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Rachael Pace 1/23/13 Responses to Stimuli: The Basis of Behavior Post-Lab Assignment 1. Responses of Brine Shrimp: Results a) We studied the response of the brine shrimp to light, or phototaxis. As shown in Figure 1, a majority (24) of the shrimp had a negative response to the light and preferred to swim in the darkened section of the test tube. Only 11 shrimp preferred the lit environment, and only one shrimp had a neutral preference. b)

Figure 1. Brine Shrimp Responses to Light - Phototaxis 30

Number of Brine Shrimp

25 20 15 10 5 0 Positive

Neutral

Negative

Animal Responses

2. Responses of Milkweed Bugs: Results a) We studied the response of milkweed bugs to temperature, or thermotaxis. As illustrated in Figure 2, a majority (four) of the bugs preferred a cooler environment, whereas only two bugs preferred a warmer environment. Only one bug had a neutral preference. b)

Num berofM ilkw eedBugs

Figure 2. Milkweed Bug Responses to Temperature (Heat) - Thermotaxis 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 Positive

Neutral Animal Responses

Negative

Rachael Pace 1/23/13 3. Discussion of Brine Shrimp and Milkweed Bugs Results Brine Shrimp a) I had hypothesized that the shrimp would prefer the lit region of their environment. I predicted that if the shrimp prefer the lit region, then the majority of the shrimp will move to the lit region of their environment. This prediction is rooted in the knowledge that brine shrimp eat phytoplankton that are most likely found in lit regions. The results from this experiment do not support this conclusion. b) The shrimp could potentially prefer darkened regions because they may hide from predators in more constrained, blocked areas than the open water. The shrimp may also live deeper in the water where less light reaches. In this case, the shrimp would move to the dark region of their environment as they did in this experiment. Milkweed Bugs a) I had hypothesized that the bugs would prefer the cooler region of their environment. I predicted that if the bugs prefer cooler temperatures, they would spend most of their time in the cooler region of their environment. The results from the experiment do support this conclusion. b) The milkweed bugs most likely prefer the cooler region of their environment because it mirrors the environment in which they spend most of their time in nature on the underside of milkweed leaves....