Cytogenetics of eight Neotropical species of Chauliognathus Henzt, 1830: implications on the ancestral karyotype in Cantharidae (Coleoptera)

Meiotic chromosomes of eight Neotropical species of the genus Chauliognathu s occurring in Southern Brazil were analysed from testis cells. The meiofor mula of all the species was n = 6 + X (with six pairs of autosomes and one X chromosome). This meioformula is also present in C. scriptus plus two oth er species of other genera of Cantharidae. suggesting an evolutionary tende ncy towards the compaction of the karyotype starting from the ancestral Pol yphagan meioformula n = 9 + Xy(p). The presence of an XO sex chromosome mec hanism in all cantharid species studied to date indicates that the reductio n of the number of autosomes was probably paralleled by the loss of the sma ll typical Polyphagan yp heterosome. Thus the meioformula n = 6 + X seems t o be an apomorphy for Cantharidae and may have evolved soon after the separ ation of the ancestral cantharid from the other families of Polyphaga.