Heterochromatin accumulation and karyotypic evolution in some dipteran insects

Abstract

Evolutionary divergence among eukaryotes always involves genetic changes at different levels of the genome. At the chromosomal level, heterochromatin differentiation resulting in karyotypic evolution provides a useful tool for cytotaxonomy of many groups of animals including the dipteran insects. In our studies, detectable differences in the amount and distribution of heterochromatin have been observed in several groups of closely related species and some sibling species complexes of Drosophila, Anopheles, and Bactrocera, for example, the D. kikkawai complex and the montium subgroup, the An. dirus complex and the maculatus group, and the B. dorsalis complex and the Zeugodacus group, respectively. Most cases, if not all, of our studies point to the fact that inter- and intraspecific differences in mitotic chromosomes are due to the acquisition of major block(s) of constitutive heterochromatin in the sex chromosome(s) and/or autosome(s), particularly at the pericentric region. Further, quantitative differences in heterochromatin of mitotic chromosomes can be successfully employed as genetic markers for separation of cryptic or isomorphic species in these groups of insects. Although the functional role and implications of heterochromatin in species differentiation is an unsolved problem, heterochromatin accumulation in the genome is clearly involved in genetic differentiation and karyotypic evolution of dipteran insects as demonstrated in the present study.