Banding of Oedionychina (Coleoptera:Alticinae) Chromosomes: C- and Ag-bands

Abstract

Banding of chromosomes was studied in about 40 species of Brazilian Oedionychina. Long sex chromosomes and large germ line cells of these fleabeetles facilitate such studies. Because the sex chromosomes comprise about 50% of the total karyotype length and do not pair in male meiosis, the spermatogenesis serves unusually well for the banding purposes. Abundant mitoses are obtained from colchicinized embryos (eggs). Conventional tapping and smearing techniques are catastrophic, because the large spermatocytes are so perishable. Squashes of Kahle-Smith-fixed tissues are safest and good for silver staining, but the fixative tends to slow down the formation of C-bands. Teasing the testes with pins on the slide saves about 25% of the Ml cells. C-bands mark procentric heterochromatin in most chromosomes, and intercalary heterochromatin of variable amount and location in the sex chromosomes. Insufficient treatment in Ba(OH)₂ induces G-band-like marking of the sex chromosomes (especially of Y) in some species. Failure of C-banding can be corrected by rebandings up to 6 times. A prolonged Giemsa staining is necessary for rebanded chromosomes. Silver staining marks kinetochore dots in most chromosomes, and intercalary bands in male diplotenic sex chromosomes. Strongest of these bands are still present at Mil. The active sites they mark are presumably related to a synthesis (through gene amplification?) of a material structurally similar to chromatoid bodies. Band differences between species show that C- and Ag-bands are powerful tools for the cytotaxonomy of these beetles. Ag-bands must be compared with care, because their number is reduced from diplotene to Ml.