Investigations into stability in the fig/ fig-wasp mutualism

Fig trees (Ficus, Moraceae) and their pollinating wasps (Chalcidoidea, Agaonidae) are involved in an obligate mutualism where each partner relies on the other in order to reproduce: the pollinating fig wasps are a fig tree’s only pollen disperser whilst the fig trees provide the wasps with places in which to lay their eggs. Mutualistic interactions are, however, ultimately genetically selfish and as such, are often rife with conflict. Fig trees are either monoecious, where wasps and seeds develop together within fig fruit (syconia), or dioecious, where wasps and seeds develop separately. In interactions between monoecious fig trees and their pollinating wasps, there are conflicts of interest over the relative allocation of fig flowers to wasp and seed development. Although fig trees reap the rewards associated with wasp and seed production (through pollen and seed dispersal respectively), pollinators only benefit directly from flowers that nurture the development of wasp larvae, and increase their fitness by attempting to oviposit in as many ovules as possible. If successful, this oviposition strategy would eventually destroy the mutualism; however, the interaction has lasted for over 60 million years suggesting that mechanisms must be in place to limit wasp oviposition. This thesis addresses a number of factors to elucidate how stability may be achieved in monoecious fig systems. Possible mechanisms include: 1) a parasitoidcentred short ovipositor hypothesis in Ficus rubiginosa, which suggests that a subset of flowers are out of reach to parasitoid ovipositors making these ovules the preferred choice for ovipositing pollinators and allowing seeds to develop in less preferred ovules; 2) the presence of third-party mutualists such as non-pollinating fig wasps (F. burkei) and patrolling green tree ants on the fig surface (F. racemosa) that limit pollinator and parasitoid oviposition respectively; and 3) selection on fig morphology which constrains the size (and therefore fecundity) of the associated pollinators. I discuss the lack of evidence for a single unifying theory for mutualism stability and suggest that a more likely scenario is the presence of separate, and perhaps multiple, stabilising strategies in different fig/ fig-wasp partnerships

A clonal theory of parasitic protozoa : the population structures of Entamoeba, Giardia, Leishmania, Naegleria, Plasmodium, Trichomonas, and Trypanosoma and their medical and taxonomical consequences

We propose a general theory of clonal reproduction for parasitic protozoa, which has important medical and biological consequences. Many parasitic protozoa have been assumed to reproduce sexually, because of diploidy and occasional sexuality in the laboratory. However, a population genetic analysis of extensive data on biochemical polymorphisms indicates that the two fundamental consequences of sexual reproduction (i.e. segregation and recombination) are apparently rare or absent in natural populations of the parasitic protozoa. Moreover, the clones recorded appear to be stable over large geographical areas and long periods of time. A clonal population structure demands that the medical attributes of clones be separately characterized; ubiquitous clones call for priority characterization. Uniparental reproduction renders unsatisfactory Linnean taxonomy; this needs to be supplemented by the "natural clone" as an additional taxonomic unit, which is best defined by means of genetic markers. (Résumé d'auteur

Deep mtDNA divergences indicate cryptic species in a fig-pollinating wasp

Background: Figs and fig-pollinating wasps are obligate mutualists that have coevolved for ca 90 million years. They have radiated together, but do not show strict cospeciation. In particular, it is now clear that many fig species host two wasp species, so there is more wasp speciation than fig speciation. However, little is known about how fig wasps speciate. Results: We studied variation in 71 fig-pollinating wasps from across the large geographic range of Ficus rubiginosa in Australia. All wasps sampled belong to one morphological species (Pleistodontes imperialis), but we found four deep mtDNA clades that differed from each other by 9–17% nucleotides. As these genetic distances exceed those normally found within species and overlap those (10–26%) found between morphologically distinct Pleistodontes species, they strongly suggest cryptic fig wasp species. mtDNA clade diversity declines from all four present in Northern Queensland to just one in Sydney, near the southern range limit. However, at most sites multiple clades coexist and can be found in the same tree or even the same fig fruit and there is no evidence for parallel sub-division of the host fig species. Both mtDNA data and sequences from two nuclear genes support the monophyly of the "P. imperialis complex" relative to other Pleistodontes species, suggesting that fig wasp divergence has occurred without any host plant shift. Wasps in clade 3 were infected by a single strain (W1) of Wolbachia bacteria, while those in other clades carried a double infection (W2+W3) of two other strains. Conclusion: Our study indicates that cryptic fig-pollinating wasp species have developed on a single host plant species, without the involvement of host plant shifts, or parallel host plant divergence. Despite extensive evidence for coevolution between figs and fig wasps, wasp speciation may not always be linked strongly with fig speciation

Detecting the elusive cost of parasites on fig seed production

Mutualisms provide essential ecosystem functions such as pollination and contribute considerably to global biodiversity. However, they are also exploited by parasites that remove resources and thus impose costs on one or both of the mutualistic partners. The fig/pollinator interaction is a classic obligate mutualism; it is pantropical and involves >750 Ficus species and their host-specific pollinating wasps (family Agaonidae). Figs also host parasites of the mutualism that should consume pollinators or seeds, depending on their larval ecology. We collected data from a large crop of figs on Ficus glandifera var. brachysyce in a Sulawesi rainforest with an unusually high number of Eukoebelea sp. parasites. We found that these parasites have a significant negative correlation with fig seed production as well as with pollinator offspring production. Eukoebelea wasps form the basal genus in subfamily Sycophaginae (Chalcidoidea) and their larval biology is considered unknown. Our analysis suggests that they feed as flower gallers and impose direct costs on the fig tree, but a strategy including the consumption of pollinator larvae cannot be ruled out. We also present baseline data on the composition of the fig wasp community associated with F. glandifera var brachysyce and light trap catch data

Discovery of mating in the major African livestock pathogen Trypanosoma congolense

The protozoan parasite, Trypanosoma congolense, is one of the most economically important pathogens of livestock in Africa and, through its impact on cattle health and productivity, has a significant effect on human health and well being. Despite the importance of this parasite our knowledge of some of the fundamental biological processes is limited. For example, it is unknown whether mating takes place. In this paper we have taken a population genetics based approach to address this question. The availability of genome sequence of the parasite allowed us to identify polymorphic microsatellite markers, which were used to genotype T. congolense isolates from livestock in a discrete geographical area of The Gambia. The data showed a high level of diversity with a large number of distinct genotypes, but a deficit in heterozygotes. Further analysis identified cryptic genetic subdivision into four sub-populations. In one of these, parasite genotypic diversity could only be explained by the occurrence of frequent mating in T. congolense. These data are completely inconsistent with previous suggestions that the parasite expands asexually in the absence of mating. The discovery of mating in this species of trypanosome has significant consequences for the spread of critical traits, such as drug resistance, as well as for fundamental aspects of the biology and epidemiology of this neglected but economically important pathogen

Ability to gall: The ultimate basis of host specificity in fig wasps?

1. Fig trees (Ficus spp.) and their host-specific pollinator fig wasps (Agaonidae) are partners in an obligate mutualism. Receptive phase figs release specific volatiles to attract their pollinators, and this is generally effective in preventing pollinator species from entering figs of the wrong hosts. 2. If entry is attempted into atypical host figs, then ostiole size and shape and style length may also prevent reproduction. In spite of these barriers, there is increasing evidence that fig wasps enter atypical hosts, and that this can result in hybrid seed and fig wasp offspring. 3. This study examines the basis of pollinator specificity in two dioecious fig species from different geographical areas. Kradibia tentacularis pollinates Ficus montana in Asia. Ficus asperifolia from East Africa is closely related but is pollinated by a different species of Kradibia. 4. In glasshouses, K. tentacularis was attracted to its normal host, F1s and backcrosses, but only rarely entered figs of F. asperifolia. Foundresses were able to lay eggs in hybrids, backcrosses, and F. asperifolia, although flower occupancy was lowest in F. asperifolia figs and intermediate in hybrids. 5. The fig wasp failed to reproduce in female F. montana, male F. asperifolia, and male F1s, and most but not all backcrosses to F. montana. This was a result of the failure to initiate gall production. 6. Host specificity in this fig wasp is strongly influenced by host volatiles, but the ability to gall may be the ultimate determinant of whether it can reproduce

First record of a non-pollinating fig wasp (Hymenoptera: Sycophaginae) from Dominican amber, with estimation of the size of its host figs

Fig trees and their pollinating fig wasps arose about 75 million years ago in the Cretaceous period. Several other groups of chalcid wasps also utilize figs for larval development, including sycophagines, the putative sister group to pollinating fig wasps. Whereas stone and amber fossil pollinators are known, no fossils representing non-pollinating fig wasp groups have been confirmed previously. Here, we describe the first Sycophaginae from the c.15–20 Ma Dominican amber, Idarnes thanatos sp. nov. Farache, Rasplus, Pereira and Compton, and discuss its relationships within the Idarnes carme species group. Additionally, we use linear regression to compare body size, ovipositor sheaths length, and host fig size data from extant Idarnes species to estimate the size of its host figs. Idarnes thanatos was most likely associated with small to medium sized figs (diameter ≤1.0 cm), that were likely to have been dispersed by birds and primates. The discovery of this close relative of extant non-pollinating fig wasps suggests that early Miocene and modern fig wasp communities may share similar ecological and functional features

Assessment of Genetic Relationship among Male and Female Fig Genotypes Using Simple Sequence Repeat (SSR) Markers

Fig (Ficus carica L.) is a traditional crop in Turkey and widely cultivated around the Mediterranean areas. The gynodioecious fig species is present in two sexual forms, i.e. the domesticated fig (female tree) and the caprifig (male tree). Caprifigs are crucial for high quality fig production and breeding while, the studies on assessment of genetic relationship among caprifigs is limited. The aim of this study was to determine genetic diversity among 45 caprifigs and 2 female figs collected from four provinces in Marmara and Aegean Sea Regions of Turkey using simple sequence repeat (SSR) markers. In this work, 24 SSR markers were tested, one was monomorphic and the remaining markers amplified 82 alleles. The number of polymorphic alleles per SSR marker ranged from 2 to 7. The observed heterozygosity (Ho) differed from 0.18 to 0.76 and expected heterozygosity (He) ranged between 0.24 and 0.81. The polymorphism information content (PIC) varied from 0.42 to 0.98. A UPGMA analysis based on Dice similarity matrix clustered fig genotypes into two main groups and similarly, STRUCTURE analysis placed fig genotypes into two different gene pools (K=2). Fig genotypes collected from the same region were not clustered together in a group indicating that the fig genotypes did not cluster on the basis of their collection sites. Our results demonstrated that caprifigs and female figs are not genetically distinct and they clustered together in a group. All fig genotypes had distinct SSR marker profiles suggesting that there were no synonyms or homonyms. These results revealed a high genetic variation among fig genotypes and 23 SSR markers were enough to discriminate all fig genotypes analysed in this study demonstrating that SSR marker system is suitable for genetic analysis in figs