Insights into the relationships of Palearctic and Nearctic lymnaeids (Mollusca : Gastropoda) by rDNA ITS-2 sequencing and phylogeny of stagnicoline intermediate host species of Fasciola hepatica

Fascioliasis by Fasciola hepatica is the vector-borne disease presenting the widest latitudinal, longitudinal and altitudinal distribution known. F. hepatica shows a great adaptation power to new environmental conditions which is the consequence of its own capacities together with the adaptation and colonization abilities of its specific vector hosts, freshwater snails of the family Lymnaeidae. Several lymnaeid species only considered as secondary contributors to the liver fluke transmission have, however, played a very important role in the geographic expansion of this disease. Many of them belong to the so-called "stagnicoline" type group. Stagnicolines have, therefore, a very important applied interest in the Holarctic region, to which they are geographically restricted. The present knowledge on the genetics of stagnicolines and on their parasite-host interrelationships is, however, far from being sufficient. The present paper analyses the relationships between Palaearctic and Nearctic stagnicoline species on the base of the new light furnished by the results obtained in nuclear rDNA ITS-2 sequencing and corresponding phylogenetic studies of the lymnaeid taxa Lymnaea (Stagnicola) occulta, L. (S.) palustris palustris (topotype specimens) and L. (S.) p. turricula from Europe. Natural infections with F. hepatica have been reported in all of them. Surprisingly, ITS-2 length and GC content of L. occulta were similar and perfectly fitted within the respective ranges known in North American stagnicolines. Nucleotide differences and genetic distances were higher between L. occulta and the other European stagnicolines than between L. occulta and the North American ones. The ITS-2 sequence of L. p. turricula from Poland differed from the other genotypes known from turricula in Europe. The phylogenetic trees using the maximum-parsimony, distance and maximum-likelihood methods confirmed (i) the inclusion of L. occulta in the branch of North American stagnicolines, (ii) the link between the North American stagnicolines-L. occulta group with Galba truncatula, and (iii) the location of the L. p. turricula genotype from Poland closer to L. p. palustris than to other European L. p. turricula genotypes. The Palaearctic species occulta is included in the genus Catascopia, together with the Nearctic species catascopium, emarginata and elodes. The results suggest a potential of transmission capacity for C. occulta higher than that of other European stagnicolines or Omphiscola glabra. The relatively low genetic distances between C. occulta and G. truncatula and the clustering of both species in the same clade suggest that C. occulta may be potentially considered as the second lymnaeid intermediate host species of F. hepatica in importance in eastern and northern Europe, and probably also western and central Asia, after G. truncatula. L. p. turricula may be considered as a potential secondary vector of F. hepatica, at a level similar to that of L. p. palustris.(VLID)221360

Variation in Desiccation Tolerance in Freshwater Snails and Its Consequences for Invasion Ability

International audienceThe freshwaters of Martinique (FrenchWest Indies) have recently been invaded by snails belonging to the Thiaridae family (Gastropoda; Prosobranchia). Eight distinct Thiarid lines have been successively introduced in Martinique, and are still in the process of sequentially replacing one another within local habitats, revealing a range of increasing invasive abilities. Our aimwas to test whether the variation in invasive ability can be partly explained by a specific lifehistory trait, desiccation tolerance, which might be important in view of the typical instability of tropical freshwater habitats. We therefore tested desiccation tolerance in both juveniles and adults under laboratory conditions. Our data show that, although all Thiarid lines resist desiccation quite well, they exhibit extreme variation in the degree of tolerance. These differences are mostly mediated by individual size, but are definitely of genetic origin given that our individuals were of similar ages and were raised under standardized laboratory conditions. The overall invasive success of a line in Martinique, deduced from field surveys, does not correlate with its desiccation tolerance. However, desiccation tolerance does seem to be a limiting factor for the invasion of the small fraction of habitats that are most exposed to drought. More generally, our study exemplifies the possibility that the invasion differential among habitats, rather than a general invasion ability, be predicted according to a particular life-history trait, within a set of closely related invasive taxa

Le contrôle de la schistosome intestinale de l'île de la Martinique

En Martinique, l'existence de la schistosomose intestinale à Schistosoma mansoni est connue depuis le début du XXe siècle. Une étude générale de la répartition de la maladie réalisée en 1977 a montré une prévalence moyenne de l'infection de 12 % pour l'ensemble de l'île (coprologies et sérologies confondues). A la suite de cette enquête, un programme de lutte associant des actions d'éducation sanitaire, le dépistage et le traitement des porteurs de la parasitose et l'amélioration de l'assainissement, a été mis en place. Par ailleurs, un programme de contrôle biologique contre le mollusque hôte intermédiaire Biomphalaria glabrata utilisant un compétiteur, Melanoides tuberculata, a été développé dans les sites actifs de transmission. En parallèle à la réduction des populations de l'hôte intermédiaire et de son parasite, une importante diminution de la prévalence globale de la parasitose chez l'homme a été observée entre 1977 et 1996. Désormais, seuls quelques cas sont encore diagnostiqués, mais il s'agit uniquement d'adultes contaminés longtemps auparavant. Cette situation épidémiologique est tout à fait différente de celle qui est observée dans l'île sœur de la Guadeloupe où bien qu'un excellent contrôle des bassins versants de la Basse-Terre ait été réalisé, un important foyer situé en arrière mangrove de la Grande-Terre fonctionne toujours avec un hôte réservoir, le rat noir. En Martinique, plusieurs enquêtes réalisées dans des milieux similaires ont démontré que de tels foyers n'existent pas