Selection for high and low number of sternopleural bristles in Drosophila ananassae: correlated response in the frequency of chromosome inversions.

Directional selection for high and low number of sternopleural bristles in Drosophila ananassae was applied for 13 generations. The selection produced a rapid divergence in the mean number of sternopleural bristles in the replicates high and low lines: i-high (H1 -25.75, H2 -25.69); ii-low (L1 -14.16 L2 -13.55); iii-control (17.21) lines in G13. Regression coefficients for the high and low lines were significantly different from zero. The realized heritability over thirteen generations was 21-23 for the high lines and 14-18 for the low lines. The results suggest that the number of sternopleural bristles in D. ananassae is under polygenic control, with a substantial amount of additive genetic variation. Flies of the base population had three chromosome inversions: AL (2L), ZE (2R) and DE (3L). The comparisons of chromosome arrangement between high and low lines (the G13 generation of selection) indicates significant changes in the inversion frequency during the course of selection, providing evidence for correlation between the bristle number and particular chromosome arrangements.