Transmission of Thelohanellus hovorkai Achmerov, 1960 (Myxosporea: Myxozoa) to common carp Cyprinus carpio through the alternate oligochaete host

Thelohanellus hovorkai (Myxosporea: Myxozoa) was transmitted to common carp Cyprinus carpio by exposing fish to Aurantiactinomyxon spores collected from the oligochaete Branchiura sowerbyi. The morphological characteristics of the actinosporean stage are described in detail. B. sowerbyi were exposed to T. hovorkai spores isolated from the experimentally infected carp, and after 3 and 4 months the worms exhibited prevalences of the actinosporean stage at 19.47% (7/36) and 14.6% (6/41), respectively. Control, unexposed worms were negative for the actinosporean infection. This is the first report of an Aurantiactinomyxon transforming into a myxosporean belonging to the suborder Platysporina.     

Geographical variation in spore morphology, gene sequences, and host specificity of Myxobolus arcticus (Myxozoa) infecting salmonid nerve tissues

Myxobolus arcticus Pugachev and Khokhlov, 1979 is a freshwater myxosporean parasite infecting the nerve tissues of salmonid fishes throughout the Pacific region of Far East Asia and North America. The principal fish host is sockeye salmon Oncorhynchus nerka in North America and masu salmon O. masou in Japan. Actinospores of M. arcticus were isolated from the lumbriculid oligochaetes Lumbriculus variegatus and Stylodrilus heringianus in Japan and Canada, respectively. Morphological comparisons indicated that Japanese actinospores from L. variegatus have significantly shorter caudal projections than Canadian isolates from S. heringianus, whereas the corresponding myxospores are indistinguishable. Transmission experiments showed that sockeye salmon were rarely susceptible to the Japanese actinospores, while masu salmon are highly susceptible to this parasite. Sequences of 4560 base pairs of the ribosomal RNA (rRNA) gene, including small subunit (SSU) and internal transcribed spacer (ITS) regions, from Japanese and Canadian isolates had a high similarity over 99.9%, suggesting that they may be conspecific. However, the biological data indicate that they are at least distinct strains. M. arcticus may be geographically isolated due to the specific homing migration of the anadromous fish hosts and has specialized its morphology and host selection for its local environment in the ongoing process of differentiation, potentially leading to speciation.     

Evaluation of a vector-control strategy of haemorrhagic thelohanellosis in carp,caused by Thelohanellus hovorkai (Myxozoa)

The life cycle of Thelohanellus hovorkai (Myxozoa), the causative agent of haemorrhagic thelohanellosis of carp Cyprinus carpio, involves the alternate oligochaete host Branchiura sowerbyi, which plays the role of vector in the parasite's transmission. Field investigations in carp farms suggested that oligochaete fauna were closely associated with the substrate type of the pond. The pond bottom in the enzootic farm consisted of clay soil and soft sediments comprised of organic mud, in which B. sowerbyi dominated in high densities, with a maximum of 5.6 ind. kg(-1) soil. In another case, in a carp farm with no previous history of the disease, the pond bottom was sandy soil, in which small-sized oligochaetes, composed mainly of Limnodrilus socialis, dominated. Laboratory studies on the substrate preference of oligochaetes proved that B. sowerbyi prefers mud to sand, whereas L. socialis has no tendency to substrate tropism. The delicate body surface of B. sowerbyi was subject to damage by rugged-edged sand particles, which inflicted severe injuries to the worms. Transmission experiments showed that L. socialis, which are non-susceptible to T. hovorkai, suppressed the production of T. hovorkai actinospores in B. sowerbyi in a mixed assemblage of oligochaetes. Field and experimental evidence in this study imply that substrate replacement in culture ponds might regulate the benthic oligochaete communities, resulting in minimization of the impact of haemorrhagic thelohanellosis. We propose that ecological control of oligochaete fauna by environmental management is a promising strategy against myxozoan diseases.     

Experimental detection of the actinospores of Myxobolus pseudodispar (Myxosporea: Myxobolidae) in oligochaete alternate hosts

The development of Myxobolus pseudodispar Gorbunova, 1936, an intracellular myxosporean muscle parasite of the roach Rutilus rutilus L., was studied in experimentally infected oligochaetes. In one experiment, uninfected Tubifex tubifex Müller and Limnodrilus hoffmeisteri (Claparéde) were exposed to mature spores of M. pseudodispar. Triactinomyxon spores developed both in T. tubifex and L. hoffmeisteri specimens. Triactinospores were first released from the oligochaetes 76 d after initial exposure. At that time, pansporocysts containing 8 triactinospores were located in the gut epithelium of experimentally infected oligochaetes, but free actinosporean stages were also found in their gut lumen. Each triactinospore had 3 pyriform polar capsules and an elongated cylindrical sporoplasm with 8 secondary cells. The spore body joined the 3 caudal projections with a relatively long style. One of the 3 caudal projections was shorter than the other two. The total length of the triactinospore was on average 206.5 microns.     

Diversifying selection and host adaptation in two endosymbiont genomes

Background  

The endosymbiont Wolbachia pipientis infects a broad range of arthropod and filarial nematode hosts. These diverse associations form an attractive model for understanding host:symbiont coevolution. Wolbachia 's ubiquity and ability to dramatically alter host reproductive biology also form the foundation of research strategies aimed at controlling insect pests and vector-borne disease. The Wolbachia strains that infect nematodes are phylogenetically distinct, strictly vertically transmitted, and required by their hosts for growth and reproduction. Insects in contrast form more fluid associations with Wolbachia. In these taxa, host populations are most often polymorphic for infection, horizontal transmission occurs between distantly related hosts, and direct fitness effects on hosts are mild. Despite extensive interest in the Wolbachia system for many years, relatively little is known about the molecular mechanisms that mediate its varied interactions with different hosts. We have compared the genomes of the Wolbachia that infect Drosophila melanogaster, w Mel and the nematode Brugia malayi, w Bm to that of an outgroup Anaplasma marginale to identify genes that have experienced diversifying selection in the Wolbachia lineages. The goal of the study was to identify likely molecular mechanisms of the symbiosis and to understand the nature of the diverse association across different hosts.     

Parasitism, host immune function, and sexual selection

Parasite-mediated sexual selection may arise as a consequence of 1) females avoiding mates with directly transmitted parasites, 2) females choosing less-parasitized males that provide parental care of superior quality, or 3) females choosing males with few parasites in order to obtain genes for parasite resistance in their offspring. Studies of specific host-parasite systems and comparative analyses have revealed both supportive and conflicting evidence for these hypotheses. A meta-analysis of the available evidence revealed a negative relationship between parasite load and the expression of male secondary sexual characters. Experimental studies yielded more strongly negative relationships than observations did, and the relationships were more strongly negative for ectoparasites than for endoparasites. There was no significant difference in the magnitude of the negative effect for species with and without male parental care, or between behavioral and morphological secondary sexual characters. There was a significant difference between studies based on host immune function and those based on parasite loads, with stronger effects for measures of immune function, suggesting that the many negative results from previous analyses of parasite-mediated sexual selection may be explained because relatively benign parasites were studied. The multivariate analyses demonstrating strong effect sizes of immune function in relation to the expression of secondary sexual characters, and for species with male parental care as compared to those without, suggest that parasite resistance may be a general determinant of parasite-mediated sexual selection.     

Differences between horse selection based on two forms of osteochondrosis in fetlock

Horses lose potential opportunities because of health problems. Available breeding strategies are not effective enough, probably also because of the different definition used and its genetic usefulness. The aim of the study was to compare the genetic background estimated by the genome-wide association study (GWAS) for osteochondrosis using two different scaling osteochondrosis (OC)/healthy and osteochondrosis dissecans (OCD)/healthy systems for evaluating the disease status of investigated fetlock joints. Two hundred one Warmblood horses trained for performance tests (87 stallions and 114 mares) were phenotyped and genotyped. Four fetlock x-ray images per horse were collected using the RTG Girth HF 80 and Vet Scan ray 3600. The DNA of each horse was genotyped using the BeadChip 70K. To identify SNPs that significantly affect the probability of osteochondrosis, two different methods were applied: the Cochran-Armitage test based on an additive mode of inheritance and logistic regression. The genetic background for osteochondrosis, expressed in the number of SNPs found with significant associations with osteochondrosis, was higher by evaluation in the scale of OCD/healthy horses (16 SNPs on several chromosomes mainly on the ECA1 and ECA10) than OC/healthy (2 SNPs on the ECA15 and one SNP on the ECA10). Detailed definition of osteochondrosis is needed in breeding and in veterinary practice. The genetic background for osteochondrosis and osteochondrosis dissecans seems not the same. Suggestive SNPs could be the candidate markers for osteochondrosis but should be checked on a larger population before usage.     

Development of Myxobolus macrocapsularis (Myxosporea: Myxobolidae) in an oligochaete alternate host,Tubifex tubifex

The development of Myxobolus macrocapsularis Reuss, 1906, a myxosporean parasite of the gills of common bream Abramis brama L., was studied in experimentally infected oligochaetes. In 3 experiments uninfected Tubifex tubifex Muller and Limnodrilus hoffmeisteri (Claparéde) were exposed to mature myxospores of M. macrocapsularis. In all experiments, typical triactinospores developed in T. tubifex specimens but no infection was found in L. hoffmeisteri. Triactinospores were released from oligochaetes 66 to 99 d after initial exposure. At that time pansporocysts containing 8 triactinospores were located in the gut epithelium of experimental oligochaetes, but free actinosporean stages were also found in the gut lumen of the oligochaetes. Each triactinospore had 3 pyriform polar capsules and a barrel-shaped sporoplasm with 32 secondary cells. The spore body joined the 3 caudal projections with a stout style.     

Myxobolus sp. can cause in vivo myoliquefaction in the host Paralichthys orbignyanus (Osteichthyes, Paralichthydae)

We found intense myoliquefaction in vivo among specimens of wild and farmed South American flatfish Paralichthys orbignyanus Valenciennes, 1839. The soft flesh condition was attributed to Myxobolus sp. since the fish were not infected by myxosporeans which are usually associated with this condition (Kudoa spp.), and other causes (bacteria, fungi) were not found. The histopathology of the infection is described.     

The apical organelles of malaria merozoites: host cell selection, invasion, host immunity and immune evasion

Malaria is caused by protozoan parasites belonging to the phylum Apicomplexa. These obligate intracellular parasites depend on the successful invasion of an appropriate host cell for their survival. This article is a broad overview of the molecular strategies employed by the merozoite, an invasive form of the malaria parasite, to successfully invade a suitable red blood cell.     

Site preference of fish myxosporeans in the gill

In addition to the morphological and size characteristics of the spores, indicating the exact location and tissue specificity is also essential for differentiation of the large number of species belonging to the group of gill-parasitic fish, the myxosporeans. According to the observations of the present author, Myxobolus, Henneguya and Thelohanellus species are characterised by strict tissue specificity, and species showing affinity to the epithelium, connective tissue, cartilage or vascular tissue usually occur in a strictly defined location within the gill apparatus. Some of the species typically form plasmodia in the lamellae of the gill and others in the gill filaments. Yet other species develop their plasmodia at the base of the gill filament or in the gill arch. Instead of the generally accepted but misleading terms 'intra-' and 'interlamellar', the present author distinguishes interlamellar-epithelial and intralamellar-vascular types in the case of plasmodia developing in the gill lamellae, and intrafilamental-epithelial, intrafilamental-vascular and intrafilamental-chondroidal types in the case of plasmodia developing in the gill filaments. Regarding site of development within the gill, the location of basifilamental plasmodia and that of plasmodia developing in the cartilaginous matrix, connective tissue or blood vessels of the gill arch are well distinguishable from the above types. The different types and their variations are shown in histological illustrations.     

Morphological,host range,and genetic characterization of two coliphages

Two coliphages, AR1 and LG1, were characterized based on their morphological, host range, and genetic properties. Transmission electron microscopy showed that both phages belonged to the Myoviridae; phage particles of LG1 were smaller than those of AR1 and had an isometric head 68 nm in diameter and a complex contractile tail 111 nm in length. Transmission electron micrographs of AR1 showed phage particles consisting of an elongated isometric head of 103 by 74 nm and a complex contractile tail 116 nm in length. Both phages were extensively tested on many strains of Escherichia coli and other enterobacteria. The results showed that both phages could infect many serotypes of E. coli. Among the enterobacteria, Proteus mirabilis, Shigella dysenteriae, and two Salmonella strains were lysed by the phages. The genetic material of AR1 and LG1 was characterized. Phage LG1 had a genome size of 49.5 kb compared to 150 kb for AR1. Restriction endonuclease analysis showed that several restriction enzymes could degrade DNA from both phages. The morphological, genome size, and restriction endonuclease similarities between AR1 and phage T4 were striking. Southern hybridizations showed that AR1 and T4 are genetically related. The wide host ranges of phages AR1 and LG1 suggest that they may be useful as biocontrol, therapeutic, or diagnostic agents to control and detect the prevalence of E. coli in animals and food.     

Computer simulated host selection in Ips typographus

Foraging behaviour by Ips typographus L. (Coleoptera; Scolytidae) was simulated to assess host finding and reproductive success of beetles following four different strategies: 1. random search, 2. upwind search, in which beetles follow a prevailing flight direction, 3. random search with short range olfactory attraction to susceptible trees (primary attraction), and 4. upwind search with primary attraction. For each strategy we varied three parameters in equidistant steps including number of susceptible trees per hectare (0.06–0.33), population size (200–1000 beetles), and flight capacity (500–3000 m). All possible combinations of these parameters were tested in 12 replicates with more than 400 000 imaginary beetles flown through the simulated forest. Reproductive success of strategy 4, which combined upwind flight with primary attraction, exceeded that of the other strategies (1–3) circa 27, 7, and 4 times, respectively. In random search, maintenance of the population required a flight capacity, population size and host tree abundance which are unlikely to occur at suboutbreak levels in nature.

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Zusammenfassung Die Wirtsbaumsuche des Buchdruckers wurde in einem Computermodell simuliert und Wirtsbaumfindung und Fortpflanzungserfolg in 4 verschiedenen Suchstrategien quantifiziert: 1. Zufallssuche, 2. Gegenwindsuche, in der die Käfer einer Hauptflugrichtung folgen, 3. Zufallssuche mit Wahrnehmung des bruttauglichen Wirtsbaumes aus kurzer Distanz (primäre Attraktivität), und 4. Gegenwindsuche mit primärer Attraktivität. Für jede Strategie wurden 3 Parameter in äquidistanten Schritten verändert: die Anzahl bruttauglicher Bäume pro Hektar (0.06–0.33), die Populationsdichte der Käfer (200–1000) und die Flugkapazität der Käfer (500–3000 m). Alle möglichen Kombinationen dieser Parameter wurden in 12 Wiederholungen getestet und daher mehr als 400 000 imaginäre Käfer durch den Modellwald geflogen. Der Fortpflanzungserfolg in Strategie 4, die Gegenwindsuche mit Wahrnehmung des Wirtsbaumes aus kurzer Distanz kombinierte, übertraf den in Strategie 1, 2 und 3 circa 27-, 7-, bzw 4-fach. Zur Erhaltung der Käferpopulation waren in der Zufallssuche eine Populationsdichte, Flugkapazität und Wirtsbaumdichte erforderlich, wie sie in der endemischen Phase wohl kaum anzutreffen sind.

     

Behaviour of the bark beetle, Ips grandicollis, during host selection

ABSTRACT. Equal numbers of dispersing Ips grandicollis adults were caught on sticky traps held on susceptible and resistant Pinus radiata trees. When beetles were attracted to the same set of trees using baits of ipsenol (aggregation pheromone), some of the beetles that landed on the boles of the trees bored into the bark. The subsequent response of the tree determined whether the tree was accepted or rejected. In resistant trees, the exudation of resin prevented continued boring and led to the retreat of the beetles. In susceptible trees, continued boring led to the establishment of the beetles. Ipsenol was not detected in males that retreated after boring into resistant trees. Beetles that bored into P. radiata logs obtained from slash, continued to bore into the bark, due to the absence of any of the resistance mechanisms; ipsenol was detected in such males. Extracts of groups of male beetles caught from the dispersing population on pheromone-baited traps, contained little or no ipsenol.     

Host age and host selection byTrichogramma nubilale

Selection byTrichogramma nubilale (Ertle & Davis) for different aged egg masses ofOstrinia nubilalis (Hübner) was examined by separating components of parasitism. FemaleT. nubilale were exposed to egg masses of 2 different ages (freshly laid egg masses versus 1, 2, 3 or 4 day old egg masses), and the age of the initial egg mass inspected, number and percent of eggs and egg masses parasitized, and the emergence rate of pharate parasitoids was recorded. When there was a large difference in age between young and old egg masses, ♀♀ inspected initially more young egg masses (>2 days difference), parasitized a greater percent of young egg masses (>2 days difference), and parasitized more eggs/parasitized egg mass in young egg masses (>3 days difference) than old egg masses. Females did not discriminate between host age when hosts were similar in age. Successful emergence of parasitoids was greater from younger eggs than older eggs, although emergence was better from one-day-old eggs than from fresh eggs. These results imply that when the hosts were sufficiently different in age, ♀♀ were attracted to younger egg masses more than older egg masses, and they tended to remain ovipositing for longer periods of time on younger egg masses than older egg masses. Moreover, ♀♀ appeared to prefer to oviposit in hosts in which their young are more likely to complete development.      

Differences in host controlled reactivation of lambdoid and T phages

Summary Phages 434, T4, T5 and T7 are studied with regard to host controlled reactivation of damage produced by UV or photodynamic action sensitized by thiopyronine. Repair of 434 phages proceeds under control of both hcr and rec genes. UV irradiated T5 and T7 phages are reactivated under control of the host's hcr genes only. If these phages are inactivated by photodynamic action they are reactivated not at all. T4 phages inactivated by both treatments are also refractory to host controlled reactivation. These differences might reflect different degrees of autarchy and different abilities of phage DNAs to serve as substrate for recombination enzymes of the host.These results were presented in an abstracted version at the V. International UV colloquium Grundlagen der UV-Wirkung, Kühlungsborn, DDR, in October 1969. The experiments with T5 were done by Mrs. E. Marx.     

Ecological and taxonomic trends in macrolepidopteran host plant selection

Patterns of host plant use by larvae of macrolepidoptera feeding on trees and shrubs in Britain and Canada are examined. The incidence of polyphagous species varies among different lepidopteran taxa. Among largely monophagous taxa host plant switching has often occurred. The greater similarity of insect faunas on closely related plants is documented using cluster analysis. The Canadian data reveal that lepidopterans feeding on conifers are less specific in their host plant choice than species feeding on angiosperms. The numerical analyses also provide evidence of greater overlap in the insect faunas of plants belonging to the same ecological association. These results are discussed with particular reference to Lepidoptera-plant coevolution.