COMPARATIVE KARYOLOGY OF THE FRESHWATER SNAILS BULINUS TROPICUS and B. NATALENSIS

Abstract

Species of the subgenus Bulinus occur in a polyploid series which is of interest because of the rarity of polyploidy in animal species and because there appears to be a relation between ploidy level and ability to transmit Schistosoma haematobium, a parasite of major [human] public health importance. A technique is described for the preparation of standard karyotypes using cell suspensions from colchicine-treated embryos. The results for 2 diploid species, B. tropicus (Krauss) and B. natalensis (Kuster), are presented. Both karyotypes consist of 15 metacentric and 3 submetacentric chromosomes. Differences in centromere position are found in 4 pairs of chromosomes, and in the appearance of a secondary constriction. Because B. natalensis may represent a relict taxon involved in the origin of the polyploids, the results are of significance for future work on the phylogeny of this group.