Animal Behavior - Biology 420/543 |
Bowling Green State University, Fall 2008 |
Discussion and Pre-Lab Preparation: Here you find a general introduction to the arthropods, and arthropod phylogeny. Animals must compete for critical resources such as food or mates, but the form of this competition can differ from one kind of animal to another. In some animals the competition is in the form of a "test of efficiency" or "scramble competition" in which there are no direct confrontations. Instead, the "winner" of the competition is the animal that acquires the critical resource the fastest, or in the greatest amount. In other cases, individuals or sometimes groups of individuals physically defend specific areas in an attempt to sequester sufficient resources. This occurs generally when a resource is in short supply. There would be no advantage to spending time and energy defending something that was so common everyone could get enough. And it would be too difficult to sequester resources that moved from place to place, or whose distribution was unpredictable in time (here today, gone tomorrow). Territory defense, then, is a sort of economic practice-individuals and species attempt to defend specific areas and maintain exclusive access to them only when the benefits of doing so outweigh any costs.
Many different kinds of animals defend territories. Sometimes a single individual defends an area against all others of the same sex and species. In other cases one individual defends an area against individuals of other species. In still others, several individuals join together to defend the territory against others of the same, or of other species. Crickets are excellent animals to use in the study of territory defense because they exhibit a wide range of behaviors, they are readily available and easy to care for, and their territories are relatively small. A territory may be defined as an area that is used more or less exclusively by an individual or a group as a result of overt defense (e.g., fighting) and advertisement (e.g., singing, posturing), which prevents others from entering. We will examine territory defense by male crickets in a three-session exercise. Data analysis and presentation of results.-The results of your two-cricket contests can be presented as percentages of encounters initiated and won or lost (or tied). Most of your results, however, will be descriptive. You must describe accurately and concisely what happened in each encounter you observed.
Question: What are the aggressive behavior patterns that occur in territorial defense of crickets? Which individual components of fighting are present?
The most common way that scientists communicate their results with others is in written journal articles. The field of animal behavior has many such journals, which specialize in publishing studies of the four aspects of animal behavior. You will present your results in the form of a formal lab report, which will mimic a journal article. Your teacher will explain in detail how to prepare your lab report, but it should contain the following elements. (1) A short but informative title. (2) The names of the authors. (3) An "abstract" or one-paragraph summary of the report. (4) An introduction that describes briefly what you did and why you did it. (5) A methods section that describes in detail exactly how, where, and when you did your study. (6) A results section that presents your results (including graphs and tables) but does not interpret them at all. (7) A discussion section in which you talk about what your results mean and why they are important, and suggest what might be done next. (8) A list of any references used in the preparation of your report.
Adult House crickets (Acheta domesticus) can be housed simply using a large plastic garbage can. Cut a hole in the lid and use duct tape to attach fiberglass screening over the hole. Put a hand-full or two of crushed dry dog food in the bottom of the can along with two or three wet sponges on dishes, and then put cardboard egg cartons in the can so the crickets can hide from one another. Be sure to check the sponges every day-these are the water sources for all of the crickets. Alternatively, you can throw in slices of apple or pear as a water source as well as a food supplement. materials needed for animal care are crushed dry dog food (oatmeal and cracked corn are alternatives), water (a wet sponge works well) or slices of an apple or pear, one aquarium (approximately 10 gallons) with screen top per three students, match boxes and (cardboard) egg cartons
plastic (not paper) cups, fiberglass screening, and rubber bands, one large aquarium with a screen top, or a large plastic garbage can with a screen cover
Preparation: Observe the behavior in a 10-gallon aquarium. It is not necessary to put any sand or soil in it, unless you want to mate the crickets to observe reproduction.
Remove your subjects from the holding tank and place each separately in a plastic cup. Cover each cup with screening and secure the top with a rubber band. Mark the cups so that you can tell which belongs to each male, and keep track of each male in all subsequent observations. Place a particular male in the arena and allow him to acclimate himself to the environment. This male will be your resident male or territory owner. Then introduce another, intruder male and observe the interactions that follow. How long would you wait to add the "intruder"? What constitutes "residence" in our study? Record the number of encounters instigated by the intruder and by the resident male. Record the number of encounters in which each cricket is dominant and subordinate. Record the number of fights and the winner and loser of each fight. Often territorial encounters end with a clear winner and loser. The loser is characterized by his determined attempts to escape. The test arena prevents losers from escaping, however, and may artificially prolong the encounter. Once it is clear that one cricket is the loser, that animal should be removed from the arena to avoid further harm and stress.
Procedures: Construct an ethogram for the behavior of adult (winged) male crickets as they interact with each other. Take a few crickets from the main holding tank and examine each closely to identify the males. Both males and females have a pair of abdominal cerci (two short "spikes" sticking out the back end of the animal), but females also have a long "ovipositor" that extends from the tip of the abdomen between the two cerci. Females use the ovipositor to lay their eggs in the ground. Place the males in an observation arena (an aquarium), record their behavior, and construct an ethogram. Be sure that some of your observations are of lone males (one male in the arena) and some are of interacting males (two or more males in the arena). Note whether interacting males perform different behaviors, whether one seems to be "dominant" over another, and whether one seems to "win" fights with others. Be sure to get good descriptions of the behaviors associated with dominance versus subordinance, and winning versus losing. One of the most familiar aspects of cricket behavior is their singing. You will notice the singing right away (if the exercise goes as it should), and you should remember that vocalization (singing) is a potential advertisement (that is, a way for a territory owner to declare his ownership). For this reason, you take note of singing rates for both resident and intruder. Does singing behavior changes over the course of an interaction (for example, does one cricket stop singing, and does this change predict which will win and lose?)
Answer questions: What are the characteristics of territory defense, and do the crickets exhibit these characteristics (that is, are they really territorial)? How do crickets attempt to defend their territories? Do you see evidence of both overt defense and advertisement? Do you see evidence of exclusive occupation or that intruders avoid territory owners? How do crickets "advertise" their ownership of territories? Does the resident always successfully defend his territory? Is he able to do this against a male that was previously dominant over him? Where in the arena are the encounters taking place? Does the outcome of the encounter depend on where it occurs? Is fighting always the ultimate resolution to conflicts over territory, or can encounters be settled without recourse to fighting? Is there any way to predict who will win an encounter between two males before the encounter is staged?
Question: Is winning determined by individual characteristics or residence? Experiment: Reverse resident - intruder roles
Preparation: see above
Procedures: Repeat the procedure with different pairs of males, and try reversing the order of introduction. That is, make male A the resident and B the intruder one time, then B the resident and A the intruder another. If you use a small number of males (say three or four) you may have time to run a complete round robin "tournament," in which all possible pairs are tested in all possible configurations (resident versus intruder).
Answer questions: What are the primary determinants of agonistic success in crickets?
Question: Do male crickets establish territories?
Preparation and Experiment:
Procedures: Place two match boxes at opposite ends of the arena, introduce three males, and observe who is able to establish a territory. Note how long it takes for territories to become established, and record the interactions of the two establishing males. Finally, place a female in the aquarium and watch the male-male and male-female interactions..
Answer questions: Does the presence of a resource (e.g., shelter, female) alter fighting behavior in cickets?
last modified: 02/17/07