Constitutive Heterochromatin Differentiation and Evolutionary Divergence of Karyotype in Oriental Anopheles (Cellia)

Abstract

Analysis of the mitotic karyotype of two clusters of closely related species of oriental Anopheles, the A . balabacensis and A. maculatus complexes, has revealed interspecific differences in the amount and distribution of constitutive heterochromatin, particularly in sex chromosomes. Such a qualitative diagnosis of heterochromatin is useful in identification of these sibling species. The cytological evidence indicates a significant role of heterochromatin in chromosomal evolution of anopheline mosquitoes. The novel heterochromatin differentiation in sex chromosomes suggests an evolutionary role in the process of species divergence. Furthermore, extensive intraspecific variations of sex chromosome heterochromatin have been observed in natural populations of A . dirus A and B, while chromosomal rearrangement is very rare , if not absent. The gross heterochromatin variation may be correlated with variability in vectorial capacity, which may reflect its functional significance in coevolutionary processes.