RESUMO
Polymorphism for B chromosomes has been detected in all nine populations of the grasshopper Eyprepocnemis plorans ssp. plorans sampled in Morocco. The most frequent B chromosome in all populations showed a C-banding pattern and size similar to those of the B1 variant found in the Iberian Peninsula. In addition, other B chromosome variants (B1iso1, B1iso2, B1d1, B1di1, B3 and B1dd1) were discovered in these populations, although at a very low frequency. No significant differences in B chromosome frequency were found either in the nine populations or, for some of them, in up to three consecutive years. These results are discussed in the light of current hypotheses on the evolution of this B chromosome polymorphism in the Iberian Peninsula.
RESUMO
Nine B chromosome variants, from seven different populations of Eyprepocnemis 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 tandem repeat and ribosomal DNA. B types, however, differ in the relative amounts of the two sequences. The most widespread one (B1) bears about the same amount of rDNA and 180 bp repeat, but three other variants that have reached a polymorphism by replacing B1 in smaller areas (B2, B5 and B24) carry a conspicuously larger amount of the 180 bp repeat. In Morocco, the most widespread B variant is also B1, and a rare variant that appeared in a single individual is also built with the same two DNA sequences. All these data point to a common origin for these B chromosomes, with B1 probably being the original one. The origin of the different B types and the possible relationship of the relative amount of 180 bp DNA repeat with B drive are discussed.