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Host Genotype (host + genotype)
Selected AbstractsEVIDENCE FOR NEGATIVE FREQUENCY-DEPENDENT SELECTION DURING EXPERIMENTAL COEVOLUTION OF A FRESHWATER SNAIL AND A STERILIZING TREMATODEEVOLUTION, Issue 9 2009Britt Koskella Host,parasite coevolution is often suggested as a mechanism for maintaining genetic diversity, but finding direct evidence has proven difficult. In the present study, we examine the process of coevolution using a freshwater New Zealand snail (Potamopyrgus antipodarum) and its common parasite (the sterilizing trematode, Microphallus sp.) Specifically, we test for changes in genotypic composition of clonal host populations in experimental populations evolving either with or without parasites for six generations. As predicted under the Red Queen model of coevolution, the initially most common host genotype decreased in frequency in the presence, but not the absence, of parasitism. Furthermore, the initially most common host genotype became more susceptible to infection by the coevolving parasite populations over the course of the experiment. These results are consistent with parasite-meditated selection leading to a rare advantage, and they indicate rapid coevolution at the genotypic level between a host and its parasite. [source] DIRECT AND CORRELATED RESPONSES TO SELECTION IN A HOST,PARASITE SYSTEM: TESTING FOR THE EMERGENCE OF GENOTYPE SPECIFICITYEVOLUTION, Issue 8 2007Thibault Nidelet Genotype × environment interactions can facilitate coexistence of locally adapted specialists. Interactions evolve if adaptation to one environment trades off with performance in others. We investigated whether evolution on one host genotype traded off with performance on others in long-term experimental populations of different genotypes of the protozoan Paramecium caudatum, infected with the bacterial parasite Holospora undulata. A total of nine parasite selection lines evolving on three host genotypes and the ancestral parasite were tested in a cross-infection experiment. We found that evolved parasites produced more infections than did the ancestral parasites, both on host genotypes they had evolved on (positive direct response to selection) and on genotypes they had not evolved on (positive correlated response to selection). On two host genotypes, a negative relationship between direct and correlated responses indicated pleiotropic costs of adaptation. On the third, a positive relationship suggested cost-free adaptation. Nonetheless, on all three hosts, resident parasites tended to be superior to the average nonresident parasite. Thus genotype specificity (i.e., patterns of local adaptation) may evolve without costs of adaptation, as long as direct responses to selection exceed correlated responses. [source] Effect of drought on the growth of Lolium perenne genotypes with and without fungal endophytesFUNCTIONAL ECOLOGY, Issue 6 2000G. P. Cheplick Abstract 1Grass leaves are often inhabited by fungal endophytes that can enhance host growth. In some forage species, endophytes improve host resistance to, and recovery from, drought. 2Our objective was to determine if the growth of genotypes of Lolium perenne L. was improved by endophytes during recovery from drought. 3Thirteen infected genotypes were cloned into ramets. Half were treated with a systemic fungicide to eliminate the endophyte (E,); half were untreated and retained high endophyte levels (E+). In a glasshouse, half of all E, and E+ ramets were watered regularly, whilst half were exposed to a 2 week drought on two occasions, each followed by a 3 week recovery period. 4After the first drought and recovery period, endophytes significantly reduced tiller production in the drought-stressed group. 5After the second drought and recovery period, effects of drought on live leaf area and dry mass were highly dependent on host genotype, but not endophytes. The mean tiller mass of E+ ramets after drought was significantly less than that of watered E+ ramets, but this was not true in E, ramets. For six genotypes there was greater mass allocation to storage in the tiller bases of E, ramets after drought. 6This perennial ryegrass population showed marked genotypic variation in the ability to recover from drought stress, but endophytes played little or no role in this ability. For some host genotypes there may be a metabolic cost of harbouring endophytes during environmentally stressful conditions. [source] Heterogeneity in the granulomatous response to mycobacterial infection in patients with defined genetic mutations in the interleukin 12-dependent interferon-gamma production pathwayINTERNATIONAL JOURNAL OF EXPERIMENTAL PATHOLOGY, Issue 1 2002D. A. LAMMAS Summary Patients with genetic lesions in the Type-1 cytokine/cytokine receptor pathway exhibit a selective susceptibility to severe infections with poorly pathogenic mycobacteria and non-typhi salmonella spp. These experiments of nature demonstrate that IL-12-dependent IFN, production is critical for granuloma formation and therefore host immunity against such pathogens. The essential role of granuloma formation for protective immunity to these organisms is emphasized by the differing granuloma forming capabilities and resultant clinical sequelae observed in these patients which seems to reflect their ability to produce or respond to IFN, (Fig. 9). At one pole of this spectrum, represented by the complete IFN,R1/2 deficient patients, there is a complete absence of mature granuloma formation, whereas with the less severe mutations (i.e. partial IFN,R1/2, complete IL-12p40 and complete IL-12R,1 deficiency), granuloma formation is very heterogenous with wide variations in composition being observed. This suggests that in the latter individuals, who produce partial but suboptimal IFN, responses, other influences, including pathogen virulence and host genotype may also affect the type and scale of the cellular response elicited. Figure 9. ,Spectrum of genetic susceptibility to intracellular bacteria. At one pole of this spectrum complete IFN,R deficiencies are found; at the other pole are healthy resistant individuals. Partial IFN,R1 deficiencies, and complete IL-12R,1 and IL-12p40 deficiencies can be positioned in between, albeit closer to the former end of the spectrum, with clinical outcome also depending on pathogen virulence and host compensatory immune mechanism(s). Abbreviations: IFN,R , interferon gamma receptor, IL-12R,1 , interleukin 12 receptor-1 (modified from Ottenhoff et al. (1998)). [source] Ample genetic variation but no evidence for genotype specificity in an all-parthenogenetic host,parasitoid interactionJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2010C. SANDROCK Abstract Antagonistic coevolution between hosts and parasites can result in negative frequency-dependent selection and may thus be an important mechanism maintaining genetic variation in populations. Negative frequency-dependence emerges readily if interactions between hosts and parasites are genotype-specific such that no host genotype is most resistant to all parasite genotypes, and no parasite genotype is most infective on all hosts. Although there is increasing evidence for genotype specificity in interactions between hosts and pathogens or microparasites, the picture is less clear for insect host,parasitoid interactions. Here, we addressed this question in the black bean aphid (Aphis fabae) and its most important parasitoid Lysiphlebus fabarum. Because both antagonists are capable of parthenogenetic reproduction, this system allows for powerful tests of genotype × genotype interactions. Our test consisted of exposing multiple host clones to different parthenogenetic lines of parasitoids in all combinations, and this experiment was repeated with animals from four different sites. All aphids were free of endosymbiotic bacteria known to increase resistance to parasitoids. We observed ample genetic variation for host resistance and parasitoid infectivity, but there was no significant host clone × parasitoid line interaction, and this result was consistent across the four sites. Thus, there is no evidence for genotype specificity in the interaction between A. fabae and L. fabarum, suggesting that the observed variation is based on rather general mechanisms of defence and attack. [source] Induction of resistance in cocoa against Crinipellis perniciosa and Verticillium dahliae by acibenzolar- S -methyl (ASM)PLANT PATHOLOGY, Issue 5 2002M. L. V. Resende The benzothiadiazole compound acibenzolar- S -methyl (ASM) was assessed as an inducer of resistance against Crinipellis perniciosa, agent of witches' broom, and Verticillium dahliae, agent of vascular wilt, both on cocoa. ASM induced a reduction in incidence of witches' broom of up to 84·5% when sprayed 30 days before inoculation on cocoa seedlings of cv. Catongo. ASM also induced a reduction in severity of Verticillium wilt to 55·4% on cv. Theobahia. For both pathosystems, effects of dose on disease were not clearly observed. The efficacy of the inducer increased with the interval between sprayings and the respective inoculations with the pathogens. In another experiment, the effect of ASM on the control of witches' broom on cocoa seedlings was compared with that of cuprous oxide and tebuconazole, all sprayed 15 days before inoculation. ASM reduced disease incidence by 60·1% compared with the inoculated control. ASM was superior to tebuconazole, and there was also a tendency for ASM to be better than cuprous oxide. To understand the mechanism of action of ASM as an inducer of resistance, alterations in the levels of total phenolics, polyphenol oxidases and peroxidases were evaluated 3, 15 and 30 days after spraying of seedlings of cv. Catongo. Enzyme activities from seedlings of cv. Theobahia were evaluated 30 days after spraying. On cv. Catongo, no significant differences in total phenolic content and polyphenol oxidase activity were detected after spraying. However, an increase in peroxidase activity was detected at all times of evaluation. On cv. Theobahia, significant increases in activities of peroxidase and polyphenol oxidase were detected, indicating that defence responses due to ASM were dependent on host genotype. [source] The importance of weather and agronomic factors for the overwinter survival of yellow rust (Puccinia striiformis) and subsequent disease risk in commercial wheat crops in EnglandANNALS OF APPLIED BIOLOGY, Issue 3 2007P. Gladders Abstract Disease survey data from 4475 randomly selected crops of wheat from England and Wales during 1985,2000 showed that yellow rust was most prevalent in 1988, 1989, 1990, 1998 and 1999. Disease severity on the upper two leaves was low as >95% crops had received foliar fungicides. Factors affecting the presence or absence (incidence) of yellow rust were investigated using random effects logistic regression (general linear mixed model). This enabled crop management (risk) variables for individual crops to be combined with meteorological variables measured at the county level. Two models are presented that analysed the effect of host genotype on incidence either solely through yellow rust resistance rating (Model 1) or by including both resistance rating (fixed effect) and cultivar (fitted as a random term) (Model 2). In both models, the percentage of crops with yellow rust decreased with cultivar disease resistance ratings ,3, the occurrence of severe frosts (<,5°C), use of systemic seed treatment and application of foliar fungicide sprays. There were no significant effects (P < 0.05) of timing of fungicide sprays, previous cropping or summer weather. The use of risk variables associated with overwintering survival may help adjust fungicide inputs to seasonal risk. [source] The effect of a pathogen epidemic on the genetic structure and reproductive strategy of the crustacean Daphnia magnaECOLOGY LETTERS, Issue 9 2004Suzanne E. Mitchell Abstract Host,parasite coevolution is potentially of great importance in producing and maintaining biological diversity. However, there is a lack of evidence for parasites directly driving genetic change. We examined the impact of an epidemic of the bacterium Pasteuria ramosa on a natural population of the crustacean Daphnia magna through the use of molecular markers (allozymes) and laboratory experiments to determine the susceptibility of hosts collected during and after the epidemic. Some allozyme genotypes were more heavily infected than others in field samples, and the population genetic structure differed during and after the epidemic, consistent with a response to parasite-mediated selection. Laboratory studies showed no evidence for the evolution of higher resistance, but did reveal an intriguing life-history pattern: host genotypes that were more susceptible also showed a greater tendency to engage in sex. In light of this, we suggest a model of host,parasite dynamics that incorporates the cycles of sex and parthenogenesis that Daphnia undergo in the field. [source] DIRECT AND CORRELATED RESPONSES TO SELECTION IN A HOST,PARASITE SYSTEM: TESTING FOR THE EMERGENCE OF GENOTYPE SPECIFICITYEVOLUTION, Issue 8 2007Thibault Nidelet Genotype × environment interactions can facilitate coexistence of locally adapted specialists. Interactions evolve if adaptation to one environment trades off with performance in others. We investigated whether evolution on one host genotype traded off with performance on others in long-term experimental populations of different genotypes of the protozoan Paramecium caudatum, infected with the bacterial parasite Holospora undulata. A total of nine parasite selection lines evolving on three host genotypes and the ancestral parasite were tested in a cross-infection experiment. We found that evolved parasites produced more infections than did the ancestral parasites, both on host genotypes they had evolved on (positive direct response to selection) and on genotypes they had not evolved on (positive correlated response to selection). On two host genotypes, a negative relationship between direct and correlated responses indicated pleiotropic costs of adaptation. On the third, a positive relationship suggested cost-free adaptation. Nonetheless, on all three hosts, resident parasites tended to be superior to the average nonresident parasite. Thus genotype specificity (i.e., patterns of local adaptation) may evolve without costs of adaptation, as long as direct responses to selection exceed correlated responses. [source] Effect of drought on the growth of Lolium perenne genotypes with and without fungal endophytesFUNCTIONAL ECOLOGY, Issue 6 2000G. P. Cheplick Abstract 1Grass leaves are often inhabited by fungal endophytes that can enhance host growth. In some forage species, endophytes improve host resistance to, and recovery from, drought. 2Our objective was to determine if the growth of genotypes of Lolium perenne L. was improved by endophytes during recovery from drought. 3Thirteen infected genotypes were cloned into ramets. Half were treated with a systemic fungicide to eliminate the endophyte (E,); half were untreated and retained high endophyte levels (E+). In a glasshouse, half of all E, and E+ ramets were watered regularly, whilst half were exposed to a 2 week drought on two occasions, each followed by a 3 week recovery period. 4After the first drought and recovery period, endophytes significantly reduced tiller production in the drought-stressed group. 5After the second drought and recovery period, effects of drought on live leaf area and dry mass were highly dependent on host genotype, but not endophytes. The mean tiller mass of E+ ramets after drought was significantly less than that of watered E+ ramets, but this was not true in E, ramets. For six genotypes there was greater mass allocation to storage in the tiller bases of E, ramets after drought. 6This perennial ryegrass population showed marked genotypic variation in the ability to recover from drought stress, but endophytes played little or no role in this ability. For some host genotypes there may be a metabolic cost of harbouring endophytes during environmentally stressful conditions. [source] Differential defoliation of Eucalyptus grandis arises from indiscriminant oviposition and differential larval survivalAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 1 2009M. L. Henery Abstract 1,The influence of six open-pollinated families (OPFs) of Eucalyptus grandis on both the growth and development of larvae and the oviposition preference of a paropsine chrysomelid (Paropsis atomaria) was investigated. The OPFs had previously been identified as differing in their susceptibility to defoliation by P. atomaria in forestry progeny trials. 2,Oviposition preference for resistant and susceptible foliage was tested using binary choice tests. These tests did not demonstrate any significant preference for either resistant or susceptible open-pollinated material indicating that adult host preference for susceptible trees was not a likely cause of differential defoliation. 3,Quantification and analysis of growth and development parameters for all larval stages of P. atomaria showed that feeding on genetic material identified as resistant resulted in a significant reduction of relative growth rate of first instar larvae and an alteration to normal feeding behaviour. There was also a trend towards increased larval mortality on resistant E. grandis. 4,We argue that although the magnitude of these effects was minor, interactions with additional biotic and abiotic sources of mortality in the field have the potential, when magnified over successive generations, to result in significant variation in defoliation of host genotypes in the field. [source] Response of quaking aspen genotypes to enriched CO2: foliar chemistry and tussock moth performanceAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 4 2002Richard L. Lindroth Abstract 1Genetic variation in the phytochemical responses of plants to CO2 enrichment is likely to alter trophic dynamics, and to shift intraspecific selection pressures on plant populations. We evaluated the independent and interactive effects of atmospheric CO2 and quaking aspen (Populus tremuloides Michx.) genotype on chemical composition of foliage and performance of the whitemarked tussock moth (Orgyia leucostigma J. E. Sm.). 2This research was conducted at the Aspen FACE (Free Air CO2 Enrichment) site in northern Wisconsin, U.S.A. Leaf samples were collected periodically from each of three genetically variable aspen genotypes growing under ambient and elevated CO2, and analysed for levels of primary and secondary metabolites. Tussock moth larvae were reared in situ on experimental trees, and development times and pupal masses were recorded. 3Foliar chemical composition varied among aspen genotypes and in response to CO2 enrichment. However, chemical responses of trees to elevated CO2 were generally consistent across genotypes. 4Larval development times varied among host genotypes and increased slightly for insects on high-CO2 plants. Enriched CO2 tended to reduce insect pupal masses, particularly for females on one of the three aspen genotypes. 5CO2 × genotype interactions observed for plant chemistry and insect performance in this study with a small number of genotypes are probably too few, and too weak, to shift selection pressures in aspen populations. These results differ, however, from earlier work in which more substantial CO2 × genotype interactions were observed for plant chemistry. [source] The genetic architecture of disease resistance in plants and the maintenance of recombination by parasitesMOLECULAR ECOLOGY, Issue 1 2001Paula X. Kover Abstract Parasites represent strong selection on host populations because they are ubiquitous and can drastically reduce host fitness. It has been hypothesized that parasite selection could explain the widespread occurrence of recombination because it is a coevolving force that favours new genetic combinations in the host. A review of deterministic models for the maintenance of recombination reveals that for recombination to be favoured, multiple genes that interact with each other must be under selection. To evaluate whether parasite selection can explain the maintenance of recombination, we review 85 studies that investigated the genetic architecture of plant disease resistance and discuss whether they conform to the requirements that emerge from theoretical models. General characteristics of disease resistance in plants and problems in evaluating resistance experimentally are also discussed. We found strong evidence that disease resistance in plants is determined by multiple loci. Furthermore, in most cases where loci were tested for interactions, epistasis between loci that affect resistance was found. However, we found weak support for the idea that specific allelic combinations determine resistance to different host genotypes and there was little data on whether epistasis between resistance genes is negative or positive. Thus, the current data indicate that it is possible that parasite selection can favour recombination, but more studies in natural populations that specifically address the nature of the interactions between resistance genes are necessary. The data summarized here suggest that disease resistance is a complex trait and that environmental effects and fitness trade-offs should be considered in future models of the coevolutionary dynamics of host and parasites. [source] Do virus-resistant plants pose a threat to non-target ecosystems?AUSTRAL ECOLOGY, Issue 5 2009Abstract One key environmental risk associated with the release of novel disease-resistant plants is the potential for non-target host populations to acquire resistance genes and undergo enemy release, leading to damage to associated native plant populations in high conservation-value ecosystems. Unfortunately, the dynamics of most natural pathosystems are poorly understood, and risk assessment of disease-resistant plants remains a challenge. Here we describe the first stage of a multi-tiered risk assessment strategy aimed at quantifying potential ecological release in a model pathosystem (the weedy pasture species Trifolium repens infected with Clover yellow vein virus; ClYVV) in order to assess the level of risk posed by genetically modified and conventionally bred disease-resistant host genotypes to non-target plant communities in south-eastern Australia. Glasshouse inoculation and growth experiments using 14 ClYVV isolates and 20 wild T. repens lines collected from high conservation-value montane grassland and woodland communities show that viral infection reduces the survival and growth of host plants by on average 10,50%. However, T. repens lines exhibited variable levels of resistance and tolerance to virus infection and ClYVV isolates differed in infectivity and aggressiveness, with grassland isolates having a greater pathogenic effect on associated host plants than woodland isolates. We conclude that ClYVV potentially plays an important role in limiting the size of T. repens populations in some at-risk non-target ecosystems and that second-tier field experiments are required to adequately quantify the risk associated with the commercial release of V-R T. repens genotypes in Australia. [source] | ||||||||||||||||||||||