April 1, 2013
Tuesdays 6:00 pm
Animals have many different ways of responding to their environment. The presence of food, light, and predators are the major factors that influence animal behavior. Those that detect predators and respond to the risk of predation have a better chance of survival (Wisenden & Millard 2001). Many aquatic animals depend on chemical cues to find food as well as avoid predators. Chemotaxis is movement toward or away from chemicals and an important influence in motility. The purpose of this experiment was to determine whether presence of predator risk over powers the presence and need of food. Dugesia dorotocephala, common name planarian (pl. planaria) or flatworm, are a small aquatic animal belonging to the phylum Platyhelminthes and class Turbellaria. According to Hickman Jr. 2012, planaria are found on the underside of stones or submerged leaves or sticks in freshwater springs, ponds, and streams. Brown planaria, which were used in this experiment, are the most common of the Dugesia. Using the planaria, we wanted to see if they still travelled toward and around the food once injured conspecifics were added in the same area. Is the need for food and nutrition more important than the risk of predation? Our null hypothesis was that their behavior and vicinity of the food would not change once the variable was added. Alternatively, we thought that the Dugesia would stay away from the area and even show abrupt direction change when reaching a certain concentration of injured conspecifics.
The experiment was performed on February 5, 2013 using two standard sized petri dishes with grids drawn on the bottom as seen in Figure 2. There were a total of 8 Dugesia used, egg yolk, ruler to draw gridlines on petri dish, permanent marker, and the water the planaria were stored in. A small amount of egg yolk was placed in the square A5. Water from the specimen jars were then added as well as four Dugesia dorotocephala to each petri dish. The planaria and water were taken from the same jar of specimens. We observed for five minutes to see the planaria responses to the food and environment. At the five minute mark, two drops of injured conspecifics were added to one of the petri dishes in square B5. The predator water consisted of other planaria that had been cut up past the point of regeneration. Following another five minutes of observations, another squirt was added in the same position. The specimens were observed for another 5 minutes before we concluded the experiment. No numerical data was collected. Our data consists of observational descriptions of the planaria movement related to the position of food and introduced variable. Charts were made at the end of each five minute interval to show the location of each Dugesia.
Once the planaria were added they started to explore the whole area. After a minute, most of the planaria had found the food and stayed by it, or under it in some cases, the first five minutes. Once the injured conspecifics were added to the water, the planaria started moving to the opposite side of the petri dish, after recognizing the addition. If a Dugesia started moving back toward the food in the first petri dish, when it came in contact with the addition and the planaria did a flipping movement to turn the opposite direction. The second petri dish had not changed. The Dugesia were still swimming around the whole dish and some stayed directly by or under the food the entire time.
We determined that survival is more important than food. Although many of the planaria attempted to get back to the food source in the first petri dish, they turned around in a drastic motion to avoid the “dangerous area.” Our hypothesis was supported whereas the null hypothesis was refuted. Similar studies have been done; Wisenden & Millard’s…