ARTIFICIAL SEXUAL SELECTION ALTERS ALLOMETRY IN THE STALK-EYED FLY CYRTODIOPSIS-DALMANNI (DIPTERA, DIOPSIDAE)

Selection for increased and decreased ratio of eye span to body length was exerted on male stalk-eyed flies (Cyrtodiopsis dalmanni) from Mal aysia using replicate selected and unselected lines. Response to selec tion was symmetrical. After 10 generations high line male eye span inc reased to 1.3 body lengths while low line male eye span declined to 1. 1 body lengths. Realized heritabilities for eye span to body length ra tio, estimated using regressions of deviations from unselected control s on cumulative selection differentials, were greater than zero for al l four selected lines with average h(2) = 0.35+/-0.06. The static line ar allometric relationship between eye span and body length diverged b etween selected lines and rotated among selected line males in the sam e direction as among males in other sexually dimorphic diopsid species . Crosses between lines after 13 generations of selection indicate tha t the genes which influence relative eye span combine additively and d o not exhibit sex linkage or maternal effects. The genetic correlation between the sexes, 0.29+/-0.05 as estimated by the regression of fema le on male change in eye span, did not prevent sexual dimorphism in ey e span from diverging between lines. These results suggest that the ex aggerated eye span of male C. dalmanni is maintained by natural select ion opposing sexual selection rather than by lack of or asymmetry in a dditive genetic variation. Furthermore, the variation in sexual dimorp hism for eye span-body length allometry observed among extant diopsid species is consistent with sexual selection of variable intensity acti ng on relative eye span.