Wolbachia symbiont infections induce strong cytoplasmic incompatibility in the tsetse fly Glossina morsitans

Tsetse flies are vectors of the protozoan parasite African trypanosomes, which cause sleeping sickness disease in humans and nagana in livestock. Although there are no effective vaccines and efficacious drugs against this parasite, vector reduction methods have been successful in curbing the disease, especially for nagana. Potential vector control methods that do not involve use of chemicals is a genetic modification approach where flies engineered to be parasite resistant are allowed to replace their susceptible natural counterparts, and Sterile Insect technique (SIT) where males sterilized by chemical means are released to suppress female fecundity. The success of genetic modification approaches requires identification of strong drive systems to spread the desirable traits and the efficacy of SIT can be enhanced by identification of natural mating incompatibility. One such drive mechanism results from the cytoplasmic incompatibility (CI) phenomenon induced by the symbiont Wolbachia. CI can also be used to induce natural mating incompatibility between release males and natural populations. Although Wolbachia infections have been reported in tsetse, it has been a challenge to understand their functional biology as attempts to cure tsetse of Wolbachia infections by antibiotic treatment damages the obligate mutualistic symbiont (Wigglesworthia), without which the flies are sterile. Here, we developed aposymbiotic (symbiont-free) and fertile tsetse lines by dietary provisioning of tetracycline supplemented blood meals with yeast extract, which rescues Wigglesworthia-induced sterility. Our results reveal that Wolbachia infections confer strong CI during embryogenesis in Wolbachia-free (Gmm(Apo)) females when mated with Wolbachia-infected (Gmm(Wt)) males. These results are the first demonstration of the biological significance of Wolbachia infections in tsetse. Furthermore, when incorporated into a mathematical model, our results confirm that Wolbachia can be used successfully as a gene driver. This lays the foundation for new disease control methods including a population replacement approach with parasite resistant flies. Alternatively, the availability of males that are reproductively incompatible with natural populations can enhance the efficacy of the ongoing sterile insect technique (SIT) applications by eliminating the need for chemical irradiation.     

Tropical Drosophila pandora carry Wolbachia infections causing cytoplasmic incompatibility or male killing

Wolbachia infections have been described in several Drosophila species, but relatively few have been assessed for phenotypic effects. Cytoplasmic incompatibility (CI) is the most common phenotypic effect that has been detected, while some infections cause male killing or feminization, and many Wolbachia infections have few host effects. Here, we describe two new infections in a recently described species, Drosophila pandora, one of which causes near‐complete CI and near‐perfect maternal transmission (the “CI” strain). The other infection is a male killer (the “MK” strain), which we confirm by observing reinitiation of male production following tetracycline treatment. No incompatibility was detected in crosses between CI strain males and MK strain females, and rare MK males do not cause CI. Molecular analyses indicate that the CI and MK infections are distantly related and the CI infection is closely related to the wRi infection of Drosophila simulans. Two population surveys indicate that all individuals are infected with Wolbachia, but the MK infection is uncommon. Given patterns of incompatibility among the strains, the infection dynamics is expected to be governed by the relative fitness of the females, suggesting that the CI infection should have a higher fitness. This was evidenced by changes in infection frequencies and sex ratios in population cages initiated at different starting frequencies of the infections.     

Wolbachia segregation dynamics and levels of cytoplasmic incompatibility in Drosophila sechellia

In Drosophila sechellia, the endocellular bacterium Wolbachia induces cytoplasmic incompatibility (CI): in crosses involving infected males, a partial or complete embryonic mortality occurs unless the female bears the same Wolbachia. D. sechellia is known to harbour two Wolbachia variants, namely wSh and wSn, closely related to wHa and wNo, respectively, two strains infecting the populations of D. simulans from the Seychelles archipelago and New Caledonia. Strikingly, the two species show similar infection patterns: in D. sechellia, wSh can be present on its own or in double infection with wSn, but individuals carrying wSn only do not occur; in D. simulans, wHa can be present on its own or in double infection with wNo, but individuals carrying wNo only do not occur, or occur at very low frequency. Previous experiments on D. simulans showed that lines singly infected by wNo can be obtained by segregation, and stably maintained. Here we investigate this issue in D. sechellia through an 18 generation experiment, and show that wSn and wSh singly infected lines can arise by segregation. Using singly infected lines obtained in this experiment, we estimate the CI intensities of wSh and wSn in D. sechellia, and compare these to the CI intensities of the same Wolbachia injected into D. simulans. Our results do not suggest any consistent effect of the host species on the CI induced by wSh. On the contrary, it seems that wSn expression is repressed by host factors in D. sechellia.     

Population dynamics of the Wolbachia infection causing cytoplasmic incompatibility in Drosophila melanogaster.

Field populations of Drosophila melanogaster are often infected with Wolbachia, a vertically transmitted microorganism. Under laboratory conditions the infection causes partial incompatibility in crosses between infected males and uninfected females. Here we examine factors influencing the distribution of the infection in natural populations. We show that the level of incompatibility under field conditions was much weaker than in the laboratory. The infection was not transmitted with complete fidelity under field conditions, while field males did not transmit the infection to uninfected females and Wolbachia did not influence sperm competition. There was no association between field fitness as measured by fluctuating asymmetry and the infection status of adults. Infected field females were smaller than uninfecteds in some collections from a subtropical location, but not in other collections from the same location. Laboratory cage studies showed that the infection did not change in frequency when populations were maintained at a low larval density, but it decreased in frequency at a high larval density. Monitoring of infection frequencies in natural populations indicated stable frequencies in some populations but marked fluctuations in others. Simple models suggest that the infection probably provides a fitness benefit for the host in order to persist in populations. The exact nature of this benefit remains elusive.     

The evolution of reproductive isolation in the Drosophila yakuba complex of species

In the Drosophila melanogaster subgroup, the yakuba species complex, D. yakuba, D. santomea and D. teissieri have identical mitochondrial genomes in spite of nuclear differentiation. The first two species can be readily hybridized in the laboratory and produce fertile females and sterile males. They also form hybrids in natural conditions. Nonetheless, the third species, D. teissieri, was thought to be unable to produce hybrids with either D. yakuba or D. santomea. This in turn posed the conundrum of why the three species shared a single mitochondrial genome. In this report, we show that D. teissieri can indeed hybridize with both D. yakuba and D. santomea. The resulting female hybrids from both crosses are fertile, whereas the hybrid males are sterile. We also characterize six isolating mechanisms that might be involved in keeping the three species apart. Our results open the possibility of studying the history of introgression in the yakuba species complex and dissecting the genetic basis of interspecific differences between these three species by genetic mapping.     

What maintains noncytoplasmic incompatibility inducing Wolbachia in their hosts: a case study from a natural Drosophila yakuba population

Cytoplasmic incompatibility (CI) allows Wolbachia to invade hosts populations by specifically inducing sterility in crosses between infected males and uninfected females. In some species, non-CI inducing Wolbachia, that are thought to derive from CI-inducing ancestors, are common. In theory, the maintenance of such infections is not possible unless the bacterium is perfectly transmitted to offspring--and/or provides a fitness benefit to infected females. The present study aims to test this view by investigating a population of Drosophila yakuba from Gabon, West Africa. We did not find any evidence for CI using wild caught females. Infected females from the field transmitted the infection to 100% of their offspring. A positive effect on female fecundity was observed one generation after collecting, but this was not retrieved five generations later, using additional lines. Similarly, the presence of Wolbachia was found to affect mating behaviour, but the results of two experiments realized five generations apart were not consistent. Finally, Wolbachia was not found to affect sex ratio. Overall, our results would suggest that Wolbachia behaves like a neutral or nearly neutral trait in this species, and is maintained in the host by perfect maternal transmission.     

Wolbachia and cytoplasmic incompatibility in the California Culex pipiens mosquito species complex: parameter estimates and infection dynamics in natural populations

Before maternally inherited bacterial symbionts like Wolbachia, which cause cytoplasmic incompatibility (CI; reduced hatch rate) when infected males mate with uninfected females, can be used in a program to control vector-borne diseases it is essential to understand their dynamics of infection in natural arthropod vector populations. Our study had four goals: (1) quantify the number of Wolbachia strains circulating in the California Culex pipiens species complex, (2) investigate Wolbachia infection frequencies and distribution in natural California populations, (3) estimate the parameters that govern Wolbachia spread among Cx. pipiens under laboratory and field conditions, and (4) use these values to estimate equilibrium levels and compare predicted infection prevalence levels to those observed in nature. Strain-specific PCR, wsp gene sequencing, and crossing experiments indicated that a single Wolbachia strain infects Californian Cx. pipiens. Infection frequency was near or at fixation in all populations sampled for 2 years along a >1000-km north-south transect. The combined statewide infection frequency was 99.4%. Incompatible crosses were 100% sterile under laboratory and field conditions. Sterility decreased negligibly with male age in the laboratory. Infection had no significant effect on female fecundity under laboratory or field conditions. Vertical transmission was >99% in the laboratory and approximately 98.6% in the field. Using field data, models predicted that Wolbachia will spread to fixation if infection exceeds an unstable equilibrium point above 1.4%. Our estimates accurately predicted infection frequencies in natural populations. If certain technical hurdles can be overcome, our data indicate that Wolbachia can invade vector populations as part of an applied transgenic strategy for vector-borne disease reduction.     

Variation in Wolbachia cidB gene,but not cidA,is associated with cytoplasmic incompatibility mod phenotype diversity in Culex pipiens

Endosymbiotic Wolbachia bacteria are, to date, considered the most widespread symbionts in arthropods and are the cornerstone of major biological control strategies. Such a high prevalence is based on the ability of Wolbachia to manipulate their hosts' reproduction. One manipulation called cytoplasmic incompatibility (CI) is based on the death of the embryos generated by crosses between infected males and uninfected females or between individuals infected with incompatible Wolbachia strains. CI can be seen as a modification‐rescue system (or mod‐resc) in which paternal Wolbachia produce mod factors, inducing embryonic defects, unless the maternal Wolbachia produce compatible resc factors. Transgenic experiments in Drosophila melanogaster and Saccharomyces cerevisiae converged towards a model where the cidB Wolbachia gene is involved in the mod function while cidA is involved in the resc function. However, as cidA expression in Drosophila males was required to observe CI, it has been proposed that cidA could be involved in both resc and mod functions. A recent correlative study in natural Culex pipiens mosquito populations has revealed an association between specific cidA and cidB variations and changes in mod phenotype, also suggesting a role for both these genes in mod diversity. Here, by studying cidA and cidB genomic repertoires of individuals from newly sampled natural C. pipiens populations harbouring wPipIV strains from North Italy, we reinforce the link between cidB variation and mod phenotype variation fostering the involvement of cidB in the mod phenotype diversity. However, no association between any cidA variants or combination of cidA variants and mod phenotype variation was observed. Taken together our results in natural C. pipiens populations do not support the involvement of cidA in mod phenotype variation.     

Multiple infections and diversity of cytoplasmic incompatibility in a haplodiploid species

Cytoplasmic incompatibility (CI) is a sperm-egg incompatibility commonly induced by the intracellular endosymbiont bacterium Wolbachia that, in diploid species, results in embryo mortality. In haplodiploid species, two types of CI exist depending on whether the incompatible fertilized eggs develop into males (male development (MD)) or abort (female mortality (FM)). CI allows multiple infections to be maintained in host populations, and thus allows interactions to occur between co-infecting strains. In Leptopilina heterotoma, three Wolbachia strains coexist naturally (wLhet1, wLhet2, wLhet3). When these three strains are all present, they induce a CI of FM type, whereas wLhet1 alone expresses a CI phenotype intermediate between MD and FM. Here, we compare CI effects in crosses involving insect lines sharing the same nuclear background, but harboring different mixtures of strains. Mating experiments showed that: (i) wLhet2 and wLhet3 also induce an intermediate CI when acting alone, and show a bidirectional incompatibility; (ii) there is no interaction between the co-infecting strains in CI expression; (iii) the diversity of Wolbachia present within a male host influences the expression of CI: an increase in the number of strains is correlated with a decrease in the proportion of the MD type, which is also correlated with an increase in bacterial density. All these data suggest that the CI of FM type results from a stronger effect than the MD type, which conflicts with the conventional hypotheses used to explain CI diversity in haplodiploids, and could provide some new information about CI mechanisms in insects.     

Loss of cytoplasmic incompatibility and minimal fecundity effects explain relatively low Wolbachia frequencies in Drosophila mauritiana

Maternally transmitted Wolbachia bacteria infect about half of all insect species. Many Wolbachia cause cytoplasmic incompatibility (CI) and reduced egg hatch when uninfected females mate with infected males. Although CI produces a frequency‐dependent fitness advantage that leads to high equilibrium Wolbachia frequencies, it does not aid Wolbachia spread from low frequencies. Indeed, the fitness advantages that produce initial Wolbachia spread and maintain non‐CI Wolbachia remain elusive. wMau Wolbachia infecting Drosophila mauritiana do not cause CI, despite being very similar to CI‐causing wNo from Drosophila simulans (0.068% sequence divergence over 682,494 bp), suggesting recent CI loss. Using draft wMau genomes, we identify a deletion in a CI‐associated gene, consistent with theory predicting that selection within host lineages does not act to increase or maintain CI. In the laboratory, wMau shows near‐perfect maternal transmission; but we find no significant effect on host fecundity, in contrast to published data. Intermediate wMau frequencies on the island of Mauritius are consistent with a balance between unidentified small, positive fitness effects and imperfect maternal transmission. Our phylogenomic analyses suggest that group‐B Wolbachia, including wMau and wPip, diverged from group‐A Wolbachia, such as wMel and wRi, 6–46 million years ago, more recently than previously estimated.     

Influence of aging on cytoplasmic incompatibility, sperm modification and Wolbachia density in Culex pipiens mosquitoes

Wolbachia are maternally inherited endocellular bacteria, widespread in invertebrates and capable of altering several aspects of host reproduction. Cytoplasmic incompatibility (CI) is commonly found in arthropods and induces hatching failure of eggs from crosses between Wolbachia-infected males and uninfected females (or females infected by incompatible strains). Several factors such as bacterial and host genotypes or bacterial density contribute to CI strength and it has been proposed, mostly from Drosophila data, that older males have a lower Wolbachia load in testes which, thus, induces a lighter CI. Here, we challenge this hypothesis using different incompatible Culex pipiens mosquito strains and show that CI persists at the same intensity throughout the mosquito life span. Embryos from incompatible crosses showed even distributions of abortive phenotypes over time, suggesting that host ageing does not reduce the sperm-modification induced by Wolbachia. CI remained constant when sperm was placed in the spermathecae of incompatible females, indicating that sperm modification is also stable over time. The capacity of infected females to rescue CI was independent of age. Last, the density of Wolbachia in whole testes was highly strain-dependent and increased dramatically with age. Taken together, these data stress the peculiarity of the C.pipiens/Wolbachia interaction and suggest that the bacterial dosage model should be rejected in the case of this association.     

Expression of cytoplasmic incompatibility in Drosophila simulans and its impact on infection frequencies and distribution of Wolbachia pipientis

The aim of this study is to examine the expression of cytoplasmic incompatibility and investigate the distribution and population frequencies of Wolbachia pipientis strains in Drosophila simulans. Nucleotide sequence data from 16S rDNA and a Wolbachia surface protein coding sequence and cytoplasmic incompatibility assays identify four distinct Wolbachia strains: wHa, wRi, wMa, and wAu. The levels of cytoplasmic incompatibility between six lines carrying these strains of bacteria and three control lines without bacteria are characterized. Flies infected with wHa and wRi are bidirectionally incompatible, and males that carry either strain can only successfully produce normal numbers of offspring with females carrying the same bacterial strain. Males infected with wAu do not express incompatibility. Males infected with the wMa strain express intermediate incompatibility when mated to females with no bacteria and no incompatibility with females with any other Wolbachia strain. We conduct polymerase chain reaction/restriction fragment length polymorphism assays to distinguish the strain of Wolbachia and the mitochondrial haplotype to survey populations for each type and associations between them. Drosophila simulans is known to have three major mitochondrial haplotypes (siI, sill, and siIII) and two subtypes (siIIA and siIIB). All infected lines of the sil haplotype carry wHa, wNo, or both; wMa and wNo are closely related and it is not clear whether they are distinct strains or variants of the same strain. Infected lines with the silIA haplotype harbor wRi and the siIIB haplotype carries wAu. The wMa infection is found in siIII haplotype lines. The phenotypic expression of cytoplasmic incompatibility and its relation to between-population differences in frequencies of Wolbachia infection are discussed.     

Hedgehog and Wingless stabilize but do not induce cell fate during Drosophila dorsal embryonic epidermal patterning

A fundamental concept in development is that secreted molecules such as Wingless (Wg) and Hedgehog (Hh) generate pattern by inducing cell fate. By following markers of cellular identity posterior to the Wg- and Hh-expressing cells in the Drosophila dorsal embryonic epidermis, we provide evidence that neither Wg nor Hh specifies the identity of the cell types they pattern. Rather, they maintain pre-existing cellular identities that are otherwise unstable and progress stepwise towards a default fate. Wg and Hh therefore generate pattern by inhibiting specific switches in cell identity, showing that the specification and the patterning of a given cell are uncoupled. Sequential binary decisions without induction of cell identity give rise to both the groove cells and their posterior neighbors. The combination of independent progression of cell identity and arrest of progression by signals facilitates accurate patterning of an extremely plastic developing epidermis.     

The impact of Wolbachia,male age and mating history on cytoplasmic incompatibility and sperm transfer in Drosophila simulans

Most insects harbour a variety of maternally inherited endosymbionts, the most widespread being Wolbachia pipientis that commonly induce cytoplasmic incompatibility (CI) and reduced hatching success in crosses between infected males and uninfected females. High temperature and increasing male age are known to reduce the level of CI in a variety of insects. In Drosophila simulans, infected males have been shown to mate at a higher rate than uninfected males. By examining the impact of mating rate independent of age, this study investigates whether a high mating rate confers an advantage to infected males through restoring their compatibility with uninfected females over and above the effect of age. The impact of Wolbachia infection, male mating rate and age on the number of sperm transferred to females during copulation and how it relates to CI expression was also assessed. As predicted, we found that reproductive compatibility was restored faster in males that mate at higher rate than that of low mating and virgin males, and that the effect of mating history was over and above the effect of male age. Nonvirgin infected males transferred fewer sperm than uninfected males during copulation, and mating at a high rate resulted in the transfer of fewer sperm per mating irrespective of infection status. These results indicate that the advantage to infected males of mating at a high rate is through restoration of reproductive compatibility with uninfected females, whereas uninfected males appear to trade off the number of sperm transferred per mating with female encounter rate and success in sperm competition. This study highlights the importance Wolbachia may play in sexual selection by affecting male reproductive strategies.     

黑腹果蝇Mst84Db敲降引起的父本缺陷类似Wolbachia诱导的细胞质不亲和

【目的】Wolbachia 是广泛存在于昆虫体内的一类通过母系传递的共生菌,能够通过多种方式影响宿主的生殖。细胞质不亲和（CI）是Wolbachia 引起的最普遍的一种表型,即感染Wolbachia的雄性和未感染的雌性宿主交配后,胚胎发育停滞于早期阶段。但目前有关CI的分子机理还不清楚。本研究组前期实验表明,Wolbachia感染引起黑腹果蝇Drosophila melanogaster 3龄幼虫精巢中Mst84Db基因的表达显著下调。本研究的目的是进一步研究Mst84Db与CI的关系。【方法】我们体外合成了Mst84Db的双链RNA（dsRNA）,注射雄性果蝇,将注射过的雄果蝇与野生雌果蝇交配,检测其繁殖力。基因表达采用定量RT-PCR方法进行检测。胚胎表型采用DAPI染色进行分析。【结果】注射dsRNA 24 h后,Mst84Db基因的表达水平发生显著下调。注射后72 h,基因表达下调幅度最大。与对照组相比,基因敲降后的雄蝇繁殖能力显著下降,与雌果蝇交配后胚胎孵化率显著低于对照组,这与Wolbachia诱导的CI现象类似。未孵化胚胎的表皮上没有体节出现,说明胚胎停滞于发育的早期。部分胚胎细胞核分裂不同步,且有染色质间桥出现,这也与CI胚胎中的细胞学表型一致。【结论】Wolbachia感染可能抑制果蝇精子发生过程中Mst84Db基因的表达,从而使精子失去正常功能,最终导致与雌性果蝇交配后,胚胎发育停滞,并最终死亡。Mst84Db基因在雄性果蝇中表达下调可能是产生CI的重要原因之一。     

On the evolution of cytoplasmic incompatibility in haplodiploid species

The most enigmatic sexual manipulation by Wolbachia endosymbionts is cytoplasmic incompatibility (CI): infected males are reproductively incompatible with uninfected females. In this paper, we extend the theory on population dynamics and evolution of CI, with emphasis on haplodiploid species. First, we focus on the problem of the threshold to invasion of the Wolbachia infection in a population. Simulations of the dynamics of infection in small populations show that it does not suffice to assume invasion by drift alone (or demographic "accident"). We propose several promising alternatives that may facilitate invasion of Wolbachia in uninfected populations: sex-ratio effects, meta population structure, and other fitness-compensating effects. Including sex-ratio effects of Wolbachia allows invasion whenever infected females produce more infected daughters than uninfected females produce uninfected daughters. Several studies on haplodiploid species suggest the presence of such sex-ratio effects. The simple metapopulation model we analyzed predicts that, given that infecteds are better "invaders," uninfecteds must be better "colonizers" to maintain coexistence of infected and uninfected patches. This condition seems more feasible for species that suffer local extinction due to predation (or parasitization) than for species that suffer local extinction due to overexploiting their resource(s). Finally, we analyze the evolution of CI in haplodiploids once a population has been infected. Evolution does not depend on the type of CI (female mortality or male production), but hinges solely on decreasing the fitness cost and/or increasing the transmission efficiency. Our models offer new perspectives for increasing our understanding of the population and evolutionary dynamics of CI.     

Male age,host effects and the weak expression or non-expression of cytoplasmic incompatibility in Drosophila strains infected by maternally transmitted Wolbachia

In Drosophila melanogaster, the maternally inherited endocellular microbe Wolbachia causes cytoplasmic incompatibility (CI) in crosses between infected males and uninfected females. CI results in a reduction in the number of eggs that hatch. The level of CI expression in this species has been reported as varying from partial (a few eggs fail to hatch) to nonexistent (all eggs hatch). We show that male age in this host species has a large impact on the level of CI exhibited and explains much of this variability. Strong CI is apparent when young males are used in crosses. CI declines rapidly with male age, particularly when males are repeatedly mated. Wolbachia from a Canton S line that was previously reported as not causing CI does in fact induce CI when young males are used in crosses, albeit at a weaker level than in other D. melanogaster strains. The strain differences in CI expression are due to host background effects rather than differences in Wolbachia strains. These results highlight the importance of undertaking crosses with a range of male ages and nuclear backgrounds before ascribing particular host phenotypes to Wolbachia strains.     

Molecular identification of Wolbachia, the agent of cytoplasmic incompatibility in Drosophila simulans, and variability in relation with host mitochondrial types.

Sequences of a segment of the 16S ribosomal DNA of Wolbachia, a rickettsia-like microorganism responsible for cytoplasmic incompatibility in Drosophila simulans, have been obtained after polymerase chain reaction (PCR) amplification. Their comparison with other eubacterial sequences allows us to assign these endosymbionts to the alpha subdivision of purple bacteria. Four related sequences have been obtained for microorganisms carried by eight isofemale lines representative of the three mitochondrial types of D. simulans. Their phylogeny and level of divergence do not parallel that of the mitochondrial DNA, suggesting that several independent infections occurred. There is no direct relation between bacterial phylogeny and formerly identified incompatibility types.     

Bidirectional cytoplasmic incompatibility and the stable coexistence of two Wolbachia strains in parapatric host populations

Wolbachiaare intracellular bacteria which are very widely distributed among arthropods. In many insect species Wolbachiaare known to induce cytoplasmic mating incompatibility (CI). It has been suggested that Wolbachiacould promote speciation in their hosts if parapatric host populations are infected with two different Wolbachiastrains causing bidirectional mating incompatibilities. A necessary condition for this speciation scenario to work is that the two Wolbachiastrains can stably coexist. The following study investigates this problem analysing a mathematical model with two host populations and migration between them. We show that the stability of bidirectional CI can be fully described in terms of a critical migration rate which is defined as the highest migration below which a stable coexistence of two Wolbachiastrains is possible. For some special cases we could derive analytical solutions for the critical migration rate; for the general case estimations of the critical migration rate are given. Our main finding is that bidirectional CI can stably persist in the face of high migration and can be as high as over 15% per generation for CI levels observed in nature. These results have implications for the potential of Wolbachiato promote genetic divergence and speciation in their hosts.     

Contrasting effects of Wolbachia on cytoplasmic incompatibility and fecundity in the haplodiploid mite Tetranychus urticae

Recent studies on Wolbachia‐induced incompatibility in haplodiploid insects and mites have revealed a diversity of cytoplasmic incompatibility (CI) patterns among host species. Here, we report intraspecific diversity in CI expression among four strains of the arrhenotokous mite Tetranychus urticae and in T. turkestani. Variability of CI expression within T. urticae ranged from no CI to complete CI, and included either female embryonic mortality or male conversion types of CI. A fecundity cost attributed to the infection with the high‐CI Wolbachia strain was the highest ever recorded for Wolbachia (?80 to ?100% decrease). Sequence polymorphism at a 550‐bp‐portion of Wolbachia wsp gene revealed two clusters distant by 21%, one of which included three Wolbachia strains infecting mite populations sampled from the same host‐plant species, but showing distinct CI patterns. These data are discussed in the light of theoretical predictions on the evolutionary pathways followed in this symbiotic interaction.