Dynamics of host plant use and species diversity in Polygonia butterflies (Nymphalidae)

The ability of insects to utilize different host plants has been suggested to be a dynamic and transient phase. During or after this phase, species can shift to novel host plants or respecialize on ancestral ones. Expanding the range of host plants might also be a factor leading to higher levels of net speciation rates. In this paper, we have studied the possible importance of host plant range for diversification in the genus Polygonia (Nymphalidae, Nymphalini). We have compared species richness between sistergroups in order to find out if there are any differences in number of species between clades including species that utilize only the ancestral host plants ('urticalean rosids') and their sisterclades with a broader (or in some cases potentially broader) host plant repertoire. Four comparisons could be made, and although these are not all phylogenetically or statistically independent, all showed clades including butterfly species using other or additional host plants than the urticalean rosids to be more species-rich than their sisterclade restricted to the ancestral host plants. These results are consistent with the theory that expansions in host plant range are involved in the process of diversification in butterflies and other phytophagous insects, in line with the general theory that plasticity may drive speciation.     

Location of Drosophila C virus target organs in Drosophila host population by an immunofluorescence technique

Using the immunofluorescence technique we attempted to locate, in the Drosophila host, Drosophila C virus (DCV) target organs after injection of adult flies. Two kinds of organs were infected: those which play a role in reproductive function, including the fat body and follicular cells, and other, including thoracic muscle fibers, tracheal cells, and the digestive tract. These organs correspond to those found in previous tests. Fat body proteins of a DCV-free host population seemed to cross-react with antivirus C antibody. This immune response depended on the origin of the host population. It is known that, when DCV is ingested from the first larval instar, it may have beneficial effects upon host development and reproduction. As DCV has a narrow host spectrum, it is suggested that it is well adapted to its natural host. Hypotheses are proposed to explain how the host resists viral infection and may in fact benefit from such an infection.     

Multiple choice: hemiparasite performance in multi‐species mixtures

Hemiparasitic plants have green leaves, but extract water and solutes from neighbouring plants. It is still poorly understood how different host plants in communities contribute to parasite performance, as species that are good hosts in single‐host experiments may not necessarily be preferred hosts in mixtures. We grew the root hemiparasite Rhinanthus alectorolophus (Orobanchaceae) together with each of 13 host species (experiment 1) and with 15 different four‐species mixtures of these hosts (experiment 2) that differed in the number of legumes and of host functional groups. Parasites profited from mixtures including more legumes and from mixtures including different host functional groups. Some host species and mixtures were very tolerant of parasitism and supported large parasites without being strongly suppressed in their own growth, but the suppression of a species in the single‐host experiment did not explain the suppression of a species in a host mixture. We thus calculated for each host species an index of the difference in suppression between the two experiments which may be related to host use in a mixture. Host quality (mean parasite biomass with a host species) in the single‐host experiment could explain 64% of the variation in parasite biomass with a host mixture when it was weighted by the proportion of the host species in the mixture without the parasite and by the suppression difference index. Our results suggest that plant species which are the best hosts in single‐host experiments are not always those used most strongly by a parasite growing with a mixture. Together with the finding that hemiparasites benefit from a mixed diet based on hosts from different functional groups this suggests that parasites prefer certain host species to obtain a mixed diet.     

Interspecific aggregation of ectoparasites on bats: importance of hosts as habitats supersedes interspecific interactions

Patterns of aggregation of species or individuals may result from combinations of interspecific interactions such as competition, facilitation, or apparent facilitation, as well as from equivalent responses to environmental factors. Host–parasite systems are ideal for the investigation of mechanisms that structure assemblages. Interspecific aggregation is documented for multiple groups that are ectoparasitic on mammals and host‐mediated apparent facilitation has been suggested to explain these aggregation patterns. To investigate the generality of this pattern and to determine likely structuring mechanisms, I analyzed species co‐occurrence, correlations of abundances, and nestedness for ectoparasite assemblages from each of 11 species of Neotropical bat. Ectoparasite assemblages on four of 11 host species exhibited significant positive co‐occurrence for the entire assemblage or for at least one pair of species in the assemblage; ectoparasites on two host species exhibited positive co‐occurrence that approached significance. There was no evidence of negative co‐occurrence. Nine species‐pairs exhibited positive abundance correlations, including seven of the eight species‐pairs that exhibited positive co‐occurrence. No species‐pair exhibited a negative correlation of abundances (i.e. density compensation). Ectoparasite assemblages from five of 11 host species exhibited nestedness, including all three assemblages that exhibited assemblage‐wide positive co‐occurrence. Multiple mechanisms associated with host characteristics may contribute to host aggregation in ectoparasite assemblages, including host body size, vagility, home range size, burrow or roost size and complexity, immunocompetence and social structure. In general, data in this study and elsewhere are not consistent with interspecific interactions among ectoparasites, including apparent facilitation, being primary structuring mechanisms of ectoparasite assemblages on mammalian hosts. Rather, host behavior and ecology are likely to affect the frequency of host–ectoparasite encounters and of conspecific host interactions that facilitate transfer of ectoparasites, thereby, molding patterns of ectoparasite co‐occurrence, abundance and species composition on mammalian hosts. Combinations of characteristics that are primarily responsible for molding ectoparasite assemblage composition likely are host‐taxon specific.     

Biological control of tortricidae in tea fields in Japan using insect viruses and parasitoids

Tea is a perennial and evergreen plant. Cultivated tea trees provide a habitat for insect pests and their natural enemies. In Japan, granuloviruses (GVs) have successfully controlled two of the most important pests of tea, Adoxophyes honmai and Homona magnanima (Tortricidae: Lepidoptera). The GVs are produced in vivo and a single application sustains pesticidal efficacy throughout a year, which encompasses 4 to 5 discrete generations of both species. A. honmai and H. magnanima also have various natural enemies, especially hymenopteran parasitoids. Such resident natural enemies also play a role in reducing the pest density in virus-controlled fields, but the effect of virus infection on parasitoids sharing the same host larva has not been well studied. Survival of one of the major parasitoids ofA. honmai, Ascogaster reticulata (Braconidae: Hymenoptera), is reduced by virus infection of the host. Viruses, including GV and entomopoxvirus (EPV), and certain koinobiont endoparasitoids, including A. reticulata, are both known to regulate host endocrinology. However, the GV and EPV have distinct host regulation mechanisms, and consequently have different impacts on the survival of A. retuculata, when A. reticulata parasitizes a host that is infected with either GV or EPV. These additional effects on host regulation displayed by both viruses and parasitoids affect the outcome of virus-parasitoid interactions.     

The Natural Host Range of Beetle Species Feeding on Broom, Cytisus scoparius (L.) Link (Fabaceae), in Southwest Europe

The natural host range of beetles feeding on broom ( Cytisus scoparius ) and 14 other species (including six other Cytisus species) in the tribe Genisteae was investigated at 39 sites in Spain , Portugal and France in 1989 and 1992 as part of a biological control programme for broom . Data on host - plant associations were analyzed for 36 phytophagous beetle species from 18 sites , and host records were listed for an additional 58 species . Nine species were apparently restricted to the genus Cytisus : Cryptocephalus octoguttatus, Gonioctena olivacea, Bruchidius lividimanus, B. villosus, Exapion elongatissimum, E. fuscirostre, Lepidapion sp . 1 , Polydrusus confluens and Tychius parallelus. These field records suggest a narrower host - plant range for some beetle species than laboratory host - range tests , and may assist in interpreting host - plant associations reported in the literature . Beetle species with a restricted host - plant range were rarely found on related non - host plants .     

A general model for host plant selection in phytophagous insects

We develop a general theoretical framework for exploring the host plant selection behaviour of herbivorous insects. This model can be used to address a number of questions, including the evolution of specialists, generalists, preference hierarchies, and learning. We use our model to: (i) demonstrate the consequences of the extent to which the reproductive success of a foraging female is limited by the rate at which they find host plants (host limitation) or the number of eggs they carry (egg limitation); (ii) emphasize the different consequences of variation in behaviour before and after landing on (locating) a host (termed pre- and post-alighting, respectively); (iii) show that, in contrast to previous predictions, learning can be favoured in post-alighting behaviour--in particular, individuals can be selected to concentrate oviposition on an abundant low-quality host, whilst ignoring a rare higher-quality host; (iv) emphasize the importance of interactions between mechanisms in favouring specialization or learning.     

转换寄主前后扶桑绵粉蚧取食行为的EPG分析

【目的】分析扶桑绵粉蚧Phenacoccus solenopsis在发生寄主转移前后的取食行为,以据此评价其寄主适应性。【方法】利用刺吸电位（EPG）技术,量化扶桑绵粉蚧转换寄主植物前后的取食行为并进行对比分析。【结果】寄主转换后,扶桑绵粉蚧的取食行为受到显著的影响,需要耗费更多的时间到达韧皮部,总取食时间显著变短,取食效率降低。但寄主转换后,下一代成虫的取食效率提高,总刺探数、取食刺探数、总刺探时间以及到达韧皮部的效率与时间均与寄主转换前的扶桑绵粉蚧个体不存在显著差异。【结论】扶桑绵粉蚧的取食行为存在高度可塑性,这种特性利于扩大其寄主植物范围,有可能是促其成为重要农业入侵生物的原因之一。     

Factors affecting host range in a generalist seed pathogen of semi-arid shrublands

Generalist pathogens can exhibit differential success on different hosts, resulting in complex host range patterns. Several factors operate to reduce realized host range relative to potential host range, particularly under field conditions. We explored factors influencing host range of the naturally occurring generalist ascomycete grass seed pathogen Pyrenophora semeniperda. We measured potential host range in laboratory experiments at high inoculum loads with 26 grass species, including the primary host Bromus tectorum, and developed models to predict susceptibility and tolerance based on host traits, including germination speed, seed hardness, seed size, and phylogenetic relations. We also examined pathogen and host density effects on infection and mortality. All species tested were at least somewhat susceptible to the pathogen at high inoculum loads, but both infection and mortality varied widely. Species more closely related to the original host (B. tectorum) were more susceptible to infection, whereas species with slower germination were less tolerant and therefore more likely to suffer mortality. Infection and mortality were sharply reduced as inoculum load was reduced. Intermediate loads had major negative impacts on dormant B. tectorum seeds but generally minimal effects on native species. In addition, field seed bank studies determined that P. semeniperda rarely exploits native grass species as hosts. This marked reduction in realized host range relative to potential host range indicates that laboratory host range studies are potentially a poor predictor of either the current or possible future realized host range for wildland plant pathogens.     

蚜虫寄主专化型及其成因

综述了蚜虫寄主专化型产生的可能原因。蚜虫寄主专化型的形成在生态学水平上主要与蚜虫对寄主的选择识别能力、天敌作用、其他共生（共存）生物作用、抗药性等有关;并且具有一定的遗传基础,主要表现在蚜虫体内酶系的变化、染色体变异、有性繁殖中同型交配行为及种群的遗传分化上。但是对某种寄主专化型蚜虫而言,其具体的成因尚不明确。     

Horizontal gene and chromosome transfer in plant pathogenic fungi affecting host range

Plant pathogenic fungi adapt quickly to changing environments including overcoming plant disease resistance genes. This is usually achieved by mutations in single effector genes of the pathogens, enabling them to avoid recognition by the host plant. In addition, horizontal gene transfer (HGT) and horizontal chromosome transfer (HCT) provide a means for pathogens to broaden their host range. Recently, several reports have appeared in the literature on HGT, HCT and hybridization between plant pathogenic fungi that affect their host range, including species of Stagonospora/Pyrenophora, Fusarium and Alternaria. Evidence is given that HGT of the ToxA gene from Stagonospora nodorum to Pyrenophora tritici-repentis enabled the latter fungus to cause a serious disease in wheat. A nonpathogenic Fusarium species can become pathogenic on tomato by HCT of a pathogenicity chromosome from Fusarium oxysporum f.sp lycopersici, a well-known pathogen of tomato. Similarly, Alternaria species can broaden their host range by HCT of a single chromosome carrying a cluster of genes encoding host-specific toxins that enabled them to become pathogenic on new hosts such as apple, Japanese pear, strawberry and tomato, respectively. The mechanisms HGT and HCT and their impact on potential emergence of fungal plant pathogens adapted to new host plants will be discussed.     

Phylogenetic relationships and host-plant evolution within the basal clade of Halictidae (Hymenoptera, Apoidea)

Bees are among the most important pollinators of angiosperm plants. Many bee species show narrow host‐plant preferences, reflected both in behavioral and morphological adaptations to particular attributes of host‐plant pollen or floral morphology. Whether bee host‐plant associations reflect co‐cladogenesis of bees and their host plants or host‐switches to unrelated host plants is not clear. Rophitinae is a basal subfamily of Halictidae in which most species show narrow host‐plant preferences (oligolecty). We reconstructed the phylogenetic relationships among the rophitine genera using a combination of adult morphology (24 characters) and DNA sequence data (EF‐1α, LW rhodopsin, wingless; 2700 bp total). The data set was analyzed by parsimony, maximum likelihood and Bayesian methods. All methods yielded highly congruent results. Using the phylogeny, we investigated the pattern of host‐plant association as well as the historical biogeography of Rophitinae. Our biogeographical analysis suggests a number of dispersal/vicariance events: (1) a basal split between North America and South America (most likely a dispersal from South America to North America), and (2) at least two subsequent interchanges between North America and Eurasia (presumably via the northern hemisphere land bridges). Our analysis of host‐plant associations indicates that Rophitinae specialized on a closely related group of angiosperm orders in the Euasterid I clade (mainly Gentianales, Lamiales and Solanales). However, there is little evidence of cocladogenesis between bees and plants and strong evidence of host switches to unrelated host plants. Based on our phylogenetic results we describe two new tribes of Rophitinae: Conanthalictini new tribe (including the genus Conanthalictus) and Xeralictini new tribe (including Xeralictus and Protodufourea). © The Willi Hennig Society 2007.     

Enteropathogenic Escherichia coli: cellular harassment

The mechanisms by which enteropathogenic Escherichia coli (EPEC) mediates diarrhea remain a mystery. Recently a number of interesting and at times surprising results have come from studying EPEC interactions with host cells. Identification and characterization of bacterial factors, including Tir, EspA, EspB and EspD, and host responses have expanded our grasp of the diverse effects of EPEC on host cells.     

Co-phylogeography and comparative population genetics of the threatened Galápagos hawk and three ectoparasite species: ecology shapes population histories within parasite communities

Comparative microevolutionary studies of multiple parasites occurring on a single host species can help shed light on the processes underlying parasite diversification. We compared the phylogeographical histories, population genetic structures and population divergence times of three co-distributed and phylogenetically independent ectoparasitic insect species, including an amblyceran and an ischnoceran louse (Insecta: Phthiraptera), a hippoboscid fly (Insecta: Diptera) and their endemic avian host in the Galápagos Islands. The Galápagos hawk (Aves: Falconiformes: Buteo galapagoensis) is a recently arrived endemic lineage in the Galápagos Islands and its island populations are diverging evolutionarily. Each parasite species differed in relative dispersal ability and distribution within the host populations, which allowed us to make predictions about their degree of population genetic structure and whether they tracked host gene flow and colonization history among islands. To control for DNA region in comparisons across these phylogenetically distant taxa, we sequenced ~1 kb of homologous mitochondrial DNA from samples collected from all island populations of the host. Remarkably, the host was invariant across mitochondrial regions that were comparatively variable in each of the parasite species, to degrees consistent with differences in their natural histories. Differences in these natural history traits were predictably correlated with the evolutionary trajectories of each parasite species, including rates of interisland gene flow and tracking of hosts by parasites. Congruence between the population structures of the ischnoceran louse and the host suggests that the ischnoceran may yield insight into the cryptic evolutionary history of its endangered host, potentially aiding in its conservation management.     

Cell Cycle-Dependent Phosphorylation of Theileria annulata Schizont Surface Proteins

The invasion of Theileria sporozoites into bovine leukocytes is rapidly followed by the destruction of the surrounding host cell membrane, allowing the parasite to establish its niche within the host cell cytoplasm. Theileria infection induces host cell transformation, characterised by increased host cell proliferation and invasiveness, and the activation of anti-apoptotic genes. This process is strictly dependent on the presence of a viable parasite. Several host cell kinases, including PI3-K, JNK, CK2 and Src-family kinases, are constitutively activated in Theileria-infected cells and contribute to the transformed phenotype. Although a number of host cell molecules, including IkB kinase and polo-like kinase 1 (Plk1), are recruited to the schizont surface, very little is known about the schizont molecules involved in host-parasite interactions. In this study we used immunofluorescence to detect phosphorylated threonine (p-Thr), serine (p-Ser) and threonine-proline (p-Thr-Pro) epitopes on the schizont during host cell cycle progression, revealing extensive schizont phosphorylation during host cell interphase. Furthermore, we established a quick protocol to isolate schizonts from infected macrophages following synchronisation in S-phase or mitosis, and used mass spectrometry to detect phosphorylated schizont proteins. In total, 65 phosphorylated Theileria proteins were detected, 15 of which are potentially secreted or expressed on the surface of the schizont and thus may be targets for host cell kinases. In particular, we describe the cell cycle-dependent phosphorylation of two T. annulata surface proteins, TaSP and p104, both of which are highly phosphorylated during host cell S-phase. TaSP and p104 are involved in mediating interactions between the parasite and the host cell cytoskeleton, which is crucial for the persistence of the parasite within the dividing host cell and the maintenance of the transformed state.     

Comprehensive analysis of endogenous bornavirus-like elements in eukaryote genomes

Bornaviruses are the only animal RNA viruses that establish a persistent infection in their host cell nucleus. Studies of bornaviruses have provided unique information about viral replication strategies and virus–host interactions. Although bornaviruses do not integrate into the host genome during their replication cycle, we and others have recently reported that there are DNA sequences derived from the mRNAs of ancient bornaviruses in the genomes of vertebrates, including humans, and these have been designated endogenous borna-like (EBL) elements. Therefore, bornaviruses have been interacting with their hosts as driving forces in the evolution of host genomes in a previously unexpected way. Studies of EBL elements have provided new models for virology, evolutionary biology and general cell biology. In this review, we summarize the data on EBL elements including what we have newly identified in eukaryotes genomes, and discuss the biological significance of EBL elements, with a focus on EBL nucleoprotein elements in mammalian genomes. Surprisingly, EBL elements were detected in the genomes of invertebrates, suggesting that the host range of bornaviruses may be much wider than previously thought. We also review our new data on non-retroviral integration of Borna disease virus.     

Functional analysis of host factors that mediate the intracellular lifestyle of Cryptococcus neoformans

Cryptococcus neoformans (Cn), the major causative agent of human fungal meningoencephalitis, replicates within phagolysosomes of infected host cells. Despite more than a half-century of investigation into host-Cn interactions, host factors that mediate infection by this fungal pathogen remain obscure. Here, we describe the development of a system that employs Drosophila S2 cells and RNA interference (RNAi) to define and characterize Cn host factors. The system recapitulated salient aspects of fungal interactions with mammalian cells, including phagocytosis, intracellular trafficking, replication, cell-to-cell spread and escape of the pathogen from host cells. Fifty-seven evolutionarily conserved host factors were identified using this system, including 29 factors that had not been previously implicated in mediating fungal pathogenesis. Subsequent analysis indicated that Cn exploits host actin cytoskeletal elements, cell surface signaling molecules, and vesicle-mediated transport proteins to establish a replicative niche. Several host molecules known to be associated with autophagy (Atg), including Atg2, Atg5, Atg9 and Pi3K59F (a class III PI3-kinase) were also uncovered in our screen. Small interfering RNA (siRNA) mediated depletion of these autophagy proteins in murine RAW264.7 macrophages demonstrated their requirement during Cn infection, thereby validating findings obtained using the Drosophila S2 cell system. Immunofluorescence confocal microscopy analyses demonstrated that Atg5, LC3, Atg9a were recruited to the vicinity of Cn containing vacuoles (CnCvs) in the early stages of Cn infection. Pharmacological inhibition of autophagy and/or PI3-kinase activity further demonstrated a requirement for autophagy associated host proteins in supporting infection of mammalian cells by Cn. Finally, systematic trafficking studies indicated that CnCVs associated with Atg proteins, including Atg5, Atg9a and LC3, during trafficking to a terminal intracellular compartment that was decorated with the lysosomal markers LAMP-1 and cathepsin D. Our findings validate the utility of the Drosophila S2 cell system as a functional genomic platform for identifying and characterizing host factors that mediate fungal intracellular replication. Our results also support a model in which host Atg proteins mediate Cn intracellular trafficking and replication.     

寄主种类、距离和种群密度对烟粉虱扩散的影响

在笼罩条件下,分别以黄瓜、棉花、蕹菜为虫源寄主和诱集寄主,研究寄主植物、空间距离、虫源密度等因子对B型烟粉虱扩散的影响。结果发现,从虫源寄主上扩散的成虫量,与烟粉虱对诱集寄主和虫源寄主的嗜性差异程度有关,诱集寄主相对于虫源寄主的嗜性越强,扩散出来的成虫数量就越多,反之扩散的成虫数量就越少。成虫扩散量与诱集寄主的距离呈负相关,并且诱集寄主的嗜性越强,随着距离的增大,诱集量下降的速率越快。成虫扩散量与虫源种群密度呈正关,但非嗜好寄主上的虫口承载量相对较低,在虫口密度相对较高时,非嗜好寄主上烟粉虱向外扩散的相对量更大。烟粉虱的扩散量与寄主营养状况呈负相关,寄主营养胁迫时,非嗜好寄主上可以获得相对更高的诱集量。