UBC Undergraduate Research

Substratum preference in the genus Dugesia Dirk, Justin


The purpose of this study was to determine if Dugesia had a preference of substratum among sand, small rocks, and pebbles. This was determined by a randomized choice experiment. Dugesia were placed in a petri dish with water and equal portions of each substratum. There were 20 replicates, with each replicate consisting of 3 minutes for the organism to make a choice. At the end of three minutes, the substratum at which the Dugesia spent the most time constituted a choice. Two trials were conducted, and the data were subjected to the chi-squared test. In both trials, Dugesia chose sand 5 times. In trial 1, they chose pebbles 6 times and small rocks 8 times. In trial 2 they chose pebbles 8 times, and small rocks 7 times. The trend shows an avoidance of sand, however the chi-squared test showed that the results of both trials were not statistically significant and therefore we fail to reject the null hypothesis. The results can be explained by the experimental protocol, and the fact that Dugesia constantly scan for food in the environment via ciliary gliding, which renders it more difficult to climb elevated surfaces. Our experimental protocol was set up such that the most time spent in a specific substratum constituted a choice. Since small rocks and pebbles are elevated with respect to Dugesia, it takes them longer to scan for food in those substrata when compared to sand thus explaining their preference for small rocks and pebbles according to our protocol.

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