Date of Award


Document Type

Restricted Thesis

Terms of Use

© 2008 Lucy McNamara. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Biology Department

First Advisor

John B. Jenkins


In populations under selective pressure, individuals adopt many adaptive strategies to ensure that they can survive and reproduce. In this study, we investigated the possibility that populations of Drosophila melanogaster had adopted either of two adaptive strategies under the selective pressure of predation. Noting that in bacteria and viruses mutation rate has been shown to increase when populations are exposed to intense selective pressure, we first investigated whether a similar increase in mutation rate might occur in D. melanogaster, a sexually reproducing eukaryotic organism. Populations of D. melanogaster were exposed to predation by the cellar spider, Pholcus phalangioides, for 8 years, then flies from the populations were exposed to X-ray irradiation. The X-ray induced sex-linked recessive lethal mutation rate and reproductive sensitivity to mutation of these populations were then compared to those of flies from control populations. The results of these experiments indicate that there is no difference in X-ray induced mutation rate between flies under predation and control flies, confirming theoretical models of mutation rate evolution in sexually reproducing populations. Next, we examined progeny production of flies under predation, a characteristic that in other organisms has been found to increase in response to predation. This experiment revealed that flies from one of the experimental populations produced on average 13 more progeny per pair per first mating than control flies, demonstrating that flies with increased reproductive potential may be selected for in the face of intense predation. We also examined the longevity of flies under predation to determine if the increased fecundity of one of these populations corresponded to a decrease in longevity, a possible evolutionary tradeoff. No sign of such a tradeoff was found; in fact, the flies from the population with increased fecundity also had significantly longer lifespans than control flies. This observation may suggest that increased longevity is itself an adaptation to predation in this population, or it may merely confirm previous studies that suggest that in the absence of selection, laboratory populations often deteriorate.