Download Laboratory 3 Agonistic behaviour and dominance hierarchies in

Laboratory 3
Agonistic behaviour and dominance hierarchies in freshwater crayfish
Introduction:
Agonistic behaviour refers to the complex of aggression, threat, appeasement
and avoidance behaviour that often occurs during encounters between members of the
same species. Most animals experience a motivational conflict between aggression and
fear when confronting a rival, and this may give rise to a number of forms of agonistic
behaviour.
A dominance hierarchy (or rank order) is a form of social organization in which
some animals in a group acquire a high social (i.e. dominant) status, usually as a result
of aggression, while other individuals retain a low (i.e. subordinate) status. Dominance
hierarchies may be linear, in which no members in the group are of equal rank, or
branching (non-linear), in which two or more individuals may be of equal rank.
Dominance hierarchies are ubiquitous and have certain features in common in
many species. They are generally established and maintained by agonistic behaviour.
If a particular individual clearly wins a fight, or a ritualized threat contest, then the
encounter may not be repeated on subsequent occasions, but instead the defeated
individual may immediately show submission. If the opponents are more evenly
matched, then a number of interactions may be necessary to establish a dominance
relationship. Once a dominance hierarchy is established, there may be no further
fighting or overt aggressive displays. Subordinate animals avoid being attacked by
dominant ones by withdrawing, remaining motionless, hiding, showing appeasement
and submissive behaviour, etc.
Dominance hierarchies are generally based on learning, but in some species
there may be immediate outward signs (correlates) of dominance. Dominant
individuals may differ in both appearance (e.g. larger body size) and behaviour (e.g.
louder vocalizations) from subordinates. The status of dominance confers many
advantages in permitting unchallenged access to limited resources, such as food,
shelters, mates, etc. Subordinate animals may also benefit from membership of the
group in terms of defence against predators, for example.
This laboratory exercise concerns the study of aggressive behaviour and
dominance hierarchies in a species of freshwater crayfish, Orconectes virilis, in a
laboratory aquarium. The study will be divided into three parts:
(1).
preliminary observation and description of discrete patterns (units) of
aggressive behaviour in a group of crayfish.
(2).
determination of a dominance hierarchy in a group of crayfish.
(3).
effect of shelter availability on the aggressive behaviour of crayfish in a
group.
Orconectes virilis commonly inhabits streams and rivers, and less commonly
lakes with rocky bottoms. Individuals usually choose large, flat rocks to hide under.
Freshwater crayfish are convenient animals for a laboratory study of agonistic
behaviour and the establishment of rank orders because they settle down quickly after
handling, they fight readily with each other when confined in a small space, and most of
their movements are performed slowly enough that the frequency of occurrence of
discrete motor patterns can be recorded accurately.
The laboratory exercise:
Materials: Per pair of students
- dipnet
- stopwatch
- aquarium
- stock tank with crayfish
- quick drying paints and paint brushes
- calipers
- hand counter
PART A. Preliminary observation and description of aggressive behaviour in
crayfish.
Purpose:
(1).
Observe and describe discrete aggressive behaviour patterns in a small
group of crayfish.
(2).
Select and name (label) appropriately four (4) discrete aggressive acts to
be recorded quantitatively in Part B.
Method:
(1).
Select 4 crayfish from the stock tank. Before placing them in your
aquarium arena, place a small identifying mark on each crayfish by drying off the
dorsal surface of the cephalothorax (Figure 1) and applying a small dot of quick drying
paint. Use a different colour for each animal. Determine then the sex of each marked
animal. In males the two most anterior pairs of abdominal appendages (pleopods) are
modified into sexual organs (stylets) for transferring sperm to the female (see Figure 2).
Also measure the cephalothorax of each animal (see Figure
1).
(2).
Place the 4 crayfish in the arena and observe them for about 15 min.,
looking especially for aggressive encounters. Prepare a preliminary list of discrete
patterns of aggressive behaviour.
(3).
The class will then compare notes and select 4 easily identifiable and
common aggressive acts for subsequent recording in Part B.
(4).
In your report, write an ethogram of these selected 4 aggressive acts by
naming each of them (give them each a label) and describing them separately with the
aid of illustrations when necessary. Use the attached drawings of crayfish as sources of
names for body parts.
PART B.
Dominance hierarchy in a group of crayfish
Purpose:
(1).
Determine the dominance hierarchy (rank order) in a group of 4 crayfish.
Method:
(1).
In the left-hand column of the attached tally sheets (under the heading
“Aggressive Acts”), write in the names (labels) of the 4 aggressive acts selected by the
class to record beside each of the letters A to D (which correspond to your 4 animals).
Note the colour of each crayfish alongside their corresponding letter.
(2).
Gently move the crayfish with a dipnet and subsequently allow them to
move about the whole aquarium. This procedure should increase aggressive
encounters among the crayfish.
(3).
Immediately begin recording aggressive acts in the appropriate cells of
one tally sheet, noting specifically the performer and the recipient of each act. To
increase recording accuracy one student should observe the animals and call out the
occurrence of each aggressive act to his(her) partner (e.g. yellow “attacks” green), who
can tally them. Continue recording for 10 min. Then disturb the crayfish again with a
dipnet and allow them to move about the whole aquarium. Record behaviour
again in identical fashion for 10 min. Repeat once more for a total of 30 minutes (3 x 10
min periods) of recording. Use a separate tally sheet for each of your three 10 min
observation periods.
(4).
Several different methods can be used to determine a dominance
hierarchy (rank order) with the same raw data. In this exercise the following method of
calculating a “rank score” will be used in determining the rank order among the 4
crayfish.
Rank score =
[
Sum of acts performed
]
Sum of acts + Sum of acts
performed
received
x 100
That is, a rank score for each animal is calculated as the total number of
acts performed by a particular animal expressed as a percentage of the sum of the acts
performed by that animal and the acts performed towards that animal (e.g. overall
Row Total for A as a % of the sum of Row Total + Column Total for A).
(5).
Calculate the rank score, using the above method, for each of the 4
crayfish for each of the 3 recording sessions. Determine the rank order among the
group for each of the 3 recording sessions by listing the calculated rank scores in
decreasing order of magnitude. Summarize your results in a table.
(6).
Correlate the rank order of each crayfish with its sex and body length.
(7).
Questions to consider in your report. Was a clear dominance hierarchy
established in your group of crayfish? How quickly was it established? Did the rank
order change over time (i.e. during the 3 recording periods)? What is the relation of
size, sex, missing body parts or any other factors to rank order?
PART C. Shelter availability and aggressive behaviour
Purpose:
(1).
Determine the effect of the availability of shelter (flower pots) on the
frequency of aggressive behaviour in a group of crayfish.
(2).
Correlate the occupancy of shelters with the crayfish rank order
established previously in Part B.
Methods:
(1).
Place 4 flower pots in the arena with the 4 crayfish.
(2).
For 5 min. record the total frequency of aggressive acts, without regard to
the identity of the animals performing them. Record the 4 aggressive acts chosen in
Part A and Part B. At the end of the min observation period, note the identity of the
crayfish occupying the flower pots (shelters).
(3).
Then remove one shelter, move the remaining shelters so as to disturb
any animals hiding in them, and immediately repeat the above recording for 5 minutes.
(4).
Repeat step #3 until all shelters are removed for a total of 25 min of
observation (5 x 5 min). Make certain that you note the identity of the animals
occupying the available shelters at the end of each min period.
(5).
Then go through the same procedure in reverse order, recording
agonistic acts for min periods as each of the shelters in turn is replaced. Again note the
identity of the occupant of each shelter at the end of each min observation period.
(6).
Summarize your results in a table and illustrate graphically the
relationship between the number of available shelters and the observed frequency of
aggressive acts (acts/5 min) using class data. What is the relationship between shelter
occupancy and rank order, as determined in Part B? Discuss the ecological significance
of your findings from Parts B and C.
Fig. 1 - Dorsal and ventral views of the crayfish, Orconectes
References:
Bovbjerg, R.V. 1953. Dominance order in the crayfish Orconectes virilis (Hagen). Physiol. Zool., 26:
173-178.
Copp, N.H. 1986. Dominance hierarchies in the crayfish Procambarus clarkii and the question of
learned individual recognition (Decapoda, Astacidea). Crustaceana, 51: 9-24.
Merkle, E.L. 1969. Home range of crayfish Orconectes juvenalis. Amer. Midl. Nat., 81: 228- 235.
Fielder, D.R. 1965. A dominance order for shelter in the spiny lobster Jasus lalandei. Behaviour, 24:
236-245.
Sheet for tabulating agonistic activities of 4 crayfish (A, toD). Reading horizontally
shows the number of acts performed by animals at left toward each of the others.
Reading vertically shows the number of acts performed by other animals toward each
of those at the top.
RECIPIENT OF AGONISTIC ACTS
Aggressive
acts
P
E
R
F
O
R
M
E
R
O
F
A
G
O
N
I
S
T
I
C
A
B
C
A
C
T
S
D
Column
totals
A
B
C
D
Sub
totals
Row
totals