Comparative karyological analysis of five species of Viviparus (Gastropoda: Prosobranchia)

Karyological analysis was performed on Viviparus ater (Cristofori & Jan. 18 32), V. acerosus Bourguignat, 1862, V. mamillatus (Kuster), V. vivparus (Li nnaeus, 1758) and V. contectus (Millet, 1813), collected from different fre shwater bodies of Switzerland, Hungary, Albania, Italy and Lithuania. The k aryotypes of V. acerosus and V. mamillatus are described for the first time . The diploid number of chromosomes in V. contectus equals 14, whereas in d iploid sets of other studied species, 18 chromosomes are present. The karyo type formula is in V. contectus (5m + 2sm, NF = 28, in V. ater, 7m + 1sm-m + 1 sm, in V. acerosus and V. viviparus, 8m + 1sm, NF = 36, in V. mamillatu s, 6m + 1m-sm + 1sm-m + 1sm, NF = 36. In females of V. ater, V. mamillatus and V, acerosus, the heteromorphism of chromosome pair no. 8 was observed. with a sex-determining mechanism-ZW female /ZZ male. Although, Z and W chro mosomes are metacentric, significant differences (P < 0.05, or P < 0.001) i n their size were determined. The interspecific significant differences (P < 0.05) in karyotypes of V. ater, V. mamillatus, V. acerosus and V. vivipar us were detected by using one-way ANOVA and Bonferroni's Multiple Compariso n tests. Only chromosomes of the pair no. 5 were of similar shape in all of these species. The smallest interspecific difference was between V. vivipa rus and V. acerosus. The intraspecific karyological differences in relative chromosome length and centromeric index of V. contectus from lakes Garda ( Italy), Olauka and Asveja Lithuania) were observed in the chromosome pair n o.