Meeting Abstract
61.3 Tuesday, Jan. 6 Does body size limit eye size in Drosophila melanogaster? MERRY, J.W.*; RUTOWSKI, R.L.; Arizona State University; Arizona State University jmerry@francis.edu
We tested the hypothesis that body size constrains the evolution of eye size in insects. We subjected flies to antagonistic artificial selection on eye height and thorax length in an effort to disrupt the relationship between these two variables. We predicted that body size-induced limits on maximum eye size would result in a smaller response among lines selected for proportionally large eyes and a greater response among lines selected for proportionally small eyes. Instead, there was an immediate and equivalent response to selection in both directions, with complete separation of both experimental lines from control lines within three generations. Realized heritability (h2) was 0.16 in "Large Eye" lines and 0.18 in "Small Eye" lines, which matches broad-sense heritability estimates (H2) from a previous experiment. Nevertheless, the specific morphological changes that produced these responses differed among treatments. Selection favoring proportionally larger eyes resulted in a large decline in thorax length and only a small increase in eye height. On the other hand, selection in lines favoring proportionally smaller eyes responded entirely via a decline in eye size. Finally, we subjected animals from each of the selection treatments to diets of varying nutritional quality to test the hypothesis that lines with proportionally large eyes were more resource limited than lines with proportionally small eyes. The dietary restriction affected all lines equally. Nevertheless, Large Eye animals showed a decline in eye size during the diet experiment across all diet treatments, which may indicate that natural selection operated against proportionally large eyes following relaxation of artificial selection.
