Animal Behavior - Biology 4200/5430

Bowling Green State University, Fall 2013

Lab Exercise: Agonistic Behavior in Crayfish (Orconectes rusticus)

Objectives:

Discussion and Pre-Lab Preparation: Here you find a general introduction to the arthropods, and arthropod phylogeny. Explore the anatomical features of crayfish with this interactive course on crayfish anatomy. Check out a picture of Orconectes rusticus.

Agonistic (fighting) behavior of many decapod crustaceans features a variety of distinct, stereotyped behavior patterns. Detailed ethograms of these patterns and their temporal structure were identified in several species using video analyses. Interactions start when animals advance to within one body length of another individual and overtly react to its presence. The approaching animal is termed the initiator. As the interaction progresses, animals may use agonistic acts of varying intensity. Use the following code to charaterize the intensity of fighting as follows: note (0) when an animal retreats from its opponent, (1) if it contests the interaction using threat displays or ritualized fighting without resorting to the use of their claws, (2) if it use its claws to grab onto the opponent, or (3) if it makes unrestrained use of the claws in an attempt to rip or tear off appendages. The fight ends when one animal turns or walks away so that separation distance exceeds one body length.

Although fighting may vary greatly, the typical scenario of an escalated encounter begins with extensive threat displays upon first contact (meral spread), continues with periods of ritualized aggression and restrained use of the claws (wrestling), and terminates in a brief session of unrestrained use of their claws. Predictions of game theory (i.e. assessment strategies) provide a useful framework for the understanding of fighting in lobsters. Duration and maximum intensity of encounters often correlate positvely indicating that fights become more intense the longer they last.

some picts digitized from video 

meral spread

meral spread

wrestling

wrestling

unrestrained use of claws

established dominance

Exercise 1:

Question: What are the aggressive behavior patterns that occur in same-sex pairs of Orconectes rusticus? Which individual components of fighting are present?

Preparation: Encounters of crayfish pairs are staged in observation tanks for groups of three students each. The tank contains gravel and is filled with de-chlorinated water at a depth of 20cm. We need a removable divider, crazyglue for marking individual crayfish, and a watch to record the timing of events.  Use our pre-canned protocol sheet, download it as a pdf version, or make your own.

Procedures: Choose two individuals of the same sex (both either male or female) of approximately similar size (within 10% of body weight). You need to be able to easily distinguish the two critters based on some external characteristics, i.e. morphology, color, etc. If you have difficulties, place a small drop of crazy glue or whiteout onto the carapace of one animal. Place the two individuals into adjacent compartments of a tank, separated by the divider. Assign the following tasks among group members before removing the divider: the timekeeper will announce the end of each10 second interval as 10, 20, 30,... 60, 10, 20, 30 ... for a total of 15 minutes; the two observers pick one individual each and focus their observations exclusively on this one animal. Remove the divider and record a "-" for each 10 second interval where the opponents did not interact. When the interaction starts, the observers records the maximum intensity (see above) that had occurred for their individual during this 10 second interval. Record on your data sheat also whether your animal had initiated the encounter (i) and whether it had retreated (r). You should observe at least five different, agonistic interactions. If there were fewer interactions present in this time frame, you may consider extending the observation time, or using a second pair of individuals.

Answer questions: What are the similarities/differences in fighting compared to that of other crustaceans shown in the pictures? Should these behaviors be considered in the context of evolutionary analogies or homologies? Explain your reasoning.

Exercise 2:

Question: Do fights in same-sex pairs escalate similar to those in related species of decapod crustaceans? Experiment: Explore whether duration and intensity of encounters show a positive association.

Preparation: see above

Procedures: test whether duration and intensity of these encounters are correlated. Use the data collected by both observers in exercise 1 to identify for each agonistic encounter: when it started, when it ended, what the maximum intensity was that either animal had shown during this interaction, which animal had initiated and which one had retreated? Duration is defined in seconds as ending time - starting time. Use a regression analysis to test whether there is a significant association between duration and intensity.

Answer questions: Why might there be such a highly structured behavioral system governing the fighting of decapod crustaceans?

Exercise 3:

Question: Do males and females fight with each other? Are there differences in aggressive behavior in fighting between males and females?

Preparation and Experiment: same as exercise 1

Procedures: Repeat experiment 1 with a male/female pair.

Answer questions: Why might there be fighting between males and females? Are they competing for a particular resource?


Links of interest


last modified: 9/2/05

Final Exam is on Wed Dec 18, 2013 1:15pm in LSC 112


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