Endosymbiont Infection Research Articles

Low prevalence of secondary endosymbionts in aphids sampled from rapeseed crops in Germany.

Peach-potato aphids, Myzus persicae Sulzer (Hemiptera:Aphididae), and cabbage aphids, Brevicoryne brassicae Linnaeus (Hemiptera:Aphididae), are herbivorous insects of significant agricultural importance. Aphids can harbour a range of non-essential (facultative) endosymbiotic bacteria that confer multiple costs and benefits to the host aphid. A key endosymbiont-derived phenotype is protection against parasitoid wasps, and this protective phenotype has been associated with several defensive enodsymbionts. In recent years greater emphasis has been placed on developing alternative pest management strategies, including the increased use of natural enemies such as parasitoids wasps. For the success of aphid control strategies to be estimated the presence of defensive endosymbionts that can potentially disrupt the success of biocontrol agents needs to be determined in natural aphid populations. Here, we sampled aphids and mummies (parasitised aphids) from an important rapeseed production region in Germany and used multiplex PCR assays to characterise the endosymbiont communities. We found that aphids rarely harboured facultative endosymbionts, with 3.6% of M. persicae and 0% of B. brassicae populations forming facultative endosymbiont associations. This is comparable with endosymbiont prevalence described for M. persicae populations surveyed in Australia, Europe, Chile, and USA where endosymbiont infection frequencies range form 0-2%, but is in contrast with observations from China where M. persicae populations have more abundant and diverse endosymbiotic communities (endosymbionts present in over 50% of aphid populations).

Ecological and evolutionary inferences from aphid microbiome analyses depend on methods and experimental design

AbstractIntroductionAphids play an important role in agroecological contexts as pests and vectors of plant diseases. Aphid performance is closely connected to microbial endosymbionts that provide different benefits or costs to both the aphids and their hosts plants. Furthermore, the microbiome of aphids is connected to soil microbiomes via the plant. Aphid microbiome experiments usually include a pooling step, where several individuals are sequenced together to obtain sufficient DNA concentrations but pooling may blur intraspecific variations.Materials and MethodsTo investigate the effects of sequencing single versus pooled aphids on the results of microbiome analyses, we compared 16S rRNA/ITS amplicon libraries from pooled and single oak aphids (Tuberculatus annulatus HARTIG) under three different soil treatments. We tested whether results quantitatively or qualitatively depend on pooling aphids, prevalence‐based in silico filtering or removal of the primary endosymbiont (Buchnera aphidicola). Buchnera phylogeny, prevalence and abundance of secondary endosymbionts and effects of soil microbiota were investigated.ResultsPooling leads to quantitative differences in bacteria and qualitative differences in fungal species richness, bacterial community composition and partially fungal community composition. Filtering‐dependent results were obtained for bacterial evenness. Buchnera phylogeny supports the hypothesis of cospeciation of primary endosymbionts in oak aphids. We detected Arsenophonus, Hamiltonella, Rickettsia, Rickettsiella, Serratia and Sphingopyxis in oak aphids, with their prevalence and abundance partially affected by pooling. Pooling leads to overestimating the frequency of multispecies endosymbiont infections, while underestimating their relative abundance.ConclusionWe hereby extend our view on non‐model aphid microbiomes and identify pitfalls in experimental design in aphid microbiome research.

Facultative endosymbionts of aphids on strawberry crops affect aphid-parasitoid interactions

Aphids are major agricultural pests and laboratory studies have shown that heritable bacterial endosymbionts can protect aphids against biocontrol parasitoids, but results from agricultural crop systems are lacking. Here we assess (1) which aphid species are present in Dutch strawberry crops, (2) which facultative endosymbionts they carry, and (3) how such facultative endosymbionts affect parasitism success of the biocontrol parasitoid wasps Aphidius ervi and Praon volucre on the most prevalent aphid species Acyrthosiphon malvae. By curing endosymbiont infections, we were able to determine the effects of endosymbionts and aphid genotypes on the parasitism success of both parasitoid species.We show that aphid species composition on strawberry crops is dynamic across the season and that facultative endosymbiont (co-)infections are common. Infection with facultative endosymbionts protected A. malvae against A. ervi, but not against P. volucre. Finally, we also found variation in levels of endogenous resistance among A. malvae lines against A. ervi. Our study is the first to show that a common aphid pest on agricultural farms can be protected against biocontrol parasitoids by both facultative endosymbionts and endogenous resistance.

Cytoplasmic incompatibility and female fecundity associated with Wolbachia infection in a cricket species

Abstract Wolbachia is a maternally inherited endosymbiont of the phylum α‐Proteobacteria that is found widely in arthropods and nematodes. Cytoplasmic incompatibility (CI) is the commonest endosymbiotic manipulation among arthropods, namely reduced embryo viability when Wolbachia‐infected males fertilize Wolbachia‐uninfected females. In this study, endosymbiont infection was investigated and crossing experiments were performed in the wing‐dimorphic cricket Velarifictorus aspersus (Walker) (Orthoptera: Gryllidae) to clarify the effects of Wolbachia on host reproduction. All the tested individuals were infected with two Wolbachia strains, wAsp‐a and wAsp‐f, which belong to supergroup A and supergroup F, respectively. There were no obvious differences in the duration of nymph development or the proportions of females between the Wolbachia‐infected and Wolbachia‐free lines. However, crossing Wolbachia‐infected males with uninfected females reduced the hatching rate by 28% compared with that when infected males were crossed with infected females. The number of eggs laid by Wolbachia‐free females was significantly lower than laid by infected females, either mating with infected males or uninfected males. These results suggest that Wolbachia induced incomplete CI and enhanced female fertility in V. aspersus. Because no homologous cifA and cifB genes, which are involved in CI, were found in supergroups C, D and F, it might be considered that the CI of V. aspersus was induced by strain wAsp‐a of supergroup A. Moreover, the significant increase in the density of wAsp‐a Wolbachia with nymph development might be related to the regulation of CI.

The association of host and vector characteristics with Ctenocephalides felis pathogen and endosymbiont infection.

Surveillance of the fleas and flea-borne pathogens infecting cats is important for both human and animal health. Multiple zoonotic Bartonella and Rickettsia species are known to infect the most common flea infesting cats and dogs worldwide: Ctenocephalides felis, the cat flea. The ability of other flea species to transmit pathogens is relatively unexplored. We aimed to determine cat host and flea factors independently associated with flea Bartonella and Rickettsia infection. We also assessed flea and cat infection by flea-host pair and location. To accomplish these aims, we performed qPCR for the detection of Bartonella, hemotropic Mycoplasma, Rickettsia, and Wolbachia DNA using paired cat and flea samples obtained from free-roaming cats presenting for spay or neuter across four locations in the United States. A logistic regression model was employed to identify the effect of cat (sex, body weight, geographic location, and Bartonella, hemotropic Mycoplasma, and Rickettsia spp., infection) and flea (clade and Rickettsia and Wolbachia infection) factors on C. felis Bartonella clarridgeiae infection. From 189 free roaming cats, we collected 84 fleas: Ctenocephalides felis (78/84), Cediopsylla simplex (4/84), Orchopeas howardi (1/84), and Nosopsyllus fasciatus (1/84). Ctenocephalides felis were phylogenetically assigned to Clades 1, 4, and 6 by cox1 gene amplification. Rickettsia asembonensis (52/84) and B. clarridgeiae (16/84) were the most common pathogenic bacteria detected in fleas. Our model identified host cat sex and weight as independently associated with B. clarridgeiae infection in fleas. Rickettsia asembonensis (52/84), Rickettsia felis (7/84) and Bartonella henselae (7/84) were detected in specific clades: R. felis was detected only in Clades 1 and 6 while B. henselae and R. asembonensis were detected only in Clade 4. Wolbachia spp., also displayed clade specificity with strains other than Wolbachia wCfeT only infecting fleas from Clade 6. There was poor flea and host agreement for Bartonella spp., infection; however, there was agreement in the Bartonella species detected in cats and fleas by geographic location. These findings reinforce the importance of considering reservoir host attributes and vector phylogenetic diversity in epidemiological studies of flea-borne pathogens. Widespread sampling is necessary to identify the factors driving flea-borne pathogen presence and transmission.

Ecological Factors Associated with the Distribution of Bemisia tabaci Cryptic Species and Their Facultative Endosymbionts

The sweetpotato whitefly, Bemisia tabaci species complex, comprises at least 44 morphologically indistinguishable cryptic species, whose endosymbiont infection patterns often varied at the spatial and temporal dimension. However, the effects of ecological factors (e.g., climatic or geographical factors) on the distribution of whitefly and the infection frequencies of their endosymbionts have not been fully elucidated. We, here, analyzed the associations between ecological factors and the distribution of whitefly and their three facultative endosymbionts (Candidatus Cardinium hertigii, Candidatus Hamiltonella defensa, and Rickettsia sp.) by screening 665 individuals collected from 29 geographical localities across China. The study identified eight B. tabaci species via mitochondrial cytochrome oxidase I (mtCOI) gene sequence alignment: two invasive species, MED (66.9%) and MEAM1 (12.2%), and six native cryptic species (20.9%), which differed in distribution patterns, ecological niches, and high suitability areas. The infection frequencies of the three endosymbionts in different cryptic species were distinct and multiple infections were relatively common in B. tabaci MED populations. Furthermore, the annual mean temperature positively affected Cardinium sp. and Rickettsia sp. infection frequencies in B. tabaci MED but negatively affected the quantitative distribution of B. tabaci MED, which indicates that Cardinium sp. and Rickettsia sp. maybe play a crucial role in the thermotolerance of B. tabaci MED, although the host whitefly per se exhibits no resistance to high temperature. Our findings revealed the complex effects of ecological factors on the expansion of the invasive whitefly.

Common facultative endosymbionts do not influence sensitivity of cereal aphids to pyrethroids

Abstract Cereal aphids, including the bird cherry‐oat aphid, Rhopalosiphum padi, and the grain aphid, Sitobion avenae, can transmit viruses that significantly reduce crop yields. To mitigate against yield losses, insecticides are routinely used to manage aphid populations. Aphids can form relationships with endosymbionts that confer fitness benefits or consequences to the aphid. Recent artificial inoculation experiments indicate that endosymbionts could increase aphid susceptibility to insecticides, but this has not been explored using aphid populations naturally infected with endosymbionts. Here, we sampled aphids from an important cereal production region in Lower Saxony, Germany. We characterized the endosymbiont profile of these aphid populations and conducted pyrethroid dose–response assays to test the hypothesis that facultative endosymbionts increase aphid susceptibility to insecticides. We find that the level of insecticide susceptibility is highly variable in S. avenae and we identify populations that are sensitive and tolerant to pyrethroids, including populations collected from the same field. For R. padi, we find evidence for decreased sensitivity to pyrethroids, representing the first report of reduced sensitivity to pyrethroids in R. padi sampled from Central Europe. We detected high endosymbiont infection frequencies in the aphid populations. 84% of aphids carry one facultative endosymbiont and 9% of aphids carry two facultative endosymbionts. We detected associations with Regiella insecticola, Fukatsia symbiotica, and Hamiltonella defensa. However, we do not identify a link between endosymbiont infection and insecticide susceptibility, indicating that other factors may govern the development of insecticide resistance and the need for alternative management strategies.

Endosymbionts Reduce Microbiome Diversity and Modify Host Metabolism and Fecundity in the Planthopper Sogatella furcifera.

ABSTRACTEndosymbionts can strongly affect bacterial microbiota in pests. The white-backed planthopper Sogatella furcifera, a notorious pest in rice, is usually co-infected with Cardinium and Wolbachia, but the effects of these endosymbionts together or individually on the host microbiome and fecundity are unclear. Here, we established three S. furcifera lines (Cardinium and Wolbachia double-infected, Cardinium single-infected, and both-uninfected lines) backcrossed to a common nuclear background and found that single and double infections reduced bacterial diversity and changed bacterial community structure across nymph and adult stages and across adult tissues. The endosymbionts differed in densities between adults and nymphs as well as across adult tissues, with the distribution of Cardinium affected by Wolbachia. Both the single infection and particularly the double infection reduced host fecundity. Lines also differed in levels of metabolites, some of which may influence fecundity (e.g., arginine biosynthesis and nicotinamide metabolism). Cardinium in the single-infected line upregulated metabolic levels, while Wolbachia in the double-infected line appeared to mainly downregulate them. Association analysis pointed to possible connections between various bacteria and differential metabolites. These results reveal that Cardinium by itself and in combination with Wolbachia affect bacterial microbiota and levels of metabolites, with likely effects on host fecundity. Many of the effects of these metabolically limited endosymbionts that are dependent on the hosts may be exerted through manipulation of the microbiome.IMPORTANCE Endosymbionts can profoundly affect the nutrition, immunity, development, and reproduction of insect hosts, but the effects of multiple endosymbiont infections on microbiota and the interaction of these effects with insect host fitness are not well known. By establishing S. furcifera lines with different endosymbiont infection status, we found that Cardinium and the combined Cardinium + Wolbachia infections differentially reduced bacterial diversity as well as changing bacterial community structure and affecting metabolism, which may connect to negative fitness effects of the endosymbionts on their host. These results established the connections between reduced bacterial diversity, decreased fecundity and metabolic responses in S. furcifera.

Rapid Divergence of Key Spermatogenesis Genes in nasuta-Subgroup of Drosophila.

The crosses between closely relatedDrosophilaspecies usually produce sterile hybrid males with spermatogenesis disrupted at post-meiotic phase, especially in sperm individualization stage than the pre-meiotic stage. This is possibly due to the rapid interspecies divergence of male sex and reproduction-related genes. Here we annotated 11 key spermatogenesis genes in 35 strains of species belonging tonasuta-subgroup ofDrosophila, where many interspecies crosses produce sterile males. We characterized the divergence and polymorphism in the protein coding regions by employing gene-wide, codon-wide, and lineage-specific selection analysis to test the mode and strength of selection acting on these genes.Our analysis showed signature of positive selection at bag of marbles (bam)andbenign gonial cell neoplasma (bgcn)despite the selection constrains and the absence of endosymbiont infection which could potentially drive rapid divergence due to an arms race whileroughex (rux)showed lineage-specific rapid divergence in frontal sheen complex ofnasuta-subgroup.cookie monster (comr)showed rapid divergence consistent with the possibility of meiotic arrest observed in sterile hybrids ofDrosophilaspecies. Rapid divergence observed atdon juan (dj) and Mst98Ca-likewas consistent with fused sperm-tail abnormality observed in the hybrids ofDrosophila nasutaandDrosophila albomicans. These findings highlight the potential role of rapid nucleotide divergence in bringing about hybrid incompatibility in the form of male sterility; however, additional genetic manipulation studies can widen our understanding of hybrid incompatibilities. Furthermore, our study emphasizes the importance of young species belonging tonasuta-subgroup ofDrosophilain studying post-zygotic reproductive isolation mechanisms.

Wolbachia-driven selective sweep in a range expanding insect species

BackgroundEvolutionary processes can cause strong spatial genetic signatures, such as local loss of genetic diversity, or conflicting histories from mitochondrial versus nuclear markers. Investigating these genetic patterns is important, as they may reveal obscured processes and players. The maternally inherited bacterium Wolbachia is among the most widespread symbionts in insects. Wolbachia typically spreads within host species by conferring direct fitness benefits, and/or by manipulating its host reproduction to favour infected over uninfected females. Under sufficient selective advantage, the mitochondrial haplotype associated with the favoured maternally-inherited symbiotic strains will spread (i.e. hitchhike), resulting in low mitochondrial genetic variation across the host species range.MethodThe common bluetail damselfly (Ischnura elegans: van der Linden, 1820) has recently emerged as a model organism for genetics and genomic signatures of range expansion during climate change. Although there is accumulating data on the consequences of such expansion on the genetics of I. elegans, no study has screened for Wolbachia in the damselfly genus Ischnura. Here, we present the biogeographic variation in Wolbachia prevalence and penetrance across Europe and Japan (including samples from 17 populations), and from close relatives in the Mediterranean area (i.e. I. genei: Rambur, 1842; and I. saharensis: Aguesse, 1958).ResultsOur data reveal (a) multiple Wolbachia-strains, (b) potential transfer of the symbiont through hybridization, (c) higher infection rates at higher latitudes, and (d) reduced mitochondrial diversity in the north-west populations, indicative of hitchhiking associated with the selective sweep of the most common strain. We found low mitochondrial haplotype diversity in the Wolbachia-infected north-western European populations (Sweden, Scotland, the Netherlands, Belgium, France and Italy) of I. elegans, and, conversely, higher mitochondrial diversity in populations with low penetrance of Wolbachia (Ukraine, Greece, Montenegro and Cyprus). The timing of the selective sweep associated with infected lineages was estimated between 20,000 and 44,000 years before present, which is consistent with the end of the last glacial period about 20,000 years.ConclusionsOur findings provide an example of how endosymbiont infections can shape spatial variation in their host evolutionary genetics during postglacial expansion. These results also challenge population genetic studies that do not consider the prevalence of symbionts in many insects, which we show can impact geographic patterns of mitochondrial genetic diversity.

Spider Mites Singly Infected With Either Wolbachia or Spiroplasma Have Reduced Thermal Tolerance.

Heritable symbionts play an essential role in many aspects of host ecology in a temperature-dependent manner. However, how temperature impacts the host and their interaction with endosymbionts remains largely unknown. Here, we investigated the impact of moderate (20°C) and high (30 and 35°C) temperatures on symbioses between the spider mite Tetranychus truncatus and two maternally inherited endosymbionts (Wolbachia and Spiroplasma). We found that the thermal tolerance of mites (as measured by survival after heat exposure) was lower for mites that were singly infected with either Wolbachia or Spiroplasma than it was for co-infected or uninfected mites. Although a relatively high temperature (30°C) is thought to promote bacterial replication, rearing at high temperature (35°C) resulted in losses of Wolbachia and particularly Spiroplasma. Exposing the mites to 20°C reduced the density and transmission of Spiroplasma but not Wolbachia. The four spider mite strains tested differed in the numbers of heat shock genes (Hsps) induced under moderate or high temperature exposure. In thermal preference (Tp) assays, the two Wolbachia-infected spider mite strains preferred a lower temperature than strains without Wolbachia. Our results show that endosymbiont-mediated spider mite responses to temperature stress are complex, involving a combination of changing endosymbiont infection patterns, altered thermoregulatory behavior, and transcription responses.

Bemisia tabaci in Java, Indonesia: genetic diversity and the relationship with secondary endosymbiotic bacteria

Bemisia tabaci is a complex of cryptic species of whitefly distributed worldwide; they are serious agricultural pests and vectors of plant viruses. Whiteflies are commonly infected by endosymbiotic bacteria, but the infection profiles among genetic groups of B. tabaci are highly complex. Here we analyzed the genetic variation of B. tabaci and endosymbiont infection patterns in Java, Indonesia. Specifically, adult B. tabaci were collected from four provinces and 43 partial cytochrome oxidase subunit I gene sequences were determined to identify the genotypes. Results showed that B. tabaci was grouped into three different cryptic species, Asia I, Asia II 5, and Asia II 7, at rates of 90.70%, 6.98%, and 2.32%, respectively. The dominant group, Asia I, was distributed throughout the island, whereas Asia II 5 and Asia II 7 were detected only in West Java. In these cryptic species, the infection rates of the secondary endosymbionts Arsenophonus, Cardinium, Hamiltonella, Rickettsia, and Wolbachia were 37.21%, 72.09%, 37.21%, 88.37%, and 90.70%, respectively. Arsenophonus and Cardinium were detected two subgroups (A1 and A2; C2 and C4), but Hamiltonella, Rickettsia, and Wolbachia were detected a one subgroup (H1, R1, and W1). The A1 and A2 subgroups were distributed in a mixed manner across the entire island; however, the C2 and C4 subgroups were distributed differentially in West Java and in Central and East Java, respectively. Multiple infections were common and their patterns were highly variable in each cryptic species. In particular, Hamiltonella was detected in Asia I and Asia II 5 but never coinfected with Arsenophonus in the same individual. Overall, this study shows that Asia I is the dominant genetic B. tabaci group on Java Island and that infection by endosymbionts occurs in a highly complex and sometimes geographically related manner.

Effect of the Genotypic Variation of an Aphid Host on the Endosymbiont Associations in Natural Host Populations.

Simple SummaryThe host–endosymbiont complex could be a key determinant in spread and maintenance of the infection polymorphism of endosymbionts. Variation among host–endosymbiont complexes can contribute to genetic variation of a host species and then provide the necessary material for the operating coevolutionary dynamics. We studied the seasonal dynamic of facultative endosymbiont infections among different host clones of the grain aphid Sitobion avenae and whether their presence affects the total hymenopteran parasitism of aphid hosts at the field level. We observed that aphid infections in the field with endosymbionts increase over time, by favoring particular aphid clones closely associated with endosymbionts, but without an effect of endosymbionts on parasitism rate in the host populations. Our results highlight the importance of host–endosymbiont couples in shaping the prevalence and distributions of symbionts throughout nature and the success of their hosts as pests.Understanding the role of facultative endosymbionts on the host’s ecology has been the main aim of the research in symbiont–host systems. However, current research on host–endosymbiont dynamics has failed to examine the genetic background of the hosts and its effect on host–endosymbiont associations in real populations. We have addressed the seasonal dynamic of facultative endosymbiont infections among different host clones of the grain aphid Sitobion avenae, on two cereal crops (wheat and oat) and whether their presence affects the total hymenopteran parasitism of aphid hosts at the field level. We present evidence of rapid seasonal shifts in the endosymbiont frequency, suggesting a positive selection of endosymbionts at the host-level (aphids) through an agricultural growing season, by two mechanisms; (1) an increase of aphid infections with endosymbionts over time, and (2) the seasonal replacement of host clones within natural populations by increasing the prevalence of aphid clones closely associated to endosymbionts. Our results highlight how genotypic variation of hosts can affect the endosymbiont prevalence in the field, being an important factor for understanding the magnitude and direction of the adaptive and/or maladaptive responses of hosts to the environment.

Endosymbiont diversity in natural populations of Tetranychus mites is rapidly lost under laboratory conditions.

Although the diversity of bacterial endosymbionts in arthropods is well documented, whether and how such diversity is maintained remains an open question. We investigated the temporal changes occurring in the prevalence and composition of endosymbionts after transferring natural populations of Tetranychus spider mites from the field to the laboratory. These populations, belonging to three different Tetranychus species (T. urticae, T. ludeni and T. evansi) carried variable infection frequencies of Wolbachia, Cardinium, and Rickettsia. We report a rapid change of the infection status of these populations after only 6 months of laboratory rearing, with an apparent loss of Rickettsia and Cardinium, while Wolbachia apparently either reached fixation or was lost. We show that Wolbachia had variable effects on host longevity and fecundity, and induced variable levels of cytoplasmic incompatibility (CI) in each fully infected population, despite no sequence divergence in the markers used and full CI rescue between all populations. This suggests that such effects are largely dependent upon the host genotype. Subsequently, we used these data to parameterize a theoretical model for the invasion of CI-inducing symbionts in haplodiploids, which shows that symbiont effects are sufficient to explain their dynamics in the laboratory. This further suggests that symbiont diversity and prevalence in the field are likely maintained by environmental heterogeneity, which is reduced in the laboratory. Overall, this study highlights the lability of endosymbiont infections and draws attention to the limitations of laboratory studies to understand host-symbiont interactions in natural populations.

Secondary endosymbiont diversity of Bemisia tabaci and its parasitoids

Cotton whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is one of the most important insect pests worldwide. It is known as a species complex consisting of at least 40 cryptic species. Although there are substantial data regarding species composition, parasitoids and endosymbionts of B. tabaci, data on relationship between the pest, parasitoids and endosymbionts are very restricted. Therefore, in this study, secondary endosymbionts in populations of B. tabaci and their parasitoids collected from Turkey and the USA were determined by PCR-based DNA analysis. Whitefly populations in Turkey represented both Mediterranean (MED) and Middle East-Asia Minor1 (MEAM1) genotypes from single or mixed populations of both genotypes. Arsenophonus, Rickettsia and Wolbachia were found in MED, while Hamiltonella and Rickettsia in MEAM1. Whitefly populations collected from Arizona were all MEAM1 and dually infected with Hamiltonella and Rickettsia. The aphelinid parasitoids Encarsia lutea and Eretmocerus mundus predominated in all Turkish populations. While almost all En. lutea populations were infected with Wolbachia, no endosymbionts were detected in any Er. mundus. Parasitoid species and the pattern of secondary endosymbiont infection in Arizona populations were different with Rickettsia detected only from Encarsia sophia while both Rickettsia and Wolbachia were found in Eretmocerus species. As a result, four secondary endosymbionts, namely, Rickettsia, Hamiltonella, Arsenophonus and Wolbachia, were detected from B.tabaci and its parasitoids. Among them only Wolbachia and Rickettsia were found in both the pest and parasitoids. It is conclude that further studies should be pursued to determine effect of these endosymbionts on biology of the parasitoids and success in biological control of B. tabaci.

Parthenogenesis and developmental constraints.

The absence of a paternal contribution in an unfertilized ovum presents two developmental constraints against the evolution of parthenogenesis. We discuss the constraint caused by the absence of a centrosome and the one caused by the missing set of chromosomes and how they have been broken in specific taxa. They are examples of only a few well-underpinned examples of developmental constraints acting at macro-evolutionary scales in animals. Breaking of the constraint of the missing chromosomes is the best understood and generally involves rare occasions of drastic changes of meiosis. These drastic changes can be best explained by having been induced, or at least facilitated, by sudden cytological events (e.g., repeated rounds of hybridization, endosymbiont infections, and contagious infections). Once the genetic and developmental machinery is in place for regular or obligate parthenogenesis, shifts to other types of parthenogenesis can apparently rather easily evolve, for example, from facultative to obligate parthenogenesis, or from pseudoarrhenotoky to haplodiploidy. We argue that the combination of the two developmental constraints forms a near-absolute barrier against the gradual evolution from sporadic to obligate or regular facultative parthenogenesis, which can probably explain why the occurrence of the highly advantageous mode of regular facultative parthenogenesis is so rare and entirely absent in vertebrates.

Quantitative methods for assessing local and bodywide contributions to Wolbachia titer in maternal germline cells of Drosophila

BackgroundLittle is known about how bacterial endosymbionts colonize host tissues. Because many insect endosymbionts are maternally transmitted, egg colonization is critical for endosymbiont success. Wolbachia bacteria, carried by approximately half of all insect species, provide an excellent model for characterizing endosymbiont infection dynamics. To date, technical limitations have precluded stepwise analysis of germline colonization by Wolbachia. It is not clear to what extent titer-altering effects are primarily mediated by growth rates of Wolbachia within cell lineages or migration of Wolbachia between cells.ResultsThe objective of this work is to inform mechanisms of germline colonization through use of optimized methodology. The approaches are framed in terms of nutritional impacts on Wolbachia. Yeast-rich diets in particular have been shown to suppress Wolbachia titer in the Drosophila melanogaster germline. To determine the extent of Wolbachia sensitivity to diet, we optimized 3-dimensional, multi-stage quantification of Wolbachia titer in maternal germline cells. Technical and statistical validation confirmed the identity of Wolbachia in vivo, the reproducibility of Wolbachia quantification and the statistical power to detect these effects. The data from adult feeding experiments demonstrated that germline Wolbachia titer is distinctly sensitive to yeast-rich host diets in late oogenesis. To investigate the physiological basis for these nutritional impacts, we optimized methodology for absolute Wolbachia quantification by real-time qPCR. We found that yeast-rich diets exerted no significant effect on bodywide Wolbachia titer, although ovarian titers were significantly reduced. This suggests that host diets affects Wolbachia distribution between the soma and late stage germline cells. Notably, relative qPCR methods distorted apparent wsp abundance, due to altered host DNA copy number in yeast-rich conditions. This highlights the importance of absolute quantification data for testing mechanistic hypotheses.ConclusionsWe demonstrate that absolute quantification of Wolbachia, using well-controlled cytological and qPCR-based methods, creates new opportunities to determine how bacterial abundance within the germline relates to bacterial distribution within the body. This methodology can be applied to further test germline infection dynamics in response to chemical treatments, genetic conditions, new host/endosymbiont combinations, or potentially adapted to analyze other cell and tissue types.

Life History Effects Linked to an Advantage for wAu Wolbachia in Drosophila.

Wolbachia endosymbiont infections can persist and spread in insect populations without causing apparent effects on reproduction of their insect hosts, but the mechanisms involved are largely unknown. Here, we test for fitness effects of the wAu infection of Drosophila simulans by comparing multiple infected and uninfected polymorphic isofemale lines derived from nature. We show a fitness advantage (higher offspring number) for lines with the wAu Wolbachia infection when breeding on grapes, but only where there was Talaromyces and Penicillium fungal mycelial growth. When breeding on laboratory medium, the wAu infection extended the development time and resulted in larger females with higher fecundity, life history traits, which may increase fitness. A chemical associated with the fungi (ochratoxin A) did not specifically alter the fitness of wAu-infected larvae, which developed slower and emerged with a greater weight regardless of toxin levels. These findings suggest that the fitness benefits of Wolbachia in natural populations may reflect life history changes that are advantageous under particular circumstances, such as when breeding occurs in rotting fruit covered by abundant mycelial growth.

The relationship of Wolbachia infection and different phenotypes in the Drosophila melanogaster natural populations from radioactively polluted and clear areas in Ukraine

Aim. The study was performed to investigate the relationship between Wolbachia infection and phenotypes that distinct from wild-type of Drosophila melanogaster from different localities in Ukraine including those from Chornobyl Exclusion Zone during 2013–2014. Methods. We have established isofemale lines from populations: Uman’, Inkerman, Odesa, Varva, Kyiv, Drogobych, Yaniv, Poliske, Chornobyl, and Chornobyl Nuclear Power Plant (NPP). The ambient radiation (µSv/h) was measured in the sample sites. The flies were reared in the laboratory through two generations. We carried out the observation of F2 flies for visibly detectable phenotypes. According to whether the trait was inherited, observations were separated into three categories: with deviations of posterior cross-vein (C2) (incomplete penetrance), visible phenotypic changes (non-inherited) and mutations (inherited). Polymerase chain reaction (PCR) with primers specific to the 16S rRNA and Wolbachia surface protein (wsp) genes were used to determine infection presence in isofemale lines of the flies established for each population. Results. Examination of different phenotypes indicates that the highest mutation rate (but not C2 and not inherited changes) is in populations from Chornobyl Exclusion Zone and, therefore, connection with ambient radiation was detected (p = 0.0241). Generalized mixed linear regression has shown evidence that the presence of phenotypes with defects of C2 vein varies with endosymbiont infection presence (p = 0.03473) in the populations from radioactively polluted areas. Conclusion. Wolbachia is not related to occurring phenotypes neither with phenotypic changes nor with mutations, at least in surveyed populations. However, C2 defected phenotypes relates to the bacterial presence in populations from the contaminated area. Nonetheless, the origin of this relationship is unknown and the mechanisms of such a connection require further research. Keywords: Drosophila melanogaster, Wolbachia, endosymbiont, ambient radiation, mutation, phenotypic change, posterior cross-vein.

A fitness cost resulting from Hamiltonella defensa infection is associated with altered probing and feeding behaviour in Rhopalosiphum padi.

Many herbivorous arthropods, including aphids, frequently associate with facultative endosymbiotic bacteria, which influence arthropod physiology and fitness. In aphids, endosymbionts can increase resistance against natural enemies, enhance aphid virulence and alter aphid fitness. Here, we used the electrical penetration graph technique to uncover physiological processes at the insect-plant interface affected by endosymbiont infection. We monitored the feeding and probing behaviour of four independent clonal lines of the cereal-feeding aphid Rhopalosiphum padi derived from the same multilocus genotype containing differential infection (+/-) with a common facultative endosymbiont, Hamiltonella defensa Aphid feeding was examined on a partially resistant wild relative of barley known to impair aphid fitness and a susceptible commercial barley cultivar. Compared with uninfected aphids, endosymbiont-infected aphids on both plant species exhibited a twofold increase in the number of plant cell punctures, a 50% reduction in the duration of each cellular puncture and a twofold higher probability of achieving sustained phloem ingestion. Feeding behaviour was also altered by host plant identity: endosymbiont-infected aphids spent less time probing plant tissue, required twice as many probes to reach the phloem and showed a 44% reduction in phloem ingestion when feeding on the wild barley relative compared with the susceptible commercial cultivar. Reduced feeding success could explain the 22% reduction in growth of H. defensa-infected aphids measured on the wild barley relative. This study provides the first demonstration of mechanisms at the aphid-plant interface contributing to physiological effects of endosymbiont infection on aphid fitness, through altered feeding processes on different quality host plants.