The Influence of Opponent-Related and Outcome-Related Memory on Repeated Aggressive Encounters in the Paradise Fish (Macropodus opercularis)

6 Pages·1995·2.6 MB·English

by  A Miklosi

Reference: Biol Bull 188: 83-88. (February/March, 1995)
The Influence of Opponent-Related and Outcome-
Related Memory on Repeated Aggressive Encounters
in the Paradise Fish (Macropodus opercularis)
ADAM MIKLOSI*, JOZSEF HALLER**, AND VILMOS CSANYI*
*Depanment ofEthology, Eotvos Lorand University and**Imtitute ofExperimentalMedicine,
Hungarian Academy ofSciences
Abstract. The aggressive behavior ofmale paradise fish the subsequent contest. Winning usually has no strong
(Macropodusopercularis)wasstudied. Fish were subjected effect, but under some experimental conditions it might
to three aggressive encounters on consecutive days. If increase the probability of winning again (Bakker and
submissive males encountered the same opponent three Sevenster, 1983; Bakker et ai, 1989).
times, the lastaggressiveencounterwasvery different than The possibility ofthe involvement ofthe second pro-
the first one. When the animals faced a new opponent cess individual recognition in agonistic encounters has
each day, the changes were much less pronounced. We been also demonstrated. Fricke (1973) showed that Am-
concludethat(1) fish areabletorecognize theiropponents phiprion bicinctus males more frequently attacked un-
at least one day afterthe encounter ("social recognition"), known individuals than known ones in a two-choice ex-
and(2)social recognition modifiestheeffectofpriordefeat periment. The importance of individual recognition in
("status-related memory") in subsequent encounters. the stickleback was demonstrated by Peeke and Veno
(1973), who observed that a resident male that had been
Introduction habituated to an intruder presented in a glass cylinder
An overwhelming amount of evidence indicates that would resume aggressive behavior ifthe individual in the
prioragonisticexperienceinfluencestheoutcomeoffuture cylinder was changed. Thresher (1979) used a similar
aggressive encounters (Beacham and Newman. 1987; method to study rival recognition in the threespot dam-
Frank and Ribowsi, 1987). Onecan hypothesizethat prior selfish (Eupomaceus planifrons), and those field obser-
aggressiveexperience may influencesubsequent aggressive vations further confirm that some fish species might be
encounters by two kinds ofprocesses: one related to the able to recognize individuals. Myrbergand Riggio (1985)
outcome of the encounter ("winner" or "loser" effect) showed that coral reef fish (Pomacentrus partitus) rec-
and the other specifically related to the opponent. The ognize territorial neighbors acoustically. Recently Waas
significance ofthe former process was recently examined and Colgan (1994) provided experimental evidence that
in detail (Bevan et a/., 1960; Poll el ai, 1982; Francis, male sticklebacks can distinguish between familiar rivals
1983; Beaugrand and Zayan, 1985; Beacham and New- on the basis ofvisual cues alone.
man, 1987; Bakkeretai. 1989). Moststudiesdemonstrate Assuming that the effects of previous encounters are
an asymmetrical effect ofprior winning orlosingon sub- mediated by memory and thatthebehavioral differences
sequentwinning probability. Forexample, in paradise fish arenotduetoenergeticconsequencesofaggression(Haller
(Macropodus opercularis; Francis, 1983) and in stickle- and Wittenberger, 1988; Haller, 1991) the problem of
backs (Gasterosteus acideatits; Bakker and Sevenster, interferencebetween social recognition andstatus-related
1983) losinggreatly enhancesthe probability ofalso losing memory arises.
Asacontinuation ofarecentstudy(Miklosi etai, 1992)
Received 15 April 1993;accepted 18 November 1994. on aggressive behavior in the paradise fish, we experi-
Addressforcorrespondence:Adam Miklosi,EotvosLorandUniversity, mentally examined these processes in the aggressive be-
Department ofEthology, God,Javorka S. u 14, H-2131. Hungary. havior ofthe paradise fish. To clarify the relationship be-
83
84 A. MIKLOSI ET AL
tween social recognition and status-related memory, two basis of earlier findings, each aggressive encounter was
questions have been posed: (1) Does the behavior ofthe divided into three main phases: latency, threatening, and
fishchangeifitencountersthesameordifferentopponents fighting. Afterthelatency forinitiation ofthefirstdisplay,
for two subsequent encounters? (2) Are there differences a second phase was defined, which lasted until the first
between these experimental manipulations? appearanceofcontact behavior(bitingormouthlocking).
This was called threatening, which in turn was followed
Materials and Methods
by the escalation of the fighting fighting phase until
Experiments were conducted with 6-month-old, 8-cm one of the males showed submissive behavior. The be-
to 10-cm-long Macropodus operadaris males, which were havior units we identified are as follows:
raised and kept in our laboratory. Three days before the
start ofthe experiment, pairs ofsize-matched fish were Display at distance (DIS): The fish stay in head-tail
placed in 40 X 20 X 20 cm glass tanks provided with position with erected tailfin, but the distance between
filtration and aeration. Each tank was separated into two them is larger then one body length.
equal parts by a green opaque screen, and a single fish Head-head display (HHD): The fish are oriented par-
was kept in each part ofthe tank. The animals were vi- allel tooneotherand face in thesamedirection, with one
sually isolated from each other: all sidesbutthe front side fish slightly behind the other.
ofthe tanks were covered with green plastic sheets. This Parallel swimming (PAS): The fish swim very close to
isolation lasted 3 days prior to the experiment. Water each other in the same direction.
temperature was kept at 28C, and a 14:10 h light:dark Head-tail display (HTD): The fish in parallel orienta-
cycle was maintained. The fish were fed daily on Tubifex tion are facing opposite directions. Sometimes this be-
worms. havior is associated with circling.
Animals were exposed to three aggressive encounters Shaking (SHA): This behavior is similar to the head-
on successive days. Encounters were begun by removing tail display, but it isassociated with fastcircling, vigorous
theplasticpartition. Allencounterswerevideotaped until body-shaking, and a downward movement of the pair;
dominance relationshipswereestablished. Wedefined this the pattern stops when the animals reach the bottom.
as the point at which one ofthe fighting males no longer Bite (BIT): One fish makes a swift dart and slashes at
participated in simultaneous orreciprocal threateningand the other fish.
fighting but instead became the "subordinate," showed Mouthlock (MOU): The fish reciprocally bite and hold
fleeing and escaping behavior when approached by the one another's mouths for up to 2 min.
"dominant," which in turn chased and bit its opponent. Airgulping(AG): A fish takesan airbubblein itsmouth
A submissive fish remains motionless for a long time in by breaking the surface ofthe water.
"oblique position" nearto thewatersurfaceanddoes not
retaliate against the winner (Miklosi el a/., unpub. obs.; Each ofthese behavioral units was recorded in all of
Forselius, 1957). Both fish wereobserved foran additional the pairs investigated. Two samples ofbehaviorwere reg-
hourto monitorthe stability ofthe dominant-subordinate istered. The first sample, which characterized behavior
relationship. Onehouraftertheendoffighting,thecontact during the threatening phase, lasted for 10 min from the
between the fish was interrupted by lowering the plastic raising of the door or until the first instance ofcontact
door, and the animals were kept in isolation forthe next behavior (biting or mouthlocking). The second sample,
24 h. which characterized the fighting phase, was a 20-min ob-
Two groups were tested: the fish in group A (n = 10) servation following the first observed bite.
faced the same opponent throughout the experiment; in To permit comparison between pairs, the values ofob-
group B (n = 10) the dominant animals were randomly served behavior units were divided by thesampling time.
changed between thetanksaftereach fight. Thus, in group This adjustment was necessary because in many contests
B, the submissive fish remained in the tank and faced a fish finished the threatening or fighting phase before our
new. previously dominant opponent each day. Thedom- predetermined interval (10 or 20 min) of observations
inant fish was changed immediately after the end ofthe ended, resulting in shortertime samples. Thus the relative
encounterand remained isolated in its new tank until the duration (minutes per hour) or frequency (number per
followingdaywhen thepartition wasremovedagain. The minute)ofbehaviorunitswas used forstatistical analysis.
timebetweentwoconsecutiveencounterswaslongenough Because the measured variableswere not normallydis-
for the dominant to acclimate to the new place (Csanyi tributed (according to the Kolgomorov-Smirnov test),
ct ai, 1985), thus the advantage ofprior residency ofthe nonparametric statistical methods were used. Kruskal-
ANOVA
submissive fish was minimized. Wallis's one-way was used separately forgroups
Videotapes were later analyzed by recording behavioral A and B to examine the change in the general pattern of
units with an event recorder (Nagy et til., 1985). On the aggressive behavior.
OPPONENT-RELATED AND OUTCOME-RELATED MEMORY 85
Results were examined further when we used the nonparametric
Mann-Whitney test to compare the behavior ofthe two
The difference between the two groups that is, the groups in the first, second, and third encounters (Fig. 1).
different effects ofthe "treatments" can be seen in Ta- The two groups did not differ in the first and second
ble I. encounter; however, with the exception ofhead-tail dis-
Repeated encounters with the same opponent, group play, they differed markedly in the third encounter. The
A,caused markedchange inaggressivebehavior. Although time spent with mouthlocking (z = -2.4, P < 0.02), the
the duration ofthe threatening phase did not change sig- number ofbites (z = -2.3, P < 0.02), and the duration
nificantly in the course ofthe three encounters, shaking of threatening (z = -2.6, P < 0.01) and fighting (z =
and air-gulping were significantly reduced. All measured -l.9,P<0.05)werelowerin thegroup(A)withthesame
variables (with the exception of head-head display) of opponent than in thegroup (B) with different opponents.
fighting, including its duration, decreased significantly The same variables were compared by the nonpara-
whensubmissivefishfacedthesameopponentthreetimes. metric Wilcoxon test to show within-group differences
Interestingly, the changes in the other group (B) were duringthethreeencounters. IngroupA sameopponent
much less pronounced. When the submissive fish repeat- in each encounter we found a significant change from
edly faced new opponents, only minor changes could be the first tothe second encounteronly in fightingduration
observed in their aggressive behavior. The threatening (z = -2.8, P < 0.01). However, significant changes oc-
phase did not change significantly; only the relative du- curred between the second and the third encounters in
ration ofshaking and the frequency of biting showed a all ofthe selected variables (head-tail display: z = -2.8,
marked decrease. P < 0.01; mouthlocking: z = -2.6, P < 0.01; biting: z =
bpoerhAtaavcniocomer.palaTrheiulsseomnheewnaitdts-htaacinuldrdriepsnaptrlaaliymte(eter.eagtr.u.sreBaasreehroeownfeddssptaehcnaidtalBsaoiemmre-- cz-o2=u.l8-,d2bP.e1<,fPo0u.<n0d10;.i0tn4ht)r.heeaItgnerncoiounnpgtr:(aBzs)t=,win-to2h.s5ui,gnnkPinf<iocwa0nn.t02od;pipfffoiengrehetnnitcnseg.:s
ends-Van Roon, 1950; Barlow, 1962; Enquist and Ja-
kobsson, 1986), biting(e.g.. Peeke and Veno, 1973; Frank Discussion
et a/.. 1985; Enquist and Jakobsson, 1986; Halperin and
Dunham, 1994), mouthlocking (e.g.. Baerends and Baer- The results clearly show that the type ofopponent (fa-
ends-Van Roon, 1950; Enquist and Jakobsson, 1986), miliar versus nonfamiliar) has a major effect on the ag-
duration ofthreatening (e.g., Frank et al.. 1985), and du- gressive behavior ofmale paradise fish. In the case offa-
ration offighting(e.g.. Enquist et al.. 1990; Haller, 1992) miliar opponents (group A), three consecutive encounters
Table I
Analysisofelementsofaggressivebehaviorshown byfightingparadisefishpairsduringthreeconsecutivecontests in bothgroups
GroupA: familiaropponent Group B: unfamiliaropponent
86 A. MIK.LOSI ET AL
Duration of threatening (a) Duration of fighting (b)
200
20
180
18
160
16
140
14
120
12
100
10
80
8
60
6
40
4
20
2
1. 2. 3. 1. 2. 3.
encounter encounter encounter encounter encounter encounter
Head-tail display (c) Mouthlocking (d)
60 20
, N 18
to 5.-0A
16
| 40 ao 14
re n> 12
I 30 10
8
$ 20
+: m 6
15 1U 4
2
1. 3. 1. 3.
encounter encounter encounter encounter
Biting (e)
1.6
'P 1.2
10
I 0.8
Group A: familiar opponents
| 0.6
0.4 Group B: unfamiliar opponents
0.2
i. 2. 3.
encounter encounter encounter
Figure 1. Themeandurationofthreatening(a)andfighting(h),andthemeanrelativedurationofhead-
tail display (c)and mouthlocking(d)andbiting(e) inthethreeconsecutiveencountersoftheexperimental
groups. In group A the opponents were the same for each contest: in group B the former dominant was
replaced hy a newdominant male foreach fight.
were needed to induce significant changes in aggression. occurred in group B are much less dramatic than those
On the other hand, repeated encounters with unfamiliar in group A.
individuals (group B) caused significant changes in only The behavior ofthe contestants was markedly similar
some parameters of fighting. However, the changes that duringthe first twoencountersinboth groups. This means
OPPONENT-RELATED AND OUTCOME-RELATED MEMORY 87
that (1) there was no significant change within a group locking, and duration offighting between the twogroups,
from the first to the second encounter, and (2) behavior which rules out the role of exhaustion. In both groups,
did notseem todepend on the familiarityoftheopponent submissive fish losttwo fightsbeforeengaging in thethird
during the second encounter. The significant decrease in contest: thus experience in submission or dominance
the duration offighting can be explained by noting that cannot explain the observed difference. As a result, the
the first encounteroccurred after 3 daysofisolation, dur- involvement of some form of social recognition should
ing which fish could build up energy reserves depleted also be taken into account for the third encounter.
during the rather long fight (about 2 h on average) at the Nevertheless, this experiment does not directly prove
first encounter (Haller and Wittenberger, 1988; Haller, that individual recognition takes place. AsWaasand Col-
1991). Withouttheseenergyreservesthesecondencounter gan (1994) recently noted, "Individual recognition implies
became shorter. However, it isalso possible that isolation that subjectscan distinguish between animalsthat belong
increased aggression levels. tothesamesocialand physicalclass." But itisverydifficult
The defeated fish in group A (same opponents) fought to tell the exact basis ofthis form ofrecognition because
very similarly during the first and second encounters. Al- individuals can be categorized into several subcategories,
though all defeated fish lost the fight again, they gave up and the same animal can use different arrays ofvariables
fighting only after a considerable time and engaged in to categorize its opponents. Because opponents were al-
both signaling behavior (e.g.. head-tail display) and ways ofthe same social class in both groups (submissive
strength-testing behavior (e.g.. mouthlocking). The same or dominant), the recognition might have occurred on a
happened in the group with unfamiliar opponents (B): different level, whichsuggeststhat paradise fisharecapable
although defeated fish lost against the formerly dominant of categorization within dominants or submissives.
opponents, the previous defeat did not seem to change Whether this can be described as individual recognition
their behavior significantly. remains to be seen, and Waas and Colgan (1994) show a
Thuscomparingthe first twoencounters in both groups good way to examine this subject.
we find the effect ofprevious experience on behavior On theotherhand, wealready havesomeevidencethat
"status-related memory" but nodirectevidenceofsocial individual recognition existsin fish (Gandolfi eta/.. 1973;
recognition. Since the initial work ofGinsburg and Allee Zayan, 1975; Myrberg and Riggio. 1985). For example,
(1942), many studies havedocumented theeffectsofprior as shown by Zayan (1975), individual recognition of
experience (e.g., Bakker and Sevenster, 1983, Beacham formerly dominant fish can reverse the effect ofprior res-
and Newman, 1987). In thecaseoftheparadisefish,defeat idence. Thus, the process ofindividual recognition inter-
decreases the probability ofsubsequent winning in an ag- acts with the effects of both prior experience and prior
gressive encounter, but prior winning has no influence residence in a way similar to that in our present experi-
(Francis, 1983). However, three other factors might de- ment.
creasethedifferencebetween a firstand second encounter. It is usually assumed that the end ofthe fight depends
(1) Following longer isolation before the first contest on the decision of the future submissive fish. This idea
(3 days) and between contests (about 22 h), fish fight stems from the classical conditioning view ofaggression,
longer in both the first and second encounters (Miklosi inwhichcontact behaviors(biting, mouthlocking)areseen
et a/., unpub. obs.). (2) The encounter was terminated as punishment forthe opponent, which learnsduring the
1 h after fighting had finished, and fish were fed only fol- aggressive encounter to avoid these aversive effects
lowing separation, thus opportunities for expressing (McDonald eta/.. 1968; Bakker el <//.. 1989). In thiscon-
dominance or submission were limited. (3) The weight text an individual opponent becomes a conditioned signal
symmetry between contestants rendered mutual assess- for future punishment, but a new opponent acts as a dis-
ment more difficult, according to the resource holding criminative signal, which does not predict aversive stim-
power (RHP) hypothesis (Parker, 1974). Usually larger ulation.
animalsinitiateaggressiveencountersand are morelikely Another theory interprets aggressive encounters in
to win in a shorter fight. Thus similarity in size will in- terms ofan associative habituation process (Peeke, 1969;
crease both the latency ofinitiation and the duration of Lorenz, 1981). New opponents (or territorial neighbors)
a contest. disrupt habituation and release an aggressive response.
The third encounter separates the two groups clearly. Forexample, Peeke and Veno ( 1973) found that resident
Forfish facingfamiliaropponents(groupA), theduration male sticklebacksattacked unknown territorial neighbor-
ofthethreateningphasedecreased by half, and previously ing sticklebacks more often than they attacked familiar
submissive fish gave up fighting soon afterthey began. In ones.
contrast, no significant change was observed in the be- The problem ofsmall changes in a complex stimulus,
havior of fish facing unfamiliar opponents (group B). like an opponent, raises a major problem to the incor-
There was about a sixfold difference in biting, mouth- poration ofindividual recognition into the learning mod-
A. MIKLOSI ET AL.
els presented above. Either dishabituation or discrimi- Enquist, M., O. I I'imar, T. I.jungberg, Y. Mallner, and N. Segerdahl.
nation suppose some form ofrecognition oftheopponent, 1990. Atestofthesequentialassessmentgame:fightinginthecichlid
but we do not know whether this categorization process ForsfeilsihusN,anSn.a1c9a5r7a.anSotmudaileaso.ftiaunniabBaenhtaovid4f0i:she1s-.14I.. A quantitativede-
is similar in the two models or not. As is the case with scription of the reproductive behaviour. Zoologixka Bidrag fran
other processes described mainly on a behavioral level i'ppxa/a32: 93-302.
(e.g.. imprinting), it is very difficult to explain them in Frank, D. R.-P. Hannes, II. LanfTermann, and A. Ribowski.
the framework ofclassical learning models. 1985. Effectsofsocial isolation onaggressivenessinfishwithspecial
At least in paradise fish, it seems that submissive fish referencetotheswordtail(Xiphophorushelleri). Behav Proc. 10:415-
427.
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ning. Winningacontest presumably hasmanyadvantages. riences on aggression measures in the male swordtail (Xiphophorus
Paradise fish malesdefendterritoriesand build bubble- hellen! Behaviour9\: 218-239.
nests in shallow waters ofrice-fields, where several males Francis, R. C. 1983. Experiential effectson agonistic behavior in the
breed at the same time near each other(Forselius. 1957). paradise fish. Maeropodits upm'iilaris. Behaviour85: 292-313.
Fricke,H.\V. 1973. Individualpartnerrecognitioninfish:fieldstudies
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Our results support the hypothesis that aggressive ex- A'< 54: 281-285.
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Acknowledgments
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