Cytogenetic characterization of Eurysternus caribaeus (Coleoptera: Scarabaeidae): evidence of sex-autosome fusion and diploid number reduction prior to species dispersion
Meiotic chromosomes of eight Neotropical species of the genus Chauliognathus occurring in Southern Brazil were analysed from testis cells. The meioformula 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 other species of other genera of Cantharidae, suggesting an evolutionary tendency towards the compaction of the karyotype starting from the ancestral Polyphagan meioformula n = 9 + Xy(p). The presence of an XO sex chromosome mechanism in all cantharid species studied to date indicates that the reduction of the number of autosomes was probably paralleled by the loss of the small typical Polyphagan yp heterosome. Thus the meioformula n = 6 + X seems to be an apomorphy for Cantharidae and may have evolved soon after the separation of the ancestral cantharid from the other families of Polyphaga.