Allozyme Variation in the African Freshwater Snail Genus Bulinus.

The African freshwater snail genus Bulinus (Basommatophora: Planorbidae) is of parasitological and public health interest because many species of the genus serve as the intermediate hosts of Schistosoma haematobium, the causative agent of human urinary bilharziasis. The genus is of additional interest because there exists within the subgenus Isidora, a polyploid series of sibling species with n = 18 (diploid), n = 36 (tetraploid), n = 54 (hexaploid) and n = 72 (octoploid) chromosomes. The polyploid snails are the actual or potential transmitters of the parasite. The diploid snails of the subgenus Isidora are generally refractory to schistosome infection. Since the only reliable method of differentiating the members of the polyploid series is by actual chromosome number determination, it was deemed worthwhile to subject the genus to an electrophoretic analysis with the specific objective of establishing an "enzyme profile" of the various ploidy groups which might then be used for definitive identification of these morphologically similar animals. The allozymes of 43 different laboratory populations in two subgenera of the genus Bulinus were investigated largely by horizontal starch gel electrophoresis. A total of 95 different alleles were resolved at 31 genetic loci distributed among 23 different protein and enzymatic activities. The following enzymatic activities were resolved: a-glycerophosphate dehydrogenase (1 locus, 4 alleles), sorbitol dehydrogenase (1 locus, 3 alleles), B-hydroxybutyrate dehydrogenase (2 loci, 8 alleles), malate dehydrogenase (1 locus, 2 alleles), malic enzyme (1 locus, 1 allele), isocitrate dehydrogenase (1 locus, 3 alleles), 6-phosphogluconate dehydrogenase (1 locus, 1 allele), glucose-6-phosphate dehydrogenase (1 locus, 1 allele), octanol dehydrogenase (1 locus, 3 alleles), hydroxyacid dehydrogenase (1 locus, 1 allele), aldehyde oxidase (1 locus, 7 alleles), xanthine oxidase (2 loci, 8 alleles), D-amino acid oxidase (1 locus, 1 allele), glutamate-oxaloacetate transaminase (1 locus, 2 alleles), phosphoglucomutase (1 locus, 3 alleles), esterase (5 loci, 24 alleles), alkaline phosphatase (1 locus, 4 alleles), acid phosphatase (2 loci, 6 alleles), peptidase (2 loci, 3 alleles), aldolase (1 locus, 4 or 5 alleles), phosphoglucose isomerase (1 locus, 3 alleles), hemoglobin (1 locus, 1 allele) and protein-1 (1 locus, 2 alleles). The Bulinus (Physopsis) populations could be differentiated from the Bulinus (Isidora) populations at a-glycero phosphate dehydrogenase, B-hydroxybutyrate dehydrogenase-1, esterase-4, esterase-8, aldolase and phosphoglucomutase. The Physopsis populations did not share common alleles with the Isidora populations at these loci. The different members of the Isidora polyploid series could also be differentiated using a similar array of enzymes. Although generally no single enzymatic activity permitted an absolute differentiation of the populations belonging to the different ploidy levels, the following loci, used in combination, usually permitted an accurate placement of the populations into their respective ploidy groups. These loci were sorbitol dehydrogenase, B-hydroxybutyrate dehydrogenase-1 and -2, isocitrate dehydrogenase, aldehyde oxidase, xanthine oxidase, aldolase, protein-1, esterase-4, esterase-5 and peptidase-1. A possible correlation between the enzyme glutamate-oxaloacetate transaminase and susceptibility of the snails to Schistosoma haematobium was observed. All non-susceptible diploid snails possessed one electromorph of this enzyme, whereas the susceptible polyploid as well as the susceptible diploid snails all possessed a different, slower electromorph.PhDZoologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158030/1/8025807.pd