Conventional Giemsa-stained and C-banded chromosomes of seven strains of Schistosoma mansoni.

Karyotypes stained with conventional Giemsa and with a C-banding method were compared among 7 strains of Schistosoma mansoni: 2 from Puerto Rico and 1 each from St. Lucia, Brazil, Venezuela, Egypt, and Kenya. A few differences were noted in relative lengths and centromeric indexes, but overall karyotypes of all strains were similar, with 2n = 16. The W chromosome of the female of all strains had a relatively large heterochromatic block, distinguishing the female from the male karyotype.

Chromosomes of Heterobilharzia americana (Digenea: Schistosomatidae), with ZWA sex determination, from Louisiana.

Mitotic chromosomes of Heterobilharzia americana from Louisiana are described from parasite material that was dissected from snails, air-dried on slides, and stained with conventional Giemsa and C-band methods. As in other schistosomes, the female is the heterogametic sex. This Louisiana strain, however, differs from a Texas strain and other schistosome species in that the male and female have different diploid numbers of chromosomes (male, 20; female, 19), and the strain has a ZZ male/ZWA female sex-determining mechanism. The chromosomes of the male resemble those of the Texas strain in number and morphology with the Z chromosomes being metacentric and the largest elements in the karyotype. The others form a series decreasing in size to very small number 10's. Chromosomes 2,3, and 4 are subtelocentric; 5 is subtelocentric to acrocentric and is satellited; 6 is submetacentric to subtelocentric; 7 is submetacentric; 8 is subtelocentric to submetacentric; 9 is metacentric to submetacentric; and 10 is metacentric. The female complement differs from the male of this strain in having only 1 normal chromosome 5. The other number 5 and most of the original W apparently have fused tandemly to form the WA chromosome (a "neo-W").

Identification of sex of schistosome larval stages.

Sex of Schistosoma mansoni cercariae was identified by a C-banding technique; interphase nuclei of females exhibited W-chromatin (heterochromatin of the W chromosome) whereas those of males did not. Similar sexual dimorphism was also shown in nuclei of S. mansoni miracidia, sporocysts, and adult worms. Cercariae of the following schistosomes could not be sexed by examination of nuclei after the C-band technique: S. japonicum, S. haematobium, and Schistosomatium douthitti . The method presented was 100% accurate and relatively rapid (total time for S. mansoni cercariae: 80 min).

Conventional giemsa and C-banded karyotypes of Schistosoma mansoni and S. rodhaini.

The karyotypes of a Puerto Rican strain of Schistosoma mansoni and a Kenyan strain of S. rodhaini are similar in number of general morphology. For each species there are eight pairs of chromosomes (2n =16) which are divided into three size groups. C-banded methods revealed, in addition to centromeric heterochromatin, a large heterochromatic block in one for the No. 2 chromosomes in females but not in the other. Neither No. 2 chromosome of males possessed the heterochromatic block. This pair (2) is interpreted as the sex chromosomes, with the female being heterogametic (ZW), the male homogametic (ZZ). Differences between karyotypes of the two species occurred. These included a satellite on the No. 3 chromosome of S. mansoni and a euchromatic tip on the otherwise heterochromatic short arm of the W chromosome of this species; neither of these was present in S. rodhaini. The two species also differed in that the centromeric index of the Z of S mansoni was smaller than that of the W, whereas in S rodhaini the reverse was true. In S. mansoni the large heterochromatic block of the W chromosome was identified in prophase and interphase nuclei as well as at metaphase.

Somatic chromosomes of Schistosoma rodhaini, S. mattheei, and S. intercalatum.

Karyotypes are reported for three African schistosomes: Schistosoma rodhaini, S. intercalatum, and S. mattheei. All have eight pairs (2n = 16) of chromosomes which comprise three distinct size groups: A, large (two pairs); B, medium (three pairs); and C, small (three pairs). Chromosomes of groups A and B are subtelocentric; those of C are more metacentric or submetacentric. These karyotypes prepared with conventional Giemsa staining are very similar to each other and to those of S. mansoni and S. haematobium. As a group, the African schistosomes studied to date exhibit clear differences in chromosome morphology from the Asian S. japonicum and S. mekongi.

Karyotype evolution and sex chromosome differentiation in Schistosomes (Trematoda, Schistosomatidae).

The morphology of C-banded metaphase chromosomes has been studied in two hermaphroditic and ten gonochoristic digenetic trematodes (schistosomes). Comparison of numbers and morphology of chromosomes indicates that the karyotype of primitive trematodes probably was composed of 10 (or 11) pairs of telocentric or subtelocentric chromosomes, and reduction of chromosome numbers in advanced species resulted from centromeric fusion rather than elimination of chromosomes. Observation of heteromorphic chromosomes in a hermaphroditic trematode (Spirorchis) suggested a differentiation of "pre-sex" chromosomes in species ancestral to dioecious trematodes which possess distinctly differentiated sex chromosomes. Our results indicate that differentiation of Z and W chromosomes in the gonochoristic trematodes resulted from: (a) partial constitutive heterochromatinization of the W chromosome (Schistosoma mansoni and S. haematobium complexes, African schistosomes), (b) deletion of part of the W (S. japonicum and S. mekongi, Asian schistosomes), and (c) translocation of part of one sex chromosome onto another (Schistosomatium douthitti and Heterobilharzia americana, American schistosomes) with subsequent heterochromatinization of the W in H. americana.

Argentophilic papillae of Schistosomatium douthitti cercariae (Trematoda: Schistosomatidae).

Argentophilic papillae of cercariae of Schistosomatium douthitti were studied by light microscopy. The basic number of body papillae was 56, excluding 20 at the anterior tip. The average number of tail papillae was 18. Average locations and spatial ranges of body papillae indicate a rather constant pattern. Tail papillae showed greater variability in location. Twenty papillae (10 on each side) at the anterior tip of cercariae were associated with gland duct openings. Two types of papillae were recognized with light microscopy--uniciliated bulbs and pits. The papilla pattern of S. douthitti differs from those of other species of schistosomes derived to date, and its constancy supports the usefulness of papillae in systematic studies.

Patterns of argentophilic papillae of Schistosoma rodhaini and S. mansoni cercariae.

Argentophilic papillar patterns on cercariae of Schistosoma rodhaini from Kenya and S. Africa, and S. mansoni from Kenya and Brazil were compared with each other and with earlier results on cercariae of a Puerto Rican stock. The basic total number of papillae of both species is the same (62), and the basic numbers of papillae in the various groups are the same: dorsal, 20; ventral, 18; lateral, 10 on each side; and acetabular, 4. The cercariae of these 2 species differ, however, in patterns of papillae, chiefly the dorsal patterns, and can be distinguished from each other.

Schistosoma mansoni miracidial behavior: an assay system for chemostimulation.

A new system for evaluating the responses of miracidia to chemostimulants is described. The apparatus consists of a translucent plastic block with a center well and a hole in the edge leading to the well. One end of a glass tube, covered with a dialysis membrane, was inserted into the hole. Experimental solutions to be tested were put into the tube and Schistosoma mansoni miracidial behavior was observed in the well on the other side of the permeable membrane. Miracidia were released near the membrane; those which contacted the membrane were scored as to whether they returned (contact with return) or did not return (contact without return) before leaving the field of view. Materials eliciting significantly more contact with return responses than did controls were considered to be stimulatory. In this assay system, snail (Biomphalaria glabrata) conditioned water elicited 75% contact with return as compared to 8% for well water control (P less than 0.05). Tracings from motion pictures showed swimming behavior of miracidia toward snail-conditioned water to be different from behavior toward well water controls. This system permits generation of dilution response curves for chemicals and provides generally quantitative results.

Fine structure of possible photoreceptor in cercariae of Schistosoma mansoni.

Two structures near the anterior end of cercariae of Schistosoma mansoni are interpreted as possible photoreceptors. Each appears to be ovoid and is composed of a thin cytoplasmic wall surrounding a cavity which contains lamellae. The lamellae are extensions of modified cilia which arise from the inner wall of the cavity.