Isolation and characterization of microsatellite loci in the freshwater gastropod, Biomphalaria glabrata, an intermediate host for Schistosoma mansoni.
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Biomedical subjects
L R Noble
Publications and source records attributed to L R Noble.
Polymorphic microsatellite loci identified in the highly clonal freshwater bryozoan Cristatella mucedo.
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Genetic variation in a freshwater bryozoan. I: Populations in the Thames basin, UK.
In spite of increasing interest in metapopulation dynamics, the genetic consequences of a metapopulation structure remain poorly understood. Here we examine the metapopulation genetic structure of the colonial, facultatively sexual freshwater bryozoan Cristatella mucedo, in the Thames basin of southern England, UK. Populations from nine sites were sampled and colonies genetically characterized using random amplified polymorphic DNA (RAPD)-PCR. A total of 78 different clones was detected over all sites. Despite the large number of clones, genetic distances among clones both within and among sites were very small. Nonetheless, no clone was present at more than one site even though C. mucedo has an asexual dispersal propagule, and clones strongly clustered by sites. No consistent pattern of clonal structure was evident, with both the number and equitability of clones varying greatly among sites. Although sites were genetically distinct, population genetic regions were absent, and a Mantel test indicated that there was no relationship between geographical distances among sites and genetic distances among populations. Our results indicate that C. mucedo exists as a classical metapopulation in the Thames basin, with dispersal independent of distance and all sites contributing to the genetic diversity of the metapopulation.
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Molecular characterisation of intermediate snail hosts and the search for resistance genes.
The relationship between schistosomes and their intermediate hosts is an extremely intricate one with strains and species of the parasite depending on particular species of snail, which in turn may vary in their susceptibility to the parasites. In order to gain a better understanding of the epidemiology of the disease we have been investigating the use of molecular markers for snail identification and for studying host-parasite relationships. In this paper we will draw on examples concerning schistosomiasis in West and East Africa to illustrate how a molecular analysis can be used as part of a "total evidence" approach to characterisation of Bulinus species and provide insights into parasite transmission. Particular emphasis is given to ribosomal RNA genes (rRNA), random amplified polymorphic DNA (RAPDs) and the mitochondrial gene cytochrome oxidase I (COI). Snails resistant to infection occur naturally and there is a genetic basis for this resistance. In Biomphalaria glabrata resistance to Schistosoma mansoni is known to be a polygenic trait and we have initiated a preliminary search for snail genomic regions linked to, or involved in, resistance by using a RAPD based approach in conjunction with progeny pooling methods. We are currently characterising a variety of STSs, (sequence tagged sites) associated with resistance. These can be used for local linkage and interval mapping to define genomic regions associated with the resistance trait. The development of such markers into simple dot-blot or specific PCR-based assays may have a direct and practical application for the identification of resistant snails in natural populations.
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Temporal patterns of clonality and parasitism in a population of freshwater bryozoans.
Clonal reproduction is commonly incorporated into the life cycles of many metazoans. However, whether and how such highly clonal animals persist in the face of natural enemies remains poorly understood. Here we report the first temporal genetic study of a clonal population, the freshwater bryozoan Cristatella mucedo, and the associated prevalence of a myxozoan parasite. High levels of both clonality and parasitism persisted over a 3 year period. Random amplified polymorphic DNA markers revealed four distinct clones of C. mucedo. The two most common clones varied in abundance with the significantly more common clone in the first year becoming the significantly less common by the third year. There was no evidence that the most common clone was disproportionately infected. These results are discussed in relation to predictions of the Red Queen and the metapopulation dynamics of clonal organisms.
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Differential male genetic success determines gene flow in an experimentally manipulated mouse population.
Sexual selection arises when genetically different males show heritable differences in reproductive success. Mouse mating behaviour involves both male competition and female choice. In this paper we show that introduced Y-linked DNA markers spread more extensively through a natural population than do genes inherited matrilineally. Differences in mating success between the sexes and among individual males may alter the pattern and rate of gene flow in natural populations. Another interesting possibility is that the success of the introduced Y chromosome may be attributable to so-called 'selfish' traits, such as sex-linked meiotic drive or intra-uterine competition. However, this study provides little unequivocal evidence to support this view. Differential success of introduced versus resident males may have implications for the reintroduction of endangered mammals into residual wild populations.
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Parent and larval RAPD fingerprints reveal outcrossing in freshwater bryozoans.
The occurrence of outcrossing in benthic hermaphroditic colonial invertebrates has received much historical debate and little demonstration. Direct genetic study of this question using routine techniques has been limited by both the amount of material required and the detection of adequate DNA polymorphisms. However, the recent development of molecular techniques that require no a-priori sequence data provides new approaches to the characterization of both tiny and genetically similar individuals. Random amplification of polymorphic DNA (the RAPD assay) was used to amplify fragments of DNA (via the polymerase chain reaction) to obtain fingerprints of parental colonies and larval offspring of the hermaphroditic freshwater bryozoan Cristatella mucedo. Here we report the first positive and direct genetic evidence for outcrossing in bryozoans. However, we find that outcrossing generates only low levels of genetic variation in populations that are highly clonal.
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Randomly amplified polymorphic DNA analysis of clonal population structure and geographic variation in a freshwater bryozoan.
The randomly amplified polymorphic DNA (RAPD) assay was used to identify genetic polymorphisms in three clonal populations of the freshwater bryozoan, Cristatella mucedo, a species with few useful biochemical genetic markers. Of the 19 decamer oligonucleotide primers screened, 13 gave clear, reproducible RAPD profiles. Clonal population structure was evident, and one clone was dominant at each site. Cluster analysis grouped populations from more distant localities separately (Thames Valley and Norfolk), whereas populations from the Thames Valley clustered together. However, even at the regional scale a high degree of relatedness pertained. This work is one of the first RAPD studies of natural populations, and demonstrates the suitability of the technique for examining population structure and geographic variation in clonal taxa.
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