ISOLATION THE EFFECT OF SOCIAL ON THE BEHAVIOUR IN A CICHLID AGGRESSIVE AND SEXUAL BURTONI FISH, HAPLOCHROMIS by ANDERS FERNÖ 1) 2) (Division of Ethology, Department of Zoology, University of Stockholm, Sweden)
INTRODUCTION Although there have been numerous suggestions that isolation from conspecif ics may affect the readiness of an animal to perform various behaviours, until recently few attempts have been made to study this question experimentally. The proposal by LORENZ (I963) that the aggressive motivation spontaneously rises if an animal has no opportunity t0' fight was supported by on a coral reef fish (RASA, A juvenile damsel fish experiments increased showed an (Alicrospathodoit chrysurus) tendency to stay in a bottle with visual contact and opportunity to aggressive display with a conspecific with increasing isolation time. This was considered to be due to a build-up of the aggressive motivation. The results can, however, be explained 2.e. an by a behavioural habitation (HEILIGENBERG & KRAMER, individual habituates to the presence of the conspecific with a subsequent decreased reaction. When isolated, however, a recovery from habituation with an increased tendency to aggressive display could take place. . Experiments with males of the sword-tail (Xiphophorus helleri) have also revealed an increased tendency to fight after isolation (FRANCh & WILHEL;.iI, 1973; WILHELINII, 1975). A reliable increase was first apparent after one week of isolation and the intensity of the fights increased further with increasing isolation time. These results could also be explained by either a spontaneous accumulation of attack readiness or by a recovery from habitand Mrs B. FALT for valuable comments on 1) I am indebted to Professor FABRICIUS the manuscript. I also wish to gratefully thank Professor FRANCKand Dr HEILIGENBERG for constructive criticism. 2) Present address: Department of Fisheries Biology, University of Bergen, Box 1839, N-5011 Bergen (Norway).
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44 uation. Likewise, in anabantoid fish there is generally an increase of aggression with increasing isolation time (PAL, 1968; DAVIS et al., 1974; HINKEL & MAIER, 1974). However, LAUDIEN (1965) found a decreased aggressiveness in Betta splendens after a long isolation. HEILIGENBERG & KRAMER (1972) have demonstrated that the attack readiness in males of the cichlid fish Haplochromis burtoni depends on a repeated exposure to adult conspecifics or fish dummies with an naturally oriented black eye-bar, a signal characteristic for territorial males. When this of stimulus the of attacks directed against juvenile number deprived fishes of another species, which was taken as a measure of the attack readiness, decreased to a very low level. Etroplus rviaculatus, another cichlid species, seems also to depend on visual stimuli to maintain a high attack readiness (REYER, 1975). Likewise, in the cichlid Pehruztochro?2is subocellatus kribensis the attack readiness decreases if there is no opportunity to fight (HEILIGENBERG, 1963) while in the cichlid Cichlasoma nigrofasciatum, there was an increased state of timidity but no further effect on the aggressive behaviour after an isolation period of seven days (GALLAGHER et al., 1972). In the bluegill sunfish (Lepomis yrcacrochirus) fish exhibited peak frequences of aggressive responses after one to seven days of social isolation depending on reproductive condition of the fish (CHISZAR et al., 1976). Apparently, the results from isolation experiments with fish are conflicting but are explainable in terms of species differences with adaptations to different social systems. There are several studies on other animal groups as well concerning the effect of isolation. Isolation of mice generally leads to an increase in aggressive behaviour (VALZELLI, 1969) and a similar effect has been found in hermit crabs (HAZLETT, 1966; COURCHESNE& BARLOW, 1971) and lobsters (HOFFMANN et al., 1975). The threshold for sexual behaviour usually falls with increasing deprivation (HINDE, 1969). The effect of isolation on the sexual behaviour in male sword-tails is an increase of those sexual behaviour patterns that depend on a high sexual readiness (FRANCK & GEISSLER, 1973; FRANCK & HENDRICKS, 1973). The increase is first apparent after 22 hours of isolation and is generally more pronounced after longer isolation periods. Males of the poeciliid fish (Poecilia sphenops) increased their sexual activity after social isolation of one hour (FRANCK, 1975). Guppy females (Poecilia reticulata) with a low responsiveness to males due to habituation did, however, show no after several weeks of isolation (LILEY & recovery of responsiveness In males of H. burtoni the frequency o?f aggressive WISHLOW, 1974). actions was influenced by visual external stimuli, whereas this was not so for the sexual activity (HEII IGENBERG & KRAMER, 1972).
45 The present study concerns the effect of isolation on the frequency of aggressive and sexual behaviour patterns in H. burtoni. In spite of the related investigation by (HEILIGENBERG and KRAMER described above, it seemed worthwhile to study the effect of complete visual isolation on the reaction towards conspecifics in a different experimental set-up, likewise study the effect of both short and long isolation periods and also closely follow if a change in the aggressive behaviour corresponded to a change in the sexual behaviour. ' MATERIALS AND METHODS In the African mouthbreeding cichlid fish H aplochramis burtoni the males defend territories which the females visit when spawning. No long-tenn pairbond exists and the female alone cares for the off-spring. There is a sexual dimorphism with the female smaller and more cryptically coloured than the male. A territorial male has colourful markings, e.g. a black line from the eye to the corner of the lips, a bright orange patch above the pectoral fins and a metallic light blue body colouration. Four males were studied concerning the effect of isolation. These males belonged to a stock of H. blowtaniwhich for some years had been held at our laboratory. As the stock originated from only one clutch of young, there is probably a considerable genetic similarity between the males. During the tests the males were between six months and two years of age. Each of the four males was kept in an aquarium of about 200 litres with 8-io smaller but sexually mature males and females. In the middle therewas an opaque wall with a movable door which could divide the aquarium into two compartments. The dominant male had his territory centre in one of the compartments and when the aquarium was not divided the other fish were mainly standing motionless near the surface in the opposite compartment. Isolation of a male began by closing the door in a moment when the male was alone in his compartment. After termination of the isolation period, the door was opened and the behaviour of the male was recorded during one or several observation periods, as described below. The males were kept in the same situation for 3-14 months interrupted by isolation periods. The frequency of aggressive and sexual behaviour patterns, although variable from one occasion to another, showed no tendency to change with time. The aggressive and sexual activity of the dominant male after a period of isolation was compared with the activity in observation periods with no prior isolation. Target fish might also change their behaviour during isolation. This could influence the behaviour of the dominant male in the abscence of internal changes. One aspect of the behaviour of the target fish, i.e. the number of intrusions in the compartment of the dominant male, was therefore recorded. Experiments were carried out with dif f erent isolation times and with slight variations in methods. For every period of isolation three males were tested. 15 minutes of isolatiosi. The males were observed r5 minutes before and after an isolation period of 15 minutes. Each of the three males was tested for 10 days, making a total observation time of 15 5 hours. The observations before the isolation commenced by closing and opening the door in the wall when the male was alone in his compartment. If the male was never seen alone during 15 minutes no observation was made that day. Using this method observations before and after isolation began correspondingly, i.e. a W ale was alone in his compartment and the door had just been moved.
46 2 and 7 hour of isolation. Observations were made for 30 minutes after a period of isolation and without any prior isolation, respectively on alternate days at the same time of the day. Observations were not made before and after isolation on the same day in order to avoid the effect of a daily rhythm in activity as there was an apparent decrease in the number of attacks and a possible decrease of the sexual activity during the course of a day. When using an isolation period of only i5 minutes the observations before and after isolation were made at approximately the same time of the day. Observations without isolation began by opening and closing the door in the wall. A total observation time of 60 hours was recorded as each male was observed for 10 days without isolation and for 10 days with prior isolation. 3 and rz days of Isolation. The males were observed during three periods of 30 minutes on the day before the isolation was started. The first observation was made in the morning and the following observations two and five hourslater. The next day isolation of a male began at the same time as the first observation started the previous day. After precisely 3 and 12 days of isolation respectively the isolation was terminated. From the moment the door was opened the males were observed for 30 minutes with two additional observation periods later in the day in accordance with the day before the isolation. For the following two days the behaviour of the males was recorded for 30 minutes in the morning. The next isolation was not started until at least one week after the previous isolation. Four experiments with 3 and 12 days of isolation respectively were made with each male making a total of 96 hours observation time. The males were observed so many times in these experiments in order to reveal possible long-term effects caused by the long isolation periods. To avoid too much disturbance of the males in connection with this extensive number of observations, the door in the wall between the compartments was only moved prior to the first observation on the first day in order to get an exact comparison with the observation immediately after termination of isolation. With these long isolation times it was also necessary to remove the male that was dominating during the isolation of the first male just before termination of isolation, otherwise long fights between the males would develop. However, this procedure did not appear to influence the external situation and change the activity of the first male, as the same tendencies in the results were recorded between 7 hours and 3 days of isolation and between 3 days and 12 days of isolation. Aggressive and sexual behaviour patterns were recorded during the observation periods. An attack is defined as an attempt to bite another fish. Two attempts to bite the same fish in rapid succession were recorded as only one attack but if a period of more than two seconds passed between the attacks they were recorded as two attacks. This was also the case if different fish were attacked regardless of the interval between the attacks. Sexual behaviour patterns were divided in side-shakes and lead-swims. While making a side-shake a male performs an undulating quivering while bending his body in a position in front of a female. A lead-swim is defined as swimming with exaggerated caudal movements often directed at the centre of the territory. These terms are equivalent to The fishes were kept at a courting and leading used by CRAPONDE CAPRONA temperature of 27° ± 1° in a photoperiod of 12 hours. In the morning they were fed with frozen liver and in the evening with commercial dry food. When testing, the observer was sitting behind a screen in order to diminish the disturbance and the movable door could be manipulated from behind the screen. Observations were spoken into a tape recorder for later transcription. In the statistical treatment of the results Mann-Whitney U test (SIEGEL,1956) was used when testing the effect of 2 and 7 hours of isolation and comparing the effect of 7 hours and 12 days of isolation. Otherwise, when not specifically stated, Wilcoxon matched-pairs signed-ranks test was used (SIEGEL,1956).
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47 RESULTS Aggressive and sexual behaviour patterns were directed at both males and females. Certainly, most of the attacks were directed at males and most of the side-shakes and lead-swims at females, but no data concerning this difference was recorded. Aggressive
behaviour.
The number of attacks directed at adult conspecifics isolation periods but after a sufficiently long isolation creased (Fig. z ) .
increased by short the attack rate de-
Fig. i. The effect of isolation on the aggressive behaviour. The mean ratio between the number of attacks in observations after and observations without isolation is shown against different isolation time. The vertical bars indicate the range of the mean ratio , for individual males. The mean increase of the number of attacks after i5 minutes of isolation found for the three males jointly was 1.06 X, but this figure was not statisFigure 2 summarizes the tests with one of the males. tically reliable (p>o.io). It is evident that the number of attacks before and after the isolation is approximately the same despite a considerable variation between days. Similar results were obtained from the two other males. After two hours of isolation there was a reliable increase ( X 1.26) in the and after seven hours of isolation there was a number of attacks (P
INTRODUCTION Although there have been numerous suggestions that isolation from conspecif ics may affect the readiness of an animal to perform various behaviours, until recently few attempts have been made to study this question experimentally. The proposal by LORENZ (I963) that the aggressive motivation spontaneously rises if an animal has no opportunity t0' fight was supported by on a coral reef fish (RASA, A juvenile damsel fish experiments increased showed an (Alicrospathodoit chrysurus) tendency to stay in a bottle with visual contact and opportunity to aggressive display with a conspecific with increasing isolation time. This was considered to be due to a build-up of the aggressive motivation. The results can, however, be explained 2.e. an by a behavioural habitation (HEILIGENBERG & KRAMER, individual habituates to the presence of the conspecific with a subsequent decreased reaction. When isolated, however, a recovery from habituation with an increased tendency to aggressive display could take place. . Experiments with males of the sword-tail (Xiphophorus helleri) have also revealed an increased tendency to fight after isolation (FRANCh & WILHEL;.iI, 1973; WILHELINII, 1975). A reliable increase was first apparent after one week of isolation and the intensity of the fights increased further with increasing isolation time. These results could also be explained by either a spontaneous accumulation of attack readiness or by a recovery from habitand Mrs B. FALT for valuable comments on 1) I am indebted to Professor FABRICIUS the manuscript. I also wish to gratefully thank Professor FRANCKand Dr HEILIGENBERG for constructive criticism. 2) Present address: Department of Fisheries Biology, University of Bergen, Box 1839, N-5011 Bergen (Norway).
_
'
44 uation. Likewise, in anabantoid fish there is generally an increase of aggression with increasing isolation time (PAL, 1968; DAVIS et al., 1974; HINKEL & MAIER, 1974). However, LAUDIEN (1965) found a decreased aggressiveness in Betta splendens after a long isolation. HEILIGENBERG & KRAMER (1972) have demonstrated that the attack readiness in males of the cichlid fish Haplochromis burtoni depends on a repeated exposure to adult conspecifics or fish dummies with an naturally oriented black eye-bar, a signal characteristic for territorial males. When this of stimulus the of attacks directed against juvenile number deprived fishes of another species, which was taken as a measure of the attack readiness, decreased to a very low level. Etroplus rviaculatus, another cichlid species, seems also to depend on visual stimuli to maintain a high attack readiness (REYER, 1975). Likewise, in the cichlid Pehruztochro?2is subocellatus kribensis the attack readiness decreases if there is no opportunity to fight (HEILIGENBERG, 1963) while in the cichlid Cichlasoma nigrofasciatum, there was an increased state of timidity but no further effect on the aggressive behaviour after an isolation period of seven days (GALLAGHER et al., 1972). In the bluegill sunfish (Lepomis yrcacrochirus) fish exhibited peak frequences of aggressive responses after one to seven days of social isolation depending on reproductive condition of the fish (CHISZAR et al., 1976). Apparently, the results from isolation experiments with fish are conflicting but are explainable in terms of species differences with adaptations to different social systems. There are several studies on other animal groups as well concerning the effect of isolation. Isolation of mice generally leads to an increase in aggressive behaviour (VALZELLI, 1969) and a similar effect has been found in hermit crabs (HAZLETT, 1966; COURCHESNE& BARLOW, 1971) and lobsters (HOFFMANN et al., 1975). The threshold for sexual behaviour usually falls with increasing deprivation (HINDE, 1969). The effect of isolation on the sexual behaviour in male sword-tails is an increase of those sexual behaviour patterns that depend on a high sexual readiness (FRANCK & GEISSLER, 1973; FRANCK & HENDRICKS, 1973). The increase is first apparent after 22 hours of isolation and is generally more pronounced after longer isolation periods. Males of the poeciliid fish (Poecilia sphenops) increased their sexual activity after social isolation of one hour (FRANCK, 1975). Guppy females (Poecilia reticulata) with a low responsiveness to males due to habituation did, however, show no after several weeks of isolation (LILEY & recovery of responsiveness In males of H. burtoni the frequency o?f aggressive WISHLOW, 1974). actions was influenced by visual external stimuli, whereas this was not so for the sexual activity (HEII IGENBERG & KRAMER, 1972).
45 The present study concerns the effect of isolation on the frequency of aggressive and sexual behaviour patterns in H. burtoni. In spite of the related investigation by (HEILIGENBERG and KRAMER described above, it seemed worthwhile to study the effect of complete visual isolation on the reaction towards conspecifics in a different experimental set-up, likewise study the effect of both short and long isolation periods and also closely follow if a change in the aggressive behaviour corresponded to a change in the sexual behaviour. ' MATERIALS AND METHODS In the African mouthbreeding cichlid fish H aplochramis burtoni the males defend territories which the females visit when spawning. No long-tenn pairbond exists and the female alone cares for the off-spring. There is a sexual dimorphism with the female smaller and more cryptically coloured than the male. A territorial male has colourful markings, e.g. a black line from the eye to the corner of the lips, a bright orange patch above the pectoral fins and a metallic light blue body colouration. Four males were studied concerning the effect of isolation. These males belonged to a stock of H. blowtaniwhich for some years had been held at our laboratory. As the stock originated from only one clutch of young, there is probably a considerable genetic similarity between the males. During the tests the males were between six months and two years of age. Each of the four males was kept in an aquarium of about 200 litres with 8-io smaller but sexually mature males and females. In the middle therewas an opaque wall with a movable door which could divide the aquarium into two compartments. The dominant male had his territory centre in one of the compartments and when the aquarium was not divided the other fish were mainly standing motionless near the surface in the opposite compartment. Isolation of a male began by closing the door in a moment when the male was alone in his compartment. After termination of the isolation period, the door was opened and the behaviour of the male was recorded during one or several observation periods, as described below. The males were kept in the same situation for 3-14 months interrupted by isolation periods. The frequency of aggressive and sexual behaviour patterns, although variable from one occasion to another, showed no tendency to change with time. The aggressive and sexual activity of the dominant male after a period of isolation was compared with the activity in observation periods with no prior isolation. Target fish might also change their behaviour during isolation. This could influence the behaviour of the dominant male in the abscence of internal changes. One aspect of the behaviour of the target fish, i.e. the number of intrusions in the compartment of the dominant male, was therefore recorded. Experiments were carried out with dif f erent isolation times and with slight variations in methods. For every period of isolation three males were tested. 15 minutes of isolatiosi. The males were observed r5 minutes before and after an isolation period of 15 minutes. Each of the three males was tested for 10 days, making a total observation time of 15 5 hours. The observations before the isolation commenced by closing and opening the door in the wall when the male was alone in his compartment. If the male was never seen alone during 15 minutes no observation was made that day. Using this method observations before and after isolation began correspondingly, i.e. a W ale was alone in his compartment and the door had just been moved.
46 2 and 7 hour of isolation. Observations were made for 30 minutes after a period of isolation and without any prior isolation, respectively on alternate days at the same time of the day. Observations were not made before and after isolation on the same day in order to avoid the effect of a daily rhythm in activity as there was an apparent decrease in the number of attacks and a possible decrease of the sexual activity during the course of a day. When using an isolation period of only i5 minutes the observations before and after isolation were made at approximately the same time of the day. Observations without isolation began by opening and closing the door in the wall. A total observation time of 60 hours was recorded as each male was observed for 10 days without isolation and for 10 days with prior isolation. 3 and rz days of Isolation. The males were observed during three periods of 30 minutes on the day before the isolation was started. The first observation was made in the morning and the following observations two and five hourslater. The next day isolation of a male began at the same time as the first observation started the previous day. After precisely 3 and 12 days of isolation respectively the isolation was terminated. From the moment the door was opened the males were observed for 30 minutes with two additional observation periods later in the day in accordance with the day before the isolation. For the following two days the behaviour of the males was recorded for 30 minutes in the morning. The next isolation was not started until at least one week after the previous isolation. Four experiments with 3 and 12 days of isolation respectively were made with each male making a total of 96 hours observation time. The males were observed so many times in these experiments in order to reveal possible long-term effects caused by the long isolation periods. To avoid too much disturbance of the males in connection with this extensive number of observations, the door in the wall between the compartments was only moved prior to the first observation on the first day in order to get an exact comparison with the observation immediately after termination of isolation. With these long isolation times it was also necessary to remove the male that was dominating during the isolation of the first male just before termination of isolation, otherwise long fights between the males would develop. However, this procedure did not appear to influence the external situation and change the activity of the first male, as the same tendencies in the results were recorded between 7 hours and 3 days of isolation and between 3 days and 12 days of isolation. Aggressive and sexual behaviour patterns were recorded during the observation periods. An attack is defined as an attempt to bite another fish. Two attempts to bite the same fish in rapid succession were recorded as only one attack but if a period of more than two seconds passed between the attacks they were recorded as two attacks. This was also the case if different fish were attacked regardless of the interval between the attacks. Sexual behaviour patterns were divided in side-shakes and lead-swims. While making a side-shake a male performs an undulating quivering while bending his body in a position in front of a female. A lead-swim is defined as swimming with exaggerated caudal movements often directed at the centre of the territory. These terms are equivalent to The fishes were kept at a courting and leading used by CRAPONDE CAPRONA temperature of 27° ± 1° in a photoperiod of 12 hours. In the morning they were fed with frozen liver and in the evening with commercial dry food. When testing, the observer was sitting behind a screen in order to diminish the disturbance and the movable door could be manipulated from behind the screen. Observations were spoken into a tape recorder for later transcription. In the statistical treatment of the results Mann-Whitney U test (SIEGEL,1956) was used when testing the effect of 2 and 7 hours of isolation and comparing the effect of 7 hours and 12 days of isolation. Otherwise, when not specifically stated, Wilcoxon matched-pairs signed-ranks test was used (SIEGEL,1956).
'
_
47 RESULTS Aggressive and sexual behaviour patterns were directed at both males and females. Certainly, most of the attacks were directed at males and most of the side-shakes and lead-swims at females, but no data concerning this difference was recorded. Aggressive
behaviour.
The number of attacks directed at adult conspecifics isolation periods but after a sufficiently long isolation creased (Fig. z ) .
increased by short the attack rate de-
Fig. i. The effect of isolation on the aggressive behaviour. The mean ratio between the number of attacks in observations after and observations without isolation is shown against different isolation time. The vertical bars indicate the range of the mean ratio , for individual males. The mean increase of the number of attacks after i5 minutes of isolation found for the three males jointly was 1.06 X, but this figure was not statisFigure 2 summarizes the tests with one of the males. tically reliable (p>o.io). It is evident that the number of attacks before and after the isolation is approximately the same despite a considerable variation between days. Similar results were obtained from the two other males. After two hours of isolation there was a reliable increase ( X 1.26) in the and after seven hours of isolation there was a number of attacks (P
