A Molecular Cytogenetic Study on Some Icelandic Amphipods (Crustacea) by Fluorescence In Situ Hybridization (FISH)

ABSTRACT

A cytogenetical investigation was carried out on 8 species of amphipods from Iceland by using conventional staining, C-banding, fluorescence in situ hybridization (FISH) with rDNA and telomeric repeat probes, and flow cytometry genome size evaluation. Previously reported data on chromosome number were confirmed and the karyotype formula was determined for the first time in 3 species. The tendency of amphipods to be endowed by high symmetric karyotypes was once again pointed out. Heterochromatin distribution on chromosomes was revealed by C-banding and DAPI staining after FISH treatment. Heterochromatic bands are mainly centromeric and their total extension is directly proportional to genome sizes. The genome size (GS) in Icelandic species was relatively higher in comparison with the GS of related species from temperate climate, as a probable pre-adaptation to cold climate. Application of FISH with a rDNA probe evidenced a great variability among species concerning the number of autosome pairs carrying the nucleolar organizer regions (from 1 to 5). A probe containing the ‘arthropod’ type telomeric motif TTAGG was the only one to hybridize with the chromosomal termini in all the investigated amphipods. The molecular cytogenetical methods demonstrated to be a powerful tool to find differences in genome organization among related species of amphipods characterized by conservative karyotypes.

Keywords:

Amphipoda, in situ hybridization, rDNA sequences, TTAGG telomeric motif, C-banding, Genome Size.