COMPARATIVE KARYOTYPE INVESTIGATIONS IN THE EUROPEAN CRAYFISH ASTACUS ASTACUS ANDA. LEPTODACTYLUS (DECAPODA, ASTACIDAE)

摘要

This study reports on the chromosome number and karyological characteristics ofthe endangered species of European crayfish, Astacus astacus and A. leptodactylus(Decapoda, Astacidae), both native to Croatian freshwater habitats. The karyotype ofA. astacus and A. leptodactylus consists of 2n = 176 and 2n = 180 chromosomes,respectively. The haploid chromosome complement of A. astacus consists of 52 metacentric,35 metacentric-submetacentric, and 1 acrocentric chromosomes. Fluorochrome staining with 4,6-diamino-2-phenylindole (DAPI) has revealed that the karyotypes of A. astacus and A. leptodactylus are characterized by large heterochromatic blocks located at centromericand intercalary positions on the chromosomes. Interstitial heterochromatic blocks were more frequent in A. astacus than in A. leptodactylus. In both species pairing of chromosomesin meiosis was regular with the majority of bivalents in a ring- and a dumbbell-form. Fluorescence in situ hybridization (FISH) has revealed that two 45S rDNA loci were present in the investigated species. In A. astacus one of the two 45S rDNA-bearing chromosome pairs was highly heteromor-phic, exhibiting a three-fold size difference between 45S rDNA siteson homologous chromosomes. Such a size difference was significantly less pronounced inA. leptodactylus. The karyotype differences between A. astacus and A. leptodactylus suggest changes in chromosome number as well as position of repetitive DNAs have played a rolein the karyotype evolution of the species of Astacus.