Selection for Rate of Growth and Its Influence On Competitive Ability of Larvae of Drosophila Melanogaster

Competition for food was studied in order to obtain an insight in the basic process and to explore its possible actions in an experimental population. 2. Early and late pupating larvae of a white Bar strain (O) were selected. These provided the basis of the E and L strains. 3. The eggs of E females were slightly larger than those of O females, while those of L females were smallest (Fig. 2). 4. There was no indication of a clear difference in the rate of embryonic development. 5. The growth rate of the three white Bar strains differed considerably (Figs. 3, 4 and 5). All have a slower growth rate than the test strain used (Bar) (Fig. 6). 6. A maternal effect on growth rate could be demonstrated (Fig. 7). 7. Moulting takes place in all strains at approximately the same weights (Fig. 9). 8. Cannibalism may occur and distort the picture of the experiments on food requirement (minimum weight). 9. The minimum weight necessary for survival is approximately the same in all strains (Fig. 9). 10. The efficiency with which the ingested food is converted into biomass is very similar in all strains, though slightly smaller in the L strain (Table VII). 11. There are no indications for a difference between the strains as regards weight loss during the starvation period after exhaustion of the food supply. 12. Growth rate is affected by the total amount of food provided. A small supply of food decreases growth rates of O and L larvae more than those of Bar and E larvae. 13. Taking the characteristics of the strains studied into account, predictions were made regarding their competitive abilities. These were tested in three experiments. 14. In the first two experiments competition for 60 and 120 mg food within and between strains was studied. The predictions came largely true. 15. By giving the three white Bar strains in the third experiment different starts (or in some cases, handicaps), the outcome of competition could be altered. The results were, again, largely predictable. 16. Knowledge of the characteristics of growth and development of the separate strains is sufficient for the prediction of the results of competition for food among larvae of Drosophila melanogaster. 17. The relevance of these results to the evidence for so-called facilitation is discussed.