Showing papers on "Bulinus truncatus published in 1997"
TL;DR: That some populations exhibit much more variability than others suggests that historical demographic processes may play a significant role, and a hierarchical analysis of the distribution of the variability across populations indicates a strong pattern of isolation by distance, whatever the geographical scale considered.
Abstract: The distribution of neutral genetic variability within and among sets of populations results from the com- bined actions of genetic drift, migration, extinction and recolonization processes, mutation, and the mating system. We here analyzed these factors in 38 populations of the hermaphroditic snail Bulinus truncatus. The sampling area covered a large part of the species range. The variability was analyzed using four polymorphic microsatellite loci. A very large number of alleles (up to 55) was found at the level of the whole study. Observed heterozygote deficiencies within populations are consistent with very high selfing rates, generally above 0.80, in all populations. These should depress the variability within populations, because of low effective size, genetic hitchhiking, and background selection, whatever the model of mutation assumed. However, that some populations exhibit much more variability than others suggests that historical demographic processes (e.g., population size variation, bottlenecks, or founding events) may play a significant role. A hierarchical analysis of the distribution of the variability across populations indicates a strong pattern of isolation by distance, whatever the geographical scale considered. Our analysis also illustrates how the mutation rate may affect population differentiation, as different mutation rates result in different levels of homoplasy at microsatellite loci. The effects of both genetic drift and gene flow vary with the temporal and spatial scales considered in B. truncatus populations.
60 citations
TL;DR: The results support a demographic model of population expansions and contractions under which available habitats, after the rainy season, are colonized by individuals originating from a smaller number of refuges (areas that never dry out in the deepest parts of the ponds) and selfing appeared to be an important force affecting the genetic structure in permanent ponds.
Abstract: We analyzed short-term forces acting on the genetics of subdivided populations based on a temporal survey of the microsatellite variability in the hermaphrodite freshwater snail Bulinus truncatus . This species inhabits temporary habitats, has a short generation time and exhibits variable rates of selfing. We studied the variability over three sampling dates in 12 Sahelian populations (1161 individuals). Classical genetic parameters (estimators of H o , H e , f selfing rate and Fst ) showed limited change over time whereas important temporal changes of allelic frequencies were detected for 10 of the ponds studied. These variations are not easily explained by selection, sampling drift and genetic drift alone and may be due to periodic migration. Indeed the habitats occupied by the populations studied are subject to large temporal fluctuations owing to annual cycles of drought and flood. In such ponds our results support a demographic model of population expansions and contractions under which available habitats, after the rainy season, are colonized by individuals originating from a smaller number of refuges (areas that never dry out in the deepest parts of the ponds). In contrast, selfing appeared to be an important force affecting the genetic structure in permanent ponds.
55 citations
TL;DR: Analysis of progeny–array analyses of the selfing rate and correlated matings in the tropical freshwater snail Bulinus truncatus suggests that high selfing rates may have a strong genetic basis, and unexpectedly suggest that phally polymorphism may be neutral with respect to selfing.
Abstract: Studies on the evolution of self-fertilization and sexual polymorphisms (the co-occurrence of several sexual morphs in a species) have focused on plants. Aphally, a sexual polymorphism occurring in gastropods, offers the opportunity to extend study of these issues to animals. We present progeny-array analyses of the selfing rate and correlated matings in the tropical freshwater snail Bulinus truncatus. This study is based on 447 offspring originating from 57 families and five natural populations. To overcome the lack of allozyme polymorphism, four polymorphic microsatellite markers were used. Selfing rates higher than 78 per cent were detected in all populations, and no correlation with the aphally ratio (the proportion of individuals lacking the male copulatory organ per population) was evident. Outcrossing was detected in 17 families only, and individual outcrossing rates were variable and did not depend on the sexual morph of the mother. These results illustrate the power of microsatellites for detailed genetic studies, indicate that high selfing rates may have a strong genetic basis, and unexpectedly suggest that phally polymorphism may be neutral with respect to selfing.
50 citations
TL;DR: 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 and revealed significantly less variation among populations compared with populations, indicative of the absence of distinct S. haematsomiasis populations.
42 citations
TL;DR: Cercarial emergence patterns were used to analyse the intraspecific variability within and between nine populations of Schistosoma haematobium collected along a transect line from the north to the South of the Ivory Coast using Bulinus truncatus or Bulinus globosus as intermediate snail hosts.
26 citations
TL;DR: The molluscicidal properties of Solanum nigrum L. were tested against three Egyptian snail species (Biomphalaria alexandrina, Bulinus truncatus and Lymnaea natalensis), each an intermediate host of parasites causing human schistosomiasis or fascioliasis, and a time-concentration relationship was observed.
Abstract: The molluscicidal properties of Solanum nigrum L. were tested against three Egyptian snail species (Biomphalaria alexandrina, Bulinus truncatus and Lymnaea natalensis), each an intermediate host of...
25 citations
TL;DR: In experiments to determine the compatibility between isolates of Schistosoma haematobium and Bulinus truncatus from Mali and Senegal, the parasite isolates were shown to differ in their intermediate host specificity.
Abstract: In experiments to determine the compatibility between isolates of Schistosoma haematobium and Bulinus truncatus from Mali and Senegal, the parasite isolates were shown to differ in their intermediate host specificity. Bulinus truncatus from the Lower and Middle Valleys (Senegal) and the Upper Valley (Mali) of the Senegal River Basin (SRB) were all susceptible to S. haematobium isolated from the urines of children living in Tenegue, Office du Niger, Mali. However, none of the B. truncatus tested was susceptible to a parasite isolated from children living in Mbodiene, a village in the Lower Valley of the SRB, where natural transmission is normally associated with B. globosus. As B. truncatus is widely distributed in the SRB, the possible appearance of a Bulinus-truncatus-borne parasite in the Middle and Lower Valleys should be carefully monitored.
9 citations
Journal Article•
7 citations
01 Jan 1997
TL;DR: The biogeographic evidence from two species of freshwater snails presently supports the Red Queen hypothesis that biparental reproduction is selected as a way to reduce the risk to progeny of parasite attack, and parthenogenetic reproduction in a third species is correlated with latitude and the presence of a non-castrating trematode that may prevent cross-fertilization.
Abstract: We review the spatial and temporal correlates of uniparental and biparental reproduction in three species of freshwater snails as they pertain to the ecological hypotheses for the maintenance of biparental sex. The biogeographic evidence from two species (Potamopyrgus antipodarum and Bulinus truncatus) presently supports the Red Queen hypothesis that biparental reproduction is selected as a way to reduce the risk to progeny of parasite attack. Uniparental reproduction in these species is associated with low levels of infection by parasites (castrating digenetic trematodes), suggesting that parthenogenesis or self-fertilization can replace cross-fertilization when the risk of infection is low. In addition, in B. truncatus, the timing of cross-fertilization coincides with the season in which parasite attack is highest. In a third species (Campeloma decisum), parthenogenetic reproduction is correlated with latitude and the presence of a non-castrating trematode that may prevent cross-fertilization; these patterns suggest that parthenogenesis has been selected as a mechanism to assure reproduction. We also discuss the taxonomic distribution of parthenogenesis in aquatic invertebrates, and suggest that brooding may be an exaptation for the evolution of parthenogenetic reproduction in these animals.
7 citations
TL;DR: A comparative analysis has been carried out between two populations of Schistosoma haematobium using the same intermediate snail host, Bulinus truncatus, but originating from two distinct ecological areas of Algeria: Khemis-El-Khechna in a sub-humid mediterranean zone and Djanet in a saharan bioclimatic zone.
Abstract: A comparative analysis has been carried out between two populations of Schistosoma haematobium using the same intermediate snail host, Bulinus truncatus, but originating from two distinct ecological areas of Algeria: Khemis-El-Khechna in a sub-humid mediterranean zone and Djanet in a saharan bioclimatic zone. Four parameters have been studied: the growth rate of adult worms, size and shape of the eggs, chronobiology of cercarial emergence and the compatibility with the intermediate host. Results showing divergences for all the characters studied are discussed for the origin of this intraspecific polymorphism of S. haematobium in Algeria.
7 citations
01 Jan 1997
TL;DR: In this paper, the authors present progeny-array analyses of the self-fertilization and correlated matings in the tropical freshwater snail Bulinus truncatus and reveal that high selfing rates may have a strong genetic basis.
Abstract: SUMMARY Studies on the evolution of self-fertilization and sexual polymorphisms (the co-occurrence of several sexual morphs in a species) have focused on plants. Aphally, a sexual polymorphism occurring in gastropods, oers the opportunity to extend study of these issues to animals. We present progeny-array analyses of the selfing rate and correlated matings in the tropical freshwater snail Bulinus truncatus. This study is based on 447 ospring originating from 57 families and five natural populations. To overcome the lack of allozyme polymorphism, four polymorphic microsatellite markers were used. Selfing rates higher than 78% were detected in all populations, and no correlation with the aphally ratio (the proportion of individuals lacking the male copulatory organ per population) was evident. Outcrossing was detected in 17 families only, and individual outcrossing rates were variable and did not depend on the sexual morph of the mother. These results illustrate the power of microsatellites for detailed genetic studies, indicate that high selfing rates may have a strong genetic basis, and unexpectedly suggest that phally polymorphism may be neutral with respect to selfing.