RESUMEN

A previous study showed that the susceptibility of hybrids between two Mus musculus musculus and Mus musculus domesticus did not apply to every parasite. The authors proposed that only parasites which exerted enough constraints would induce the selection of poorly compatible systems of resistance in the subspecies. This study completes the previous work. Experimental infections of mice of the two subspecies and their hybrids with the tissue-dwelling protozoan Sarcocystis muris show that hybrids are more susceptible to the coccidian than M. m. musculus and M. m. domesticus individuals. This result demonstrates that the hybrids are not only susceptible to intestinal helminths, and confirms the 'constraint hypothesis'.

Asunto(s)

RESUMEN

This study characterises the extent of the susceptibility to parasites (first demonstrated with helminths) of hybrids between Mus musculus domesticus and Mus musculus musculus. Experimental infections with Trypanosoma musculi of M. m. domesticus, M. m. musculus and their natural hybrids have been performed to compare their level of resistance/susceptibility. It appears that contrary to the results with helminths, hybrid mice present the same level of resistance/susceptibility to the trypanosome as M. m. musculus and M. m. domesticus individuals. This result is interpreted in the light of the modalities of host parasite interactions and leads us to hypothesise on the role of parasitism in the evolution of the house mouse hybrid zone.

Asunto(s)

Asunto(s)

RESUMEN

Sixteen laboratory and 7 wild-derived strains of mice were infected with the pinworm Aspiculuris tetraptera in order to compare their resistance levels estimated by the intestinal parasite loads. It appears that (i) in 4 strains out of 23, females and males harbour different parasite loads; (ii) wild and laboratory mice display a broad range of infection levels when compared independently; (iii) the laboratory strains are more resistant than the wild ones. We suggest that (i) compared to sex, the strain (i.e. genetic) effect is the main parameter which determines the levels of infection; (ii) resistance was selected in laboratory strains during their breeding because of the parasite pressure present in captivity.

Asunto(s)

RESUMEN

The resistance and susceptibility to the intestinal pinworm Aspiculuris tetraptera, a natural parasite of the house mouse Mus musculus, is experimentally analysed using both the F1 from wild-type mice of the two subspecies (M. m. domesticus and M. m. musculus) and the F1 from different laboratory inbred mice. The results show that: (i) the F1 from wild-type mice harbour a lower parasite load than the parental mice, suggesting a phenomenon of hybrid vigour; and (ii) the F1 from inbred mice harbour parasite loads similar to the resistant parent, suggesting that resistance is inherited as a dominant feature in these laboratory mice. This analysis supports the hypothesis that recombinations occurring between the two mouse genomes (i.e. M. m. domesticus and M. m. musculus) are responsible for the hybrid dysgenesis observed in the natural hybrid zone between the two mice subspecies.

Asunto(s)

RESUMEN

Microsporidium acanthocephali n. sp. and Microsporidium propinqui n. sp. are two microsporidian species hyperparasitic in the tegumentary syncytium of salt-water fishes. Their ultrastructural study shows that both species have diplocaryotic meronts and spores, anisofilar polar filaments; meronts and some sporogonic stages of M. acanthocephali are surrounded by a parasitic vacuole. Spores of both parasites are oviform; those of M. acanthocephali are gigantic, 12-14 micron long and 6-7 micron broad, those of M. propinqui are only 3-4 micron X 1.25-1.50 micron. A poor knowledge of some sporogonic aspects prevents us from all precise generic assigning of these two parasites which may coexist in the same Helminth.

Asunto(s)

RESUMEN

Synaptinemal complexes have been demonstrated in 7 microsporidian species belonging to 6 different genera (Gurleya, Thelohania, Pleistophora, Tuzetia, Baculea, Glugea). Thus, it can be presumed that a meiosis and consequently a karyogamy occur during their life cycle. Meisis occurs at the beginning of sporogony; therefore, karyogamy, must occur between spore and merogany, i.e. during the poorly known part of the life cycle. In the microsporidian species studied, with uninucleate spores and diplokaryotic merogony (Thelohania for instance), the 2 joined nuclei, each of them containing meiotic chromosomes, not only fail to fuse, but actually separate at the beginning of sporogony; afterwards, each of them undergoes meiosis. Their separation is accompanied by the appearance of an organelle whose structure and function are poorly understood. However, its structure resembles that of the kinetic center. The Nosema species studied do not have synaptinemal complexes; thus, their life cycle is difficult to understand: either karyogamy and meiosis occur during the unobserved part of the life-cycle, or sexual phanomena are absent altogether. In the latter case, the Nosema-type life cycle might be limited to vegetative multiplication which could be explained by the dimorphism theory of Microsporidia. It is shown also in the present study that the life cycle of Microsporidia does not involve haploid organisms which it might be thought to contain by comparing it with the cycles of sporozoa.

Asunto(s)

RESUMEN

This work is the summary of our present knowledge about the ultrastructure of Simuliids larvae Microsporidans, including several new data concerning: 1. Pleistophora simulii (Lutz et Splendore, 1904): reticulated or net-like plasmodial envelope, formation of pansporoblastic structures looking like short pipes. 2. Stempellia simulii Maurand et Manier, 1968: plasmodial envelope as Pleistophora simulii, granular-textured polaroplast. 3. Thelohania fibrata (Strickland, 1913): ultrastructural study of the sporogonic sequence nerve done so far. 4. Thelohania bracteata (Stickland, 1913): its relations with Thelohania minuta, T. canningi, Amblyospora bracteata, Pegmatheca simulii. 5. Tuzetia debaisieuxi (Jirovec, 1943): formation of pseudopansporoblasts by the host-cell membrane.

Asunto(s)

RESUMEN

Synaptonemal complexes are described in the prophasic nucleus of young pansporoblasts of Gurleya chironomi. Consequently the first mitosis of this nucleus might be a reductional one and sporogony a haploid phase in the life cycle of this Microsporidia.

Asunto(s)

RESUMEN

A cytochemical study of Microsporidia in Carcinus mediterraneus points out the following data: acid or very acid intrasporoblastic mucopolysaccharids, are found in Thelohamia maenadis which react as sulfomucins in opposition to external asulfated mucosubstances rich in electronegative groups. In Nosema pulvis, the mucopolysaccharid compound is nearly equivalent of that of Nosema orthocladii. Both species are also characterized by the abundance of sulfured proteins in their spore walls and the lack of stock substances.

Asunto(s)

RESUMEN

A new microsporidian parasitic in Myriapoda-Diplopoda of Sud-Dahomey (Habrodesmus falx Cook & Oxydesmus granulosus Palisot de Beauvois) is described by photonic microscopy. It can be recognized by its thick-enveloped pansporoblasts yielding from 30 to 66 elongate and ovoid spores measuring 4,8 mum in length and 2,2 mum in diameter. The spore is uninucleate. This microsporidian forms cysts in the anterior part of the host affecting the musculature of the digestive tract, the adipose tissue and segmentary muscles. However, it appears necessary to study this parasite again by means of electron microscopy for a better understanding of its life-cycle and in order to place it in the Microsporidian taxonomy.

Asunto(s)

Asunto(s)