The B-chromosome polymorphism of the grasshopper Eyprepocnemis plorans in North Africa: II. Parasitic and neutralized B1 chromosomes

Abstract

The transmission of the B1 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 (kB) variation at two levels: intra-individual (to test female age effects) and inter-individual (to test for A chromosome effects). In 81.8% of females, kB did not differ among successive egg-pods, suggesting no effect of female age. The remaining females (18.2%), showed significant differences in kB values among egg-pods, but without clear temporal patterns. In Smir, kB 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 B1 at a Mendelian rate, with a mean kB equal to 0.512 ± 0.020. In Mechra, kB ranged from 0.341 to 0.972, with mean kB (0.575 ± 0.029) showing a net B accumulation. All these observations suggest that the B1 chromosome could be at a drive-suppression stage in Smir and Mechra, but that it has already been neutralised in SO.DE.A.