Parasite (Schistosoma mansoni) and host (Biomphalaria glabrata) genetic diversity: population structure in a fragmented landscape.

Random amplified polymorphic DNA (RAPD) markers were used to quantify genetic diversity within and between 5 populations of Schistosoma mansoni within its definitive host (Rattus rattus) and the 5 corresponding populations of the snail intermediate host (Biomphalaria glabrata) from a limited endemic area of murine schistosomiasis on the island of Guadeloupe. Analysis of molecular variance (AMOVA) and canonical correspondence analysis (CCA) were used to test the significance of genetic differentiation between populations. Both methods gave similar results. Of total gene diversity, 15.1% (AMOVA) and 18.8% (CCA) was partitioned between localities for S. mansoni with an absence of association between genetic and geographical distances. Geographical localities accounted for 20.5% (CCA) of the total diversity for B. glabrata populations. The genetic distances between pairs of parasite populations were not correlated with the genetic distances between the corresponding pairs of snail host populations. Such strong patterns of local differentiation of both parasite and snail populations are consistent with predictions based on metapopulation dynamics and may have implications on host-parasite susceptibility relationship through local adaptation processes.

Comparative genetic diversity of parasites and their hosts: population structure of an urban cockroach and its haplo-diploid parasite (oxyuroid nematode).

Few studies have investigated the genetic structure of both host and parasite populations at a level of populations and at a level of individuals. We investigated the genetic structure of the urban cockroach Blattella germanica and its oxyuroid parasite Blatticola blattae. Random amplified polymorphic DNA (RAPD) markers were used to quantify genetic diversity between and within four populations (from two cities in France) of the host and its parasite. Diversity based on phenotypic frequencies was calculated for each RAPD marker using Shannon-Wiener's index. We used multivariate analyses to test the significance of genetic differentiation between host and parasite populations. Analysis of molecular variance was also used. Both methods gave similar results. Diversity between pairs of individuals was estimated by Nei & Li's index. Genetic diversity was higher within host or parasite populations (80% and 82%, respectively, of explained diversity) than between host or parasite populations (20% and 18%, respectively, explained diversity). The genetic distances between pairs of parasite populations (or individuals) were not correlated with the genetic distances between the corresponding pairs of host populations (or individuals).

Heritable non-susceptibility in an allopatric host-parasite system: Biomphalaria glabrata (Mollusca)-Echinostoma caproni (platyhelminth Digenea).

We studied the heritability of adult nonsusceptibility/susceptibility in an allopatric host-parasite system, Biomphalaria glabrata (Brazil)-Echinostoma caproni (Egypt). In this system, the fitness of the infected host is substantially reduced because of castration. Mean frequencies of susceptibility among progeny of individual susceptible or nonsusceptible parents were compared, and heritabilities of susceptibility and nonsusceptibility were calculated under a quantitative genetic model. A Monte-Carlo simulation was used to assess the significance of the heritability estimates under the hypothesis of normal standard deviation. The results showed high heritability of both nonsusceptibility (0.56) and susceptibility (0.91).

Distribution and genetic diversity of Schistosoma haematobium within its bulinid intermediate hosts in Mali.

Random amplified polymorphic DNA (RAPD) markers were used to assess distribution and genetic diversity of Schistosoma haematobium populations within their bulinid intermediate hosts in Mali. Naturally infected snails (Bulinus truncatus and B. globosus) were collected at four sites in the Bamako district. S. haematobium cercariae from single snails were used to infect mice and genotypes of the resultant adult worms were characterized using RAPD markers. Diversity indices were calculated at the scale of one snail, both within and among sites. One third of the molluscs harboured multiple miracidial infections (the maximum number equal to five) with slightly overdispersed distributions in three sites and a random distribution at one site. Similarity indices revealed significantly less variation among populations compared with populations, indicative of the absence of distinct S. haematobium populations within the Bamako district. RAPD markers represent an accurate tool for determining genetic diversity and amount of gene flow among parasite populations contained within different individual snails and among intermediate host populations.

Detection of genetic diversity within snail intermediate hosts of the genus Bulinus by using random amplified polymorphic DNA markers (RAPDs).

A polymerase chain reaction-based polymorphic assay procedure (RAPD) was used to study the genetic diversity of intermediate host snails within the genus Bulinus. Genetic differentiation was detected between two closely related species: Bulinus globosus and Bulinus umbilicatus. Evidence is presented demonstrating the potential of RAPD markers for differentiating populations of B. forskalii from different countries (Cameroon, Equatorial Guinea and Ivory Coast) or from the same country (Cameroon). RAPDs may be also used to identify offspring from cross- and self-fertilized hermaphrodite bulinid snails. RAPDs provide a cost-effective and routine method for genetic studies of snails transmitting schistosomiasis and for the evaluation of diversity between snail populations.