B Chromosome Variants of the Grasshopper Xyleus discoideus angulatus Are Potentially Derived from Pericentromeric DNA.

ABSTRACT

B chromosomes, extra elements present in the karyotypes of some eukaryote species, have been described in the grasshopper Xyleus discoideus angulatus. Although some studies have proposed an autosomal origin of the B chromosome in X. d. angulatus, little is known about its repetitive DNA composition and evolutionary dynamics. The aim of the present work was to shed light on the B chromosome evolution in X. d. angulatus by cytogenetic analysis of 27 populations from Pernambuco and Ceará states (Brazil). The frequency of B chromosomes in the different populations was determined, and chromosome measurements and fluorescence in situ hybridization (FISH) with C0t-DNA and telomeric and B chromosome sequences were performed in cells from B-carrying individuals. The results revealed variations in B chromosome prevalence among the populations and showed that some B chromosomes were smaller in certain populations. FISH produced similar patterns for the C0t-DNA probe in all hybridized individuals, whereas telomeric and B chromosome probes, obtained by microdissection, exhibited variations in their distribution. These results indicate the presence of 3 morphotypes of B chromosomes in X. d. angulatus, with variation in repetitive DNA composition during their evolution. In this species, B chromosomes have an intraspecific origin and probably arose from the pericentromeric region of A chromosomes.