Date of Award

Spring 2006

Document Type

Restricted Thesis

Terms of Use

© 2006 Anisha Chandra. 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


Six life history traits were examined in Drosophila melanogaster populations that had been under predation over a period of five years by the cellar spider Pholcus phalangioides. The reproductive traits studied were copulation latency (CL), courtship index (CI), and copulation duration (CD). CL was found to be significantly longer in predation populations (µ=774.10 ± 45.20 seconds) than in control populations (µ=620.07 ± 47.50 seconds) (F=6.25, DF=l, P=O.Ol). Courtship index for predation populations was significantly higher (µ=0.36 ± 0.03) than for control populations (µ=0.28 ± 0.04)(F=5.17, DF =1, P=0.02). Courtship duration was found to be significantly longer in predation populations (µ=1007.23 ± 15.20) than in control populations (µ=960.63 ± 16.00)(F=5.33, DF=l, P=0.02). Other traits considered were average daily activity, periodicity (τ), and weight for both males and females. Average daily activity in predation populations (µ=1442.17) was significantly lower than in control populations (µ=1991.34) (F=25.50, DF=1, P<0.000l). There were no significant differences in τ between predation and control populations (F=2.77, DF=l, P=0.10). Male weight for predation populations was not significantly different from control populations (F=0.08, DF =1, P=0.78). Female weight for predation populations was significantly lower (µ=0.00557 ± 0.00008 grams) than control populations (µ=0.00567 ± 0.00013 grams) (F=7.43, DF =1, P=0.007). Except for CD, all traits also showed significant differences between individual cages within each predation condition (P<0.05). These results suggest that small, isolated populations of limited gene variance may be more resistant to drift than previously believed, although drift does play a role. With evolutionary rates ranging from 10.3 to 77.1 10³ darwins in the traits under consideration, the responses to natural selection in these populations were as rapid as those seen in artificial selection experiments. This finding lends additional weight to the argument that small, isolated populations can retain variation in life history traits.