Chromosome Numbers of Some Schistosomes

Abstract

To date, the chromosome numbers of 11 species of schistosomes in six genera are known. They range from 2n = 14 to 2n = 18 with 9 species having the diploid number equal to 16 (Short and Menzel, 1960, J. Parasitol. 46: 273-287; Southgate and Knowles, 1977, Z. Parasitenk. 54: 233-250; Atkinson, 1980, Can. J. Genet. Cytol. 22: 143-147). Our study verifies the chromosome number of Gigantobilharzia huronensis and presents for the first time, chromosome numbers for Schistosoma bovis, S. intercalatum, and S. mattheei. The squash technique was used to determine chromosome numbers and observe chromosome morphology. Testes of adult worms were used to demonstrate meiosis. The intramolluscan stages were employed to observe mitotic metaphases (see LoVerde, 1979, Trans. Amer. Micros. Soc. 98: 280-285 for details). The diploid chromosome number 16 was determined from more than 30 mitotic metaphase cells from the intramolluscan stages of at least 20 Gigantobilharzia huronensis (Fig. 1) obtained from snails maintained in the laboratory. This verifies the number reported by Short and Menzel (loc. cit.) from a single, naturally infected snail. The longest chromosome measured about 4.4 /um while the shortest measured about 1.3 /m. Examination of meiotic metaphases derived from testes showed Schistosoma bovis, S. intercalatum, and S. mattheei to exhibit 8 pairs of chromosomes (Fig. 2). This brings the number of schistosome species subjected to chromosome counts to 14 and demonstrates that the family Schistosomatidae is conservative as regards chromosome numbers. This work was supported, in part, by the 2