Cytogenetics of nine species of Mediterranean blennies and additional evidence for an unusual multiple sex-chromosome system in Parablennius tentacularis (Perciformes, Blenniidae)

The chromosomal complements of nine species of Blenniidae (Aidablennius sph ynx, Blennius ocellaris, Lypophris adriaticus, L. pavo, L. trigloides, Para blennius gattorugine, P. ponticus, P. sanguinolentus, P. tentacularis) from the Adriatic Sea were analysed with several banding methods and in-situ hy bridization. In all species, the diploid set consists of 48 mostly acrocent ric chromosomes and has a similar location (terminal centromeric) of NORs, except for L. pavo (interstitial pericentric) and P. ponticus (terminal on the long arm). There are major differences in karyotype with regard to the amount and distribution of heterochromatin. Parablennius tentacularis shows a distinctive sex-chromosome system involving 2n = 48 males with a large t otally heterochromatic Y chromosome, and males with 2n = 47. This differenc e is likely to be the consequence of a translocation of an autosome on the original Y. This finding constitutes an additional instance of the great va riability in origins of multiple sex chromosome systems in vertebrates.