Cytogenetic features of the invasive crayfish Procambarus clarkii (GIRARD, 1852) and comparison with other crustacean decapods

The Louisiana crayfish Procambarus clarkii (Girard, 1852) is an invasive freshwater crustacean species present in several European countries. Within the last years, P. clarkii has been successfully established in various sites of Sardinian basins. Although their economic and ecological value, the cytogenetics of crustacean decapods is poorly studied. This is principally due to technical constraints in obtaining good chromosomal preparations as well as the features of the chromosome complement. In many species a high number (generally more than 100) of little sized chromosomes are present, and the highest number among Metazoa, 2n=376, belongs to the Astacidae Pacifastacus leniusculus trowbridgii; as a result, different authors’ data concerning the decapod karyotypes differ significantly. Moreover, modern molecular cytogenetic techniques, such as Fluorescence In Situ Hybridization, have been applied to a few species of decapods. With the aim to shed light on the data reported by different authors, here we examine the cytogenetic features of P. clarkii. Chromosome preparations were obtained by the air drying method from testicular and somatic tissues of males captured in Sardinian basins, C-banding and FISH were performed to localize the heterochromatin and ribosomal and telomeric sequences, respectively. Our results confirmed the 2n=188, and pointed out the presence of A-T rich heterochromatic blocks. By FISH mapping, the major ribosomal genes were localized on four chromosome pairs and the telomeric repeat (TTAGG)n, besides the chromosomal ends, was detected in interstitial position of a large chromosome pair; the presence of two pairs of close ITS signals may be due to a telomeric association. Data obtained have been compared with other decapods with the aim to provide chromosome markers useful for cytotaxonomic analyses. This study was supported by the Fondazione di Sardegna (year 2016) and Regione Sardegna (LR 7/2007) for the project: Impact of Invasive Alien Species on Sardinian ecosystems.