Studies on the Chromosomal Analysis and Shell Measurements of Two

_??_1991 by Cytologia, Tokyo Cytologia 56: 503-509, 1991 Studies on the ChromosomalAnalysis and Shell Measurements of Two Species, Bellamya unicolar and Lanistes bolteni (Prosobranchiata: Gastropoda) Ahmed E. Yaseen, Abdel-Baset M . Ebaid and I. S. Kawashti1 Zoology Department, Faculty of Science (Qena) , Assiut University, Qena, Egypt AcceptedMay 16, 1991 Because of the scarcity of workers in the field of cytogenetic of invertebrates , molluscan cytogenetic has lagged behind the rapid techniological developments in the cytogenetric of man and other vertebrates. Early work in molluscan cytogenetic was generally aimed at the establishment of chromosome counts for fresh-water snails by Patterson (1971). Later work ers were able to obtain information about the chromosome size and centromeric position , Babrakzia and Miller (1974) and some excellent results have been obtained including G and C banding preparation from land snails by Babrakzia et al. (1975). From the taxonomic standpoint, the number and the behaviour of chromosomes seem to have a great deal of uniformity in species within a single genus, even among species of closely related genera and therefore may be of some significance. Chromosome cytology provides imnumerable examples of clear-cut differences between the karyotype of species so similar morphologically that they are barley or not at all distinguishable classical taxonomic methods (Huettel and Dickson 1981, Valero et al. 1983, Hirai et al. 1985). The shell characters are frequently just as important or even more important than the soft parts in respect to the classification of snails. The taxonomy of African fresh-water snails is frequently based upon both anatomical characters and shell features (Brown et al. 1967). To the best of our knowledge, no information are found in the literature on the chromo somal studies and shell measurements of these two species Bellamya unicolor and Lanistes bolteni 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 these two species. Materials and methods The specimens were collected from different localities around Qena City. They were housed in the laboratory tanks of areated fresh-water, they were fed continuously on lettuce and supplement containing Cerophyl, Wheat germ and tetra-min fish food to promote somatic growth (Dixon and Clarke 1982). Chromosomal preparations The materials were prepared by the warm-dry method of Kligerman and Bloom (1977) with some modification made by Nakamura (1986) as follows: The snails were kept in 0.005% 0.01% coichicine solution for 2-6 hr before being sacrificed, then the gonads were removed and cut into small pieces and soaked in 0.075M KCI hypotonic solution these pieces were fixed in freshly mixed Cornoy'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 suspension 1 Zoology Deparment , Faculty of Science, Al-Azhar University, Egypt. 504 Ahmed E. Yaseen, Abdel-Baset M. Ebaid and I. S. Kawashti Cytologia 56 was pipetted out and placed on heated clean glass slides. The cell left on the slide were dried and then stained for 20min in 2% Giemsa solution. The prepared slides were examined under a research microscope, and phtographs were taken with a high contrast film and enlarged. The following morphological features were used to compare the karyotypes: relative length, arm ratio and centromeric index. No menclature of chromosome types adopted by Levan et al. (1964) were used in the present study. Shell measurements About fifty individuals from each species 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 using a dial caliper and a calibrated eye-piece. Spire shape (L/AL), shell shape (L/W) and aperture shape (AL/AW) were calcu lated as shown in Table 3a according to James (1968). The results obtained from the present investigation were statistically analyzed using the methods described by Snedecor (1946) and Goulden (1960) for the analysis of variance and regression analysis. Fig. 1. A cell spread [a] and karyotype [b] of the snail Bellamya unicolor [2n=18]. Results and discussion The photograph of the cell spread and the karyotype of the two species Bellamya unicolor and Lanistes bolteni was found to have a diploid chromosome number of 18 and 26 respectively as shown in Figs. I and 2. Arm ratio, relative length and centromeric indices are given in Tables 1 and 2. An idiogram (Figs. 3, 4) was constructed from relative lengths and centromeric indices with the centromeres drawn at the same level to make visual comparison easier . The karyotype of Bellamya unicolor consists of: five metacentric pairs (arm ratio 1.14 1.32), two submetacentric pairs (arm ration 1.81-1.89) and, two subtelocentric pairs (arm ratio 3.04-3.07) while the karyotype of Lanistes bolteni consist of: eight metacentric pairs (arm ratio 1.19-1.42), two subtelocentric pairs (arm ratio 3.53-3.80) and, three telocentric paires (arm ratio •å). The karyological studies described in this paper allow a more detailed analysis of the chromosomes of the two species Bellamya unicolor and,Lanistes bolteni . In our samples, Table 1. Averages often cell spreads of chromosomes measurements and classification of Bellamya unicolor Table 2. Averages of ten cell spreads of chromosomes measurements and classification of Lanistes bolleni 506 Ahmed E. Yaseen, Abdel-Baset M. Ebaid and I. S. Kawashti Cytologia 56 possible existence of polyploidy was absent. Shell measurements were carried out on 50 samples of each species. In Bellamya uni color the shell has a true dextral, broad to narrow shaped shell measuring L/W ratio range Fig. 2. A cell spread [a] and karyotype [b] of the snail Lanistes bolteni [2n=26]. Table 3a. Showing the appoved description and ranges of shell spire and aperture shapes Table 3b. Summary of ranges of some shell measurements of the two species studied L=Length AL=Aperture Length W=Width AW=Aperture Width 1991 Chromosomal Analysis and Shell Bellamya unicolor and Lanistes bolteni 507 from 1.1 to 1.4 the shell spire ranges from short to medium with a mean L/AL ratio of 1.3 to 1.6 and the shell aperature is very wide to wide measuring about 0.9-1.3. While in Lanistes bolteni the shell has an ultra dextral fairly broad-shaped shell measaring L/W ratio from 1.1 to 1.3, the shell spire ranger from short to medium with a mean L/AL ratio of 1.4-1.6 and the shell aperature is very wide to wide measuring about 1.1 to 1.4 as shown in Table 3b. Table 4a. Linear regressions of shell width on shell aperture length , shell length on shell aperture length, and shell aperture length on shell apperture width as obtained from the results of 50 samples of each of the two species studied Table 4b. The results obtained from comporing regression coefficient of the two species *** Statistically significant at the 0.1% level of siginificance (P<0.001) Table 5a. Linear regressions of shell length on shell width, shell length on shell aperture width, and shell width on shell aperture width as obtained from the results of 50 samples of each of the two species Table 5b. The results obtained from comparing regression coefficient of the two species *** Statistically significant at the 0.1% level of significance (P<0.001). 508 Ahmed E. Yaseen, Abdel-Baset M. Ebaid and I. S. Kawashti Cytologia 56 Shell shape as indicated by the standard approved dimensions used in this text-varies considerably between species. The linear regression of shell dimentions and the corresponding correlation coefficients in the two species were found to be statistically highly significant as shown in Tables 4a and 5a. On the other hand, regression coefficients of the relationship between shell width and shell aperture length, shell aperture length and shell length and, shell aperture width and shell Fig. 3. Idiogram of the chromosomes of Fig. 4. Idiogram of the chromosomes of Bellanrya unicolor. Idiogram was constructed Lanistes bolteni. Idiogram was constructed relative to the relative length [I] and to the relative to the relative length [I] and to the centromeric index [II]. centromeric index [H]. 1991 Chromosomal Analysis and Shell Bellamya unicolor and La nistes bolteni 509 aperture length of the two species Bellamya unicolor and Lanistes bolteni as sh own in Table 4b were statisticelly highly significant from each other . Furthermore, the regression coef ficients of Bellamya unicolor and Lanistes bolteni of the relationship between shell length and shell width, shell length and shell aperture width and , shell width and shell aperture width as shown in Table 5b were statistically not significant from each other . The authors concluded that the chromosomal analysis is more important to the taxon omist than the morphological descriptions and that coupling of both approaches is ultimetely useful in this respect. Summary Chromosomes were counted in the preparations of gonad tissues from the two species Bellamya unicolor and Lanistes bolteni collected from different localities around Qena City in Upper Egypt. A basic diploid chromosome number of 18 and 26 were presented in Bellamya unicolor and Lanistes bolteni, respectively. The karyotype of Bellamya unicolor consists of: five metacentric pairs, two submetacentric pairs and two subtelocentric pairs , while the kary otype of Lanistes bolteni consists of: eight metacentric pairs two subtelocentric pairs and three telocentric pairs. Shell measurements for these two species are also described in details in this paper. These results are reported for the first time in Egypt. References Babrakzai, N.

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