Chapter 45, Problem 1Q

Summary Introduction

To analyze:

The capability of the response of moths with disrupted tymbal organs to the evasive behaviors of bats. The importance of this parameter for the validity of given experiment.

Given information:

Researchers used tiger moths (Bertholdia trigona) to test whether ultrasonic clicks produced by unique tymbal organs located in the thorax of moths, jam the echolocation to avoid capture by bats. Bats are known to catch these moths by echolocation.

Experiments were conducted on two groups of moths, out of which they punctured the tymbal organs of one group carrying 41 moths that makes moth unable to produce sounds (silenced) that can protect them from capture. The other group (38 moths) were kept normal with intact tymbal organs. They were released into the areas where bats were allowed to feed on them. The following tables show the results of this experiment.

Figure 1(A) depicts the number of attacks on the bars when silenced or clicking moths exhibited a particular evasive behavior. There is clearly no difference between behaviors or between silenced moths and clicking moths. However, in Figure 1(B), the number of captures that were made when silenced or clicking moths exhibited a particular evasive behavior is depicted that shows a huge difference between them.

Figure 1: (A) number of attacks; (B) Number of captures in moths showing evasive behaviors.

Introduction:

Bats capture their prey moths by the mechanism of echolocation. They generate ultrasonic signals that strike on flying moths and echo back to the bat, signaling them to capture their prey. Moths have the ability to sense those ultrasonic signals with the help of tympana and exhibit some behaviors to prevent capture. Capture is prevented by changes in their flight, dives, and production of ultrasonic clicks.

Explanation of Solution

The evolution of certain mechanisms in the moths to prevent capture by prey includes the changes in their flight, dive, or by producing ultrasonic clicks. These ultrasonic clicks have echo jamming mechanisms and are produced by tymbal membranes of moths to protect them from being captured.

The data given in Figure 1(A) shows the number of moths that showed evasive behaviors when attacked. It was observed that both the silenced moths and clicked moths respond to the attack by the bats. The silenced moths do not lose its ability to respond and prevent capture by other mechanisms like changes in flight and diving mechanisms. This shows that silencing affects only the responses that are caused by tymbal membranes and moths respond to the ultrasonic waves of bats by showing evasive behaviors.

This is significant for validity of experiment to effectively test the hypothesis made by the researchers that the clicks served as the echolocation jammers.

Conclusion

Thus, moths in the given experiment with disrupted tymbal organ are capable of responding to the ultrasonic waves of the bats with evasive behavior. This indicates that even in the absence of tymbal organs moths prevent capture by other mechanisms.