Chromosome evolution in ground beetles: localization of the rDNA loci in the tribe Harpalini (Coleoptera, Carabidae)

摘要

The pattern of localization of the ribosomal genes was studied by means of fluorescence in situ hybridization in 39 species of the tribe Harpalini. Most of them show one pair of amosomes carrying the ribosomal genes in a distal position of a single chromosome arm. This pattern is hypothesized to be ancestral for the whole tribe. Both, chromosome number and the number and localization of rDNA loci, show little variation and are therefore of little phylogenetic value. Only in the subtribe Ditomina is there enough variation to characterize phyletic relationships. The stability of rDNA loci is even higher than the constancy of chromosome number, as most species of Ditomina (genera Dixus, Eocarterus, Carterus, Odontocarus and Ditomus) have the usual pair of amosomes with rDNA loci, in spite of remarkable differences in the diploid number. Only Dixus sphaerocephalus and Dixus clypeatus have two amosomal pairs with a fluorescent signal. These results do not support the hypothesis that the high chromosome numbers found within Ditomina are the result of polyploid change from the ancestral 2n = 37 karyotype of the tribe Harpalini. Chromosomal translocations or the presence of mobile genetic elements are plausible sources of the few cases of intraspecific polymorphism in the rDNA loci found in species of Harpalus.