Mealwormzzz...

Devansh Taori (Period the Second)
Biology Advanced Placement | Mister Rodney Wong

Introduction

Ethology is the study of an animal’s response to sensory input. Or, put more simply, the study of animal behavior. Behaviors fall into one of two basic categories: learned and innate. Innate behaviors are instinctual, such as the suckling response of mammals or the begging response of baby birds. These behaviors do not have to be learned, and all animals of that species show the same type of behavior in those circumstances. Learned behaviors are based on experience in each situation. A dog might learn that they receive a reward when they urinate outside, and therefore will continue to do so in hope that the reward continues. They have learned that a given behavior leads to this favorable response. All behaviors are generally considered adaptive, meaning that they give the organism some benefit towards survival and/or reproduction.

In this lab we studied orientation behaviors as a representation of how to observe, record, and interpret behaviors. There are two basic kinds of behavioral movement. Taxis is a movement towards or away from a stimulus. The stimulus can be light, heat, odor, chemicals, color, sound, etc. Kinesis is random movement that is not related to the stimulus. For example if an organism responds to a source of heat by moving away from it, this is taxis. If the organism moves in random directions and not always towards or away from the heat source, it is kinesis.

Our lab will involve observations of mealworms, the larval form of the darkling beetle (Tenebrio molitor). Adult beetles are 3⁄4 to 1 inch long and found throughout the United States. The larvae have three pairs of legs and two short, horn-like appendages on their abdomen. Once the eggs hatch, mealworms will feed and grow for an average of 6-9 months, molting (ecdysis) 14-15 times. Adults will live 2-3 months. The larvae are scavengers, and found mainly in damp, spoiled grains. Both adults and larvae can be found anywhere grains are stored, such as cereal boxes, bags of pasta, grain silos, and so on. Mealworms are a common and popular bait, as well as a routine source of food for many small pets.

Materials

Mealworms (10 per group)
Petri dishes (or, if possible, small boxes such as a shoebox) White and black paper
Moist & dry paper towels
Bran cereal
Apple slices
Hot plate

Procedure (Experiment 1)

1. Place 10 mealworms in a petri dish or box. If they are trying to climb out, you will need to cover the container with a clear top.
   
2. Observe the mealworms for 10 minutes. Record your observations of their general movements, interactions with each other, and appearance. Do they spend more time in one part of the dish more than another? Do they keep moving, move sporadically, or eventually settle down? Are there any actions or behaviors that involve two or more mealworms? It is important not to interfere with the mealworms in any way during this observation period! Doing so may alter the data you are recording. Don’t worry, we’ll get to change their environment soon!
   
3. Performing this step will allow you to see what “normal” mealworm behavior is like, and therefore be able to better compare it to our experimental behaviors. 
   

Procedure (Experiment 2)

1. Place white paper in one half of the box (or under the half of the petri dish), and black paper in (or under) the other half.
   
2. Place 10 mealworms in the very center of the container.
   
3. Every minute for 10 minutes count the number of mealworms on each half of the container. Continue
   counting for the full time period even if the mealworms have stopped moving or all are on one side.
   
4. Is the hypothesis supported or rejected? 
   
5. If the hypothesis is supported, which side is preferred? 
   
6. Is what you observed taxis or kinesis? 

Procedure (Experiment 3)

1. Put damp paper towel in one half of the box (or petri dish) and dry paper towel in the other half.
   
2. Place 10 mealworms in the very center of the container.
   
3. Every minute for 10 minutes count the number of mealworms on each half of the container. Continue
   counting for the full time period even if the mealworms have stopped moving or all are on one side.
   

4. Is the hypothesis supported or rejected? 
   
5. If the hypothesis is rejected, which side is preferred? 
   
6. Is what you observed taxis or kinesis? 

Procedure (Experiment 6)

1. Set up a container as in experiment #2. Place a slice of apple on the far edge of the light side.
   
2. Place 10 mealworms in the center as container.
   
3. Allow the mealworms to move towards the apple, but remove them once they reach it.
   
4. Remove all mealworms after 5 minutes.
   
5. Repeat steps 2-5 four times. Between each trial rinse and dry the container (if not a waterproof substance, have enough to replace with each trial.
   
6. Remove all food, rinse, and dry the container after the 4th trial. Set it up again as in experiment #2, excluding the apple this time.
   
7. Place 10 mealworms in the center of the container.
   
8. Every minute for 10 minutes count the number of mealworms on each half of the container. Continue
   counting for the full time period even if the mealworms have stopped moving or all are on one side.
   
9. Is the hypothesis supported or rejected? 
   
10. If the hypothesis is rejected, which side is preferred? 
    
11. Is what you observed taxis or kinesis? 
    
12. Is the result different or the same as in experiment #2? 
    
13. Based on your results, can you conclude that mealworms have some degree of memory? 
    

Results (Experiment 1)

We found that the mealworms didn't confine themselves to any side of the dish. They were freely moving around for all 10 minutes.

Results (Experiment 2)

We found that there was no significant effect of brightness on mealworm movement.

The hypothesis that mealworms will orient themselves toward bright backgrounds is rejected. According to the data, it seems that the side that was preferred overall was the dark side. I believe that the movement is kinesis, although the data could also prove it to be taxis. However, since it's inconclusive, it's more likely that it is kinesis.

Results (Experiment 3)

We found that the mealworms oriented themselves more towards moisture as opposed to dryness.

The hypothesis that mealworms orient themselves according to the moisture of their environment is proven true. The side of wetness was preferred (significantly toward the end). What we observed is taxis because a stimuli did influence mealworm movement.

Results (Experiment 6)

We found that mealworms cannot learn and remember where food is in relation to environmental stimuli.

According to the data, the hypothesis that mealworms cannot learn and remember where food is in relation to their environment is proven true. No side was preferred. What we observed is kinesis because the stimuli didn't influence mealworm movement.

Analysis

Based on your data in each experiment, what conclusions can you make about the type of environment that mealworms prefer?
Based on our data, we found that mealworms prefer a strictly moist environment. While they probably also prefer dark environments, that wasn't proven by our data. At the end of Experiment 3, nearly all (8) of the mealworms had reached the dark side, and they stayed there, proving that they definitely prefer that kind of environment.

What physiological reasons could explain your conclusions in #1?
The physiological reason explaining this is that staying next to moisture helps ensure that mealworms are next to a water source, so that they never run out of water. In addition, with moisture around, it's easier for mealworms to move and gain a source of nutrients. That helps them survive.

How are the behaviors observed considered adaptive for the mealworms (improving their chances of survival and reproduction)? 
The behaviors observed are considered adaptive for the mealworms because they enable them to live longer lives since they have easier access to water. Without the water, they would likely die. However, because they can reach the water in the ground that is moist, they are more likely to survive and reproduce.

Conclusion
In conclusion, two of the three hypotheses were proven true. First, mealworm behavior was not substantially affected by the brightness of the background. Over the course of ten minutes, they moved all over from the light to dark side and vice versa. Second, mealworm behavior was substantially affected by moisture. They all moved toward the more moist side. As I explained in the analysis, this is likely because of the water content that is necessary for their survival. Third, mealworms couldn't remember where food is located in relation to environmental stimuli. The data from the table shows that they moved all over the place irrespective of where food was placed.

Possible error in this experiment involves wrong counting of the mealworms and random chance that the mealworms are located in one side as opposed to the other. If we were to do this experiment again, we'd try doing more experiments, like Experiment 4 and Experiment 6. 

Thank you to Mr. Wong for letting us complete this! It was tons of fun eating observing  the mealworms!