Analysis of Karyotypic Evolution in Natural Populations of Cynolebias(Pisces: Cyprinodontiformes, Rivulidae) Using Banding Techniques.

High levels of variation in chromosome numbers and N. F. s from 48-80. C-banding analysis allowed us to detect C-positive regions in three positions: centromeric, telomeric and interstitial. A differential C-banding pattern was found in each species. These banding patterns can be interpreted as a result of namely pericentric inversions and centric fusions occuring alternatively during the karyotypic reorganization of these species.The karyotypic analysis of 17 specimens of Cynolebias using silver stain NOR technique showed 3-6 rDNA active regions among these species. A reduction in the number or expression of NORs occurred in the species with lower chromosome number as a result of centric fusions. Terminal active NORs seem to be the most common situation among these species. Other positions of the active rDNA cistrons can be explained through chromosomal rearrangements.All present data are consistent with Scheel's hypothesis that pericentric inversions and centric fusions occurred in the karyotypic reorganization in the Rivulinae.