Publications

bacterial infection changes the elemental composition of daphnia magna.	1. an animal's elemental composition can be an important indicator of its physiological state and role in ecosystem nutrient cycling. we examined the interactive effects of bacterial (pasteuria ramosa) infection and phosphorus (p)-poor food on the body stoichiometry of daphnia magna. daphnia were exposed to or held free of a bacterial parasite and fed algal food of different c:p ratios (100-500) over a 28-day period. 2. to assess the effects of exposure and infection on daphnia stoichiometry, we ...	2008	18631369
host-parasite coevolution: insights from the daphnia-parasite model system.	daphnia and its parasites have become recognized as a model system for studying the epidemiological, evolutionary and genetic interactions between hosts and parasites. the key advantages of the daphnia-parasite system are the propagation of the host as iso-female lines, that is clonal, but at the same time the possibility to cross lines. furthermore, daphnia have diverse parasites, including bacteria, fungi, microsporidia and helminths, which can be kept in culture with the hosts. for two parasi ...	2008	18556238
experimental evolution of field populations of daphnia magna in response to parasite treatment.	although there is little doubt that hosts evolve to reduce parasite damage, little is known about the evolutionary time scale on which host populations may adapt under natural conditions. here we study the effects of selection by the microsporidian parasite octosporea bayeri on populations of daphnia magna. in a field study, we infected replicated populations of d. magna with the parasite, leaving control populations uninfected. after two summer seasons of experimental evolution (about 15 genera ...	2008	18462312
responses of a bacterial pathogen to phosphorus limitation of its aquatic invertebrate host.	host nutrition is thought to affect the establishment, persistence, and severity of pathogenic infections. nutrient-deficient foods possibly benefit pathogens by constraining host immune function or benefit hosts by limiting parasite growth and reproduction. however, the effects of poor elemental food quality on a host's susceptibility to infection and disease have received little study. here we show that the bacterial microparasite pasteuria ramosa is affected by the elemental nutrition of its ...	2008	18409420
the effects of multiple infections on the expression and evolution of virulence in a daphnia-endoparasite system.	multiple infections of a host by different strains of the same microparasite are common in nature. although numerous models have been developed in an attempt to predict the evolutionary effects of intrahost competition, tests of the assumptions of these models are rare and the outcome is diverse. in the present study we examined the outcome of mixed-isolate infections in individual hosts, using a single clone of the waterflea daphnia magna and three isolates of its semelparous endoparasite paste ...	2008	18384658
variable-number-of-tandem-repeats analysis of genetic diversity in pasteuria ramosa.	variable-number-of-tandem-repeats (vntr) markers are increasingly being used in population genetic studies of bacteria. they were recently developed for pasteuria ramosa, an endobacterium that infects daphnia species. in the present study, we genotyped p. ramosa in 18 infected hosts from the united kingdom, belgium, and two lakes in the united states using seven vntr markers. two daphnia species were collected: d. magna and d. dentifera. six loci showed length polymorphism, with as many as five ...	2008	18214600
a quantitative test of the relationship between parasite dose and infection probability across different host-parasite combinations.	epidemiological models generally assume that the number of susceptible individuals that become infected within a unit of time depends on the density of the hosts and the concentration of parasites (i.e. mass-action principle). however, empirical studies have found significant deviations from this assumption due to biotic and abiotic factors, such as seasonality, the spatial structure of the host population and host heterogeneity with respect to immunity and susceptibility. in this paper, we exam ...	2008	18198145
genetic and immunological comparison of the cladoceran parasite pasteuria ramosa with the nematode parasite pasteuria penetrans.	pasteuria penetrans, an obligate endospore-forming parasite of meloidogyne spp. (root knot nematodes), has been identified as a promising agent for biocontrol of these destructive agricultural crop pests. pasteuria ramosa, an obligate parasite of water fleas (daphnia spp.), has been shown to modulate cladoceran populations in natural ecosystems. selected sporulation genes and an epitope associated with the spore envelope of these related species were compared. the sige and spoiiaa/spoiiab genes ...	2008	17933927
parasite variation and the evolution of virulence in a daphnia-microparasite system.	understanding genetic relationships amongst the life-history traits of parasites is crucial for testing hypotheses on the evolution of virulence. this study therefore examined variation between parasite isolates (the bacterium pasteuria ramosa) from the crustacean daphnia magna. from a single wild-caught infected host we obtained 2 p. ramosa isolates that differed substantially in the mortality they caused. surprisingly, the isolate causing higher early mortality was, on average, less successful ...	2008	18005474
inter- and intra-specific cuticle variation between amphimictic and parthenogenetic species of root-knot nematode (meloidogyne spp.) as revealed by a bacterial parasite (pasteuria penetrans).	specific host-parasite interactions exist between species and strains of plant parasitic root-knot nematodes and the gram-positive bacterial hyperparasite pasteuria penetrans. this bacterium produces endospores that adhere to the cuticle of migrating juveniles, germinate and colonise the developing female within roots. endospore attachment of p. penetrans populations to second-stage juveniles of the root-knot nematode species meloidogyne incognita and meloidogyne hapla showed there were interact ...	2008	18171577
temperature-dependent costs of parasitism and maintenance of polymorphism under genotype-by-environment interactions.	the maintenance of genetic variation for infection-related traits is often attributed to coevolution between hosts and parasites, but it can also be maintained by environmental variation if the relative fitness of different genotypes changes with environmental variation. to gain insight into how infection-related traits are sensitive to environmental variation, we exposed a single host genotype of the freshwater crustacean daphnia magna to four parasite isolates (which we assume to represent dif ...	2008	18557795
prophenoloxidase in daphnia magna: cdna sequencing and expression in relation to resistance to pathogens.	invertebrates utilise the innate immune system when defending against pathogenic attack. however, except for some effectors as prophenoloxidase (propo), the innate immune response is less well understood outside model insect species, and its role in natural host-pathogen systems is generally not well documented. we have therefore initiated studies on the immune response of the crustacean daphnia when exposed to the specialist endobacterial pathogen, pasteuria ramosa. this study was focused on th ...	2009	19103220
understanding the interaction between an obligate hyperparasitic bacterium, pasteuria penetrans and its obligate plant-parasitic nematode host, meloidogyne spp.	pasteuria penetrans is an endospore-forming bacterium, which is a hyperparasite of root-knot nematodes meloidogyne spp. that are economically important pests of a wide range of crops. the life cycle of the bacterium and nematode are described with emphasis on the bacterium's potential as a biocontrol agent. two aspects that currently prohibit the commercial development of the bacterium as a biocontrol agent are the inability to culture it outside its host and its host specificity. vegetative gro ...	2009	19289196
an ancient immunity gene duplication in daphnia magna: rna expression and sequence analysis of two nitric oxide synthase genes.	no (nitric oxide) is a highly reactive free radical gas thought to play a major role in the invertebrate immune response by harming pathogens and limiting their growth. here we report on studies of nitric oxide synthase (nos) genes in the crustacean daphnia, one of the few non-insect arthropod models used to study host-pathogen interactions. while the nos gene is found as a single copy in other invertebrates, we found two copies (nos1 and nos2), which a phylogenetic reconstruction showed to be t ...	2009	19416737
measuring parasite fitness under genetic and thermal variation.	accurate measures of parasite fitness are essential to study host-parasite evolution. parasite fitness depends on several traits involved in establishing infection, growth and transmission. individually, these traits provide a reasonable approximation of fitness, but they may also be under the shared control of both host and parasite genetics (g(h) x g(p) interactions), or be differentially sensitive to environmental variation. using the natural host-parasite system daphnia magna-pasteuria ramos ...	2009	19455181
identification of a polymorphic collagen-like protein in the crustacean bacteria pasteuria ramosa.	pasteuria ramosa is a spore-forming bacterium that infects daphnia species. previous results demonstrated a high specificity of host clone/parasite genotype interactions. surface proteins of bacteria often play an important role in attachment to host cells prior to infection. we analyzed surface proteins of p. ramosa spores by two-dimensional gel electrophoresis. for the first time, we prove that two isolates selected for their differences in infectivity reveal few but clear-cut differences in p ...	2009	19770039
exploring the molecular landscape of host-parasite coevolution.	host-parasite coevolution is a dynamic process that can be studied at the phenotypic, genetic, and molecular levels. although much of what we currently know about coevolution has been learned through phenotypic measures, recent advances in molecular techniques have provided tools to greatly deepen this research. both the availability of full-genome sequences and the increasing feasibility of high-throughput gene expression profiling are leading to the discovery of genes that have a key role in a ...	2009	19843595
a method for release and multiple strand amplification of small quantities of dna from endospores of the fastidious bacterium pasteuria penetrans.	to establish a reliable protocol to extract dna from pasteuria penetrans endospores for use as template in multiple strand amplification, thus providing sufficient material for genetic analyses. to develop a highly sensitive pcr-based diagnostic tool for p. penetrans.	2010	20302597
genetic variation in the cellular response of daphnia magna (crustacea: cladocera) to its bacterial parasite.	linking measures of immune function with infection, and ultimately, host and parasite fitness is a major goal in the field of ecological immunology. in this study, we tested for the presence and timing of a cellular immune response in the crustacean daphnia magna following exposure to its sterilizing endoparasite pasteuria ramosa. we found that d. magna possesses two cell types circulating in the haemolymph: a spherical one, which we call a granulocyte and an irregular-shaped amoeboid cell first ...	2010	20534618
pathogen dose infectivity curves as a method to analyze the distribution of host susceptibility: a quantitative assessment of maternal effects after food stress and pathogen exposure.	stress conditions have been found to change the susceptibility of hosts or their offspring to infection. the usual method of testing at just one parasite dose level does not allow conclusions on the distribution of susceptibility. to better understand the epidemiology and evolution of host-parasite systems, however, knowledge about the distribution of host susceptibility, the parameters that characterize it, and how it changes in response to environmental conditions is required. we investigated ...	2010	19911987
transgenerational effects of poor elemental food quality on daphnia magna.	environmental effects on parents can strongly affect the phenotype of their offspring, which alters the heritability of traits and the offspring's responses to the environment. we examined whether p limitation of the aquatic invertebrate, daphnia magna, alters the responses of its offspring to inadequate p nutrition. mother daphnia consuming p-poor algal food produced smaller neonates having lower body p content compared to control (p-rich) mothers. these offspring from p-stressed mothers, when ...	2010	19957090
'candidatus pasteuria aldrichii' sp. nov., an obligate endoparasite of the bacterivorous nematode, bursilla sp.	a pasteuria species was discovered parasitizing the bacterivorous nematode, bursilla sp. from selected bermudagrass (cynodon sp.) field plots in davie, fl. soil containing this bacterium was isolated and supplied with bi-weekly inoculations of cultured bursilla sp. in order to build and maintain a source of endospores for continuous in vivo maintenance of the pasteuria for further study and characterization. 16s rdna sequence homology supported its congeneric ranking with other pasteuria species ...	2010	20870891
successfully resisting a pathogen is rarely costly in daphnia magna.	a central hypothesis in the evolutionary ecology of parasitism is that trade-offs exist between resistance to parasites and other fitness components such as fecundity, growth, survival, and predator avoidance, or resistance to other parasites. these trade-offs are called costs of resistance. these costs fall into two broad categories: constitutive costs of resistance, which arise from a negative genetic covariance between immunity and other fitness-related traits, and inducible costs of resistan ...	2010	21083915
cloning of the unculturable parasite pasteuria ramosa and its daphnia host reveals extreme genotype-genotype interactions.	the degree of specificity in host-parasite interactions has important implications for ecology and evolution. unfortunately, specificity can be difficult to determine when parasites cannot be cultured. in such cases, studies often use isolates of unknown genetic composition, which may lead to an underestimation of specificity. we obtained the first clones of the unculturable bacterium pasteuria ramosa, a parasite of daphnia magna. clonal genotypes of the parasite exhibited much more specific int ...	2010	21091597
identifying energy constraints to parasite resistance.	life-history theory suggests that energetically expensive traits may trade off against each other, resulting in costs associated with the development or maintenance of a particular phenotype. the deployment of resistance mechanisms during parasite exposure is one such trait, and thus their potential benefit in fighting off parasites may be offset by costs to other fitness-related traits. in this study, we used trade-off theory as a basis to test whether stimulating an increased development rate ...	2011	21210532
resolving the infection process reveals striking differences in the contribution of environment, genetics and phylogeny to host-parasite interactions.	infection processes consist of a sequence of steps, each critical for the interaction between host and parasite. studies of host-parasite interactions rarely take into account the fact that different steps might be influenced by different factors and might, therefore, make different contributions to shaping coevolution. we designed a new method using the daphnia magna - pasteuria ramosa system, one of the rare examples where coevolution has been documented, in order to resolve the steps of the i ...	2011	21342515
evolutionary ecotoxicology of pesticide resistance: a case study in daphnia.	natural populations that are exposed to pesticides in their environment may at the same time be exposed to natural stressors like parasites and predators, which may interact with pesticide exposure. this may not only impact target pest species but also a wide variety of non-target species. this review reports on a joint research program in the water flea daphnia magna, a non-target species often used as model organism in ecology and ecotoxicology. the focus is on different aspects that are of ke ...	2011	21380529
identification of new snp- based markers for inter and intra-species discrimination of obligate bacterial parasites (pasteuria spp.) of invertebrates.	protein encoding and 16s rrna genes of pasteuria penetrans populations from a wide range of geographic locations were examined. most inter-population single nucleotide polymorphisms (snps) were detected in the 16s rrna gene. however, in order to fully resolve all populations these were supplemented with snps from protein-encoding genes in a multi-locus snp typing approach. examination of individual 16s rrna gene sequences revealed the occurrence of 'cryptic' snps which were not present in the co ...	2011	21803895
characterisation of a large family of polymorphic collagen-like proteins in the endospore-forming bacterium pasteuria ramosa.	collagen-like proteins containing glycine-x-y repeats have been identified in several pathogenic bacteria potentially involved in virulence. recently, a collagen-like surface protein, pcl1a, was identified in pasteuria ramosa, a spore-forming parasite of daphnia. here we characterise 37 novel putative p. ramosa collagen-like protein genes (pcls). pcr amplification and sequencing across 10 p. ramosa strains showed they were polymorphic, distinguishing genotypes matching known differences in daphn ...	2011	21726633
Who benefits from reduced reproduction in parasitized hosts? An experimental test using the Pasteuria ramosa-Daphnia magna system.	SUMMARYWe investigated whether parasites or hosts benefit from reduced reproduction in infected hosts. When parasites castrate their hosts, the regain of host reproduction is necessary for castration to be a host adaptation. When infecting Daphnia magna with Pasteuria ramosa, in a lake water based medium, 49·2% of the castrated females regained reproduction. We investigated the relationship between castration level, and parasite and host fitness proxies to determine the adaptive value of host ca ...	2011	21854675
phenoloxidase but not lytic activity reflects resistance against pasteuria ramosa in daphnia magna.	the field of ecological immunology strongly relies on indicators of immunocompetence. two major indicators in invertebrates, the activity of phenoloxidase (po) and lytic activity have recently been questioned in studies showing that, across a natural range of baseline levels, these indicators did not predict resistance against a manipulated challenge with natural parasites. we confirmed this finding by showing that baseline levels of po and lytic activity in the host daphnia magna were not relat ...	2011	20810432
genetic variation for maternal effects on parasite susceptibility.	the expression of infectious disease is increasingly recognized to be impacted by maternal effects, where the environmental conditions experienced by mothers alter resistance to infection in offspring, independent of heritability. here, we studied how maternal effects (high or low food availability to mothers) mediated the resistance of the crustacean daphnia magna to its bacterial parasite pasteuria ramosa. we sought to disentangle maternal effects from the effects of host genetic background by ...	2011	21848987
Pasteuria endospores from Heterodera cajani (Nematoda: Heteroderidae) exhibit inverted attachment and altered germination in cross-infection studies with Globodera pallida (Nematoda: Heteroderidae).	The Pasteuria group of Gram-positive, endospore-forming bacteria are parasites of invertebrates and exhibit differences in host specificity. We describe a cross-infection study between an isolate of Pasteuria from pigeon pea cyst nematode, Heterodera cajani, which also infects the potato cyst nematode, Globodera pallida, from the United Kingdom. A proportion of the attached endospores, 13% on H. cajani and 22% on G. pallida adhere to the cuticle in an inverted orientation. Inverted and conventio ...	2011	22092805
fitness and virulence of a bacterial endoparasite in an environmentally stressed crustacean host.	host-parasite interactions are shaped by the co-evolutionary arms race of parasite virulence, transmission success as well as host resistance and recovery. the virulence and fitness of parasites may depend on host condition, which is mediated, for instance, by host energy constraints. here, we investigated to what extent stress imposed by predation threat and environmental pollutants influences host-parasite interactions. we challenged the crustacean host daphnia magna with the sterilizing bacte ...	2011	20663250
epidemiological, evolutionary, and coevolutionary implications of context-dependent parasitism.	abstract victims of infection are expected to suffer increasingly as parasite population growth increases. yet, under some conditions, faster-growing parasites do not appear to cause more damage, and infections can be quite tolerable. we studied these conditions by assessing how the relationship between parasite population growth and host health is sensitive to environmental variation. in experimental infections of the crustacean daphnia magna and its bacterial parasite pasteuria ramosa, we show ...	2011	21460572
the expression of virulence during double infections by different parasites with conflicting host exploitation and transmission strategies.	in many natural populations, hosts are found to be infected by more than one parasite species. when these parasites have different host exploitation strategies and transmission modes, a conflict among them may arise. such a conflict may reduce the success of both parasites, but could work to the benefit of the host. for example, the less-virulent parasite may protect the host against the more-virulent competitor. we examine this conflict using the waterflea daphnia magna and two of its sympatric ...	2011	21481055
candidate innate immune system gene expression in the ecological model daphnia.	the last ten years have witnessed increasing interest in host-pathogen interactions involving invertebrate hosts. the invertebrate innate immune system is now relatively well characterised, but in a limited range of genetic model organisms and under a limited number of conditions. immune systems have been little studied under real-world scenarios of environmental variation and parasitism. thus, we have investigated expression of candidate innate immune system genes in the water flea daphnia, a m ...	2011	21550363
collateral damage: rapid exposure-induced evolution of pesticide resistance leads to increased susceptibility to parasites.	although natural populations may evolve resistance to anthropogenic stressors such as pollutants, this evolved resistance may carry costs. using an experimental evolution approach, we exposed different daphnia magna populations in outdoor containers to the carbamate pesticide carbaryl and control conditions, and assessed the resulting populations for both their resistance to carbaryl as well as their susceptibility to infection by the widespread bacterial microparasite pasteuria ramosa. our resu ...	2011	21884064
resistance to a bacterial parasite in the crustacean daphnia magna shows mendelian segregation with dominance.	the influence of host and parasite genetic background on infection outcome is a topic of great interest because of its pertinence to theoretical issues in evolutionary biology. in the present study, we use a classical genetics approach to examine the mode of inheritance of infection outcome in the crustacean daphnia magna when exposed to the bacterial parasite pasteuria ramosa. in contrast to previous studies in this system, we use a clone of p. ramosa, not field isolates, which allows for a mor ...	2011	22167056