The B-chromosome polymorphism of the grasshopper Eyprepocnemis plorans in North Africa: II. Parasitic and neutralized B-1 chromosomes

The transmission of the B-1 chromosome through females has been analysed in three Moroccan populations (Smir, SO.DE.A. and Mechra) of the grasshopper Eyprepocnemis plorans. We analysed transmission ratio (k(B)) variation at two levels: intra-individual (to test female age effects) and interindividual (to test for A chromosome effects). In 81.8% of females, k(B) did not differ among successive egg-pods, suggesting no effect of female age. The remaining females (18.2%), showed significant differences in k(B) values among egg-pods, but without clear temporal patterns. In Smir, k(B) ranged between B elimination (0.244) and B accumulation (0.689) but there was no net accumulation (mean +/- s.e. = 0.463 +/- 0.045). In SO.DE.A., all females analysed transmitted B-1 at a Mendelian rate, with a mean k(B) equal to 0.512 +/- 0.020. In Mechra, k(B) ranged from 0.341 to 0.972, with mean k(B) (0.575 +/- 0.029) showing a net B accumulation. All these observations suggest that the B-1 chromosome could be at a drive-suppression stage in Smir and Mechra, but that it has already been neutralised in SO.DE.A.