High incidences and similar patterns of Wolbachia infection in fig wasp communities from three different continents

Abstract Wolbachia are endosymbiotic bacteria that infect numerous arthropod species. Previous studies in Panama and Australia revealed that the majority of fig wasp species harbor Wolbachia infections, but that similar patterns of incidence have evolved independently with different wasp species and Wolbachia strains on the two continents. We found Wolbachia infections in 25/47 species (53%) of fig wasp associated with 25 species of Chinese figs. Phylogenetic analyses of Wolbachia wsp sequences indicated that very similar strains are not obviously found in either closely related or ecologically linked fig wasps species. The extremely high prevalence of Wolbachia in fig wasps (over 50% of species infected) is not constrained by geographical origin and is a recurrent theme of fig wasp/Wolbachia interactions.     

The distribution of Wolbachia in fig wasps: correlations with host phylogeny,ecology and population structure

We surveyed for the presence and identity of Wolbachia in 44 species of chalcid wasps associated with 18 species of Panamanian figs. We used existing detailed knowledge of the population structures of the host wasps, as well as the ecological and evolutionary relationships among them, to explore the relevance of each of these factors to Wolbachia prevalence and mode of transmission. Fifty-nine per cent of these wasp species have Wolbachia infections, the highest proportion reported for any group of insects. Further, neither the presence nor the frequency of Wolbachia within hosts was correlated with the population structure of pollinator hosts. Phylogenetic analyses of wsp sequence data from 70 individuals representing 22 wasp species show that neither the close phylogenetic relationship nor close ecological association among host species is consistently linked to close phylogenetic affinities of the Wolbachia associated with them. Moreover, no genetic variation was detected within any Wolbachia strain from a given host species. Thus, the spread of Wolbachia within host species exceeds the rate of horizontal transmission among species and both exceed the rate of mutation of the wsp gene in Wolbachia. The presence and, in some cases, high frequency of Wolbachia infections within highly inbred species indicate that the Wolbachia either directly increase host fitness or are frequently horizontally transferred within these wasp species. However, the paucity of cospeciation of Wolbachia and their wasp hosts indicates that Wolbachia do not persist within a given host lineage for long time-periods relative to speciation times.     

Horizontal transmission of Wolbachia in a Drosophila community

Abstract.  1.  Wolbachia bacteria are reproductive parasites of arthropods and infect an estimated 20% of all insect species worldwide. In order to understand patterns of Wolbachia infection, it is necessary to determine how infections are gained or lost. Wolbachia transmission is mainly vertical, but horizontal transmission between different host species can result in new infections, although its ecological context is poorly understood. Horizontal transmission is often inferred from molecular phylogenies, but could be confounded by recombination between different Wolbachia strains.
2. This study addressed these issues by using three genes: wsp , ftsZ , and groE , to study Wolbachia infections in fruit- and fungus-feeding Drosophila communities in Berkshire, U.K.
3. Identical sequences were found for all three genes in Drosophila ambigua and Drosophila tristis. This suggests horizontal transmission of Wolbachia between these two previously unstudied Drosophila species, which may be the result of the two host species sharing the same food substrates or parasites.
4.  Wolbachia infections might be lost from species due to curing by naturally occurring antibiotics and the presence of these is likely to vary between larval food substrates.
5. It was investigated whether Wolbachia incidence was lower in fungus-feeding than in fruit-feeding Drosophila species, but no significant difference based on food substrate was found.     

Distribution Patterns of Wolbachia Endosymbionts in the Closely Related Flower Bugs of the Genus Orius: Implications for Coevolution and Horizontal Transfer

Vertical transmission is the primary route of the endosymbiont Wolbachia for its own spread among invertebrate hosts, but horizontal transmission between different hosts is believed to have occurred multiple times. However, it is not well known how Wolbachia commonly spread among closely related hosts. We focused on the closely related species of the minute pirate bugs belonging to the genus Orius, which are important biological control agents in agricultural crops because they are the most useful natural enemy of various tiny pests, such as thrips. Here, we examined five Orius species (Orius sauteri, Orius nagaii, Orius minutus, Orius strigicollis, and Orius tantillus) from eight geographic localities in Japan for Wolbachia infection. Two distinct strains, wOus1 and wOus2, were detected based on Wolbachia surface protein (wsp) gene sequencing. Furthermore, multilocus sequence typing revealed that each of the strains comprised two variants that differed in a single nucleotide. The overall distribution patterns of the two Wolbachia strains were found to differ among host species: prevalent double infection with wOus1 and wOus2 in O. strigicollis; fixation of single infection with wOus2 in O. nagaii; occurrence of single infection with wOus1 in O. sauteri; prevalence of single infection with wOus1 in O. minutus with an exception in a single population; and lack of Wolbachia infection in O. tantillus. Such differences in the distribution patterns of Wolbachia may reflect the evolutionary history of Wolbachia infection among Orius species and/or ecological and physiological differences among the Orius species that determine the invasiveness and maintenance of the two Wolbachia strains.     

On the ubiquity and phylogeny of Wolbachia in lice

Wolbachia are intracellular bacteria that occur in an estimated 20% of arthropod species. They are of broad interest because they profoundly affect the reproductive fitness of diverse host taxa. Here we document the apparent ubiquity and diversity of Wolbachia in the insect orders Anoplura (sucking lice) and Mallophaga (chewing lice), by detecting single or multiple infections in each of 25 tested populations of lice, representing 19 species from 15 genera spanning eight taxonomic families. Phylogenetic analyses indicate a high diversity of Wolbachia in lice, as evidenced by the identification of 39 unique strains. Some of these strains are apparently unique to lice, whereas others are similar to strains that infect other insect taxa. Wolbachia are transmitted from infected females to their offspring via egg cytoplasm, such that similar species of lice are predicted to have similar strains of Wolbachia. This predicted pattern is not supported in the current study and may reflect multiple events of recent horizontal transmission between host species. At present, there is no known mechanism that would allow for this latter mode of transmission to and within species of lice.     

Molecular approaches to identify cryptic species and polymorphic species within a complex community of fig wasps

Cryptic and polymorphic species can complicate traditional taxonomic research and both of these concerns are common in fig wasp communities. Species identification is very difficult, despite great effort and the ecological importance of fig wasps. Herein, we try to identify all chalcidoid wasp species hosted by one species of fig, using both morphological and molecular methods. We compare the efficiency of four different DNA regions and find that ITS2 is highly effective for species identification, while mitochondrial COI and Cytb regions appear less reliable, possibly due to the interference signals from either nuclear copies of mtDNA, i.e. NUMTs, or the effects of Wolbachia infections. The analyses suggest that combining multiple markers is the best choice for inferring species identifications as any one marker may be unsuitable in a given case.     

Consistently high incidence of Wolbachia in global fig wasp communities

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Widespread Wolbachia infection in terrestrial isopods and other crustaceans

Wolbachia bacteria are obligate intracellular alpha-Proteobacteria of arthropods and nematodes. Although widespread among isopod crustaceans, they have seldom been found in non-isopod crustacean species. Here, we report Wolbachia infection in fourteen new crustacean species. Our results extend the range of Wolbachia infections in terrestrial isopods and amphipods (class Malacostraca). We report the occurrence of two different Wolbachia strains in two host species (a terrestrial isopod and an amphipod). Moreover, the discovery of Wolbachia in the goose barnacle Lepas anatifera (subclass Thecostraca) establishes Wolbachia infection in class Maxillopoda. The new bacterial strains are closely related to B-supergroup Wolbachia strains previously reported from crustacean hosts. Our results suggest that Wolbachia infection may be much more widespread in crustaceans than previously thought. The presence of related Wolbachia strains in highly divergent crustacean hosts suggests that Wolbachia endosymbionts can naturally adapt to a wide range of crustacean hosts. Given the ability of isopod Wolbachia strains to induce feminization of genetic males or cytoplasmic incompatibility, we speculate that manipulation of crustacean-borne Wolbachia bacteria might represent potential tools for controlling crustacean species of commercial interest and crustacean or insect disease vectors.     

Determinants of species richness in southern African fig wasp assemblages

Summary We investigated the species richness of 24 fig wasp (Hymenoptera) assemblages associated with southern African fig trees (Ficus species, Moraceae). Assemblage sizes ranged between 3 and 30 species on different host tree species, with parasitoids slightly outnumbering gall-forming phytophages. Ten potential taxonomic, geographic and ecological determinants of assemblage richness were examined. Galler richness differed significantly between taxonomic sub-groups of Ficus and was significantly correlated with several ecological characteristics of the host trees, but there was no species-area effect. Parasitoid richness was strongly correlated with galler richness. We conclude that both ecological and historical factors have combined to determine the numbers of species that form fig wasp assemblages.     

Virulence, multiple infections and regulation of symbiotic population in the Wolbachia-Asobara tabida symbiosis

The density and regulation of microbial populations are important factors in the success of symbiotic associations. High bacterial density may improve transmission to the next generation, but excessive replication could turn out to be costly to the host and result in higher virulence. Moreover, differences in virulence may also depend on the diversity of symbionts. Using the maternally transmitted symbiont Wolbachia, we investigated how bacterial density and diversity are regulated and influence virulence in host insects subject to multiple infection. The model we used was the wasp Asobara tabida that naturally harbors three different Wolbachia strains, of which two are facultative and induce cytoplasmic incompatibility, whereas the third is necessary for the host to achieve oogenesis. Using insect lines infected with different subsets of Wolbachia strains, we show that: (i) some traits of A. tabida are negatively affected by Wolbachia; (ii) the physiological cost increases with the number of co-infecting strains, which also corresponds to an increase in the total bacterial density; and (iii) the densities of the two facultative Wolbachia strains are independent of one another, whereas the obligatory strain is less abundant when it is alone, suggesting that there is some positive interaction with the other strains.     

The incidence and diversity of Wolbachia in gallwasps (Hymenoptera; Cynipidae) on oak

Wolbachia bacteria infect approximately 20% of all insect species, and cause a range of alterations to host reproduction, including imposition of thelytoky. The incidence and phenotypic impact of Wolbachia remains to be established in many insect taxa, and considerable research effort is currently focused on its association with particular reproductive modes and the relative importance of the various pathways via which infection occurs. Gallwasps represent an attractive system for addressing these issues for two reasons. First, they show a diversity of reproductive modes (including arrhenotoky, thelytoky and cyclical parthenogenesis) in which the impact of Wolbachia infection can be examined. Second, they occupy two intimately linked trophic niches (gall-inducers and inquilines) between which there is potential for the horizontal exchange of Wolbachia infection. In the arrhenotokous gallwasp lineages screened to date (the herb-galling 'Aylacini' and the rose-galling Diplolepidini), Wolbachia infection always induces thelytoky. The impact of Wolbachia in other arrhenotokous clades, and in the cyclically parthenogenetic clades remains unknown. Here we use polymerase chain reaction (PCR) screening and sequence data for two Wolbachia genes (wsp and ftsZ) to examine the prevalence and incidence of Wolbachia infection in 64 species (a total of 609 individuals) in two further tribes: the arrhenotokous inquilines (tribe Synergini), and the cyclically parthenogenetic oak gallwasps (tribe Cynipini). We ask: (i) whether Wolbachia infection has any apparent impact on host reproduction in the two tribes and (ii) whether there is any correlation between Wolbachia infection and the apparent lack of an arrhenotokous generation in many oak gallwasp life cycles. We show: (i) that Wolbachia infection is rare in the Cynipini. Infected species show no deviation from cyclical parthenogenesis, and infection is no more common in species known only from a thelytokous generation; (ii) that there is a higher incidence of infection within the arrhenotokous inquilines, and generally in gallwasp tribes without cyclical parthenogensis; (iii) all Wolbachia-positive inquiline species are known to possess males, implying either that Wolbachia infection does not result in loss of sex in this tribe or, more probably, that (as for some rose gallwasps) Wolbachia infection leads to loss of sex in specific populations; and (iv) although we find some inquilines and gall inducers to be infected with Wolbachia having the same wsp sequence, these hosts are not members of the same gall communities, arguing against frequent horizontal transmission between these two trophic groups. We suggest that exchange may be mediated by the generalist parasitoids common in oak galls.     

Reproductive effects and geographical distributions of two Wolbachia strains infecting the Neotropical beetle, Chelymorpha alternans Boh. (Chrysomelidae, Cassidinae)

Wolbachia are maternally inherited endocellular bacteria known to alter insect host reproduction to facilitate their own transmission. Multiple Wolbachia infections are more common in tropical than temperate insects but few studies have investigated their dynamics in field populations. The beetle, Chelymorpha alternans, found throughout the Isthmus of Panama, is infected with two strains of Wolbachia, wCalt1 (99.2% of beetles) and wCalt2 (53%). Populations infected solely by the wCalt1 strain were limited to western Pacific Panama, whereas populations outside this region were either polymorphic for single (wCalt1) and double infections (wCalt1 + wCalt2) or consisted entirely of double infections. The wCalt2 strain was not found as a single infection in the wild. Both strains caused cytoplasmic incompatibility (CI). The wCalt1 strain caused weak CI (approximately 20%) and the double infection induced moderate CI (approximately 70-90%) in crosses with uninfected beetles. The wCalt1 strain rescued about 75% of eggs fertilized by sperm from wCalt2 males. Based on the relationships of beetle mtDNA and infection status, maternal transmission, and repeated population sampling we determined that the double infection invaded C. alternans populations about 100,000 years ago and that the wCalt2 strain appears to be declining in some populations, possibly due to environmental factors. This may be the first study to demonstrate an association between widespread strain loss and environmental factors in the field.     

Patterns of diversification of Afrotropical Otiteselline fig wasps: phylogenetic study reveals a double radiation across host figs and conservatism of host association

We studied the phylogenetic relationships of Otiteselline fig waSPS associated with Ficus in the Afrotropical region using rDNA sequences. African fig species usually host two species of Otiteselline fig waSPS. Phylogenetic analyses reveal that this pattern of association results from the radiation of two clades of waSPS superimposed on the fig system. Within each clade, wasp species generally cluster according to their host classification. The phylogenies of the two clades are also generally more congruent than expected by chance. Together these results suggest that Otiteselline wasp speciation is largely constrained by the diversification of their hosts. Finally, we show a difference in ovipositor length between the two Otiteselline species coexisting in the same Ficus species, which probably corresponds to ecological differences. The diversification of ecological niches within the fig is probably, with cospeciation, one of the key factors explaining the diversification and maintenance of species of parasites of the fig/pollinator system.     

Wolbachia infection suppresses both host defence and parasitoid counter-defence

Endosymbiotic bacteria in the genus Wolbachia have been linked to several types of reproductive parasitism, which enhance their own transmission, while their direct effects on the host vary from beneficial to neutral or detrimental. Here, we report negative effects of infection on immunity-related traits of Drosophila simulans and the parasitoid wasp Leptopilina heterotoma. Infected D. simulans showed a reduced ability to encapsulate parasitoid eggs, compared to a tetracycline-treated, bacterium-free line. Challenging the two lines with a fungal pathogen, Beauveria bassiana, on the other hand, revealed no differences in survival. Moreover, elimination of Wolbachia was beneficial for the parasitoid wasp, as eggs laid by uninfected females suffered significantly lower encapsulation rates. We discuss possible origins of these fitness costs and their implications for infection dynamics and the interactions between host species.     

Wolbachia infection and dramatic intraspecific mitochondrial DNA divergence in a fig wasp

Mitochondria and Wolbachia are maternally inherited genomes that exhibit strong linkage disequilibrium in many organisms. We surveyed Wolbachia infections in 187 specimens of the fig wasp species, Ceratosolen solmsi, and found an infection prevalence of 89.3%. DNA sequencing of 20 individuals each from Wolbachia-infected and -uninfected subpopulations revealed extreme mtDNA divergence (up to 9.2% and 15.3% in CO1 and cytochrome b, respectively) between infected and uninfected wasps. Further, mtDNA diversity was significantly reduced within the infected group. Our sequencing of a large part of the mitochondrial genome from both Wolbachia-infected and -uninfected individuals revealed that high sequence divergence is common throughout the mitochondrial genome. These patterns suggest a partial selective sweep of mitochondria subsequent to the introduction of Wolbachia into C. solsmi, by hybrid introgression from a related species.     

Figs,pollinators, and parasites: A longitudinal study of the effects of nematode infection on fig wasp fitness

Mutualisms are interactions between two species in which the fitnesses of both symbionts benefit from the relationship. Although examples of mutualism are ubiquitous in nature, the ecology, evolution, and stability of mutualism has rarely been studied in the broader, multi-species community context in which they occur. The pollination mutualism between figs and fig wasps provides an excellent model system for investigating interactions between obligate mutualists and antagonists. Compared to the community of non-pollinating fig wasps that develop within fig inflorescences at the expense of fig seeds and pollinators, consequences of interactions between female pollinating wasps and their host-specialist nematode parasites is much less well understood. Here we focus on a tri-partite system comprised of a fig (Ficus petiolaris), pollinating wasp (Pegoscapus sp.), and nematode (Parasitodiplogaster sp.), investigating geographical variation in the incidence of attack and mechanisms through which nematodes may limit the fitness of their wasp hosts at successive life history stages. Observational data reveals that nematodes are ubiquitous across their host range in Baja California, Mexico; that the incidence of nematode infection varies across seasons within- and between locations, and that infected pollinators are sometimes associated with fitness declines through reduced offspring production. We find that moderate levels of infection (1–9 juvenile nematodes per host) are well tolerated by pollinator wasps whereas higher infection levels (≥10 nematodes per host) are correlated with a significant reduction in wasp lifespan and dispersal success. This overexploitation, however, is estimated to occur in only 2.8% of wasps in each generation. The result that nematode infection appears to be largely benign – and the unexpected finding that nematodes frequently infect non-pollinating wasps – highlight gaps in our knowledge of pollinator-Parasitodiplogaster interactions and suggest previously unappreciated ways in which this nematode may influence fig and pollinator fitness, mutualism persistence, and non-pollinator community dynamics.     

Wolbachia infection frequencies in insects: evidence of a global equilibrium?

Wolbachia are a group of cytoplasmically inherited bacteria that cause reproduction alterations in arthropods, including parthenogenesis, reproductive incompatibility, feminization of genetic males and male killing. Previous general surveys of insects in Panama and Britain found Wolbachia to be common, occurring in 16-22% of species. Here, using similar polymerase chain reaction methods, we report that 19.3% of a sample of temperate North American insects are infected with Wolbachia, a frequency strikingly similar to frequencies found in two other studies in widely separated locales. The results may indicate a widespread equilibrium of Wolbachia infection frequencies in insects whose maintenance remains to be explained. Alternatively, Wolbachia may be increasing in global insect communities. Within each of the three geographic regions surveyed, Hymenoptera are more frequently infected with A group Wolbachia and Lepidoptera more frequently infected with B group Wolbachia.     

Pollinating fig wasps: genetic consequences of island recolonization

The levels of genetic diversity and gene flow may influence the long-term persistence of populations. Using microsatellite markers, we investigated genetic diversity and genetic differentiation in island (Krakatau archipelago, Indonesia) and mainland (Java and Sumatra, Indonesia) populations of Liporrhopalum tentacularis and Ceratosolen bisulcatus, the fig wasp pollinators of two dioecious Ficus (fig tree) species. Genetic diversity in Krakatau archipelago populations was similar to that found on the mainland. Population differentiation between mainland coastal sites and the Krakatau islands was weak in both wasp species, indicating that the intervening 40 km across open sea may not be a barrier for wasp gene flow (dispersal) and colonization of the islands. Surprisingly, mainland populations of the fig waSPS may be more genetically isolated than the islands, as gene flow between populations on the Javan mainland differed between the two wasp species. Contrasting growth forms and relative 'immunity' to the effects of deforestation in their host fig trees may account for these differences.     

小麦和大豆蚜虫中内共生菌Wolbachia的感染检测和系统发育分析

Wolbachia是一类在节肢动物中广泛感染的胞内共生菌。为了了解其在我国蚜虫中的感染情况, 本研究通过扩增wsp基因片段对采集自我国多个地区的3种小麦蚜虫（荻草谷网蚜Sitobion miscanthi、 麦二叉蚜Schizaphis graminum和禾谷缢管蚜Rhopalosiphum padi）和1种大豆蚜虫（大豆蚜Aphis glycines）样品进行了内共生菌Wolbachia的感染检测。结果显示： 3种小麦蚜虫中均未检测出Wolabchia。大豆蚜也仅在采集自北京和杭州的种群中发现了Wolbachia的感染, 感染率分别为95.8%和22.9%, 并且所检测的个体均为单株系感染。wsp基因序列的比对分析显示, 大豆蚜感染的Wolbachia株系与多个亲缘关系较远的昆虫物种中所感染的Wolbachia株系间具有高度一致的基因序列。wsp基因序列构建的系统发育关系和序列一致性均表明大豆蚜感染的Wolbachia株系属于B大组CauB组。本研究为今后探讨Wolbachia在我国蚜虫中的寄主范围和株系多样性提供了数据支持。     

Intraspecific specialization of the generalist parasitoid Cotesia sesamiae revealed by polyDNAvirus polymorphism and associated with different Wolbachia infection

As a result of an intense host-parasite evolutionary arms race, parasitic wasps frequently display high levels of specialization on very few host species. For instance, in braconid wasps very few generalist species have been described. However, within this family, Cotesia sesamiae is a generalist species that is widespread in sub-Saharan Africa and develops on several lepidopteran hosts. In this study, we tested the hypothesis that C.?sesamiae may be a cryptic specialist when examined at the intraspecific level. We sequenced exon 2 of CrV1, a gene of the symbiotic polyDNAvirus that is integrated into the wasp genome and is associated with host immune suppression. We found that CrV1 genotype was more closely associated with the host in which the parasitoid developed than any abiotic environmental factor tested. We also tested a correlation between CrV1 genotype and an infection with Wolbachia bacteria, which are known for their ability to induce reproductive isolation. The Wolbachia bacteria infection polymorphism was also found as a major factor explaining the genetic structure of CrV1, and, in addition, the best model explaining CrV1 genetic structure involved an interaction between Wolbachia infection and host species. We suggest that Wolbachia could act as an agent capable of maintaining advantageous alleles for host specialization in different populations of C.?sesamiae. This mechanism could be applicable to other insect models because of the high prevalence of Wolbachia in insects.