383,299 research outputs found
Within-Host Dynamics of Multi-Species Infections:Facilitation, Competition and Virulence
No full textHost individuals are often infected with more than one parasite species (parasites defined broadly, to include viruses and bacteria). Yet, research in infection biology is dominated by studies on single-parasite infections. A focus on single-parasite infections is justified if the interactions among parasites are additive, however increasing evidence points to non-additive interactions being the norm. Here we review this evidence and theoretically explore the implications of non-additive interactions between co-infecting parasites. We use classic Lotka-Volterra two-species competition equations to investigate the within-host dynamical consequences of various mixes of competition and facilitation between a pair of co-infecting species. We then consider the implications of these dynamics for the virulence (damage to host) of co-infections and consequent evolution of parasite strategies of exploitation. We find that whereas one-way facilitation poses some increased virulence risk, reciprocal facilitation presents a qualitatively distinct destabilization of within-host dynamics and the greatest risk of severe disease.</p
The influence of root diffusate and host age on hatching of the root-knot nematodes, Meloidogyne chitwoodi and M-fallax
No full textThe root-knot nematodes, Meloidogyne chitwoodi and M. fallax, cause severe damage to economically important crops and, in 1998, both species were listed as quarantine pests in Europe. Comparative studies were made on the effects of root diffusates and host age on the in vitro hatching of M. chitwoodi and M. fallax. There is a marked contrast in the hatching response of the two species. Hatching of second-stage juveniles (J2) of M. chitwoodi produced on young plants did not require host root diffusate stimulus, whereas at the end of the plant growing season, egg masses contained a percentage of unhatched J2 that require host root diffusate to cause hatch. This form of obligate quiescence at the end of the host growing season was not found in M. fallax. This species hatched well in water and did not require hatch stimulation from root diffusate, irrespective of the age of the plant on which the egg masses were produced. The number of eggs per egg mass for M.,fallax collected on senescing plants was significantly greater than the number of eggs per egg mass for M. chitwoodi. The number of eggs per egg mass of M. chitwoodi decreased with plant age. The results are discussed in the context of the differing survival strategies of the two species
U of M Crookston to host author Sarah Stonich at Fournet Building October 23
No full textBengtson, Jess. (2024). U of M Crookston to host author Sarah Stonich at Fournet Building October 23. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/270925
Morphological and physiological variability of species of Meloidogyne in West Africa and implications of their control
No full textThe extreme morphological and physiological variability of certain rootknot nematodes (Meloidogyne spp.) and its implication on the development of control methods of these parasites, based upon crop rotations and the use of resistant varieties of otherwise susceptible crops are discussed.In a review of the systematics of the genus Meloidogyne reestablished in 1949 by Chitwood to replace the polyphagous species Heterodera marioni Cornu, 1887, the variability of the so-called perineal pattern of the females, the most important character to distinguish species within the genus, is emphasized.The results of the cytological investigations of Triantaphyllou are briefly discussed. It has been shown that most species studied are characterized by a parthenogenetic mode of reproduction. Two types of non-amphimictic reproduction have been observed: mitotic and meiotic parthenogenesis. Meloidogyne incognita, M. javanica and M. arenaria are characterized by mitotic parthenogenesis.An analysis of the number of publications appearing between 1949 and 1976. dealing with identified species of Meloidogyne has revealed that 93% of the articles concern Chitwood's species of 1949, and that 76% refer to M. incognito, M. javanica and M. arenaria.Faunistic studies in West Africa have shown that the most frequently encountered root-knot nematodes belong to the species M. incognita, M. javanica and M. arenaria. Identification of West African populations are complicated by the occurrence of mixtures of species, the great morphological variability and the existance of populations possessing rather large proportions of individuals exhibiting characters intermediate between species.Certain morphometric characters of perineal patterns (width of vulva and distance between phasmids) were measured in a number of clones of Meloidogyne populations. These observations have demonstrated that although these characters are stable within clones, they cannot distinguish M. javanica from M. incognita.The distance of the excretory pore of females from the anterior end, expressed in stylet lengths might possibly be an aid to distinguish M. incognita from M. arenaria and M. javanica.The author is reluctant to describe populations characterized by unusual perineal patterns as new species and suggests inclusion of host-plant and cytological data in the description of new species.Data presented indicate that length of juveniles could not be used to distinguish among M. incognita, M. javanica and M. arenaria.Observations of juveniles from a population of M. incognita acrita have demonstrated that the inflation of the rectum is not an absolute criterium to distinguish M. incognita and M. acrita. A critical evaluation of the data of TERENTEVA (1967) concerning the height of the lip region of males of M.incognita and M. incognita acrita makes the author reject the statement that this character might be useful to distinguish between these two taxa.The author concludes that up till now, no infallible methods have been found to identify naturally occurring populations of Meloidogyne in West Africa.After the splitting of the polyphagous Heterodera marioni into a number of species of Meloidogyne it became possible to assemble host lists for each species. In principal this information should provide a basis for crop rotation recommendations, intended to reduce root-knot nematodes infestation, provided that the Meloidogyne populations could be identified to the species level. Comparison of the host ranges of M. incognita, M. javanica and M. arenaria emphasized that these species have a great number of host plants in common, many of which are important crops. Only a few species could be used as differential plants to distinguish among these three species.Published data and original results presented show that when many populations of the same species of Meloidogyne are studied, resistance/susceptibility of a given plant species cannot be predicted with confidence. Certain populations are able to parasitize a given plant and others are not.The same phenomenon is observed with resistant varieties of otherwise susceptible crops. When several populations of the same species of Meloidogyne are tested against such a variety, those populations capable of parasitizing the resistant varieties are often called 'B races'. Studies concerning development of 'B races' on resistant tomatoes in Senegal have shown that some populations of Meloidogyne are able to parasitize resistant varieties strongly and immediately. others are able to form 'B races' after a selection has taken place, the majority however, is not capable of parasitizing resistant tomatoes.Indications have been obtained that a gene for gene relation exists between nematode populations and resistant tomato varieties and a code indicating nematode and resistant variety genotype is proposed.It is assumed that most plant species are attacked by Meloidogyne populations; the reaction of the plant attacked towards the specific Meloidogyne population concerned, determines if a successful parasitic relation develops.It is proposed to consider as a group the tropical polyphagous species of Meloidogyne, which are characterized by a certain degree of polyploidy and a mitotic parthenogenetic mode of reproduction. This group should comprise M. incognito, M. javanica, M. arenaria, populations intermediate between these species, possibly undescribed species and certain described species for which information on mode of reproduction and physiological characters (host-range) is lacking.On the basis of an actual field trial in Senegal, it is shown that recommendations for crop sequences or rotations should be based on testing different crops and varieties against naturally occurring populations of root-knot nematodes. Incorrect choice of crops may be made if rotations are based upon Meloidogyne identifications only. It is recommended that different populations in an area be tested on cash, food, and cover crops and resistant varieties.Selection of resistant varieties should be based on reactions to as many different populations of Meloidogyne as possible. Using such a technique 'B races' may be detected, and in addition much material not possessing root-knot resistance in the area where the varieties are developed, may be found to have resistance against other populations elsewhere.In order to obtain the maximum value of non-hosts and resistant varieties, it is recommended to use these plants as a preventive measure rather than as a cure. Therefore, their use should be recommended in slightly infested or Meloidogyne- free soils.The author has observed in fact, that non-hosts planted in heavily infested soil may be badly damaged because of a necrotic reaction to invading juveniles. In extreme cases this may give rise to dead patches in the field and a resultant increase of weed growth, accompanied by an increase of Meloidogyne on susceptible weeds. Thus, usefulness of the non-host can be nullified. Moreover the risk of selecting 'B races' is much higher in heavily infested land than in nonor slightly infested fields.Thus it is recommended to use non-hosts and resistant varieties as preventive treatments within an integrated control including the various chemical and physical treatments available
Probing Host Pathogen Cross-Talk by Transcriptional Profiling of Both Mycobacterium tuberculosis and Infected Human Dendritic Cells and Macrophages.
No full textBACKGROUND: Transcriptional profiling using microarrays provides a unique opportunity to decipher host pathogen cross-talk on the global level. Here, for the first time, we have been able to investigate gene expression changes in both Mycobacterium tuberculosis, a major human pathogen, and its human host cells, macrophages and dendritic cells.
METHODOLOGY/PRINCIPAL FINDINGS: In addition to common responses, we could identify eukaryotic and microbial transcriptional signatures that are specific to the cell type involved in the infection process. In particular M. tuberculosis shows a marked stress response when inside dendritic cells, which is in accordance with the low permissivity of these specialized phagocytes to the tubercle bacillus and to other pathogens. In contrast, the mycobacterial transcriptome inside macrophages reflects that of replicating bacteria. On the host cell side, differential responses to infection in macrophages and dendritic cells were identified in genes involved in oxidative stress, intracellular vesicle trafficking and phagosome acidification.
CONCLUSIONS/SIGNIFICANCE: This study provides the proof of principle that probing the host and the microbe transcriptomes simultaneously is a valuable means to accessing unique information on host pathogen interactions. Our results also underline the extraordinary plasticity of host cell and pathogen responses to infection, and provide a solid framework to further understand the complex mechanisms involved in immunity to M. tuberculosis and in mycobacterial adaptation to different intracellular environments
Host choice and host leaving in Rhopalosiphum padi (Hemiptera: Aphididae) emigrants and repellency of aphid colonies on the winter host
No full textHost choice and winter-host leaving in emigrants of bird cherry–oat aphid,
Rhopalosiphum padi (Linnaeus), were investigated in the laboratory. In settling
choice tests, emigrants collected from the winter host, Prunus padus, preferred this
plant over a summer host, oats. Emigrants which had left P. padus for up to 24 h
did not express a preference as a group, and those which had left for 24–48 h
preferred oats. Eighty seven percent of emigrants caged as fourth-instar nymphs
on P. padus leaves abandoned the host by the second day of adult life, and
apparently did not subsequently return to the leaf. In an olfactometer, P. padus
leaves which had supported spring generations of R. padi were repellent to
emigrants. Volatiles were entrained from uninfested and R. padi-infested P. padus
using cut twigs in the laboratory as well as intact twigs on a tree in the field.
Entrainment extracts from uninfested P. padus had no effect on emigrants in the
olfactometer, whereas those from twigs infested with nymphal emigrants were
repellent. The study indicates that in R. padi, host-alternation is driven by
behavioural changes which occur in individuals as well as between morphs
Diet quality determines interspecific parasite interactions in host populations
No full textThe widespread occurrence of multiple infections and the often vast range of nutritional resources for their hosts allow that interspecific parasite interactions in natural host populations might be determined by host diet quality. Nevertheless, the role of diet quality with respect to multispecies parasite interactions on host population level is not clear. We here tested the effect of host population diet quality on the parasite community in an experimental study using Daphnia populations. We studied the effect of diet quality on Daphnia population demography and the interactions in multispecies parasite infections of this freshwater crustacean host. The results of our experiment show that the fitness of a low-virulent microsporidian parasite decreased in low, but not in high-host-diet quality conditions. Interestingly, infections with the microsporidium protected Daphnia populations against a more virulent bacterial parasite. The observed interspecific parasite interactions are discussed with respect to the role of diet quality-dependent changes in host fecundity. This study reflects that exploitation competition in multispecies parasite infections is environmentally dependent, more in particular it shows that diet quality affects interspecific parasite competition within a single host and that this can be mediated by host population-level effects
Host specificity and genetics of host resistance in the "Daphnia-Pasteuria" host-parasite system
No full textAntagonistic coevolution plays an important role in a large number of evolutionary and ecological phenomena. Furthermore, according to the Red Queen Theory coevolution between hosts and their parasites may explain the maintenance of sexual reproduction and genetic variation, pertinent issues in evolutionary biology. For antagonistic coevolution to lead to negative frequency dependent selection, preserve genetic variation and select for sexual reproduction parasites need to have high host specificity and this specificity has to have a simple genetic basis. In this thesis I investigate these two criteria in the Daphnia-Pasteuria system. Daphnia magna and its bacterial pathogen Pasteuria ramosa have become one of the prime model systems for antagonistic coevolution between hosts and parasites and one of the few systems with empirical evidence consistent with antagonistic coevolution by frequency dependent selection.
In the first chapter I show that specificity in the Daphnia-Pasteuria system is much stronger than previously reported. By using a novel technique I obtain single genotypes (clones) from the unculturable P. ramosa. Infections with these single parasite genotypes either result in hosts that are fully resistant or in hosts that are fully susceptible. High specificity for just some genotypes of D. magna as found in the first chapter contrast with reports from infections in natural populations which suggested that P. ramosa has a broad host range and is able to simultaneously infect highly diverged species of Daphnia. In the second chapter I address this apparent controversy. My findings of a controlled infection experiment with multiple host species and parasite lineages suggest that P. ramosa is a species complex consisting of multiple morphologically cryptic species each highly specialized for some genotypes within their host species. In addition I find that although infection does only occur in native host-parasite combinations, attachment of spores to the host esophagus, a necessary step in the infection process is conserved and polymorphic between highly diverged species of Daphnia. In chapters 3 & 4 I investigate the genetic basis of the observed specificity. Using a large array of crosses and two parasite genotypes I find that resistance is coded for by a single Mendelian inherited locus with three alleles with an allele hierarchy. An alternative, but more complex, explanation for our results is based on two closely linked diallelic loci with interlocus epistasis.
In conclusion both my findings on host specificity and the genetics of host resistance suggest that Daphnia and Pasteuria have the potential to undergo antagonistic coevolution by negative frequency dependent selection. Furthermore, the finding that genetics of resistance in Daphnia are consistent with a matching allele model will allow the Daphnia-Pasteuria system to become a powerful tool for empirical testing of population level predictions of this model. Indeed, the Daphnia-Pasteuria system could be used to experimentally test for negative frequency dependent selection, the maintenance of genetic variation and the notion that antagonistic coevolution may favor genetic mixing
The fitness of African malaria vectors in the presence and limitation of host behaviour
No full text<p>Background
Host responses are important sources of selection upon the host species range of ectoparasites and phytophagous insects. However little is known about the role of host responses in defining the host species range of malaria vectors. This study aimed to estimate the relative importance of host behaviour to the feeding success and fitness of African malaria vectors, and assess its ability to predict their known host species preferences in nature.</p>
<p>Methods
Paired evaluations of the feeding success and fitness of African vectors Anopheles arabiensis and Anopheles gambiae s.s in the presence and limitation of host behaviour were conducted in a semi-field system (SFS) at Ifakara Health Institute, Tanzania. In one set of trials, mosquitoes were released within the SFS and allowed to forage overnight on a host that was free to exhibit natural behaviour in response to insect biting. In the other, mosquitoes were allowed to feed directly on from the skin surface of immobile hosts. The feeding success and subsequent fitness of vectors under these conditions were investigated on 6 host types (humans, calves, chickens, cows, dogs and goats) to assess whether physical movements of preferred host species (cattle for An. arabiensis, humans for An. gambiae s.s.) were less effective at preventing mosquito bites than those of common alternatives.</p>
<p>Results
Anopheles arabiensis generally had greater feeding success when applied directly to host skin than when foraging on unrestricted hosts (in five of six host species). However, An. gambiae s.s obtained blood meals from free and restrained hosts with similar success from most host types (four out of six). Overall, the blood meal size, oviposition rate, fecundity and post-feeding survival of mosquito vectors were significantly higher after feeding on hosts free to exhibit behaviour, than those who were immobilized during feeding trials.</p>
<p>Conclusions
Allowing hosts to move freely during exposure to mosquitoes was associated with moderate reductions in mosquito feeding success, but no detrimental impact to the subsequent fitness of mosquitoes that were able to feed upon them. This suggests that physical defensive behaviours exhibited by common host species including humans do not impose substantial fitness costs on African malaria vectors.</p>
High water availability increases the negative impact of a native hemiparasite on its non-native host
No full textEnvironmental factors alter the impacts of parasitic plants on their hosts. However, there have been no controlled studies on how water availability modulates stem hemiparasites' effects on hosts. A glasshouse experiment was conducted to investigate the association between the Australian native stem hemiparasite Cassytha pubescens and the introduced host Ulex europaeus under high (HW) and low (LW) water supply. Cassytha pubescens had a significant, negative effect on the total biomass of U. europaeus, which was more severe in HW than LW. Regardless of watering treatment, infection significantly decreased shoot and root biomass, nodule biomass, nodule biomass per unit root biomass, F-v/F-m, and nitrogen concentration of U. europaeus. Host spine sodium concentration significantly increased in response to infection in LW but not HW conditions. Host water potential was significantly higher in HW than in LW, which may have allowed the parasite to maintain higher stomatal conductances in HW. In support of this, the delta C-13 of the parasite was significantly lower in HW than in LW (and significantly higher than the host). C. pubescens also had significantly higher F-v/F-m and 66% higher biomass per unit host in the HW compared with the LW treatment. The data suggest that the enhanced performance of C. pubescens in HW resulted in higher parasite growth rates and thus a larger demand for resources from the host, leading to poorer host performance in HW compared with LW. C. pubescens should more negatively affect U. europaeus growth under wet conditions rather than under dry conditions in the field
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