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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Virulence contribution and recognition of homologs of the Verticillium dahliae effector Ave1
Boshoven, Jordi C. - \ 2017
Wageningen University. Promotor(en): Bart Thomma; Pierre de Wit. - Wageningen : Wageningen University - ISBN 9789463436441 - 183
verticillium dahliae - plant pathogenic fungi - plant pathogens - disease resistance - virulence factors - virulence - immunity - host parasite relationships - plant-microbe interactions - symbiosis - mutagenesis - resistance breeding - plantenziekteverwekkende schimmels - plantenziekteverwekkers - ziekteresistentie - virulente factoren - virulentie - immuniteit - gastheer parasiet relaties - plant-microbe interacties - symbiose - mutagenese - resistentieveredeling

Disease resistance in crops is an important aspect of securing global food security. Resistant plants carry immune receptors that sense pathogen invasion often through the recognition of important pathogen virulence factors, known as effectors. Thus, identification and characterization of effectors is important for the fundamental understanding of virulence mechanisms and to aid in resistance breeding. In this thesis the VdAve1 effector of the soil-borne fungal pathogen Verticillium dahliae is studied that is recognized by tomato immune receptor Ve1. Homologs were found in other plant pathogens and the role in virulence in these pathogens was analyzed. Ave1 homologs are differentially recognized by Ve1 and with a combination of domain swaps and truncations a surface exposed patch was identified that contributes to the recognition by Ve1. Knowledge of specific effector-receptor combinations and knowledge of effectors in general can be exploited to aid in breeding for durable resistance in crops.

Exploring the resistance against root parasitic plants in Arabidopsis and tomato
Cheng, Xi - \ 2017
Wageningen University. Promotor(en): H.J. Bouwmeester, co-promotor(en): Carolien Ruyter-Spira. - Wageningen : Wageningen University - ISBN 9789463437004 - 305
plants - parasitic plants - arabidopsis thaliana - solanum lycopersicum - host parasite relationships - plant growth regulators - resistance - planten - parasitaire planten - gastheer parasiet relaties - plantengroeiregulatoren - weerstand
Root parasitic plant species such as broomrapes (Orobanche and Phelipanche spp.) and witchweeds (Striga spp.) are notorious agricultural weeds. They cause damage to crops by depriving them of water, nutrients and assimilates via a vascular connection. The difficulty in controlling root parasitic weeds is largely due to their intricate lifecycle and partially underground lifestyle. Their life cycle includes processes such as germination of the seed, the formation of the vascular connection with the host, the growth and development of the parasite after attachment and the emergence of shoots and flowers aboveground. The germination of many parasitic plants is induced by strigolactones that were recently shown to also be signalling compounds that stimulate mycorrhizal symbiosis. In addition, in the past few years, their role in plant development and plant defense has been established revealing them as a new class of plant hormones that exert their function likely in interaction with other hormones.
Community ecology of Neotropical ticks, hosts, and associated pathogens
Esser, Heleen J. - \ 2017
Wageningen University. Promotor(en): Herbert Prins; Frans Bongers, co-promotor(en): Patrick Jansen. - Wageningen : Wageningen University - ISBN 9789463436908 - 200
metastigmata - host specificity - host parasite relationships - biodiversity - species diversity - pathogens - size - community ecology - tickborne diseases - panama - tropics - hosts - gastheerspecificiteit - gastheer parasiet relaties - biodiversiteit - soortendiversiteit - pathogenen - grootte - gemeenschapsecologie - ziekten overgebracht door teken - tropen - gastheren (dieren, mensen, planten)

The ongoing loss of global biodiversity is unprecedented in both magnitude and pace, raising urgent questions as to how this loss will affect ecosystem functioning and human well-being. Control of infectious diseases has been proposed as an important ecosystem service that is likely to be affected by biodiversity loss. A negative relationship between biodiversity and disease risk could offer a win-win situation for nature conservation and human health. However, the generality of this relationship remains the subject of contentious debate. The aim of this thesis was to contribute to a better understanding of the interactions between ticks and their vertebrate hosts in a biodiversity hotspot, and how loss of biodiversity affects these interactions and ultimately, tick-borne disease risk. My study was unique in that I simultaneously considered and directly assessed broader communities of Neotropical wildlife, ticks, and tick-borne pathogens across an anthropogenic disturbance gradient.

Determining whether and how biodiversity loss affects tick-borne disease risk in tropical forests requires a thorough understanding of tick-host associations, which are a function of tick-host specificity as well as host biological and ecological traits. In chapter 2, I therefore quantified the degree to which adult ticks are host-specific in my study region: Panama. Using quantitative network analyses and phylogenetic tools with null model comparisons, I found that the adult life stages of most tick species were specific to a limited number of host species that were phylogenetically closely related. In Chapter 4 I showed that species assemblages of adult ticks became increasingly diverse on larger-bodied host species, indicating that adult ticks in Panama tend to select for large reproduction hosts.

In contrast to adult ticks, understanding the ecological interactions between immature ticks and their hosts in the tropics has long been hampered by a lack of morphological identification keys. Therefore, in Chapter 3, I describe the development of a DNA barcode reference library for the molecular identification of larvae and nymphs. This reference library was highly effective in species-level identification of immature ticks collected from birds (Chapter 3) and small mammals (Chapter 4 and 6). Several avian ecological traits were positively associated with tick parasitism, but the potential role of wild birds in tick-borne disease transmission seems to be limited in Panama. Immature ticks did not show any specificity to particular bird species or avian ecological traits (Chapter 3), and species assemblages of immatures ticks were equally diverse across a large number of host taxa (Chapter 4). This suggests that larvae and nymphs may feed more opportunistically than their adult counterparts.

High host specificity in adult ticks implies high susceptibility to tick-host coextinction, even if immature ticks feed opportunistically. In chapter 5, I tested this hypothesis by surveying tick and vertebrate host communities across a forest fragmentation gradient. Forest fragments consisted of previously connected islands and peninsulas in the Panama Canal and ranged 1000-fold in size. Abundance and species richness of ticks was positively related to that of wildlife, which in turn was related to the size of the forest fragment. Specialist tick species were only present in fragments where their specific reproduction hosts were captured by camera traps. Further, less diverse tick communities were dominated by a generalist tick species. These results indicate that loss of wildlife had cascading effects on tick communities through local host-parasite coextinction.

In Chapter 6, I studied how communities of wildlife, ticks, and tick-borne microbes changed along a more ‘typical’ disturbance gradient, in which forest fragments were embedded in an agricultural and sub-urban landscape, rather than surrounded by water. I found that wildlife community disassembly either diluted, amplified, or had no effect on infection prevalence in ticks, depending on the pathogen and degree of disturbance. However, hyperabundance of medium- to large-sized frugivores and herbivores (important reproduction hosts for adult ticks) in sites that lacked apex predators was related to exponential increases in tick density, negating any effect of reduced pathogen prevalence. Moreover, high tick species richness in these sites was related to high microbial and pathogen richness. High parasite diversity is thus a source of infectious diseases. When medium- to large-sized frugivores and herbivores also disappeared, densities of infected ticks declined, suggesting a non-linear relationship between biodiversity loss and tick-borne disease risk, in which initial loss of apex predators increases disease risk, but further loss of species decreases disease risk again.

In this thesis, I have quantified host-feeding relationships of adult and immature Neotropical ticks, many of which (in the case of larvae and nymphs) were largely unknown. I have shown that adult ticks tend to be highly host-specific, particularly to larger-bodied vertebrates, whereas immature ticks appear to have broader host-use patterns. I found that ticks are susceptible to local host-tick coextirpation, and that the relationship between biodiversity loss and tick-borne disease risk is non-linear. My results emphasize the importance of directly assessing host community composition and suggest that the presence of specific (reproduction) hosts are a more important factor than species richness per se for tick population and tick-borne disease dynamics.

The wild life of tick-borne pathogens
Hofmeester, Tim R. - \ 2016
Wageningen University. Promotor(en): Herbert Prins, co-promotor(en): Sip van Wieren. - Wageningen : Wageningen University - ISBN 9789462579699 - 224
ixodes ricinus - metastigmata - life cycle - tickborne diseases - disease vectors - mammals - birds - hosts - population ecology - tick infestations - host parasite relationships - levenscyclus - ziekten overgebracht door teken - vectoren, ziekten - zoogdieren - vogels - gastheren (dieren, mensen, planten) - populatie-ecologie - tekenbesmettingen - gastheer parasiet relaties

Diseases that are transmitted by arthropod vectors from animal hosts to humans – so called zoonotic vector-borne diseases – have increased in incidence in the last decades. In North America and Europe, tick-borne pathogens cause the majority of vector-borne diseases, including Lyme borreliosis and tick-borne encephalitis. The pathogens causing these diseases are transmitted by tick species within the Ixodes ricinus complex. These are generalist ticks that have a multi-year lifecycle with three active stages, larva, nymph and adult. Each stage passively waits for a vertebrate host by questing in the vegetation. Once a host is encountered these ticks feed on the host for several days sucking blood, after which they detach and moult to the next stage or lay eggs. Although these ticks spend the majority of their life in the vegetation, the availability of hosts is an important determinant of tick densities.

In Europe, the Sheep tick (Ixodes ricinus) is the most important vector for tick-borne pathogens. These pathogens include Borrelia burgdorferi sensu lato (s.l.), the causative agent of Lyme borreliosis, Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis, Borrelia miyamotoi, the causative agent of acute febrile illness and Candidatus Neoehrlichia mikurensis, the causative agent of neoehrlichiosis. There are several genospecies within the B. burgdorferi s.l. complex, among which B. afzelii, B. bavariensis, B. garinii, B. lusitaniae, B. spielmanii, and B. valaisiana are found in questing ticks and patients in the Netherlands. All of these pathogens are maintained and amplified by vertebrate hosts. Host species differ in their ability to transmit the different pathogens (reservoir competence), as well as in their competence for ticks. Therefore, it has been hypothesized that changes in vertebrate assemblage composition can change tick-borne pathogen dynamics and thereby tick-borne disease risk, where a decrease in host species diversity might lead to an increased disease risk, the so-called dilution effect of host species richness hypothesis.

In his thesis, Tim Hofmeester describes his research on the role of different vertebrate host species in maintaining I. ricinus populations and in infecting I. ricinus larvae with different tick-borne pathogens. By performing a systematic review, Hofmeester found that for both mammals and birds, there was a positive correlation between host body mass and tick burden for the different stages. Nymphal burden was positively correlated with infection prevalence with B. burgdorferi s.l. in hosts, which was again positively correlated with the average number of larvae that got infected with B. burgdorferi s.l. while feeding on a host. He also showed that the majority of I. ricinus individuals of the three stages (larva, nymph and adult) feed on only a few vertebrate host species (rodents, thrushes and deer, respectively). Using camera traps, Hofmeester showed that the presence of deer, such as Roe deer and Red deer, was a more important determinant of I. ricinus density than the number of deer available to ticks in twenty forested areas in the Netherlands. Ixodes ricinus densities were significantly reduced after two years of excluding deer by fencing four 0.75 ha forest plots in a forest near Apeldoorn, the Netherlands. Therefore, tick-borne disease risk can be reduced by placing fences around small forested areas with a high recreational pressure.

Hofmeester showed that tick burdens on rodents were higher in areas with large numbers of deer, while they were lower in areas with large numbers of carnivores. These differences in tick burden on rodents between areas were strongly correlated to the number of questing nymphs in the vegetation that were infected with tick-borne pathogens that are transmitted by rodents. This implies that changes in vertebrate assemblage can lead to cascading effects on rodent-transmitted tick-borne disease risk, via larval burden on rodents. Furthermore, Hofmeester found that the percentage of ticks infected with a specific pathogen was correlated to the number of animals in an area that could transmit this pathogen, while this percentage decreased with the number of animals that could not transmit this pathogen. These parameters were, however, not correlated to species richness, something that was expected based on the dilution effect of species richness hypothesis. Therefore, there is no support for a dilution effect of species richness on tick-borne pathogens in the Netherlands.

In his synthesis, Hofmeester presents a mathematical model in which the importance of spatial behaviour of hosts for tick-borne pathogens is shown and he proclaims the need for the integration of the field of behavioural ecology into disease ecology to better understand the effect of changes in vertebrate assemblages on pathogen prevalence and ultimately, disease risk. The data presented in this thesis show that it is not host diversity but the presence, abundance and behaviour of specific host species that drives tick-borne pathogen dynamics (identity effect). Vertebrate species change their behaviour in the presence or absence of predators and competitors. Hofmeester shows that this, theoretically, can have a major influence on the density of infected nymphs in the vegetation. Therefore, behavioural changes of reservoir-competent hosts should be taken into account when modelling the effect of changes in vertebrate assemblage composition on tick-borne disease risk.

The behaviour of vertebrate species in Europe is changing, as multiple species have adapted to human-dominated and fragmented landscapes. The adaptation of small mammals, thrushes and deer to fragmented landscapes might be one of the driving factors behind the increase in tick-borne disease incidence in Europe. A further adaptation of important host species to urbanized landscapes might be expected as these are the safest areas for vertebrate species trying to avoid predation. This might result in an increase in population density of reservoir-competent host species in urban areas with a corresponding increase in tick-borne pathogen prevalence and therefore, tick-borne disease risk.

Concluding, our world is changing and as a consequence vertebrate assemblages are also changing. This may lead to changes in I. ricinus density and infection prevalence with tick-borne pathogens. From the studies presented in his thesis Hofmeester concludes that the abundance and behaviour of several host species (e.g., Bank vole, Blackbird, Red deer, Red fox, Roe deer, and Wood mouse) determines tick-borne disease risk. Therefore, studying the drivers of animal abundance and behaviour related to ticks and pathogens will be the next step in better understanding and describing tick-borne disease risk. The ecology of tick-borne pathogens is very complex and targeting vertebrate hosts for intervention strategies will be both inefficient and costly due to the intricate interplay between multiple vertebrate host species. Therefore, Hofmeester concludes that prevention of tick bites is the best way to reduce tick-borne disease incidence.

Foraging behaviour of parasitoids in multi-herbivore communities
Rijk, M. de - \ 2016
Wageningen University. Promotor(en): Marcel Dicke, co-promotor(en): Erik Poelman. - Wageningen : Wageningen University - ISBN 9789462576377 - 217 p.
016-3931 - parasitoids - parasitoid wasps - feeding behaviour - plant-herbivore interactions - hosts - host parasite relationships - host preferences - host-seeking behaviour - cotesia glomerata - pieris brassicae - brassica oleracea - parasitoïden - sluipwespen - voedingsgedrag - plant-herbivoor relaties - gastheren (dieren, mensen, planten) - gastheer parasiet relaties - gastheerpreferenties - gedrag bij zoeken van een gastheer

Foraging behaviour of parasitoids in multi-herbivore communities

Parasitic wasps, or parasitoids, use herbivore-induced plant volatiles and infochemicals produced directly by the herbivore to locate their herbivorous hosts. This process could be interrupted by the presence of herbivores that are not suitable for the development of parasitoid offspring. These non-host herbivores could affect the behaviour of parasitoids both when parasitoids are foraging for host-infested plants by using plant volatiles and when parasitoids are foraging for hosts on the plant by using herbivore infochemicals.

The aim of this thesis was to study the impact of non-host presence on the parasitoid-host-food plant complex of the parasitoid Cotesia glomerata with its host caterpillar Pieris brassicae and a monoculture of the cultivated plant Brassica oleracea. To study the influence of non-hosts on the plant-volatile-based searching behaviour of the parasitoid, a wind-tunnel set-up in the laboratory was used. In this set-up, the parasitoids were given a choice between two plants or between the leaves of one plant. The plant/leaf on which the parasitoid landed was considered the preferred plant/leaf. A second laboratory set-up was used to study the influence of non-host herbivores on the host-infochemical-based searching behaviour of the parasitoid. In this on-plant experiment, the behaviour of the parasitoid was observed after landing on the plant. The influence of non-hosts on the combination of plant-volatile-based and host-infochemical-based searching, i.e. the total foraging efficiency of the parasitoid, was investigated using an outdoor tent set-up in an agricultural field. In this semi-field experiment, parasitoids were allowed to parasitize their hosts in a non-host environment for one to three days.

This thesis firstly shows that the feeding guild of non-host herbivores influenced the foraging behaviour of C. glomerata. Leaf-chewing non-hosts negatively impacted the plant-volatile-based searching behaviour of the parasitoid, whereas phloem-feeding non-hosts positively impacted the host-infochemical-based searching. The resulting host-finding efficiency was in general positively affected by phloem-feeding non-hosts. Secondly, the position of host and non-host herbivores on the plant affected the plant-volatile-based and the host-infochemical-based foraging behaviour of the parasitoid, but not the host-finding efficiency. An unnatural distribution of herbivores over the plant (host feeding on old leaf, non-host feeding on young leaf), negatively affected the choice of the parasitoid for a leaf to land on, i.e. the parasitoid more often landed on the non-host infested leaf. Combined feeding by the host and non-host on one leaf positively affected the number of hosts parasitized on that plant compared with the number of hosts parasitized when herbivores were separated. However, the parasitoid was able to compensate for these effects as a result of which the foraging efficiency was unaltered. Thirdly, the density of non-hosts did influence the plant-volatile-based searching of the parasitoid. A high non-host density negatively affected parasitoid preference for host-infested plants. However, the host-infochemical-based foraging and the total foraging efficiency remained unaffected. Fourthly, rather than the species diversity, the species identity of non-host herbivores had an influence on parasitoid host-infochemical-based searching. One of the tested non-host species negatively affected the behaviour of the parasitoid when searching on the plant. However, neither non-host species identity nor diversity affected plant-volatile-based searching of the parasitoid. Fifthly, this thesis investigated if a parasitoid could learn to associate non-host cues with the presence of hosts and if the parasitoid changed the parasitization preference accordingly. After receiving a learning experience, the parasitoid showed an altered landing preference for infested plants according to the learned cues. However, in an outdoor tent set-up, the parasitoid did not show an altered parasitization preference.

The results of this thesis show that non-host herbivore traits can affect the different phases of parasitoid foraging either positively, negatively or neutrally. The non-host effect on the total foraging efficiency is not necessarily a result of the sum of the effects on the first and the second foraging phase. In fact, the results of two out of three outdoor-tent experiments that investigated the foraging efficiency of the parasitoid showed no non-host effect, while the separate foraging phases were affected by non-host presence.

It is concluded that the foraging efficiency of the parasitoid C. glomerata when searching for its host P. brassicae is not strongly affected by non-host herbivore presence. The use of herbivore-induced plant volatiles by C. glomerata during this foraging process is not interrupted by non-host herbivores. It is advised to consider all phases of the foraging process in studies of parasitoid foraging behaviour, preferably in one experiment that covers the whole searching process. Altogether, this thesis gives a clear and comprehensive overview of the impact of non-host presence on a parasitoid-host-food plant complex and it thereby contributes to the fundamental knowledge of insect foraging in a multi-herbivore context.

Tonderzwammen en insecten
Moraal, L.G. - \ 2015
Vakblad Natuur Bos Landschap 12 (2015)120. - ISSN 1572-7610 - p. 20 - 21.
fomes fomentarius - insecten - bedreigde soorten - soorten - parasieten - coleoptera - gastheer parasiet relaties - insects - endangered species - species - parasites - host parasite relationships
Parasieten op bomen, zijn op hun beurt ook weer een plek waar allerlei soorten voorkomen. Op de zeldzame tonderzwam kunnen zich unieke insectencombinaties ontwikkelen. Nu de tonderzwam aan een opmars bezig is, komen ook deze bijzondere insecten weer terug.
Actuele ontwikkelingen in de preventie en bestrijding van maagdarmwormen bij schapen : Kernpunten uit een literatuurstudie
Bokma-Bakker, M.H. ; Antonis, A.F.G. ; Ploeger, H. ; Vellema, P. ; Verkaik, J.C. - \ 2014
Wageningen UR/Universiteit Utrecht
schapenhouderij - maagdarmziekten - wormen - dierparasitaire nematoden - nematodirus battus - haemonchus contortus - teladorsagia circumcincta - schapenziekten - gastheer parasiet relaties - graslandbeheer - ziektebestrijding - dierveredeling - selectief fokken - voedersupplementen - schapenvoeding - sheep farming - gastrointestinal diseases - helminths - animal parasitic nematodes - sheep diseases - host parasite relationships - grassland management - disease control - animal breeding - selective breeding - feed supplements - sheep feeding
De schapensector gaat de parasitaire resistentie-ontwikkeling terugdringen. Ze wil dat doen door verbetering van de preventie en de bestrijding van maagdarmwormen. Experts hebben in 2013 een literatuurstudie uitgevoerd. Hierin zijn de belangrijkste binnen- en buitenlandse innovatieve ontwikkelingen voor verlaging van de infectiedruk opgenomen en vertaald naar toepasbaarheid onder de Nederlandse omstandigheden. Bekeken zijn de gebieden fokkerij, voeding, vaccinatie, beweiding, inzet van natuurlijke middelen en diagnostiek. In deze brochure zijn de belangrijkste bevindingen samengevat.
Lokschapen vangen teken in het bos
Sikkema, A. ; Wieren, S.E. van - \ 2014
Wageningen UR/Stichting voor Duurzame Ontwikkeling
schapen - gastheer parasiet relaties - vangmethoden - lokken - natuurgebieden - borrelia burgdorferi - humane ziekten - lyme-ziekte - infectieziekten - insecticiden - experimenten - wetenschappelijk onderzoek - bosecologie - sheep - host parasite relationships - trapping - baiting - natural areas - human diseases - lyme disease - infectious diseases - insecticides - experiments - scientific research - forest ecology
De Wageningse onderzoeker Sip van Wieren wil lokschapen inzetten om teken weg te vangen in natuurgebieden. Op die manier kunnen schaapskuddes er voor zorgen dat mensen prettig kunnen recreëren in het bos.
Lokschapen tegen teken
Wieren, S.E. van - \ 2014
Wageningen UR
schapen - gastheer parasiet relaties - lokken - humane ziekten - lyme-ziekte - vangmethoden - experimenten - natuurgebieden - bosecologie - sheep - host parasite relationships - baiting - human diseases - lyme disease - trapping - experiments - natural areas - forest ecology
Teken vormen een lastig probleem voor bezoekers van natuurterreinen en bossen. Onderzoekers gaan nu met ‘lokschapen’ teken vangen.
Bacterie beschermt zalmeitje tegen schimmel (interview met I. de Bruijn en Y. Liu)
Ramaker, R. ; Bruijn, I. de; Liu, Y. - \ 2014
Resource: weekblad voor Wageningen UR 8 (2014)16. - ISSN 1874-3625 - p. 9 - 9.
aquacultuur - zalmteelt - gastheer parasiet relaties - saprolegnia - oömyceten - visseneieren - actinobacteria - wetenschappelijk onderzoek - aquaculture - salmon culture - host parasite relationships - oomycetes - fish eggs - scientific research
Een bacterie die leeft op zalmeitjes, beschermt zijn gastheer tegen een schadelijke schimmelsoort. Dit ontdekten ecologen van Wageningen Universiteit en het NIOO. De vinding moet ervoor zorgen dat minder eitjes sterven tijdens de zalmkweek.
Climbing the walls : behavioural manipulation of insects by baculoviruses
Houte, S. van - \ 2014
Wageningen University. Promotor(en): Just Vlak; Monique van Oers, co-promotor(en): Vera Ros. - Wageningen : Wageningen University - ISBN 9789461738301 - 228
baculoviridae - insecten - rupsen - lepidoptera - gastheer parasiet relaties - diergedrag - gedragsveranderingen - hyperactiviteit - moleculaire biologie - insects - caterpillars - host parasite relationships - animal behaviour - behavioural changes - hyperactivity - molecular biology

Parasites often have severe effects on their hosts by causing developmental and physiological alterations in their hosts. These alterations may contribute to parasite growth, reproduction and survival. For example, host development may be inhibited so that more nutrients become available for the parasite. Parasites can also interfere with host behavior as a strategy to increase parasite survival or transmission. This phenomenon is known as ‘parasitic manipulation’ or ‘behavioural manipulation’. Although many examples of parasitic manipulation are known, the genetic basis underlying such manipulations is largely unexplored. A thorough understanding of how parasites manipulate their hosts’ behavior is therefore lacking, but it can be hypothesized that parasites carry specific genes that induce these behavioural alterations. Such ‘behavioural’ parasite genes likely affect one or more host proteins directly or via the expression of specific target genes in the host, which subsequently leads to altered behaviour. Understanding the details of such interactions between parasite and host is important as parasitic manipulation is thought to be wide spread in nature and to be a strong driver of the co-evolutionary arms race between parasite and host. Furthermore, the strategies employed by parasites to alter behavior likely provide important insights in the molecular mechanism of many behavioural processes. Chapter 2 of this thesis reviews our current understanding of the mechanisms of behavioural manipulation in invertebrates. It discusses known examples of behavioural manipulation and the present knowledge on the mechanistic basis of these manipulations. Furthermore, an overview of host genes and proteins that play a conserved role in behavioural traits in different invertebrate species is given. These genes and proteins are worthwhile to be studied in more detail in the context of parasitic manipulation, as they might be suitable targets for parasites to induce behavioural changes.

This thesis focuses on behavioural manipulation in insect hosts by baculoviruses. Baculoviruses are DNA viruses that infect the larval stages of mainly lepidopteran insects. These viruses alter host behaviour in multiple ways. They induce hyperactivity in the larvae, which likely contributes to virus dispersal over a large area. In addition, baculoviruses alter host climbing behaviour leading to death at elevated positions, a phenomenon known as ‘tree-top disease’ or ‘Wipfelkrankheit’. This latter manipulation is thought to contribute to optimal virus dispersal on plant foliage. In the research described in this thesis baculoviruses and their lepidopteran insect hosts are used as a model system to study molecular mechanisms of behavioural manipulation. In Chapter 3 of this thesis the involvement of the protein tyrosine phosphatase (ptp) gene from the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) in the induction of hyperactivity of the beet armyworm Spodoptera exigua was studied. A homolog of this gene in Bombyx mori nucleopolyhedrovirus (BmNPV) was previously shown to be important in hyperactivity in the silkworm B. mori. The results in Chapter 3 showed that the AcMNPV ptp gene induces hyperactive behaviour in S. exigua larvae and that the phosphatase activity of the encoded PTP enzyme is crucial for this behavioural change. Phylogenetic inference revealed that the baculovirus ptp is presumably transferred from a (ancestral) lepidopteran host to a baculovirus. Within the family Baculoviridae, ptp is only present in group I NPVs, which are a group of phylogenetically related baculoviruses. It is hypothesized that ptp-induced hyperactivity is an evolutionarily conserved strategy of group I NPVs to manipulate host behaviour.

To obtain insights into the target proteins of the baculovirus PTP enzyme to achieve hyperactive behaviour in infected caterpillars, a PTP substrate analysis was performed. Chapter 4 describes host and viral proteins that were found to co-purify with AcMNPV PTP. Many of these host proteins are known to be important in signalling pathways and behavioural traits. For one of these proteins, 14-3-3 z, mRNA transcript levels were found to be significantly higher in wild type AcMNPV-infected S. exigua larvae as compared to larvae infected with a mutant virus from which the ptp gene has been deleted (AcMNPV Δptp). The 14-3-3 protein is a known activator of the enzymes tryptophan hydroxylase and tyrosine hydroxylase, which in turn are required for synthesis of the neurotransmitters serotonin and dopamine. These signalling molecules are both important determinants in hyperactive behaviour in various organisms, and are associated with behavioural manipulation in several parasite-host systems. In Chapter 9 a model is proposed of how the putative interaction between baculovirus PTP and host 14-3-3 zmay lead to hyperactive behaviour.

Within the baculoviruses two different genes that encode protein tyrosine phosphatases, ptp and ptp2, are found. While the ptp gene induces hyperactivity (described in Chapter 3), no function has yet been assigned to the ptp2 gene. Chapter 5 describes the functional

characterization of the baculovirus ptp2 gene. PTP2 protein carries a conserved consensus sequence that is characteristic for mitogen-activated protein kinase (MAPK) phosphatases. SeMNPV ptp2 induced a mild apoptosis and caspase activation in insect cells upon transient expression, which may be related to its putative function as MAPK phosphatase. Several host proteins that co-purified with SeMNPV PTP2 have known functions in apoptosis and/or MAPK signalling, rendering them promising candidate proteins to be involved in SeMNPV PTP2-induced apoptosis and possibly MAPK signalling. Whether PTP2 also has any behavioural effect is unknown, but the data from this chapter indicate that PTP2 likely has a cellular function during virus infection.

Baculoviruses are known to alter host climbing behaviour, commonly leading to death at elevated positions (tree-top disease). In Chapter 6 the hypothesis was tested that baculovirus-induced hyperactive behaviour and tree-top disease are induced by a single baculovirus gene. To this aim the effect of the hyperactivity-inducing ptp gene (Chapter 3) on tree-top disease was investigated. The results demonstrated that AcMNPV ptp, known to cause hyperactive behaviour in S. exigua, is not involved in tree-top disease in this host. This indicates that hyperactivity and tree-top disease induced by baculoviruses are governed by independent mechanisms. Furthermore, a moulting-dependent effect on tree-top disease in S. exigua was found, which may relate to physiological and/or ecological differences between moulted and unmoulted larvae. In the next chapter (Chapter 7) the effect of AcMNPV infection on tree-top disease was investigated for two different host species, Trichoplusia ni and S. exigua. Data show that in T. ni larvae AcMNPV induces tree-top disease, causing death at elevated positions. In contrast, in S. exigua a moulting-dependent effect on the height at death was observed, as was also described in Chapter 6. Furthermore, in this chapter the role of the AcMNPV egt gene, encoding ecdysteroid UDP glucosyl transferase, on tree-top disease in T. ni and S. exigua larvae was analysed. A homolog of this gene causes tree-top disease in Lymantria dispar larvae infected with L. dispar (Ld) MNPV. The results (Chapter 7) show that AcMNPV egt does not play a role in the observed death at elevated positions in the two host systems studied. This indicates that the role of egt in tree-top disease may not be conserved among members of the family Baculoviridae.

In addition to the mechanisms employed by the generalist baculovirus AcMNPV to alter climbing behaviour, the effect of the specialist baculovirus S. exigua (Se) MNPV on tree-top disease in its only known host S. exigua was studied. In Chapter 8 it is shown that SeMNPV induces tree-top disease by triggering an aberrant response to light, and this positive phototaxis leads to death at elevated positions. A hypothesis is put forward that SeMNPV hijacks a host behavioural pathway that is involved in light perception to induce this positive phototactic response.

Overall, the results of this thesis show that hyperactivity and tree-top disease are induced by baculoviruses through independent mechanisms and that distinct baculovirus species presumably use different genes and proximate mechanisms to induce tree-top disease. While the baculovirus ptp gene induces hyperactivity, possibly by targeting host 14-3-3 z, the baculovirus ptp2 gene may function as a pro-apoptotic gene. The baculovirus egt gene does not have a conserved function in tree-top disease, indicating that other viral genes may underlie this host manipulative strategy. This thesis also demonstrates that tree-top disease in SeMNPV-infected caterpillars is the result of a strong attraction to light.

Parasitic manipulation is a fascinating biological phenomenon that can provide crucial information on how behavioural traits are controlled at the molecular level. The research described in this thesis provides several new insights in the mechanisms by which parasites manipulate the behaviour of their hosts.

Meer teken in de natuur : een goed teken?
Sprong, H. ; Takken, W. - \ 2013
Zoogdier 24 (2013)2. - ISSN 0925-1006 - p. 1 - 4.
tekenbesmettingen - natuurgebieden - fauna - gastheer parasiet relaties - zoogdieren - tick infestations - natural areas - host parasite relationships - mammals
Veel natuurliefhebbers weten dat teken de ziekte van Lyme kunnen overbrengen. Dat zoogdieren daarbij een dubbele rol spelen, is veel minder bekend. Toename van de ziekte heeft gezorgd voor meer onderzoek naar de ziekte en de teken. Wat weten we nu over de overdracht van die ziekte, de rol van zoogdieren hierin en de impact van meer natuur in Nederland
De bijzondere levensloop van de sluipwesp Acrodactyla quadrisculpta op de schaduwstrekspin Tetragnata montana
Belgers, J.D.M. ; Zwakhals, C.J. ; Helsdingen, P.J. van - \ 2013
Nederlandse Faunistische Mededelingen 39 (2013). - ISSN 0169-2453 - p. 1 - 6.
sluipwespen - gastheer parasiet relaties - gedragspatronen - parasitoid wasps - host parasite relationships - behaviour patterns
Sluipwespen van de groep van de Polysphinctini hebben een bijzondere levenswijze. Het vrouwtje van wesp legt een eitje op het achterlijf van een spin. Wanneer het eitje is uitgekomen brengt de larve haar hele leven op het achterlijf van de spin door. Ze maakt kleine wondjes in de huid en voedt zich met lichaamsvloeistof van de spin. Na verloop van tijd ontwikkelt de larve bulten op de rug, een teken dat ze bijna volgroeid is. Ze zuigt dan de spin leeg, de 'grote slurp' genaamd, en verpopt zich in het web. In dit artikel wordt de levenswijze van één van deze soorten, Acrodactyla quadrisculpta, voor het eerst beschreven en geïllustreerd.
Ecology of parasite-vector interactions
Takken, W. ; Koenraadt, C.J.M. - \ 2013
Wageningen : Wageningen Academic Publishers (Ecology and control of vector-borne diseases vol. 3) - ISBN 9789086861880 - 272
gastheer parasiet relaties - parasieten - vectoren, ziekten - ziekten overgebracht door vectoren - vectorbestrijding - ecologie - medische entomologie - host parasite relationships - parasites - disease vectors - vector-borne diseases - vector control - ecology - medical entomology
Vector-borne diseases continue to be one of the most important determinants affecting human and animal health. Large numbers of people suffer from diseases like malaria, dengue, filariasis and leishmaniasis, especially in the tropics. Whereas these diseases were eradicated from the temperate climate zones, in recent years the rising incidence of 'emerging' vector-borne diseases such as bluetongue, West Nile Virus, Lyme disease, tick-borne encephalitis and the recent outbreaks of chikungunya and dengue in southern Europe provide evidence that these diseases are resilient and can disperse to other regions and continents where before they were not present or relevant. Many tools for the management of vector-borne diseases are currently under pressure because of increasing drug and insecticide resistance, as well as the realization of biological variation of parasites and vectors and their ecosystems. At the same time, progress in our understanding of genetics, immunology, population biology and epidemiology allow for a better understanding of parasite-vector interactions. Here the state-of-the-art of these interactions is being reviewed, and means for using this information for advanced strategies of vector-borne disease control are proposed. This 3rd edition of ECVD aims to provide a rapid overview of recent developments in the field of parasite-vector interactions and how this can be used for more effective and sustainable disease control.
The role and evolution of fungal effectors in plant pathogenesis
Jonge, R. de - \ 2012
Wageningen University. Promotor(en): Pierre de Wit, co-promotor(en): Bart Thomma. - S.l. : s.n. - ISBN 9789461733917 - 148
plantenziekteverwekkende schimmels - moleculaire plantenziektekunde - evolutie - gastheer parasiet relaties - pathogenese - genomica - immuniteit - genomen - plant pathogenic fungi - molecular plant pathology - evolution - host parasite relationships - pathogenesis - genomics - immunity - genomes - cum laude
cum laude graduation (with distinction)
Temporal dynamics of induced responses in Brassica juncea
Mathur, V. - \ 2012
Wageningen University. Promotor(en): Louise Vet; N.M. van Dam, co-promotor(en): A.S. Reddy. - S.l. : s.n. - ISBN 9789461733085 - 219
brassica juncea - insectenplagen - insect-plant relaties - gastheer parasiet relaties - herbivoren - brassicaceae - entomologie - ecologie - herbivoor-geinduceerde plantengeuren - insect pests - insect plant relations - host parasite relationships - herbivores - entomology - ecology - herbivore induced plant volatiles

Plants induce a suite of direct and indirect responses after herbivore attack. For utilizing these plant attributes in agriculture, it is important to compare the relative importance of these two defence types in the same plant species. Precise timing of these responses is vital for their effect on the herbivores feeding on the plant.
In my thesis, I present an analysis of the temporal dynamics of various direct and indirect responses in Indian/ Brown mustard, Brassica juncea due to herbivory by a generalist Spodoptera spp, a specialist Plutella xylostella or both of these herbivores together. Morphological (leaf size and trichome densities) and chemical (volatiles, glucosinolates, amino acids, sugars) responses were analysed over temporal range of 24 hours to 20 days. The effect of direct systemic responses was assessed using a specialist (Plutella xylostella) and a generalist (Spodoptera litura) herbivore. In addition, to investigate indirect responses, orientation experiments were conducted on the generalist (Cotesia marginiventris) and specialist (C. plutellae) parasitoids. Results were validated with analysis of genes involved in signalling and biosynthetic pathways that govern the expression of these responses.
For the first time, the presence of extrafloral nectar (EFN) in Brassicaceae is being reported. Their sugar and amino acid contents were measured in five different varieties of B. juncea. The indirect function of these EFN droplets was assessed by testing their inducibility and attraction and survival of parasitoids on them.
These studies thus show that although morphological responses are slower than chemical responses, they also contribute to induced plant resistance in a relatively short time span. Moreover, before considering induced responses as resistance factors, their effect should be assessed at different points in time with both generalist and specialist herbivores.

The ecology of plant secondary metabolites : from genes to global processes
Iason, G.R. ; Dicke, M. ; Hartley, S.E. - \ 2012
Cambridge [etc.] : Cambridge University Press (Ecological reviews ) - ISBN 9780521157124 - 335
secundaire metabolieten - planten - plantensamenstelling - verdedigingsmechanismen - ziekteresistentie - gastheer parasiet relaties - ecologie - genen - biosynthese - herbivoren - secondary metabolites - plants - plant composition - defence mechanisms - disease resistance - host parasite relationships - ecology - genes - biosynthesis - herbivores
Plant secondary metabolites (PSM) such as terpenes and phenolic compounds are known to have numerous ecological roles, notably in defence against herbivores, pathogens and abiotic stresses and in interactions with competitors and mutualists. This book reviews recent developments in the field to provide a synthesis of the function, ecology and evolution of PSM, revealing our increased awareness of their integrative role in connecting natural systems. It emphasises the multiple roles of secondary metabolites in mediating the interactions between organisms and their environment at a range of scales of ecological organisation, demonstrating how genes encoding for PSM biosynthetic enzymes can have effects from the cellular scale within individual plants all the way to global environmental processes. A range of recent methodological advances, including molecular, transgenic and metabolomic techniques, are illustrated and promising directions for future studies are identified, making this a valuable reference for researchers and graduate students in the field.
Fusarium Screen voor tulp: inzicht in de interactie - inzicht in voorkomen
Boer, M. de; Breeuwsma, S.J. ; Duyvesteijn, R.G.E. ; Lee, T.A.J. van der; Jalink, H. ; Waalwijk, C. ; Dijksterhuis, J. - \ 2012
fusarium oxysporum - tulpen - gastheer parasiet relaties - plantenziekteverwekkende schimmels - bloembollen - plantenziektekunde - tulips - host parasite relationships - plant pathogenic fungi - ornamental bulbs - plant pathology
Poster met onderzoeksinformatie.
Tick tactics : interactions between habitat characteristics, hosts and microorganisms in relation to the biology of the sheep tick Ixodes ricinus
Gassner, F. - \ 2010
Wageningen University. Promotor(en): Willem Takken; Marcel Dicke, co-promotor(en): Leo van Overbeek. - [S.l.] : S.n. - ISBN 9789085858058 - 162
ixodes ricinus - ziekten overgebracht door teken - metastigmata - borrelia burgdorferi - gastheer parasiet relaties - habitats - distributie - ruimtelijke variatie - variatie in de tijd - nederland - tickborne diseases - host parasite relationships - distribution - spatial variation - temporal variation - netherlands
Evolutionary consequences of reproductive parasites in spider mites
Ros, V.I.D. - \ 2010
Entomologische Berichten 70 (2010). - ISSN 0013-8827 - p. 154 - 161.
tetranychidae - gastheer parasiet relaties - host parasite relationships
Een vlinderpopulatie waarin alle mannelijke nakomelingen doodgaan, een mijtensoort die zich geheel aseksueel voortplant, of een pissebed die eigenlijk man is maar zich voortplant als vrouw - dit zijn enkele voorbeelden van merkwaardige verschijnselen die volop te vinden zijn in het veld, en die vaak door zelfzuchtige bacterien veroorzaakt worden. Hoe kan dat? Dit betreft bacterien die de gastheer infecteren en verticaal, van moeder op nakomelingen, worden doorgegeven.
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