the carbohydrases were present in the alimentary tracts of the pest. Optimum pH for α-glucosidase and β-glucosidase activity was at pH 6.0 and 7.0, respectively. Maximum activity of α-galactosidase and β-galactosidase occurred at pH 6.0. Total proteolitic activity against the substrate azocasein was optimally occurred at pH 10.0. The greatest activity of trypsin, chymotrypsin and elastase was determined at pH 10.0, 11.0 and 11.0, respectively. Zymogram analyses using nitrocellulose membrane revealed two trypsin isoforms in which one of them was completely inhibited by Soybean Kunitz inhibitor and the other was notably inhibited.     

Can chemical signals,responsible for mutualistic partner encounter,promote the specific exploitation of nursery pollination mutualisms? – The case of figs and fig wasps

In nursery pollination mutualisms, where pollinators reproduce within the inflorescence they pollinate, floral scents often play a major role in advertizing host location and rewards for the pollinator. However, chemical messages emitted by the plant that are responsible for the encounter of mutualist partners can also be used by parasites of these mutualisms to locate their host. Each species of Ficus (Moraceae) is involved in an obligatory nursery pollination mutualism with usually one pollinating fig wasp (Hymenoptera: Chalcidoidea: Agaonidae). In this interaction, volatile compounds emitted by receptive figs are responsible for the attraction of their specific pollinator. However, a large and diverse community of non-pollinating chalcidoid wasps can also parasitize this mutualism. We investigated whether the chemical message emitted by figs to attract their pollinator can promote the host specificity of non-pollinating fig wasps. We analysed the volatile compounds emitted by receptive figs of three sympatric Ficus species, namely, Ficus hispida L., Ficus racemosa L., and Ficus tinctoria G. Forster, and tested the attraction of the pollinator of F. hispida ( Ceratosolen solmsi marchali Mayr), and of one species of non-pollinating fig wasp [ Philotrypesis pilosa Mayr (Hymenoptera: Chalcidoidea: Pteromalidae)] to scents emitted by receptive figs of these three Ficus species. Analysis of the volatile compounds emitted by receptive figs revealed that the three Ficus species could be clearly distinguished by their chemical composition. Behavioural bioassays performed in a Y-tube olfactometer showed that both pollinator and parasite were attracted only by the specific odour of F. hispida . These results suggest that the use by non-pollinating fig wasps of a specific chemical message produced by figs could limit host shifts by non-pollinating fig wasps.     

Micropropagation of socotran fig, <Emphasis Type="Italic">Dorstenia gigas</Emphasis> schweinf. Ex Balf. F. —A threatened species,endemic to the island of Socotra,Yemen

Summary As an alternative to seed propagation, and efficient micropropagation system based on axillary shoot formation and subsequent rooting was developed for the threatened and medicinal plant species Dorstenia gigas (Moraceae). Three different basal media were tested. For the best basal medium, a modified WPM medium, different concentrations of the carbohydrates sucrose, glucose, fructose and maltose were tested. The total number of shoots was not markedly affected. For all carbohydrates but maltose, however, there was a reduction in the number of normal, healthy shoots for carbohydrate concentrations greater than 14.6 mM for the disaccharides and 27.8 mM for the monosaccharides (i.e., approximately 5 gl⁻¹). Using 14.6 mM (5 gl⁻¹) sucrose it has been possible to produce vigorous and true-to-type plants with a multiplication factor of approximately 2.6 per 6 wk.