Chromosomal Studies of the Freshwater Snail Cleopatra Bulimoides Common in Upper Egypt
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_??_1994 The Japan Mendel Society Cytologia 59: 317 -322 , 1994 Chromosomal Studies of the Freshwater Snail Cleopatra bulimoides Common in Upper Egypt Ahmed E. Yaseen Cytogenetic Lab., Zoology Dept., Faculty of Science (Qena) Assiut University , Egypt Accepted July 4, 1994 Chromosome study of molluscs is of special interest to the cytologist because of the extreme diversity in morphology, number of species and number of other qualities (Babrakzia et al. 1976). In Makino's list (1950), chromosome number of 127 species and subspecies were recorded. Then just two decades after Makino's work , the chromosome number of 622 species and subspecies were recorded (Patterson 1969). The present work deals with the chromosomal studies of the Egyptian freshwater opercul ate snail, Cleopatra bulimoides (Olivier 1804), belonging to the family thiaridae . The shell of this species either have dark brown bands on their outer surface or not . There are no available publication however showing the taxonomical bases on which the two forms of this species were assigned to one species except Mohamed (1987) who insisted that the two forms belonging to one species, Cleopatra bulimoides. A perusal of the literature on the chromosome number of prosobranchiata has revealed that the genus Cleopatra has not received considerable attention by cytologists especially in Egypt, so the aim of the present study is to determine the chromosome number, describe the karyotype and shell measurements in details for the freshwater operculate snail, Cleopatra bulimoides common in Upper Egypt. Materials and methods The specimens of Cleopatra bulimoides were collected from certain freshwater courses and irrigation canals around Qena City. They were housed in the laboratory tanks of aerated freshwater, they were fed continuously on lettuce and supplement containing wheat germ and tetra-min fish food to promote somatic growth (Dixon and Clarke 1982). The chromosomal preparations were made by the warm-dry method of Kligerman and Bloom (1977) with some modifications made by (Nakamura 1986) as follows: the snails were kept in 0.005-0.01% colchicine solution for 2-4 hr before being sacrificed, then the gonads were removed and cut into small pieces and soaked in 0.075 M KCl (hypotonic) solution, and fixed in freshly mixed Carnoy's fixative (3:1 methyl alcohol: acetic acid). Tissues were then minced gently in 50% acetic acid to prepare a cell suspension. A drop of the cell suspention was pipetted out and placed on warm clean glass slides. The cell left on the slide were dried and then stained for 20 min in 2% Giemsa solution. The slides were examined under a research microscope and photographs were taken with a high contrast film and enlarged. Nomenclature of the chromosome types adopted by Levan et al. (1964) were used in the present study. About hundred individual (fifty with banded and fifty with unbanded shells) were used in the morphological analysis of shell parameters. Four shell dimentions which are length (L), width (W), aperture length (AL) and aperture width (AW) were measured for each snail. Spire shape (L/AL), shell shape (L/W) and aperture shape (AL/AW) were calculated accord ing to James (1968) and Gregoire (1972). 318 Ahmed E. Yaseen Cytologia 59 Results and discussion Somatic chromosomes of twenty five mitotic metaphase plates for each banded and unbanded specimens of Cleopatra bulimoides were analysed. The photographs of the cell spread of the two forms (which have banded and unbanded shell) had the same diploid chromosome Fig. 1. A cell spread (a) and karyotype (b) of the snail Cleopatra bulimoides (2n=28) . Fig. 2. Idiogram of the chromosomes of Cleopatra bulimoides. Idiogram was constructed relative to the relative length. Table 1. Average of ten cell spreads of chromosomes measurements and classification of Cleoparta bulimoides 320 Ahmed E. Yaseen Cytologia 59 Fig. 3. Giemsa stained structures of meiotic and mitotic chromosomes of Cleopatra bulimoides. a-a group of cells in leptotene stage, b-pachytene stage, c-haploid chromosome number n=14, d-late prophase, e-early metaphase, f-tetraploidy, g-pentaploidy, h-hexaploidy, i-heptaploidy and j-octaploidy. •~2500. number, 2n=28 (Fig. 1a). The chromosomes from ten spreads were cut out and arranged in pairs on the basis of size and centromeric position of the karyotype. Arm ratios, relative lengths and centromeric indices are given in Table 1. Three groups of chromosomes were recognized according to the centromeric index for the two forms as shown in Fig. 1b. Group A, four pairs of metacentrics (Arm ratio 1.00-1.30), group B, eight pairs of submetacentrics (Arm ratio, 2.20-2.57) and group C, two paris of telocentrics (Arm ratio •‡). Idiogram Fig. 2 was constructed based on relative length. The different behaviors of chromosomes through meiotic and mitotic division in Cleopatra bulimoides (Fig. 3a-j) is very interesting. During the early stages of first meiotic division the 1994 Chromosomal Studies of the Freshwater Snail 321 chromosomes are randomly distributed in the nucleus, the length of these leptotene threads (Fig. 3a) is drastically diminished at pachytene (Fig. 3b). A weak orientatien was observed in the early stages of the pachytene, but the bivalents soon appeared more intensively stained o wing to gradual condensation. In consequence the haploid chromosom number could be counted (Fig. 3c). Late prophase and early metaphase were the most suitable stages for observing the morphology of individual chromosomes in mitosis (Fig. 3d, e). Increased levels of polyploidy, in the form of tetraploidy 4n=56, pentaploidy 5n=70, hexaploidy 6n=84, neptaploidy 7n=98 and octaploidy 8n=112 were determined only in the specimens which have dark brown bands (Fig. 3f-j). The shell of the two forms had a broad to narrow-shaped, i.e. L/W range from 1.10 to 1.40 322 Ahmed E. Yaseen Cytologia 59 Table 2. Summary of ranges of some shell measurement of the two forms of Cleopatra bulimoides species mm. The shell spire ranges from short to tall, i.e. L/Al range from 1.4 to 1.8. The shell aperture is very wide to wide, i.e. Al/Aw range from 1.2 to 1.3 (Table 2). The above results suggest that the two forms with and without dark band belong to the same species Cleopatra bulimiodes being in agreement with Mohamed (1987). The author claimed that the phenomena of polyploidy which appears only in the specimens which have dark brown band may play a role in the appearence of these bands. Summary Chromosomes were counted in the preparation of gonad tissues from Cleopatra bulimoides collected from different localities around Qena City in Upper Egypt. The diploid chromosome number of this species was determined to be twenty eight (2n=28). The karyotype was made up of four metacentric, eight submetacentric and two telocentric chromosome pairs. Increased levels of polyploidy in the form of tetraploidy, pentaploidy, hexaploidy, heptaploidy and octaploidy were determined only in the specimens which have dark brown bands on their shells of this species. Shell measurements are also described in details. (These results are reported for the first time in Egypt.) References Babrakzai, N., Miller, W. B. and Samsam, N. S. 1976. Procedures and methods in Molluscan cytology and cytogenetics. Bull. Amer. Molacological Unipon. 57-61. Dixon, D. R. and Clarke, K. R. 1982. Sister chromatid exchange a sensetive method for detecting damage caused by exposure to enviromental mutagens in chromosomes of adult Mytilus edulis. Marine Biol . Letters 3: 163-172. Gregorie, C. 1972. Structure of molluscan shell. In Chemical Zoology (M. Florkin and B . T. Sckeer ed.) 3: 5-101. Academic Press, New York. James, B. L. 1968. The characters and distribution of subspecies and varieties of Lottorina saxatalis (Olivi) in Britain . 9: 143-165. Kligerman, A. D. and Bloom. S. E. 1977. Rapid chromosome preparation from solid tissues of fishes . J. Fish Res. Board. Can. 34: 266-269. Levan, A., Fredga, K. and Sandberg, A. A. 1964. Nomenclature of centromeric position on chromosomes . Hereditas 52: 201-220. Makino, S. 1950. An Atlas of Chromosome Numbers in Animals. The Iowa State College Press . Ames, Iowa. Mohamed, A. S. 1987. Studies on the functional morphology of one of the fresh-water snails Cleopatra bulimoides . M. Sc. Thesis, Faculty of Science, Assiut University, Egypt . Nakamura, H. K. 1986. Chromosome of the Archaeogastropoda (Mollusca-Prosobranchiata) with some remarks on their cytotaxonomy and phylogeny. Publ. Seto. Mar. Biol. Lab. 31: 191-267. Olivier, G. A. 1804. Voyage dans L. Empire Othoman L . Egypt et al. Perse, 3: Paris. Patterson, C. M. 1969. Chromosome of Molluscs. In Marine Biological Association of India, Proceedings of symposium on Mollusca, Part II, p. 635-686..