No description available.

The salmon louse (Lepeophtheirus salmonis) is recognised as a major pathogen of farmed Atlantic salmon (Salmo salar). With the growth in salmon farming in Scotland and Norway the problem of lice and the need to understand more about their biology and population dynamics has grown. The aims of this study were to examine various aspects of the reproductive biology of L. salmonis and increase fundamental knowledge of this area. It was discovered that the male reproductive system consisted of a pair of testes, vasa deferentia, spermatophore sacs and cement glands and the female reproductive system consisted of a pair of ovaries, oviducts, cement glands, and a single receptaculum seminis. The processes of spermatogenesis, cogenesis and spermatophore formation were examined and compared with those of other species of copepod. Mating in L. salmonis began with the establishment of a precopulatory pair, between an adult male and predominantly a preadult II female. Following the final moult of the female, copulation proceeded and a pair of spermatophores were transferred by the male onto the female. Details of the mating process and associated reproductive behaviour are described. The possible involvement of sex pheromones in mate location was examined. Both adult males and preadult II females were extremely mobile and freely changed host individual. Some evidence was found to suggest preadult II females produced a chemical stimulus to attract conspecifics. Reproductive output and investment by adult female L. salmonis were examined. Distinct seasonal variation in reproductive output existed in the field and under laboratory conditions. Summer generation females produced 6 batches of eggs whereas winter generation females may have produced 4 or 5 batches. Egg strings produced in summer were shorter and had fewer, larger, eggs compared to egg strings produced in winter. Summer generation females invested more protein per egg than winter generation females, which invested more protein per string. It appeared that total reproductive investment by winter and summer generation females may have been equal. Differences in reproductive output and investment were influenced by changes in environmental parameters, particularly temperature. Preliminary studies into the effect of egg size on hatching and nauplius survival were carried out. These results suggested different reproductive strategies were adopted by winter and summer generations of adult female L. salmonis under different environmental conditions. The causes and implications of these different reproductive strategies are discussed.

No description available.

Inaug.-Diss.--Bonn. / Vita. "Literaturverzeichnis": p. 95-100.

All filarial nematodes of the family Onchocercidae are parasites of vertebrates and require intermediate insect hosts for completion of their life-cycles. Eighteen genera within this family are known to infect birds but very few of the associated intermediate hosts have been elucidated. Sarconema eurycerca (Wehr) is a filarial nematode of swans and geese. A recent study of S. eurycerca in American Whistling Swans (Cygnus c. columbianus ) has demonstrated that the intermediate insect host is a feather louse, Trinoton anserinum (Fabricius) (Seegar, 1977). The main aim of the present study was to investigate the relationship between S. eurycerca and British swans and to determine whether T. anserinum is the intermediate host of the parasite in this country. A total of 1128 swans (of all species) were examined from sites in Britain, Denmark and Iceland. Infected swans were detected by examining blood samples for larval stages of S. eurycerca (microfilariae) using a new sedimentation technique developed in the study. An overall incidence of 15.0% was recorded with a significantly higher proportion of juvenile swans being infected. The microfilariae of S. eurycerca exhibited a diurnal sub-periodic rhythm within the host, with maximum counts occurring between 11.00 and 19.00 hours in the peripheral blood supply. T. anserinum was found to satisfy all the attributes required of an intermediate insect host. As an obligate ectoparasite, T. anserinum has a close spatial and temporal relationship with the swan. T. anserinum appears to be capable of ingesting microfilarie of S. eurycerca whilst feeding on blood. All developing larval stages of S. eurycerca were found in T. anserinum and the louse was very mobile and capable of transmitting the nematode from one swan to another. Examinations were made of the nematode, its morphology and pathological effects on both heart tissue and blood components of the swan. Significantly higher lymphocyte percentages and lower eosinophil percentages, haematocrit and red blood corpuscle counts were recorded in swans infected with S. eurycerca.

No description available.

Le pou de tête et le pou de corps sont deux écotypes indiscernables occupant chacun une niche écologique différente. Le pou de corps représente une menace réelle pour l'Homme en raison de son rôle de vecteur dans la transmission de trois maladies graves pour l'Homme à savoir: le typhus épidémique, la fièvre des tranchées et la fièvre récurrente. Dans cette thèse, nous avons obtenu des résultats concrets dans chacune des thématiques abordées. En effet, nous avons (i) mis en place un outil moléculaire qui permet de différencier pour la première fois entre le pou de tête et le pou de corps qui a montré efficacité sur le terrain, (ii) mis en évidence l'existence d'un nouveau clade mitochondrial (Clade D) renfermant des poux de tête et des poux de corps susceptible de vectoriser Bartonella quintana et Yersinia pestis, (iii) retracé les migrations humaines à travers l'analyse de poux anciens provenant de différentes périodes et localisations, (iv) démontré pour la première fois que Pediculus mjobergi est génétiquement proche du pou humain et confirmé l'hypothèse qu'à l'origine Pediculus mjobergi était un pou humain qui a été transféré aux singes du Nouveau Monde par les premiers Hommes à avoir atteint le continent américain il y a des milliers d'années et (v) mis en place un outil de détection et de contrôle de la résistance moléculaire des poux à la perméthrine. Cet outil fut particulièrement utile dans l'étude clinique que nous avons menée pour déterminer si l'utilisation de sous-vêtements imprégnés d'insecticide offrait une protection efficace à long terme contre les poux de corps infestant les personnes sans-abri. / Head louse (Pediculus humanus capitis) and body louse (Pediculus humanus humanus) are two indistinguishable ecotypes each occupying an ecological niche: hair for head louse and clothing for the body louse. Body louse represents a real threat to humans because of its role as vector for the transmission of three deleterious diseases namely epidemic typhus, trench fever and relapsing fever.In this thesis, we obtained concrete results that have led to scientific publications. Indeed, we (i) implemented a molecular tool to differentiate for the first time between head and body louse, (ii) we highlighted the existence of a fourth mitochondrial clade (Clade D) comprising head and body lice that can vectorize Bartonella quintana and Yersinia pestis, (iii) we traced human migration through the analysis of ancient lice from different periods and different area, (iv) we demonstrated for the first time that Pediculus mjobergi is genetically close to human louse and confirmed the hypothesis that initially Pediculus mjobergi was a human louse has been transferred to New World monkeys by the first humans who have reached the American continent thousands of years ago and (v) we have implemented a tool for detecting and monitoring the molecular resistance to permethrin of body lice that parasite sheltered homeless persons in Marseille. This tool was particularly useful in the clinical study we conducted to determine whether the use of long-lasting insecticide-treated underwear provides effective long-term protection against body lice in homeless persons.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Within southern Africa, the widely distributed four-striped mouse Rhabdomys is parasitized by, amongst others, the host-specific ectoparasitic sucking louse, Polyplax arvicanthis. The present study investigated this parasite-host association from a phylogenetic and phylogeographic perspective utilizing mitochondrial and nuclear DNA markers. The findings support the existence of four species within Rhabdomys (three distinct lineages within the previously recognized arid-adapted R. pumilio and the mesic-adapted R. dilectus). These species have distinct geographic distributions across vegetational biomes with two documented areas of sympatry at biome boundaries. Ecological niche modelling supports a strong correlation between regional biomes and the distribution of distinct evolutionary lineages of Rhabdomys. A Bayesian relaxed molecular clock suggests that cladogenesis within the genus coincides with paleoclimatic changes (and the establishment of the biomes) at the Miocene-Pliocene boundary. Strong evidence was also found that the sucking louse P. arvicanthis consists of two genetically divergent lineages, which probably represent distinct species. The two lineages have sympatric distributions throughout most of the sampled range across the various host species and also occasionally occur sympatrically on the same host individual. Further, the absence of clear morphological differences among these parasitic lineages suggests cryptic speciation. Limited phylogeographic congruence was observed among the two P. arvicanthis lineages and the various Rhabdomys species and co-phylogenetic analyses indicated limited co-divergence with several episodes of host-switching, despite the documented host-specificity and several other traits predicted to favour congruence and co-divergence. Also, despite the comparatively smaller effective population sizes and elevated mutational rates found for P. arvicanthis, spatial genetic structure was not more pronounced in the parasite lineages compared to the hosts. These findings may be partly attributed to high vagility and social behaviour of Rhabdomys, which probably promoted parasite dispersal among hosts through frequent inter-host contact. Further, the complex biogeographic history of Rhabdomys, which involved cyclic range contractions and expansions, may have facilitated parasite divergence during periods of host allopatry, and host-switching during periods of host sympatry. Intermittent contact among Rhabdomys lineages could also have prevented adaptation of P. arvicanthis to specific host lineages, thus explaining the lack of host-specificity observed in areas of host sympatry. It is thus evident that the association between Polyplax arvicanthis and Rhabdomys has been shaped by the synergistic effects of parasite traits, biogeography, and host-related factors over evolutionary time. / AFRIKAANSE OPSOMMING: Binne suidelike-Afrika word die wyd-verspreide gestreepte veldmuis, Rhabdomys, onder andere deur die gasheer-spesifieke ektoparasitiese luis, Polyplax arvicanthis, geparasitiseer. Die huidige studie het hierdie parasiet-gasheer interaksie vanuit ‘n filogenetiese en filogeografiese oogpunt ondersoek deur van beide mitokondriale en nukluêre merkers gebruik te maak. Die bevindinge dui op die bestaan van vier spesies binne Rhabdomys, waaronder drie nuwe genetiese groepe binne die voorheen erkende R. pumilio asook R. dilectus. Hierdie spesies het nie-oorvleulende geografiese verspreidings binne spesefieke plantegroei biome met twee geidentifiseerde areas van simpatriese voorkoms by bioom grense. Ekologiese nis modellering ondersteun ‘n sterk korrelasie tussen biome en die verspreiding van die evolusionêre groepe binne Rhabdomys. ‘n Bayesiaanse verslapte molekulêre klok dui daarop dat kladoginese binne die genus gedurende paleoklimatiese veranderinge, wat tot die totstandkoming van die huidige biome gelei het, by die Mioseen-Plioseen grens plaasgevind het. Sterk bewyse is ook gevind dat die parasitiese luis P. arvicanthis uit twee geneties verskillende groepe, wat heel moontlik afsonderlike spesies verteenwoordig, bestaan. Hierdie genetiese groepe het simpatriese verspreidings oor meeste van die gebestudeerde geografiese area op die verskeie gasheer spesies en mag ook soms simpatries op dieselfde gasheer individu voorkom. Verder dui die afwesigheid van duidelike morfologiese verskille tusssen die parasiet genetiese groepe op moontlike kriptiese spesiasie. Beperkte filogeografiese ooreenstemming is tussen die P. arvicanthis genetiese groepe en die Rhabdomys spesies waargeneem en die vergelykende-filogenetiese analises het aangedui dat daar beperkte gesementlike-divergensie plaasgevind het met verskeie episodes van gasheer-wisseling, ten spyte van die gasheer-spesifieke aard van die parasiete asook verskeie ander kenmerke wat veronderstel is om filogeografiese ooreenstemming en gesementlike-divergensie te bevorder. Ten spyte van die vergelykbaar kleiner effektiewe bevolking groottes en verhoogde mutasie tempo wat vir P. arvicanthis gevind is, is die geografiese genetiese struktuur nie meer gedifferensieёrd in die parasiet groepe as in die gasheer nie. Hierdie bevindinge mag deels verklaar word deur die hoё beweeglikheid asook die sosiale gedrag van Rhabdomys, wat waarskynlik parasiet beweging tussen gashere bevorder deur gereelde tussen-gasheer kontak. Die komplekse biogeografiese geskiedenis van Rhabdomys, wat sikliese inkrimping en uitsetting van die geografiese verspreiding behels het, het heel moontlik parasiet divergensie tydens tydperke van gasheer allopatrie asook gasheer-wisseling tydens tydperke van gasheer simpatrie, gefasiliteer. Tussentydse kontak tussen Rhabdomys genetiese groepe kon aanpassing van P. arvicanthis tot sekere gasheer genetiese groepe verhoed het en verklaar dus die afwesigheid van waargenome gasheer-spesifisiteit in areas van gasheer simpatrie. Dit is dus duidelik dat die assosiasie tussen P. arvicanthis en Rhabdomys deur die sinergistiese uitwerking van parasiet kenmerke, biogeografie, asook gasheer-verwante faktore oor evolusionêre tyd gevorm is. / National Research Foundation (NRF)

Title from title page of PDF (University of Missouri--St. Louis, viewed March 23, 2010). Includes bibliographical references.

Background Atlantic salmon (Salmo Salar) is a key aquaculture species in several countries. Since its critical role in economic sector and scientific research, this species has been relatively extensively investigated, in comparison with other farmed and wild aquatic species. However, the genetic components associated with growth and fillet-related traits are lack consistency, and the issue of sea louse disease in both wild and famed salmon is still unsolved. Objectives Overall aim of this project was to understand the genetic basis of growth-related traits and host resistance to sea lice using three large commercial farmed salmon populations. Specifically, the method of quantitative trait loci (QTL) mapping, genome-wide association study (GWAS), and genomic prediction (GS) were utilized to dissect the genetic architectures associated with traits of interest in our experimental populations. Prior to this, linkage mapping was performed to construct a high-density linkage map for Atlantic salmon. Results Linkage map A linkage map was firstly constructed underlying a SNP array containing 132 K validated SNPs. 96,396 SNPs were successfully assigned to 29 chromosomes that correspond to the linkage group number of European Atlantic salmon. 6.5 % of unassigned contigs, which was equal to 1 % of recent whole genome reference assembly (GCA_000233375.4) anchored to exist chromosomes by referring to linkage mapping result. Genetic components associated with growth traits Heritabilities of growth-related traits were about 0.5 to 0.6 in adult and juvenile farmed salmon. The QTL mapping and GWAS suggested the growth-related traits are likely a polygenic genetic architecture with no major QTL segregating. The prediction accuracy estimated by genomic prediction showed that approximately 5,000 SNP markers could achieve the highest accuracy in body weight and length in juvenile salmon within population. Genetic components associated with lice resistance The heritability of lice resistance was 0.22 to 0.33 using pedigree and genetic relationship matrices respectively. GWAS indicated that the host resistance to sea lice was likely polygenic with no individual SNP surpassed the genome-wide significance threshold. Genomic prediction showed that about 5 to 10 K SNPs was able to achieve the asymptote of accuracy in closely related animals, while the greatest advantage of genomic prediction was observed in non-sibling test within population. Conclusions As the growth-related traits and lice resistance are both likely polygenic and population-specific, the genomic prediction is an efficient approach to capture the genetic variances of the traits in selection candidates in experimental population, especially for traits with low heritability such as flesh colour and lice resistance. Family-based selection method is the better choice than mass selection to accumulate the genetic effects in corresponding SNP platform. Given the high cost of genotyping and field data collection, the genotyping-by-sequencing and genotype imputation are likely the way to make significant improvements in relevant research.