Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Diploid males support a two-step mechanism of endosymbiont-induced thelytoky in a parasitoid wasp
    Ma, W.J. ; Pannebakker, B.A. ; Zande, L. van de; Schwander, T. ; Wertheim, B. ; Beukeboom, L.W. - \ 2015
    BMC Evolutionary Biology 15 (2015). - ISSN 1471-2148
    leptopilina-clavipes hymenoptera - sex-determination - parthenogenetic populations - quantitative pcr - insect sex - wolbachia - host - reproduction - braconidae - determines
    Background Haplodiploidy, where females develop from diploid, fertilized eggs and males from haploid, unfertilized eggs, is abundant in some insect lineages. Some species in these lineages reproduce by thelytoky that is caused by infection with endosymbionts: infected females lay haploid eggs that undergo diploidization and develop into females, while males are very rare or absent. It is generally assumed that in thelytokous wasps, endosymbionts merely diploidize the unfertilized eggs, which would then trigger female development. Results We found that females in the parasitoid wasp Asobara japonica infected with thelytoky-inducing Wolbachia produce 0.7–1.2 % male offspring. Seven to 39 % of these males are diploid, indicating that diploidization and female development can be uncoupled in A. japonica. Wolbachia titer in adults was correlated with their ploidy and sex: diploids carried much higher Wolbachia titers than haploids, and diploid females carried more Wolbachia than diploid males. Data from introgression lines indicated that the development of diploid individuals into males instead of females is not caused by malfunction-mutations in the host genome but that diploid males are most likely produced when the endosymbiont fails to activate the female sex determination pathway. Our data therefore support a two-step mechanism by which endosymbionts induce thelytoky in A. japonica: diploidization of the unfertilized egg is followed by feminization, whereby each step correlates with a threshold of endosymbiont titer during wasp development. Conclusions Our new model of endosymbiont-induced thelytoky overthrows the view that certain sex determination mechanisms constrain the evolution of endosymbiont-induced thelytoky in hymenopteran insects. Endosymbionts can cause parthenogenesis through feminization, even in groups in which endosymbiont-diploidized eggs would develop into males following the hosts’ sex determination mechanism. In addition, our model broadens our understanding of the mechanisms by which endosymbionts induce thelytoky to enhance their transmission to the next generation. Importantly, it also provides a novel window to study the yet-poorly known haplodiploid sex determination mechanisms in haplodiploid insects.
    Lateral gene transfer between prokaryotes and multicellular eukaryotes: ongoing and significant?
    Ros, V.I.D. ; Hurst, G.D.D. - \ 2009
    BMC Biology 7 (2009). - ISSN 1741-7007
    wolbachia - chromosome - evolution - genomes - insect
    The expansion of genome sequencing projects has produced accumulating evidence for lateral transfer of genes between prokaryotic and eukaryotic genomes. However, it remains controversial whether these genes are of functional importance in their recipient host. Nikoh and Nakabachi, in a recent paper in BMC Biology, take a first step and show that two genes of bacterial origin are highly expressed in the pea aphid Acyrthosiphon pisum. Active gene expression of transferred genes is supported by three other recent studies. Future studies should reveal whether functional proteins are produced and whether and how these are targeted to the appropriate compartment. We argue that the transfer of genes between host and symbiont may occasionally be of great evolutionary importance, particularly in the evolution of the symbiotic interaction itself
    Novel bacterial pathogen Acaricomes phytoseiuli causes severe disease symptoms and histopathological changes in the predatory mite Phytoseiulus persimilis (Acari, Phytoseiidae)
    Schütte, C. ; Gols, R. ; Kleespies, R.G. ; Poitevin, O.J.L. ; Dicke, M. - \ 2008
    Journal of Invertebrate Pathology 98 (2008)2. - ISSN 0022-2011 - p. 127 - 135.
    induced plant volatiles - metaseiulus-occidentalis - biological-control - adult females - spider-mites - gen-nov - wolbachia - cardinium - prey - endosymbionts
    Adult female Phytoseiulus persimilis Athias-Henriot (Acari, Phytoseiidae) of a laboratory population show a set of characteristic symptoms, designated as non-responding (NR) syndrome. Mature predators shrink, cease oviposition and die. They show a lower degree of attraction to herbivore-induced plant volatiles and a greater tendency to leave prey patches carrying ample prey. Moreover, predators may carry excretory crystals in the legs, may cease prey consumption and have a low excretion rate. Here, we satisfy Koch¿s postulates for a strain of Acaricomes phytoseiuli (DSM 14247) that was isolated from symptomatic female P. persimilis of the NR-population. Adult female P. persimilis were either exposed to a bacterial inoculum suspension (treatment) or to sterile distilled water (control) for a period of 3 days. Control and treated predators were examined for the occurrence of six symptoms characteristic for the NR-syndrome and the presence of A. phytoseiuli after inoculation. The latter was done by re-isolation of A. phytoseiuli from individual predators and predator feces placed on nutrient agar, by PCR-based identification and by histopathological studies of individual predators. The NR-syndrome was clearly induced in those predators that had been exposed to the bacterial inoculum (incubation time = 2¿5 days, fraction shrunken females = 80%), whereas predators exposed to water did not show the NR-syndrome. A. phytoseiuli was never isolated from control predators whereas it could be re-isolated from 60% of the treated predators (N = 37) and from feces of 41% of treated predators (N = 17). Only one day after exposure A. phytoseiuli could not be re-isolated from treated predators and their feces. Light and electron microscope studies of predators exposed to A. phytoseiuli revealed striking bacterial accumulations in the lumen of the alimentary tract together with extreme degeneration of its epithelium. In addition, bacterial foci also occurred in the fat body. These phenomena were not observed in control predators that were exposed to sterile water. The present data prove that A. phytoseiuli can infect the predatory mite P. persimilis and induce the NR-syndrome and characteristic histopathological changes in adult female P. persimilis. This is the first record of a bacterial pathogen in a phytoseiid mite and the first description of pathogenic effects of a bacterial species in the genus Acaricomes.
    De vrouwen doen het werk
    Huigens, M.E. - \ 2008
    In: Natuur als Bondgenoot / Osse, J.W.M, Schoonhoven, L.M., Dicke, M., Buiter, R., Leiden : Stichting BWM (Cahiers bio-wetenschappen en maatschappij 4) - ISBN 9789073196490 - p. 37 - 39.
    insecten - ichneumonidae - wolbachia - biologische bestrijding - plaagbestrijding met natuurlijke vijanden - organismen ingezet bij biologische bestrijding - insects - ichneumonidae - wolbachia - biological control - augmentation - biological control agents
    Biologische bestrijding van veel plaaginsecten gebeurt met hulp van sluipwespen. Uiteraard leggen alleen vrouwelijke sluipwespen eitjes in of op plaaginsecten. De larven die uit die eitjes komen vreten het plaaginsect vervolgens op. Mannetjeswespen lijken daarmee eigenlijk nutteloos voor de biologische bestrijding. Voor bedrijven die 'biologische bestrijders' produceren lijkt het dus handig om alleen maar vrouwtjeswespen te kweken. Dat is tot op zekere hoogte mogelijk: veel sluipwespsooren produceren alleen maar dochters
    Onion thrips, Thrips tabaci, have gut bacteria that are closely related to the symbionts of the western flower thrips, Frankliniella occidentalis
    Vries, E.J. de; Wurff, A.W.G. van der; Jacobs, G. ; Breeuwer, J.A.J. - \ 2008
    Journal of Insect Science 8 (2008). - ISSN 1536-2442 - p. 1 - 11.
    microbial ecology - thysanoptera - transmission - insects - growth - evolutionary - association - resistance - wolbachia - termites
    It has been shown that many insects have Enterobacteriaceae bacteria in their gut system. The western flower thrips, Frankliniella occidentalis Pergande [Thysanoptera: Thripidae], has a symbiotic relation with Erwinia species gut bacteria. To determine if other Thripidae species have similar bacterial symbionts, the onion thrips, Thrips tabaci, was studied because, like F. occidentalis, it is phytophagous. Contrary to F. occidentalis, T. tabaci is endemic in Europe and biotypes have been described. Bacteria were isolated from the majority of populations and biotypes of T. tabaci examined. Bacteria were present in high numbers in most individuals of the populations studied. Like F. occidentalis, T. tabaci contained one type of bacterium that clearly outnumbered all other types present in the gut. This bacterium was identified as an Erwinia species, as was also the case for F. occidentalis. However, its biochemical characteristics and 16S rDNA sequence differed from the bacteria present in F. occidentalis.
    A novel disease affecting the predatory mite Phytoseiulus persimilis (Acari, Phytoseiidae): evidence for the involvement of bacteria
    Schütte, C. ; Poitevin, O.J.L. ; Dicke, M. - \ 2008
    Biocontrol Science and Technology 18 (2008)1. - ISSN 0958-3157 - p. 1 - 19.
    athias-henriot - rickettsiella-phytoseiuli - biological-control - adult females - transmission - reproduction - wolbachia - gamasoidea - system
    Adult female Phytoseiulus persimilis Athias-Henriot (Acari, Phytoseiidae) of a laboratory population show drastic changes in foraging behavior, anatomy and life history compared to typical laboratory populations. We demonstrated earlier that the set of characteristic symptoms, called non-responding (NR) syndrome, is transmitted horizontally between and among predator generations via feces and debris deposited by symptomatic females. Here, we prove that bacteria present in feces and debris deposited by symptomatic females are involved in the induction of the NR-syndrome. The potential of predator products to induce the NR-syndrome was assayed by keeping healthy adult female predators during a period of 3 days on prey-infested bean leaves, which had previously been sprayed with an aqueous suspension of feces and debris. The NR-syndrome was clearly induced in those predators that had been exposed to a suspension collected from symptomatic females (incubation time 4-6 days, 93% shrunken females), whereas predators exposed to a suspension collected from non-symptomatic females did not show the NR-syndrome. Moreover, predators from the first group transmitted infectious products themselves already 5 days after the initial exposure, whereas this was not the case for the second predator group. The bioassay used in the present study is important for laboratories and companies as it can be applied for testing the presence of the novel disease in populations of P. persimilis. To investigate the involvement of bacteria in syndrome induction we (1) eliminated bacteria from a feces-and-debris suspension of symptomatic females by passing the suspension through a bacterial microfilter and (2) added the antibiotic tetracycline to a suspension of feces and debris from symptomatic females. A suspension of feces and debris collected from symptomatic females did not induce the NR-symptom after bacteria had been eliminated, whereas an untreated portion of the same suspension did so. Moreover, the NR-syndrome was induced in predators exposed to an aqueous suspension of the residues that had not passed the bacterial filter. A suspension of feces and debris collected from symptomatic females, to which the antibiotic tetracycline had been added, did not induce the NR-syndrome whereas the same suspension did induce all symptoms when no tetracycline was added. These findings prove that bacteria are involved in the induction of the NR-syndrome. The results are discussed in the context of mite pathology and biological control.
    The evolution of obligate mutualism: if you can't beat
    Aanen, D.K. ; Hoekstra, R.F. - \ 2007
    Trends in Ecology and Evolution 22 (2007)10. - ISSN 0169-5347 - p. 506 - 509.
    cell-death - wolbachia - populations - cooperation - drosophila
    Wolbachia is best known as a facultative endosymbiotic parasite, manipulating host reproduction. However, it has also evolved as an obligate mutualist at least twice. In a recent paper, Pannebakker et al. identify a possible mechanism for such a transition from facultative parasitism to obligate mutualism in a parasitic wasp in which Wolbachia are required for producing eggs (oogenesis). Their proposed mechanism suggests that compensatory evolution in the host to counter the harmful effects of Wolbachia is the basis of this evolutionary transition.
    Influence of postzygotic reproductive isolation on the interspecific transmission of the paternal sex ratio chromosome in Trichogramma
    Jeong, G.S. ; Stouthamer, R. - \ 2006
    Entomologia Experimentalis et Applicata 120 (2006)1. - ISSN 0013-8703 - p. 33 - 40.
    selfish genetic elements - nasonia hymenoptera - incompatibility - wolbachia
    The paternal sex ratio (PSR) chromosome is a supernumerary chromosome that causes the destruction of the paternal chromosome set in the first mitosis in a fertilized egg. It is known from parasitoid wasps in the genera Nasonia and Trichogramma (Hymenoptera). In these haplodiploids, the egg fertilized by sperm carrying PSR matures as a haploid male that again carries, and is capable of transmitting, the PSR chromosome. Because of its unique transmission behavior, the PSR chromosome may be easily transmitted between species. This study tests whether the interspecific transmission of PSR between Trichogramma kaykai Pinto and Stouthamer and Trichogramma deion Pinto and Oatman (Hymenoptera: Trichogrammatidae) is affected by two types of postzygotic reproductive isolation, i.e., hybrid inviability and hybrid sterility. The results show that PSR can rescue fertilized eggs that would normally be inviable in the interspecific cross and the rescued eggs develop into male offspring that carry PSR. The results suggest that the two types of postzygotic reproductive isolation have no effect on the transmission of PSR between the two Trichogramma species.
    Whitefly control potential of Eretmocerus parasitoids with different reproductive modes
    Ardeh, M.J. - \ 2005
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): Peter de Jong. - [S.l.] : S.n. - ISBN 9789085041740 - 104
    insectenplagen - bemisia tabaci - biologische bestrijding - eretmocerus - voortplanting - wolbachia - insect pests - bemisia tabaci - biological control - eretmocerus - reproduction - wolbachia
    Whiteflies (Homoptera; Aleyrodidae) are amongst the key pests of vegetable, ornamental, and agronomic crops throughout the world. Because of failing and expensive chemical control, much research has been directed at developing biological control by searching for efficient natural enemies of whiteflies. Among different categories of natural enemies, parasitoids have been efficient control agents and cost effective. The aim of the work described in this thesis was to find an efficient parasitoid to control Bemisia tabaci . 

    As a first step I collected data that were available in the literature to give an overview of the importance of the damage, the biology, and the management of whiteflies. I explained (1) why we have to use biological control agents, particularly parasitoids, to control whiteflies, and (2) why we chose the genus Eretmocerus as a potential candidate to control B. tabaci.

    I concluded from available literature data that the two populations of E. mundus might be good candidates for control of B. tabaci : the sexual population from theMediterranean, which is commercially available, and an asexual population, which has been found inAustralia. In theory, whenever a parasitoid produces more females, it potentially can achieve better pest control if other aspects of its biology are similar to that of the population that produces fewer females. Therefore, asexuality (i.e. females that produce only female progeny) might boost the effectiveness of a parasitoid as a biological control agent. Therefore, I evaluated the biology of an arrhenotokous (sexual) population versus a thelytokous (asexual) population.

    The two populations have already shown compliance with essential qualitative criteria as a biocontrol of B. tabaci (chapter 1). I conducted experiments to further compare their characteristics and studied several new elements of their biology. In chapter 2, Icompared the impact of the mode of reproduction (sexual and asexual)in two populations of E. mundus. I could not find any significant differences inthe developmental time and immature mortality between the two populations. However, the number of progeny showed differences. Both populations had the largest progeny on tomato and lowest on gerbera plants, and intermediate offspring production on poinsettia. A large number of progeny was recorded during the first two days of the female's life for both populations on different host plants. The arrhenotokous population produced more progeny than the thelytokous one, but the intrinsic rate of population increase, r m , did not differ a lot between the two populations.

    Sexual females need to find mates to produce female progeny. In chapter 3, I described some challenges in mate finding in sexual populations. To get better insight into mate finding and mating behavior I included a sexual population of E. eremicus in the experiments, along with two E. mundus populations. I found that in both sexual populations males reacted to volatile and non-volatile pheromones of conspecific virgin females. E. eremicus males reacted interspecifically to the sex pheromones of E. mundus virgin females, but E. mundus males did not react to virgin E. eremicus females. However, asexual females were not attractive for any male. Three phases of mating behavior, pre-mating, mating and post-mating were distinguished for the sexual populations. I could not record any successful copulation that led to a hybrid female between the sexual and asexual E. mundus populations. Based on these results I suspect that speciation might have occurred in E. mundus .

    In parasitoid wasps the asexual reproductive mode is induced by the cytoplasmic bacterium Wolbachia. It has been reported that the infection could lead to speciation. To investigate the speciation hypothesis, I studied the divergences of two nuclear genomic regions (ITS1 and ITS2) and a mitochondrial region (COII) in several sexual populations of E. mundus fromEurope, an asexual E. mundus population fromAustralia, and a sexual population of E. eremicus.Their phylogenetic relationship was analysed using additionaldata of other populations and species retrieved from Genbank.Analyses of the sequence divergences and constructed trees showed differences among populations and species, where the ITS2 regions showed clearer differences than the ITS1 or COII regions. Trees that were constructed using different clustering methods, and based on sequence differences of the three regions, were congruent. In all cases, sexual European and asexual Australian populations of E. mundus formed two different groups, showing genetic diversity exceeding that between recognized species such as E. eremicus and E. warrae . Therefore, I suggest that Wolbachia may have played a role in this speciation through pre-mating effects, and argue that the two E. mundus populations should be considered different species.

    To investigate any influences of Wolbachia infection and genetic variation on the fitness of E. mundus, three fundamental aspects of foraging behavior -host handling behavior, host discrimination - and competition between the two populations- were studied.

    In chapter 5, I described and compared different components of the host-handling behaviors of E. mundus with different reproductive modes along with E. eremicus under laboratory conditions . There was no correlation among the durations of different phases across parasitoid populations/species or host nymphal instars. But for some components of the behavior significant differences were found. Overall, the actual oviposition had the longest duration of all host-handling behaviors, and was longer on third nymphal instars than on younger ones . Females of the three populations/species accepted the first three nymphal stages either for oviposition or for host feeding . I recorded a relatively long time for host feeding, especially for making wounds in the host. Host feeding eventually leads to the death of the host .

    In the next chapter (6) I described how Eretmocerus species and populations can discriminate a parasitized- from an unparasitized host, which has direct consequences for their reproductive success and efficiency as biocontrol agents. I noticed that experienced females avoided to oviposit under hosts that had previously been parasitized by conspecific females, but naïve females did not. I also found that E. eremicus females avoided hosts parasitised by E. mundus , so they prevented multi-parasitism. In contrast, E. mundus females do parasitize the hosts that had been parasitized earlier by E. eremicus , so E. mundus does multi-parasitize . In the case of super-parasitism, the outcome shows that neither of the E. mundus populations is stronger, whereas in the case of multi-parasitism E. mundus appears to be stronger than E. eremicus . Since morphological identification of these populations and species are difficult, I used the sequence divergences to develop a molecular method to identify these populations and species (appendix to chapter 6).

    In the last chapter, I summarized and synthesized the most important results and I answered the research questions as formulated in the general introduction:

    ·  Is there any difference between the biology of the asexual and sexual populations of E. mundus ? Y es there is .

    ·  Is there any mating challenge in sexual populations? Yes there is.

    ·  Does genetic variation support the hypothesis of speciation between the sexual and the asexual populations of E. mundus? Yes it does.

    ·  Does the mode of reproduction (sexual / asexual) have an impact on behavioral components in Eretmocerus species? No, it has no impact on host-handling behavior, host discrimination, and competition in the larval stage.

     

    Finally, I have presented the following ideas for future studies on Eretmocerus :

    ·  Systematics and speciation in order to be able to select the correct species and populations for biological control.

    ·  Foraging behavior and patch marking in order to be able to determine the host-searching efficiency of the different populations under field conditions.

    ·  Transmission of Wolbachia between populations and species to find out if asexual populations can be created that might be cheaper and better biocontrol agents.

    Trichogramma and its relationship with Wolbachia: Identification of Trichogramma species, phylogeny, transfer and costs of Wolbachia symbionts
    Almeida, R.P. de - \ 2004
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): R. Stouthamer. - [S.I.] : S.n. - ISBN 9789058089427 - 142
    trichogramma - identificatie - fylogenie - wolbachia - symbionten - horizontale ziekteoverdracht - thelytoky - trichogramma - identification - phylogeny - wolbachia - symbionts - horizontal transmission - thelytoky
    Identification of Trichogramma individuals has long been very difficult. No reliable character was known for the identification of species in this genus, until the utility of male genitalia was recognized in 1968, some 135 years after the first Trichogramma was described ( T.evanescens Westwood, 1833). However, the presence of completelyparthenogeneticlines in this species remained an identification problem because the no reliable female characters exist that allowed identification. The discovery of Wolbachiaas a cause for the complete parthenogenesis in this genus has allowed the identification of such thelytokouslines. Antibiotic treatment couldrevert Wolbachiainfectedthelytokousspecies to sexual ones, thus producing males and allowing their identification in the morphological system. However, the lack of morphological identification of Trichogramma females was only solved with the use of molecular techniques based on rDNAsequencing of the internal transcribed spacer 2 (ITS2) region. Here, this technique was proved to be a reliable tool for the identification of T.cacoeciae , a thelytokousspecies where the parthenogenetic reproduction is not due to Wolbachia infection. In this thesis we report the first record of this species in Peru ( Chapter 2 ). This species is the only thelytokousTrichogramma known in which Wolbachia is not present. T. cacoeciaepresence in South America is discussed. Identification of seventeen native/introduced Trichogramma species using rDNAsequences was done. A molecular key based on restriction analysis allowed identification of the species through the size of the PCR product and the generation of the restriction patterns. Thelytoky in Trichogramma species caused by Wolbachia collected in Peru, Colombia and USA were reported ( Chapter 3 ).Phylogenetic analysis and comparison of DNA sequences of the Wolbachiawsp gene allowed for the recognition of new Wolbachia group "Ato" in the clade of Wolbachia that infect Trichogramma species. The construction ofWolbachia phylogenetic tree showed four distinct groups. The similarities in the Wolbachia sequences for the studied groups suggested the possibility of horizontal transmission between Trichogramma species ( Chapter 4 ). Natural inter- andintraspecifichorizontal transfer of PI Wolbachia between wasps of the genus Trichogramma was shown. Wolbachia infection in uninfected Trichogramma females was possible when infected and uninfected immature wasps shared the same host egg. On the whole, intraspecificinterspecifictransfer ( Chapter 5 ). In T.atopovirilia, Wolbachia infection did not lead to any negative effect on the walking activity, walking speed or other behaviour components studied ( Chapter 6 ).Finally, an overview of the most important outcomes and conclusions of this thesis is presented  ( Chapter 7).
    Evolutionary interactions between sex ratio distorters and their hosts
    Jeong, G.S. - \ 2004
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): R. Stouthamer. - [S.I.] : S.n. - ISBN 9789058089441 - 167
    hymenoptera - gastheren (dieren, mensen, planten) - wolbachia - geslachtsverhouding - gastheer parasiet relaties - parthenogenese - evolutie - hymenoptera - hosts - wolbachia - sex ratio - host parasite relationships - parthenogenesis - evolution
    The paternal sex ratio chromosome in the parasitic wasp Trichogramma kaykai condenses the paternal chromosomes into a dense chromatin mass
    Vugt, J.J.F.A. van; Salverda, M. ; Jong, J.H.S.G.M. de; Stouthamer, R. - \ 2003
    Genome 46 (2003). - ISSN 0831-2796 - p. 580 - 587.
    selfish b-chromosome - nasonia-vitripennis - cytoplasmic incompatibility - wolbachia - hymenoptera - bacteria - genome - origin - psr
    A recently discovered B chromosome in the parasitoid wasp Trichogramma kaykai was found to be transmitted through males only. Shortly after fertilization, this chromosome eliminates the paternal chromosome set leaving the maternal chromosomes and itself intact. Consequently, the sex ratio in these wasps is changed in favour of males by modifying fertilized diploid eggs into male haploid offspring. In this study, we show that in fertilized eggs at the first mitosis the paternal sex ratio (PSR) chromosome condenses the paternal chromosomes into a so-called paternal chromatin mass (PCM). During this process, the PSR chromosome is morphologically unaffected and is incorporated into the nucleus containing the maternal chromosomes. In the first five mitotic divisions, 67% of the PCMs are associated with one of the nuclei in the embryo. Furthermore, in embryos with an unassociated PCM, all nuclei are at the same mitotic stage, whereas 68% of the PCM-associated nuclei are at a different mitotic phase than the other nuclei in the embryo. Our observations reveal an obvious similarity of the mode of action of the PSR chromosome in T kaykai with that of the PSR-induced paternal genome loss in the unrelated wasp Nasonia vitripennis.
    On the evolution of Wolbachia-induced parthenogenesis in Trichogramma wasps
    Huigens, M.E. - \ 2003
    Wageningen University. Promotor(en): Joop van Lenteren. - [S.l.] : S.n. - ISBN 9789058088475 - 183
    wolbachia - parthenogenese - evolutie - geslachtsverhouding - trichogramma - trichogramma - wolbachia - parthenogenesis - evolution - sex ratio

    Organisms display a great variety of sex ratios (ratios of females vs. males), ranging from 100% females to a male bias. These sex ratios are not always only determined by the genes of the organism itself but may actually often be manipulated or distorted by "sex ratio distorters". One sex ratio distorter, the bacterium Wolbachia that lives in the cytoplasm of the cells of its host organism, has received much attention by biologists all over the world. This interest mainly arises from the fact that it manipulates arthropod or nematode reproduction in several ways - feminization, induction of cytoplasmic incompatibility, male-killing and parthenogenesis-induction - to enhance its own inheritance from mother to daughter. Because sperm cells do not contain enough cytoplasm, they cannot transmit Wolbachia and males are a dead end for the bacterium. Recent estimates of Wolbachia 's prevalence range from 17 to even 76% of the insect species.

    In many wasp, thrips and mite species Wolbachia has switched the mode of reproduction from sexuality to complete parthenogenesis (±100% females). However, in minute parasitoid wasps of the genus Trichogramma , which are used worldwide as natural enemies in biological control of lepidopteran pests, only a part of the females in a population is infected with Wolbachia and can therefore reproduce through parthenogenesis. My aim in this thesis is to gain more insight in the dynamics of parthenogenesis-inducing (PI) Wolbachia and to explain the coexistence of infected and uninfected forms in Trichogramma wasps. After first reviewing the literature on PI Wolbachia in chapter 2 , I tried to further our understanding of the coexistence of the two reproductive forms in natural Trichogramma kaykai and T. deion populations by combining fieldwork, molecular techniques, behavioural- and crossing experiments with model studies.

    Vertical transmission of Wolbachia from mother to daughter has been viewed as the main mode of transmission but in chapter 3 & 4 we show an unexpectedly frequent natural inter- and intraspecific horizontal transmission between and within Trichogrammakaykai and T. deion larvae sharing a common food source, a butterfly egg. Originally uninfected immature wasps could acquire Wolbachia inside the host egg but not all newly infected females exhibit parthenogenesis. In T. kaykai, intraspecific horizontal transfer was followed by complete parthenogenesis in future generations but when T. kaykai females received Wolbachia from T. deion , the infection tended to be lost several generations after interspecific horizontal transfer. Our results largely explain the discordance between Wolbachia - and (Trichogrammatid) host phylogenies. Frequent horizontal transfer might select for high virulence in these bacteria .

    Because of a nuclear-cytoplasmic conflict between Wolbachia and the nuclear genes of Trichogramma and the previously described horizontal transfer of Wolbachia , the infection is most likely associated with fitness costs in populations where infected and uninfected individuals coexist. In chapter 5 we show that infected T. kaykai suffer a reduced survival compared to uninfected conspecifics when they shared the same host. The survival rate of infected immatures was higher when they competed with other infected immatures from a different infected parent than in competition with uninfected immatures. This shows that PI Wolbachia -infected Trichogramma can suffer a substantial fitness cost. Because of this reduced competitive ability of infected larvae, horizontal transfer that occurs under the same superparasitism circumstances does not contribute much to an increase in the infection rate in the population.

    Previous work showed that the presence of another sex ratio distorter in males, a B chromosome called PSR (Paternal Sex Ratio) that destroys the paternal chromosomes after fertilization thereby causing an all-male or a male-biased offspring sex ratio, contributes to a low infection frequency in T. kaykai . In chapter 6 we determined if a PSR factor causes low infection frequencies in other species as well. Therefore, we studied natural populations of three Trichogramma species - T. kaykai , T. deion and T. pratti - from the Mojave Desert. Our data showed that all the male-biased and all-male Trichogramma broods collected from the butterfly Apodemia mormo deserti that contained males expressing the PSR phenotype, belonged to T. kaykai. In laboratory tests, 71.4% of the T. kaykaiPSR males horizontally transmitted the PSR phenotype to T. deion . This percentage is comparable to the transmission rate of PSR to T. kaykai females, namely 81.6%. Consequently, the PSR can be transmitted to T. deion and we expect this to happen in the field because T. kaykai and T. deion sometimes emerge from the same butterfly egg. Despite this, we cannot find PSR in T. deion . Modeling shows that low Wolbachia infection frequencies can only be attained when the PSR rates are very high. Therefore, other factors should keep the PI Wolbachia -infection from spreading to fixation in this species, e.g. nuclear suppressor genes.

    The mating structure in the host population plays a major role in the dynamics of PI Wolbachia and PSR . A PSR factor prevents the Wolbachia infection from spreading to all the females in T. kaykai because uninfected T. kaykai females show a high level of sib (brother-sister) mating. Sib mating is a barrier against the destructive effect of mating with a PSR -carrying male. Infected females do not have this advantage. Using a population genetic model with microsatellites as genetic markers in chapter 7 , we estimated high levels of sib-mating of 70% and an off-patch mating of 15%. Thirty-five percent of the patches were estimated to be parasitized by two T. kaykai females. Incorporating such levels of sib mating in a previously developed model describing the dynamics of PI Wolbachia and PSR in a Trichogramma population, resulted in stable low frequencies of infection, i.e., a coexistence between infected and uninfected individuals, and of the PSR chromosome. Our results show how mating structure allows the two sex ratio distorters to coexist in the population.

    The main conclusion from this thesis is that, despite the high vertical transmission and regular horizontal transfer of Wolbachia , a PI Wolbachia -infection can be attained at low frequencies in Trichogramma , due to the presence of a non-mendelian suppressor, like the male-biasing PSR factor in T. kaykai, but also due to other factors. In T. deion, for example, PSR does not keep the infection frequency at low levels but a nuclear mendelian suppressor against the PI Wolbachia might have evolved.

    Next to their significance for the understanding of the evolutionary pathways of Wolbachia -host interactions, the results reported in this thesis may also have important implications for future use of natural enemies, and more specifically Trichogramma wasps, in inundative biological control. We may now have a good method to render wasps parthenogenetic, via super- or multiparasitism by infected and uninfected females, thereby increasing the efficacy of parasitoid releases against lepidopteran pests.

    Phylogeny and host-symbiont interactions of thelytoky inducing Wolbachia in Hymenoptera
    Meer, M.M.M. van - \ 1999
    Agricultural University. Promotor(en): J.C. van Lenteren; R. Stouthamer. - S.l. : Van Meer - ISBN 9789058080509 - 118
    wolbachia - symbionten - gastheren (dieren, mensen, planten) - hymenoptera - gastheer parasiet relaties - thelytoky - fylogenie - biologische bestrijding - landbouwkundige entomologie - insectenplagen - wolbachia - symbionts - hosts - hymenoptera - host parasite relationships - thelytoky - phylogeny - biological control - agricultural entomology - insect pests

    Summary and conclusions

    Bacteria of the genus Wolbachia (α-Proteobacteria, Rickettsia) are widespread in arthropods and can induce thelytoky (T) in parasitoids (Hymenoptera). Infection with thelytoky inducing Wolbachia (T- Wolbachia ) enables infected females to produce daughters from unfertilised eggs. Thelytokous strains can be maintained without the involvement of males. T- Wolbachia may represent a tool to improve biological control because only female parasitoids attack target pest species. Advantages of thelytokous reproduction of parasitic wasps in biological control programs may include: lower costs of mass rearing; faster population growth after release and easier establishment of thelytokous wasps in pest populations.Therefore, it was suggested to render sexual reproducing parasitoids thelytokous by infecting them with T- Wolbachia . To determine whether this approach was feasible, several experiments were done to improve our understanding of this specific host-symbiont relationship.

    Phylogeny

    The phylogeny of Wolbachia has been studied using 16S ribosomal DNA (rDNA) and the cell cycle gene ftsZ but sequence variation of those genes is limited. The spacer 2 region (SR2), the region between 23S rDNA and 5S rDNA, was amplified to determine if this region would improve phylogenetic resolution. The SR2 of Wolbachia is 66 basepairs (bp) long and shows slightly higher sequence differences between strains than ftsZ . Due to the short length of SR2 of Wolbachia , little phylogenetic information could be retrieved. Additional phylogenetic research was done using the sequence of an outer membrane protein ( wsp ) of Wolbachia . Previous research in Yale (USA) showed that this gene evolved at a much faster rate than 16S rDNA or ftsZ and the Wolbachia clade was subdivided into twelve distinct groups based on the proposed 2.5% wsp sequence divergence grouping criterion. We extended this former Wolbachiawsp data set with fifteen T- Wolbachia strains and our results showed that: 1)Four new tested thelytokous parasitoids species were as well infected with Wolbachia ( Amitus fuscipennis , Apoanagyrus diversicornis , Coccidoxenoides peregrinus , Eretmocerus staufferi ); 2) T- Wolbachia clones are not closely related; 3) Based on identical wsp sequences of the moth Ephestia kuehniella (Lepidoptera) and its parasitoid Trichogramma , possible horizontal Wolbachia transfer between them was postulated. The exact mechanism of horizontal transfer remains to be clarified.

    Micro-injection

    Our goal was to do a T- Wolbachia transfer experiment between hymenopteran species to test whether arrhenotokous wasps could be rendered thelytokous. Infection of a host with Wolbachia can be accomplished by microinjection of the bacteria in an insect egg as shown for Drosophila sp. However, no suitable micro-injection protocol for parasitoids was available. We developed a injection protocol for the gregarious fly pupa parasitoid Nasoniavitripennis because with this species, large number of eggs could be collected relatively easy. This facilitated the testing of the different steps of the micro-injection procedure. Different available micro-injection protocols of Drosophila spp. and Tribolium confusum were combined and optimal conditions for each of the different steps were determined. In addition, an in vitro incubation step for the N. vitripennis larvae had to be included. The final protocol enables us to do Wolbachia transfer studies in this species.

    Host Wolbachia interactions

    Different fitness parameters of T- Wolbachia infected and non-infected Trichogramma species were studied. Trichogramma are minute wasps which are widely used in biological control programs against lepidopteran pests. We distinguished two different Trichogramma populations: 1) 'Fixed' populations in which the infection is fully established so that only thelytokous females are present and 2) 'Mixed' populations in which thelytokous females coexist with arrhenotokous ones. In mixed populations thelytokous females are still able to mate and to produce daughters sexually. In mixed populations, a potential cytoplasmic-nuclear conflict exists but in fixed populations, this conflict is absent. It is theorised that fixation of the infection results in a reduction of negative impact of the symbiont on its host. This hypothesis was tested with the egg parasitoid Trichogramma because both mixed and fixed populations exist within this genus.

    Two isofemale lines from fixed populations and four isofemale lines from mixed populations were 'cured' of Wolbachia infection using antibiotics and different lifespan fitness parameters were measured. Daughter production was significantly higher for the thelytokous fixed lines (16-131% more daughters) compared to the conspecific arrhenotokous ones. This is in contrast to the three mixed lines where the opposite was found (6-61% less daughters). Only slight fecundity effects of Wolbachia were found in the fixed lines (varying among 19% less offspring and 6% more offspring) while these effects are clearly negative in the mixed lines (34-49% less offspring).

    Finally, we determined whether thelytokous wasps do equally well as biological control agents as their arrhenotokous counterparts. Theoretically, thelytokous wasps may be better biological control agents than the arrhenotokous ones. However, previous studies, show that Wolbachia can have a negative fecundity impact on their host. Therefore, other fitness parameters such as host searching efficacy, dispersal etc. could also be affected. We assessed whether Wolbachia infection had an impact on the 'parasitization efficiency' of the Trichogramma species T. deion and T. cordubensis in greenhouse compartments. Laboratory studies, to assess the effect of Wolbachia on host fecundity and dispersal were also done to correlate these results with the greenhouse experiment results. Laboratory results showed: 1) The fecundity of the thelytokous wasps species was reduced compared to the arrhenotokous counterparts; 2) Experiments of Trichogramma in a laboratory chamber showed that for both species, the arrhenotokous lines dispersed more than their thelytokous counterparts, suggesting a negative effect of Wolbachia on dispersal.Greenhouse experiments showed for both species that thelytokous wasps parasitize approximately equal number of patches but parasitize fewer eggs per patch than the arrhenotokous females.

    These results correspond with the laboratory fecundity experiments. However, in contrast to laboratory chamber experiments, thelytokous T. deion females dispersed equally well as their arrhenotokous counterparts while thelytokous T. cordubensis females showed significant more dispersal than the arrhenotokous ones. No explanation was found for these dispersal differences in greenhouse or laboratory chamber experimental set-ups. According to calculations, it is still advantageous to use thelytokous parasitoids for biological control when the negative impact of Wolbachia on host fitness is taken into account.

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