E. Catalano

Multiple-chromosome sex systems in the darkling beetles Blaps gigas and Blaps gibba (Coleoptera, Tenebrionidae)

We have studied mitotic and meiotic chromosomes in the males of two species of Blaps: B. gigas and B. gibba. Karyological characteristics such as the occurrence of a multivalent configuration at diakinesis and two types of metaphase-II spreads support the notion that multiple-chromosome sex systems involving five chromosomes in B. gigas and eight chromosomes in B. gibba have developed in these species. Results obtained by means of silver staining and C-banding techniques suggest that the complex sex systems occurring in B. gigas and B. gibba may have originated from exchanges of terminal ribosomal genes among the Y chromosome and some autosomes.

Intra-populational and intra-individual mosaicisms of Uranoscopus scaber L. (Perciformes, Uranoscopidae)

Karyotypic analysis on 25 specimens of Uranoscopus scaber from the Gulf of Palermo has revealed the occurrence of an intra-populational mosaicism of Robertsonian type with three distinct diploid numbers: 2n = 30, 2n = 29 and 2n = 28. Intra-individual mosaicism in the chromosome number (2n = 30 and 31 in two specimens and 2n = 28 and 29 in one specimen) is also reported. One large metacentric pair is characterized by secondary constrictions, variable in length in different fish. Polymorphisms of these areas seem to have a genetic, rather than transcriptional, basis.

Multiple sex-chromosome system and other karyological characterizations of Pterotrachea hippocampus (Mollusca: Mesogastropoda)

Two modal diploid numbers of chromosomes were found for Pterotraches hippocampus Philippi (Mollusca: Mesogastropoda) collected from the Gulf of Palermo in 1990: 2n=31 and 32 for males and females, respectively. This, along with other karyological characteristics such as the occurrence of a trivalent configuration at diakinesis and two types of metaphase-II spreads in spermatocytes, supports the notion that a X1X2Y♂/X1X1X2X2♀ sex mechanism operates in the species investigated here. Silver nitrate procedure revealed an intraindividual variation in the Ag-staining pattern occurring in this species. The majority of the chromosome pair displayed terminal and/or interstitial heterochromatic blocks after C-banding.

Karyotypic variability associated with Robertsonian fusion in two species of the family Ophidiidae (Pisces, Perciformes)

Abstract Diploid modal numbers of 2n = 44, and 2N = 43 for different specimens of Ophidion barbatum L., and Paropbidion vassali (Risso) in populations of the Gulf of Palermo are reported. An inter‐individual polymorphism due to Robertsonian fusion is suggested for these species.

Chromosomes of the Parasitic Isopod Anilocra Physodes

Counts of mitotic chromosomes have allowed to determine 2n = 12 as the modal diploid number of Anilocra physodes. Application of the C-banding technique reveals that two hetero-chromatic blocks bordering the centromeric region occur in each chromosome. This supports the notion that the actual low chromosome number of A. physodes may have been derived through a process of Robertsonian fusion.