卷蛾赤眼蜂体内共生菌Wolbachia对寄主产雌孤雌生殖行为的影响

在30℃的条件下,连续饲养卷蛾赤眼蜂Trichogramma cacoeciaeMarchall10代,观察每代蜂的生物学特性,并进行Wolbachia的wsp基因的分子检测,以研究卷蛾赤眼蜂产雌孤雌生殖行为与其体内共生菌Wolbachia的关系。结果表明,高温下卷蛾赤眼蜂体内的Wolbachia被抑制,4代以后wsp基因的PCR检测结果变为阴性;同时赤眼蜂的产雌孤雌生殖行为的改变程度也随着世代的增加呈递增趋势。这显示卷蛾赤眼蜂的产雌孤雌生殖行为与其体内的共生菌Wolbachia具有一定程度的相关性。     

A new cytogenetic mechanism for bacterial endosymbiont-induced parthenogenesis in Hymenoptera

Vertically transmitted endosymbiotic bacteria, such as Wolbachia, Cardinium and Rickettsia, modify host reproduction in several ways to facilitate their own spread. One such modification results in parthenogenesis induction, where males, which are unable to transmit the bacteria, are not produced. In Hymenoptera, the mechanism of diploidization due to Wolbachia infection, known as gamete duplication, is a post-meiotic modification. During gamete duplication, the meiotic mechanism is normal, but in the first mitosis the anaphase is aborted. The two haploid sets of chromosomes do not separate and thus result in a single nucleus containing two identical sets of haploid chromosomes. Here, we outline an alternative cytogenetic mechanism for bacterial endosymbiont-induced parthenogenesis in Hymenoptera. During female gamete formation in Rickettsia-infected Neochrysocharis formosa (Westwood) parasitoids, meiotic cells undergo only a single equational division followed by the expulsion of a single polar body. This absence of meiotic recombination and reduction corresponds well with a non-segregation pattern in the offspring of heterozygous females. We conclude that diploidy in N. formosa is maintained through a functionally apomictic cloning mechanism that differs entirely from the mechanism induced by Wolbachia.     

Cytology of Wolbachia-induced parthenogenesis in Leptopilina clavipes (Hymenoptera: Figitidae).

Parthenogenesis induced by cytoplasmatically inherited Wolbachia bacteria has been found in a number of arthropod species, mainly Hymenoptera. Previously, two different forms of diploidy restoration have been reported to underlie parthenogenesis induction in Hymenoptera by Wolbachia. Both are a form of gamete duplication, but each differs in their timing. We investigated the cytology of the early embryonic development of a Wolbachia-infected strain of the parasitoid wasp Leptopilina clavipes and compared it with that of an uninfected sexual strain. Both strains have a similar meiosis. In the infected parthenogenetic strain, diploidy is restored by anaphase restitution during the first somatic mitosis, similar to Trichogramma, but not to Muscidifurax. Our results confirm the occurrence of different cytological mechanisms of diploidy restoration associated with parthenogenesis-inducing Wolbachia in the order Hymenoptera.     

Effects of repeated thermic and antibiotic treatments on a Trichogramma (Hym., Trichogrammatidae) symbiont

Each individual of all populations of the thelytokous species Trichogramma cordubensis is infected by Wolbachia . Populations are composed of females, a few rare males and some intersexual or gynandromorphic individuals often capable of normal reproduction as females. Antibiotic (minocycline) and high temperature (30°C) treatments inactivate Wolbachia and induce male production. After these treatments, the sex ratio depending on the remaining frequency of thelytoky shows a genetic variability. Effect of cycles with and without treatments (minocycline or 30°C) on the thelytokous reproduction of 'individuals' (one 'individual' being one Trichogramma + n Wolbachia ) was studied. The resistance of thelytokous reproduction to 30°C but not to minocycline, probably due to Wolbachia genes, increased. It is concluded that potentialities of adaptation to high temperature exist in Wolbachia and can explain a part of the spreading of these symbionts among host populations.     

Diploidy restoration in Wolbachia-infected Muscidifurax uniraptor (Hymenoptera: Pteromalidae)

Thelytokous reproduction, where females produce diploid female offspring without fertilization, can be found in many insects. In some Hymenoptera species, thelytoky is induced by Wolbachia, a group of cytoplasmically inherited bacteria. We compare and contrast early embryonic development in the thelytokous parthenogenetic species Muscidifurax uniraptor with the development of unfertilized eggs of the closely related arrhenotokous species, Muscidifurax raptorellus. In the Wolbachia-infected parasitic wasp M. uniraptor, meiosis and the first mitotic division occur normally. Diploidy restoration is achieved following the completion of the first mitosis. This pattern differs in the timing of diploidy restoration from previously described cases of Wolbachia-associated thelytoky. Results presented here suggest that different cytogenetic mechanisms of diploidy restoration may occur in different species with Wolbachia-induced thelytoky.     

Microsatellites reveal the genetic structure of thelytokous strains of the migratory locust

This study reports on two parthenogenetic strains of the migratory locust Locusta migratoria. The offspring of thelytokou females had a single fragment per microsatellite loci. All offspring of the parthenogenetic F1 females were genetically identical. These results further confirmed that restitution of the sister products of early cleavage mitoses and cell fusion might be the most likely diploidization mechanisms in the thelytokous locusts. Polymerase chain reaction amplification results demonstrated that thelytoky in the locust was not induced by Wolbachia bacteria. Apart from the low fitness gained in thelytokous females, large populations with migration and losing heterozygosity may be other reasons why regular parthenogenesis has not evolved in the locust.     

Studies on three species of Trichogramma. I. Foraging behaviour for food or hosts

The foraging strategies for both food or hosts of three trichogrammatid species: Trichogramma evanescens, Trichogramma cacoecia and Trichogramma dendrolimi were compared using artificial patches of Sitotroga cerealella eggs. In all experiments, inexperienced and newly emerged wasps of < 1 h old were singly tested. When the females were allowed to land upon the hosts, the decision-making process for initial acceptance or rejection was species-dependent. The initial search in T. evanescens was for food, whereas T. dendrolimi or T. cacoeciae start to oviposit immediately after their emergence. When honey-deprived or undeprived females were each exposed to single patches for 20 or 60 min, variations in mean number of probing females 'drilling and ovipositing' were also species-dependent. Acceptance of host eggs by honey-deprived females and subsequent egg deposition were higher in both T. cacoeciae and T. dendrolimi than in T. evanescens . For all species, the probing of honey-undeprived females was higher than that of deprived ones. When the exposure period was prolonged to 24 or 48 h and the number of patches per female increased to three, most of the honey-deprived or undeprived T. evanescens females attacked one patch, and only a few of them attacked two patches. Foraging activity of honey-deprived females of T. cacoeciae was restricted to single patches, whereas most undeprived ones attacked more than one patch. In contrast, honey-deprived or undeprived T. dendrolimi females attacked more than one patch. The experiments showed that T. dendrolimi females have more powerful ovipositing urges than looking for food and that the opposite was the case for T. evanescens , with T. cacoeciae being intermediate.     

Natural interspecific and intraspecific horizontal transfer of parthenogenesis-inducing Wolbachia in Trichogramma wasps

The intracellular bacterium Wolbachia is one of the most common symbionts in arthropods and, because of its manipulative effects on host reproduction, is assumed to be an important factor in several evolutionary processes. These bacteria are mainly vertically transmitted from mother to daughter through the egg cytoplasm, and horizontal transmission is generally assumed to be rare. Here, we show natural inter- and intraspecific horizontal transfer of parthenogenesis-inducing Wolbachia between parasitoid wasps of the genus Trichogramma. Horizontal transfer was observed when infected and uninfected larvae shared the same host egg. This is the first report, to our knowledge, on interspecific horizontal transfer of Wolbachia between closely related sympatric species. Some originally uninfected immature wasps acquired Wolbachia while inside the host egg, but not all of these newly infected females exhibited the parthenogenesis phenotype. In general, intraspecific horizontal transfer was more successful than interspecific transfer. Wolbachia underwent vertical transmission in the new species but the infection tended to be lost within several generations. Our results have important implications for understanding the evolution of Wolbachia-host associations.     

孤雌产雌生殖品系松毛虫赤眼蜂产卵强度对Wolbachia诱导的其生殖表型的影响

[目的]松毛虫赤眼蜂Trichogramma dendrolimi是一种用于鳞翅目害虫生物防治的重要卵期寄生蜂.本研究旨在明确孤雌产雌生殖品系松毛虫赤眼蜂的产卵强度对其体内Wolbachia滴度及Wolbachia诱导的孤雌产雌生殖表型的影响.[方法]在室内调查了3个处理组松毛虫赤眼蜂雌蜂不同产卵强度(每日仅1 h供寄...     

Biological Control Potential of Wolbachia -infected Versus Uninfected Wasps: Laboratory and Greenhouse Evaluation of Trichogramma cordubensis and T. deion Strains

The effects of thelytoky-inducing Wolbachia ( &#102 -proteobacteria) on Trichogramma cordubensis and T. deion (Hymenoptera, Trichogrammatidae) were studied in laboratory and greenhouse conditions. One infected (thelytokous, all female) line of each wasp species was compared with its conspecific uninfected (arrhenotokous, sexual) counterpart for several fecundity and dispersal traits. Arrhenotokous lines had a higher fecundity than their thelytokous counterparts, which suggests that Wolbachia negatively affect the fecundity of Trichogramma females. The arrhenotokous females dispersed more in the laboratory than their thelytokous counterparts. In the greenhouse, the opposite effect or no difference between lines was found, indicating that the laboratory set-up used to measure dispersal is not useful to predict relative dispersal of the females in the greenhouse. Calculations show that by releasing 100 adult wasps of both lines, thus including arrhenotokous males in the sexual line, more eggs are parasitized by the thelytokous wasps. Therefore, in spite of their lower individual female fecundity, thelytokous lines have a better potential for biological control than their arrhenotokous counterparts.     

How does infection with parthenogenesis-inducing Wolbachia reduce the fitness of Trichogramma?

We analyzed the survival rate of the immature stages of Trichogramma species and lines that differed in their mode of reproduction. Specifically, we compared the mortality of arrhenotokous (W(-)), irrevertable thelytokous (W(-)), and Wolbachia-associated thelytokous (W(+)) forms. The embryonic mortality of the W(+) strains was significantly higher than that of the W(-) lines. The embryonic mortality was negligible for the arrhenotokous Trichogramma evanescens and the thelytokous Trichogramma cacoeciae, which is not infected with Wolbachia. Only 30% of the eggs of the Wolbachia-infected strains developed to adults, while the emergence rate of the Wolbachia-free strains was more than 78%, irrespective of the origin of the strains. More than 78% of the overall mortality in W(+) strains happened during the early stages of development. About 35% of embryos of W(+) strains remain in the mitotic stage even 48 h after oviposition. Most embryos of W(-) strains had already developed to cellular blastoderm after 6 h, regardless of strains. The mortality of immature stages in W(+) strains was mainly caused by the failure of the mitotic divisions.     

Use of tetracycline in larval diet to study the effect of Wolbachia on host fecundity and clarify taxonomic status of Trichogramma species in cured bisexual lines

Endosymbionts of the genus Wolbachia were efficiently cured from Trichogramma species by incorporating 0.02% tetracycline into the artificial diet used to rear larvae. Use of this technique yielded stable cured lines (bisexual and arrhenotokous lines) in which no Wolbachia organisms were detected by PCR for up to 14 generations after curing. Four cured strains of Trichogramma pretiosum showed a significantly lower total fecundity compared to their Wolbachia-infected counterpart. However, the fecundity of a single cured strain of Trichogramma evanescens was similar to its Wolbachia-infected counterpart. These differences in the effect on fecundity may be due to differences between the Wolbachia strains infecting T. pretiosum or T. evanescens, providing additional evidence for the hypothesis that a specific interaction exists between some Trichogramma species and their Wolbachia symbionts. Tetracycline in larval diet was also used to generate bisexual strains of Trichogramma oleae and Trichogramma cordubensis so that these species could be crossed with the closely related species, respectively, T. pretiosum and T. evanescens, to test their compatibility. These crosses showed a lack of compatibility, validating maintenance of these as distinct species.     

Automictic parthenogenesis in the parasitoid Venturia canescens (Hymenoptera: Ichneumonidae) revisited.

Both arrhenotokous and thelytokous reproduction are known to occur in the parasitoid wasp Venturia canescens. The cytological mechanism of thelytoky was previously reported to involve the formation of a restitution metaphase after the reduction division, but the exact nature of the subsequent divisions, whether reductional or equational, remained unclear. We reinvestigated the cytological mechanisms in a thelytokous strain collected in France. Our observations confirm previous results, but an equational and not a reduction division was observed after restitution. This type of reproduction can be classified as central fusion automictic parthenogenesis. In two arrhenotokous strains the normal pattern of oogenesis and syngamy of Hymenoptera was observed. In addition, we used PCR amplification to show that thelytoky in V. canescens is not caused by Wolbachia bacteria. The results are discussed in relation to maintenance of heterozygosity and female sex.     

Selfish element maintains sex in natural populations of a parasitoid wasp

Genomic conflicts between heritable elements with different modes of inheritance are important in the maintenance of sex and in the evolution of sex ratio. Generally, we expect sexual populations to exhibit a 1:1 sex ratio. However, because of their biology, parasitoid wasps often exhibit a female-biased sex ratio. Sex-ratio distorters can further alter this optimum, sometimes leading to the complete loss of sexual reproduction. In the parasitoid wasp Trichogramma kaykai ca. 4-26% of females in field populations are infected with a bacterial sex-ratio distorter, Wolbachia, allowing virgin mothers to produce daughters. In some micro-Hymenoptera these infections have led to the complete loss of sex, but in field populations of T. kaykai the proportion of individuals infected remains relatively stable. We tested several hypotheses to explain this low infection level, including inefficient and horizontal transmission of Wolbachia, suppressor genes negating the effect of Wolbachia and the presence of male-biasing sex-ratio distorters. Here, a male-biasing sex-ratio distorter, a parasitic B chromosome, causing females to produce only sons, keeps the frequency of Wolbachia low. The male-biasing factor of T. kaykai is the second known case of a B chromosome manipulating the reproduction of a parasitoid wasp.     

Wolbachia-induced parthenogenesis in a genus of phytophagous mites.

The vertically transmitted endosymbiotic bacterium Wolbachia modifies host reproduction in several ways in order to enhance its own spread. One such modification results in the induction of parthenogenesis, where males, which are unable to transmit Wolbachia, are not produced. Interestingly, parthenogenesis-inducing Wolbachia have only been found within haplodiploid insects and it is not known whether this exclusivity is the result of functional constraints of Wolbachia. Here we find a unique pattern of Wolbachia infection that is associated with parthenogenesis in six species within the phytophagous mite genus Bryobia. Through antibiotic treatment we show that, in two species, Bryobia praetiosa and an unidentified species, the Wolbachia infection is strictly associated with parthenogenesis. Microsatellite loci show the mechanism of parthenogenesis to be functionally apomictic and not gamete duplication, with progeny identical to their infected mother. Crossing experiments within B. praetiosa showed no evidence of sexual reproduction. These results are discussed with reference to the distribution of parthenogenesis-inducing Wolbachia and the diversification of the Bryobia genus.     

Wolbachia对赤眼蜂的性别调控机制及生理影响

沃尔巴克氏体(Wolbachia)是广泛分布于节肢动物生殖组织内的一类共生细菌。它们通过共生诱导宿主赤眼蜂的产雌孤雌生殖,在生物防治上具有重要意义。文章概述了Wolbachia在赤眼蜂中的分布状况,对赤眼蜂的性别调控机制,在赤眼蜂种群中的传播及限制因素,以及对赤眼蜂适合度的影响。     

沃尔巴克氏体在中国三种稻飞虱中的感染

用PCR方法检测了采集于不同地域稻田的3种稻飞虱共生菌沃尔巴克氏体(Wolbachia)的感染,发现灰飞虱Laodelphax striatellus、褐飞虱Nilaparvata lugens、白背飞虱Sogatella furcifera为沃尔巴克氏体所感染。克隆了编码沃尔巴克氏体外膜蛋白质的wsp基因并进行了序列测定。对wsp的RFLP分析证实了这些飞虱为单一沃尔巴克氏体感染。研究了灰飞虱中沃尔巴克氏体所诱导的胞质不相容性及其在不同地域灰飞虱中的分布。还发现能寄生于上述3种飞虱的稻虱红螯蜂也受同种沃尔巴克氏体感染。沃尔巴克氏体可能通过这种寄生蜂在不同昆虫间横向传播。     

Host genotype determines cytoplasmic incompatibility type in the haplodiploid genus Nasonia

In haplodiploid species, Wolbachia-induced cytoplasmic incompatibility (CI) can be expressed in one of two ways: as a "conversion" of diploid fertilized eggs into haploid males or as embryonic mortality. Here we describe CI-type variation within the parasitic wasp genus Nasonia and genetically analyze the basis of this variation. We reach four main conclusions: (i) CI is expressed primarily as conversion in N. vitripennis, but as embryonic mortality in the sibling species N. giraulti and N. longicornis; (ii) the difference in CI type between N. giraulti (mortality) and N. vitripennis (conversion) is determined by host nuclear genotype rather than by Wolbachia differences; (iii) N. vitripennis "conversion genes" are recessive in hybrid females; and (iv) a difference in CI level between the sibling species N. giraulti and N. longicornis is due to the different Wolbachia infections in the species rather than to the host genotype. These results show that host nuclear genes can influence the type of CI present in a species. On the basis of these findings, we propose a model for how different CI types evolve in haplodiploids due to selection on nuclear genes modifying CI.     

Pattern of Egg Management by Trichogramma cacoeciae and T. dendrolimi (Hymenoptera: Trichogrammatidae)

The effect of temporary host deprivation on parasitization rates of Trichogramma cacoeciae Marchal and T. dendrolimi Matsumura was investigated. The study was conducted with females that we allowed to engage in 3 days of oviposition after various periods of host deprivation. It seems that the production and management of eggs by the two species is completely different. During the first day of oviposition, parasitization by T. cacoeciae was almost unaffected after 1 to 5 days of host deprivation. As deprivation time increased, however, the number of parasitized hosts decreased from an average of 28.6 ±2.0 hosts provided at emergence to an average of 12.5 ±2.3 hosts when the waiting time was 10 days. The number of hosts parasitized on the first day of parasitization by T. dendrolimi were not affected whatever the waiting test period. During the second or third days of oviposition, the lack of suitable hosts for T. cacoeciae did not depress egg-laying potentiality, whereas a strong reduction in parasitization rates by T. dendrolimi occurred in the next 2 days of oviposition whatever was the waiting period. This leads to ca. 50% reduction in total activity of 3 days of oviposition. Only in T. cacoeciae was it possible to distinguish between ageing and host deprivation. The data suggest that T. dendrolimi is a typical proovigenic species, while T. cacoeciae is neither definitely proovigenic nor synovigenic. A slight decrease in rate of emergence of offspring of T. cacoeciae females that had waited 8 to 10 days for their hosts was observed. As far as biological control is concerned, the efficiency of T. dendrolimi females may be more sensitive to host deprivation than T. cacoeciae.     

Wolbachia-mediated parthenogenesis in the predatory thrips Franklinothrips vespiformis (Thysanoptera: Insecta)

Wolbachia are bacterial endosymbionts in arthropods and filarial nematodes. They cause thelytoky, which is a form of parthenogenesis in which females produce females without males, in hymenopteran insects. Infection of this parthenogenesis-inducing Wolbachia has been restricted to the order Hymenoptera, but was found in another insect order, Thysanoptera. A parthenogenetic colony of a predatory thrips Franklinothrips vespiformis (Aeolothripidae) possessed B-group Wolbachia. Male progeny were produced from this thrips by heat and tetracycline treatments. Males produced motile sperm, which were transferred to the female spermatheca by mating. However, the mating did not affect the sex ratios of the next generation, suggesting that the sperm do not fertilize the eggs.