Phenotypic plasticity and reaction norms of abdominal bristle number in Drosophila melanogaster.

The phenotypic plasticity of abdominal bristle number (segments 3 and 4 in females) was investigated in 10 isofemale lines from a French population, grown at 7 constant temperatures, ranging from 12 to 31 degrees C. Overall concave reaction norms were obtained with a maximum around 20-21 degrees C. Intraclass correlation (isofemale line heritability) was not affected by temperature. Correlations between segments 3 and 4 strongly contrasted a low within-line phenotypic correlation (r=0.39+/-0.04) and a high, between-line genetic correlation (r=0.89+/-0.03). A significant decrease of the genetic correlation was observed when comparing more different temperatures. Finally, among 7 other morphometrical traits which were measured on the same set of lines, 3 provided a significant positive genetic correlation with abdominal bristles: thoracic bristles, abdomen pigmentation and thoracic pigmentation.