Population biology of Schistosoma mansoni in the black rat: host regulation and basic transmission rate.

A simple mathematical model was built to investigate the population biology of Schistosoma mansoni in its natural definitive host, the black rat (Rattus rattus). Prevalence and parasite abundance over 13 years from field studies and data from laboratory experiments were used to set up the model. Sensitivity analysis showed that the abundance of parasites is strongly influenced by variation in the values of infection parameters. The model shows that the parasite is able to control populations of definitive hosts. We discuss the factors that may explain the long-term persistence of S. mansoni among its natural definitive host, R. rattus and its intermediate host, the snail Biomphalaria glabrata in Guadeloupe (French West Indies). The impact of the parasite does not appear to explain the apparent persistence of the host-parasite association over a 13 year period. Our results seem to support the influence of environmental factors, which may act on the infection process by reducing, or increasing, the rate of encounters between hosts and free-living stages of the parasite.     

Intrauterine Growth Retardation (Malnutrition by Vascular Ligation) Induces Modifications in Fatty Acid Composition of Neurons and Oligodendrocytes

Intrauterine growth retardation (IUGR) induced by ligation of one uterine artery on day 17 of pregnancy in the rat lead to major abnormalities in the fatty acid content of neurons and oligodendrocytes but not in astrocytes. In neurons from IUGR rats, monounsaturated fatty acids were decreased; in the polyunsaturated series, ω-3 fatty acids were increased and Ω-6 fatty acids were decreased. In oligodendrocytes, monounsaturated fatty acids were also decreased, but the modifications in polyunsaturated fatty acids were the opposite of those in neurons: Ω-3 being decreased and w-6 increased. Although the animals received a normal diet after birth, the alterations were still present in adulthood. In addition, fatty acid composition of brain cells is a very indicative criterion of brain maturation.     

Morphological study of Eudromoxyura aspiculuris (Nematoda,Heteroxynematidae) from the tinamou Eudromia elegans (Aves,Tinamidae)

Eudromoxyura aspiculuris (Boero &; Led, 1971) is a parasite of a tinamid bird in Argentina. This is the type and only one known speices so far described in the genus Eudromoxyura Anderson &; Prestwood, 1972. It is here redescribed, and Eudromoxyura elonbyrdi Anderson &; Prestwood 1972 is considered a synonym. The morphological characters and systematic position of the genus Eudromoxyura are discussed. The genera Syphaciella (Mönning, 1920) and Eudromoxyura, the only oxyurids known parasitising birds, have probably arisen independently.     

Patterns of Local Distribution of Labroides Dimidiatus in French Polynesian Atolls

Cleaning behaviour by fishes has been described to be either facultative or specialised. If being specialised in cleaning is more advantageous than to be a facultative cleaner, cleaner fishes would prefer to settle on reefs were ecological conditions promote specialisation. To test this hypothesis, we looked at the influence of physical and ecological factors on cleaner wrasse abundance, studying variations in L. dimidiatus density between 10 atolls of French Polynesia. We used a multiple regression method based on permutations of distance matrices. Our study reveals that L. dimidiatus are significantly more numerous at sites where ecological factors, such as the species richness of the fish community, may promote their cleaning activity. Moreover, they were significantly more abundant in atolls presenting a large number of sedentary fish species, few predators and few fishes living in large groups. Finally, physical factors, such as the distance between atolls, the lagoon surface, the mean percentage of hard substrate, the mean current index, and the mean depth, play a minor role in the occurrence of L. dimidiatus.