Common origin of B chromosome variants in the grasshopper Eyprepocnemis plorans

Nine B chromosome variants, from seven different populations of Eyprepocnem is plorans collected at four localities in Spain and three in Morocco, have been shown to be mainly composed of two DNA sequences, i.e. a 180-bp tande m repeat and ribosomal DNA. B types, however, differ in the relative amount s of the two sequences. The most widespread one (B-1) bears about the same amount of rDNA and 180 bp repeat, but three other variants that have reache d a polymorphism by replacing B-1 in smaller areas (B-2, B-5 and B-24) carr y a conspicuously larger amount of the 180 bp repeat. In Morocco, the most widespread B variant is also B-1, and a rare variant that appeared in a sin gle individual is also built with the same two DNA sequences. All these dat a point to a common origin for these B chromosomes, with B-1 probably being the original one. The origin of the different B types and the possible rel ationship of the relative amount of 180 bp DNA repeat with B drive are disc ussed.