Breeding territoriality and pair formation in the convict cichlid (Cichlasoma nigrofasciatum; Pisces, Cichlidae)

ROBERT W. MACKERETH~ AND MILES H. A. KEENLEYSIDE Department of Zoology, University of Western Ontario, London, Ont., Canada N6A 5B7

Received May 6, 1992 Accepted November 25, 1992

MACKERETH, R. W., and KEENLEYSIDE, M. H. A. 1993. Breeding territoriality and pair formation in the convict cichlid (Cichlasoma nigrofasciatum ; Pisces, Cichlidae). Can. J . Zool . 71 : 960 - 967.

In many biparental species a sex difference in parental investment in a brood before fertilization, such as establishing a breeding territory or preparing a nest, may be an important component of the overall pattern of parental investment. Prefertili- zation investment patterns have been described for several species of biparental cichlid fishes, but there are discrepancies in the descriptions for the convict cichlid, Cichlasoma nigrofasciatum. This study describes quantitatively the prespawning behaviour of male and female convict cichlids and examines the influence on their behaviour of limiting the number of avail- able spawning sites. The results indicate that pair formation begins several days before spawning when the female begins to follow a male and chase other females away from him. The pair then begins to spend more time in a smaller area where spawning eventually~occurs. The breeding territory is usually established by the pair on the day of spawning. 'There was little difference in the pattern of prespawning behaviour of fish with abundant versus limited spawning sites. It appears that neither sex will establish a territory until the female is ready to spawn and the pair has formed.

MACKERETH, R. W., et KEENLEYSIDE, M. H. A. 1993. Breeding territoriality and pair formation in the convict cichlid (Cichlasoma nigrofasciatum; Pisces, Cichlidae). Can. J . Zool. 71 : 960-967.

Chez plusieurs espkces biparentales, la diffkrence entre les efforts diployks par le mile et la femelle avant la fkcondation, notamment l'ktablissement d'un territoire de reproduction ou la prkparation du nid, peut constituer une composante impor- tante du pattern gkniral de I'investissement parental. L'effort diploye avant la fkcondation a 6tk dkcrit chez plusieurs espkces de poissons cichlidks biparentaux, mais il existe des contradictions entre les divers travaux sur le Cichlide a bande noire, Cichlasoma nigrofasciatum. On trouvera dans ce travail une description quantitative des comportements du mile et de la femelle de ce poisson avant la fkcondation ainsi qu'une Ctude de l'influence de la reduction du nombre de sites de fraye sur leur comportement. Les risultats indiquent que la formation d'un couple s'amorce plusieurs jours avant la fraye, au moment ou la femelle commence a suivre un mile et a en iloigner les autres femelles. Le couple commence alors a passer plus de temps dans un territoire plus restreint ou se fera Cventuellement la ponte. Le territoire de fraye est ordinairement dklimiti par le couple le jour mtme de la fraye. I1 existe peu de diffirences dans les comportements d'avant la fraye chez les poissons a sites de fraye nombreux et chez les poissons mis en presence d'un nombre limit6 de sites de fraye. 11 semble que ni le mile, ni la femelle ne dilimitent de territoire avant que la femelle ne soit prtte a pondre et que la couple ne soit reuni.

[Traduit par la rkdaction]

Introduction have produced conflicting results regarding prefertilization

In those fishes of the family Cichlidae that exhibit extended biparental care, both parents make a large parental investment (PI) in each brood. As well as incurring the cost of producing gametes, the parents care for the eggs and free embryos (wrig- glers) and defend the juveniles (fry) from predators for up to several weeks (Keenleyside 199 1). Parental investment also includes prefertilization behavioural investment, such as pre- paring and defending a spawning site, which may be an impor- tant component of overall investment in the brood (Trivers 1972).

Early studies of reproductive behaviour in captive biparental cichlids indicated that males are primarily responsible for establishing the breeding territory and are more active in initiating courtship than females (Noble and Curtis 1939; Baerends and Baerends-van Roon 1950; Oehlert 1956). More recent observations of free-living species in Central America showed that either the male alone or the pair together acquire a breeding territory (McKaye 1977; Perrone 1978; Zaret 1980; Neil 1984). In general, these studies suggest that males make a greater prefertilization investment than do females. However, studies of the biparental convict cichlid (Cichla- soma nigrofasciatum), both in the laboratory and in nature,

'Present address: Department of Zoology, University of Guelph, Guelph, Ont., Canada N1G 2W1.

investment by males and females (Williams 1972; Meral 1973; McKaye 1977; Patterson 1985).

The main purpose of this paper is to present the results of experiments designed to clarify prefertilization investment patterns by both sexes of the convict cichlid. These forms of PI, along with courtship behaviours, which we collectively refer to as prespawning behaviour, may have an important influence on the overall PI pattern of this and other biparental cichlids, including differences between the parents in con- tinuing to provide care until the offspring reach independence (Keenleyside 199 1 ; Keenleyside and Mackereth 1992).

The size of the aquarium in which potential breeding convict cichlids are held may influence their patterns of prefertiliza- tion PI. For example, Williams (1972) found that in small (45 L) tanks males established and defended breeding terri- tories, but in large (800 L) tanks females established territories and then followed and courted males. Eventually a pair formed, returned to the female's territory, and began nest preparation. On the other hand, Patterson (1985) found that in a large pool (2.5 x 2.5 x 0.25 m deep) male convict cichlids quickly established territories and were then joined by females, sug- gesting that male prespawning territoriality is not simply a function of confinement in small aquaria.

Williams' (1972) large tank observations were supported by a field study in Nicaragua and Costa Rica by Meral(1973). He observed convict cichlid females defending an area against

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MACKERETH AND KEENLEYSIDE 96 1

other females and courting passing males. The female occa- sionally travelled and fed with a male and attacked other females. The pair then settled at a site where territory defense, courtship, and nest preparation occurred. Although it is not clear if the final breeding territory is the same area that was initially defended by the female, Meral's description clearly suggested that the female plays the major role in initiating courtship.

Another field study in Lake Jiloa, Nicaragua, reported that in nine species of cichlids, including convicts, pair formation occurred in feeding schools away from potential breeding sites (McKaye 1977). The pair then established a breeding terri- tory, in some cases after evicting a resident pair. At the height of breeding it appeared that competition for breeding terri- tories was so intense that both members of a pair were needed to successfully establish a breeding territory (McKaye 1977). However, it was not clear which sex, if either, played the more important role in initiating prespawning events.

A possible reason for the variation in reported prespawning behaviour of convict cichlids is that convicts alter their behav- iour to maximize their reproductive success depending on resource availability. For example, in a tank that is too small for more than one breeding territory, the best chance of suc- cessful spawning is for a pair to be the first to establish and defend a breeding site. This may require initial efforts by the male, who is always larger and presumably stronger than the female within breeding pairs (McKaye 1977). The male will first establish a territory and then court females, because the territory is the limiting resource while mates are not. On the other hand, in a stream or lake with abundant suitable breeding sites and a long season of continuous breeding, it may be most efficient if females who are ready to spawn advertise this by courting males. Once a pair has formed they can establish a territory together rather than either sex expending a large amount of energy defending an abundant resource without the help of a mate.

Another problem is that, in all the studies mentioned above, descriptions of prespawning behaviour were based mainly on qualitative observations. In order to understand subtle varia- tions in prespawning behaviour patterns, quantitative analysis of data collected under standardized conditions is required.

This study included two experiments. The purpose of experi- ment I was to quantify prespawning events in convict cichlids in an environment with spawning site availability similar to that of their natural environment. Three questions were asked: (i) which sex selects and initially defends the spawning terri- tory? (ii) which sex selects and prepares the spawning site? and (iii) which sex initiates courtship? In addition, the order in which these events occurred was examined. Experiment 2 assessed the effect of limiting the number of potential spawn- ing sites to determine if convict cichlids alter their behaviour and general pattern of PI in response to this variation in resource availability.

Methods

Experimental jish Stock originated from individuals captured in Costa Rica i n 1984

and bred with fish purchased from local aquarists. Experimental fish had prior breeding experience, but not in the study pools. Fish were held in six 90-L aquaria, each visually isolated from the others and holding fish of one sex only. Water temperature was maintained at 26 f 1°C and lighting was on a 12 h L : 12 h D cycle. Fish were fed once daily with either cichlid pellets (Tropic Aquaria Ltd., stock

No. A149), dried flake food (Tetramin), or frozen brine shrimp (Artrmia salina). About one-third of the water in each tank was changed every 3rd day.

Three males and three females were used in each trial. Each fish was taken from a different holding tank, so that none had recent expe- rience with the others. Fish were anaesthetized with tricane methane- sulfonate (MS222), weighed, and measured. The three fish of each sex were similar in size; females were, on average, 80% of male standard length (males: 6.88 f 0.09 cm (mean f sE); females: 5.47 f 0.07 cm) and 60% of male weight (males: 13.09 f 0.63 g; females: 7.27 f 0.27 g).

Each fish was marked for individual identification. The technique, modified from Lotrich and Meredith (1974), involved injecting red or yellow acrylic polymer emulsions with a needle under a scale on the fish's side, anterior to the spiny dorsal fin. The acrylic polymer was injected as the needle was being removed, leaving a coloured spot approximately 4 x 2 mm. Marks were placed on both sides of the fish and were clearly visible for at least 2 months. After recovery from the anaesthetic, the six fish were placed in one of the study pools.

Study pools Two round plastic wading pools with filters, 2.24 m in diameter

with a bottom area of 3.34 m?, and a water depth of 34 cm, were used as experimental arenas. The bottom of each pool was covered with 6-8 cm of gravel on top of which was placed a grid system made of plastic-coated wire. Grid squares were 30 x 30 cm, although squares were incomplete along the curved edge of the pool. Tempera- ture and light conditions were the same as in the holding tanks.

Each pool also contained eight juvenile convict cichlids (less than 2 cm standard length) which served as potential brood predators. The juveniles were replaced before each replicate trial to ensure that their size remained constant throughout the study. During trials the fish were fed once daily, after the first observation period. Cichlid pellets were evenly distributed throughout the pool so there was no concen- tration of food in any area.

The experimental pools differed only in the number of rock clumps they contained. In experiment 1, 16 clumps of one to four rocks were placed, in a regular pattern, within grid squares away from the wall. Because convict cichlids are cave spawners (McKaye 1977; Keenley- side et al. 1990), we predicted they would use the larger rock clumps as nest sites, and potential brood predators could approach the nest from all sides. In experiment 2, one clump of three rocks was placed in the centre of the pool.

Rocks were taken from a nearby stream bed and were thoroughly cleaned before use. All rocks were roughly round or oblong in shape and ranged in diameter on the longest axis from 9 to 30 cm. Maxi- mum height of the rocks above the gravel surface was approximately 15 cm.

Obsewations Observations were made twice each day, between 09:OO and 1 1 :00,

and again between 15:OO and 17:00, beginning on the day the fish were put into the pool. Each of the six adult fish, in random order, was observed for 10 min. Every 10 s the location of the fish was plotted on a scale map of the pool and the identity of any fish of the opposite sex within two body lengths of the focal fish was recorded (occurrence with other fish, see below). The location of the focal animal when it performed certain behaviours and the identity of the interacting fish, if appropriate, were recorded. Behaviours were grouped into three general categories: aggression (frontal display, chase, bite, and pendel); courtship (greet, circle, tailbeat, quiver, and occurrence with other); and nest preparation (nip, skim, and dig). These behaviours were chosen during preliminary observations and are described by Baerends and Baerends-van Roon (1950) and Williams (1972).

Results from the two daily observation periods were pooled to give 20 min of data per day for each fish. For experiment 1, recordings ended after the afternoon recording on the day the second pair of fish

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962 CAN. J. ZOOL. VOL. 71. 1993

spawned. For experiment 2, recordings ended after the afternoon recording on the day the first pair spawned.

Dcita analysis When a trial ended, behaviour and space-use data collected each

day for the pair that spawned were categorized relative to the day of spawning. The day of spawning was labelled day 0 , the preceding day was day - 1 (one day prespawning), and so on. Days earlier than -4 were pooled into the Early Prespawning (EPS) period and data collected for a fish during that period were averaged to give a single EPS value. In experiment 1 , data collection from the first pair to spawn continued after spawning until the second pair spawned. Days after day 0 were pooled into the Parental Care (PC) period and data collected for a fish during this period were averaged to give a single PC value.

Behaviour Because the frequencies of most behaviours were low, those within

each general category (aggression, courtship, and nest preparation) were pooled for analysis. For each sex, aggressive behaviours were analyzed as aggression towards males, females, or juveniles. Court- ship behaviours, and occurrence with other fish, were divided into behaviours directed towards the focal fish's eventual mate (courting a mate, occurrence with mate) and towards other members of the opposite sex (courting other, occurrence with other).

Activity The plots of the focal fish's location every 10 s were pooled for the

two 10-min observation periods each day. The outermost location points were connected to form a polygon. The fish's use of space was then measured in two ways. First, the "activity area" (AA) was the area enclosed by the polygon. Second, the "activity pattern" (AP) was the standard deviation (SD) of the mean number of times the focal fish occurred in any grid square within the AA. This value pro- vides an index of how clumped or dispersed the location points within the AA were; a low SD indicates a relatively uniform distribution of points, while a high SD indicates a more clumped distribution.

Repeated measures ANOVA was used to analyze all behavioural and activity data. The repeated measures factor was the day, in relation to spawning day, on which data for the dependent variable were col- lected. Because repeated measures ANOVA requires a balanced sample size within all repeated measures categories, only data from days 0, - 1 , and -2 could be included in the analysis. Means from other days are presented for comparison.

Results Ten replicates were done for experiment 1 and data were

collected for 21 pairs. It took an average of 2.6 f 0.31 days (f SE) from the day of introduction to the pool for the first pair to spawn. These 10 pairs are referred to as first-spawners. The additional 11 pairs, referred to as second-spawners, took 5 f 0.62 days from the day of introduction to the pool to spawn. There is variation in the number of pairs for which data were recorded on days before spawning. Sample sizes increased from seven pairs during the EPS period to all 21 pairs by day -2. Data were collected for 10 pairs during the PC period.

Eleven replicates were done for experiment 2, and data were collected for 1 1 pairs. On average, pairs took 3.6 f 0.4 days to spawn. Sample sizes increased from three pairs during the EPS period to 1 1 pairs by day -2. Because all trials ended on spawning day, there was no PC category in experiment 2.

Behaviour Aggression In both experiments the aggressive behaviours recorded

were mainly intrasexual. Females were much more aggressive towards females than were males on all days before spawning,

V) - m

0 - EPS -4 -3 -2 - 1 0 PC

EPS -4 -3 -2 - 1 0

Day

FIG. 1 . Mean frequency per 20 min of aggression towards females by males (open bars) and females (solid bars) observed in experiment 1 (A) and experiment 2 (B). Vertical lines show standard error.

but by day 0 females decreased their aggression towards other females while males increased theirs. Analysis of this varia- tion produced a significant sex x day interaction in both experiments (experiment 1 : F2,76 = 6.2 1 , P = 0.003, Fig. 1A; experiment 2: F2,40 = 9.06, P = 0.001, Fig. 1B). During the PC period male aggression towards females increased slightly from day 0, while aggression by females continued to decline (Fig. 1A).

Aggression towards males showed a pattern opposite to that of aggression towards females. Males were significantly more aggressive towards males than were females across all days in both experiments (experiment 1: Fl,38 = 13.83, P = 0.001, Fig. 2A; experiment 2: F,,20 = 10.61, P = 0.004, Fig. 2B). Male aggression towards other males remained at a high level on all days, including the PC period.

In both experiments aggression towards juveniles, which consisted only of chasing, was infrequent until day 0. On day 0 aggression towards juveniles, especially by females, increased. In experiment 1 , the large sex difference on day 0 produced a significant interaction between sex and day in the ANOVA (F2,76 = 14.53, P < 0.001, Fig. 3A). The analysis also showed that second-spawning pairs were significantly more aggressive towards juveniles than were first-spawning pairs (Fl ,38 = 4.5, P = 0.04). Consequently, the means for fish in first- and second-spawning pairs are presented sepa- rately for days - 2, - l , and 0 (Fig. 3A). During PC, female aggression towards juveniles remained high (Fig. 3A). In

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L

EPS -4 -3 -2 - 1 0 PC V) -

EPS -4 -3 -2 -1 0

Day

FIG. 2. Mean frequency per 20 min of aggression towards males by males (open bars) and females (solid bars) observed in experiment 1 (A) and experiment 2 (B). Vertical lines show standard error.

experiment 2, aggression towards juveniles increased signifi- cantly from day -2 to day 0 and, although females were more aggressive than males on day 0 , the sex x day interaction was not quite significant (day: F,.40 = 1 1.3 1 , P < 0.00 1 ; sex x day: F2,4() = 2.79, P = 0.073, Fig. 3B).

Courtship Courtship behaviour occurred infrequently during the experi-

ments. The frequency of courtship towards the mate in both experiments was less than three acts per 20 minutes on all days up to and including day 0. There were no significant effects shown by the ANOVA.

The frequency of occurrence with the mate in experiment 1 was consistently low from EPS to day -3 (Fig. 4A). For first- spawners, the frequency of occurrence with the mate remained low on day -2 and increased to a higher level by day 0. For second-spawners, occurrence with the mate was consistently high from day -2 to day 0. Analysis of this difference produced a significant day X spawn-order interaction (F2,7h = 8.37, P = 0.001, Fig. 4A). Occurrences with the mate decreased slightly during PC. In experiment 2, occurrence with the mate was low during EPS and began to increase on day - 3. The increase was significant from day -2 to day 0 (F2,40 = 1 3.27, P < 0.00 1, Fig. 4B).

The courtship of and occurrence with fish other than the mate were infrequent and occurred only several days before spawning. No significant effects were shown by the ANOVA.

3 .- EPS -4 -3 -2 -1 0 PC V)

E g - I (B) -

EPS -4 -3 -2 -1 0

Day

FIG. 3. Mean frequency per 20 min of aggression towards juveniles observed in experiment 1 (A) and experiment 2 (B). For experiment 1 , on days -2, - 1 , and 0 , the means of first-spawning males (open bars) and females (solid bars) are shown separately from those of second-spawning males (cross hatch) and females (single hatch). Ver- tical lines show standard error.

Nest preparation For both experiments, the frequency of nest preparation

activities was low. Nest preparation consisted mainly of digging to move gravel and enlarge the spaces within the rock clumps. In experiment 1 the analysis showed no significant effects, although males performed slightly more nest prepara- tion than did females on days -4, -3, and -2, while females did slightly more than males on days - 1 and 0 and during PC (Fig. 5A). In experiment 2, nest preparation was performed mainly by males during EPS and on days -4, -3, and -2, while females increased their nest preparation behaviour on days - 1 and 0. 'These changes produced a significant sex x day interaction in the ANOVA (F2.40 = 3.48, P = 0.04, Fig. 5B).

A repeated measures ANOVA comparing males and females in first-spawning pairs in experiment I with males and females that spawned in experiment 2 revealed no significant differ- ences in any behaviours measured.

Activity In experiment 1 , the average activity area (AA) of the fish

was about two-thirds of the total 3.34 m2 area of the pool during EPS and on days -3 and -3 (Fig. 6A). From day -2 to day 0, the mean AA of first-spawners was significantly larger than that of second-spawners (Fl.3X = 6.71, P =

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CAN. J . ZOOL. VOL. 71. 1993

g - EPS - 4 - 3 - 2 -1 0 PC -

C 0 . - EPS - 4 - 3 - 2 - 1 0 PC -

EPS - 4 - 3 - 2 - 1 0 EPS - 4 - 3 - 2 -1 0

Day Day

FIG. 4. Mean frequency per 20 min of occurrence with mate by FIG. 5. Mean frequency per 20 min of nest preparation by males males and females observed in experiment 1 (A) and experiment 2 (open bars) and females (solid bars) observed in experiment 1 (A) and (B); symbols as in Fig. 3. Vertical lines show standard error. experiment 2 (B). Vertical lines show standard error.

0.014). Between day - 1 and day 0 , the AA of all fish declined, although the females' decline (to about 1 m2) was greater than that of males, producing a significant sex x day interaction in the ANOVA (F2.7h = 3.71, P = 0.029, Fig. 6A). During the PC period the AA among females decreased to less than 1 square metre, while the male AA was about 1.5 m' (Fig. 6A).

From EPS to day - 1 in experiment 1 , both sexes had low activity pattern (AP) values, indicating that their location points were evenly distributed within the AA (Fig. 6C). On day 0, females' AP values increased more than 3 times while those of males almost doubled; these changes produced a highly significant sex x day interaction in the ANOVA (F7.7h =

12.00, P < 0.001). Combined with the decreased AA, the increased AP indicates that females, in particular, spent most of their time in a small area around the spawning site and only occasionally moved around within their AA. During the PC period, the APs of both sexes were similar to those on day 0 (Fig. 6C).

In experiment 2, the mean AA for both sexes was about two- thirds of the total area, from the EPS period to day -2 (Fig. 6B). On day - 1, it declined to about 1.5 m2, and by day 0 the female AA had declined to about 0.5 m2 while the male AA remained at 1.5 m2. The difference in the decline in AA between the sexes produced a significant sex x day inter- action in the ANOVA (F2.40 = 6.72, P = 0.003, Fig. 6B).

The AP measures for both sexes were low from EPS to day

-2. indicating that locations within the AA were relatively evenly distributed (Fig. 6D). The AP of both sexes increased slightly on day - 1 and then female AP increased greatly on day 0. This change produced a significant sex x day inter- action in the ANOVA (F7.40 = 19.78, P < 0.001).

A repeated measures ANOVA comparing males and females in first-spawning pairs in experiment 1 with males and females that spawned in experiment 2 revealed a significant experi- mental effect on AA and AP. Experiment 2 fish had signifi- cantly smaller AAs on each of days -2, - 1 , and 0 than did first-spawning fish in experiment 1 (F1.38 = 12.05, P = 0.001). Experiment 2 fish of both sexes had higher AP measures than did experiment 1 first-spawners (F1,38 = 6.3, P = 0.016), indicating that experiment 2 fish spent more time in a smaller area within their AAs than did experiment 1 fish.

Discussion

The main purpose of experiment 1 was to describe the pattern of and quantify the sex differences in prefertilization PI in an environment with resource availability similar to that seen in convict cichlids' natural habitat. The results suggest that neither sex is primarily responsible for establishing the spawning territory, selecting and preparing the spawning site, or initiating courtship. Pair formation seems to occur several days before spawning, with both sexes performing only occa- sional courtship behaviour, and the territory established by the

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EPS - 4 - 3 - 2 -1 0 PC EPS - 4 - 3 - 2 -1 0

EPS - 4 - 3 - 2 - 1 0 PC EPS - 4 - 3 - 2 -1 0

Day Day

FIG. 6. Mean activity areas per 20 min observed in experiment 1 (A) and experiment 2 (B) and mean activity pattern (see Methods) observed in experiment 1 (C) and experiment 2 (D); symbols as in Fig. 3. Vertical lines show standard error.

pair on the day spawning occurs. These observations are simi- lar to those made in the field by McKaye (1977) on several cichlid species, including convict cichlids, and by Itzkowitz and Nyby ( 1982) on Cichlasoma cvanoguttatum.

The observed patterns of aggression suggest that neither sex was strongly territorial before day 0. When the fish were released into the pool they exhibited intrasexual aggressive behaviour within 1 h. This appeared to establish a dominance hierarchy, although no data on rank order were obtained. The most aggressive male, which appeared to be dominant, wandered around the pool, and often swam more than 1 m to attack another male. The most aggressive female generally followed the dominant male and chased other females that approached him. The most aggressive fish of each sex were usually the first to form a pair and spawn. Cichlasoma cvano- guttatum individuals also display intrasexual aggression before pair formation when they wander in large groups (Itzkowitz and Nyby 1982). The more dominant individuals in such groups are the first to form pairs and may aggressively prevent subordinates from doing so (Haley 1987).

Further evidence that territories were not being established before day 0 is provided by the AA and AP data. The AA remained at a constant level, with only slight sex differences, until it declined significantly on the day of spawning, particu- larly for females (Fig. 6A). The difference in AA size between first- and second-spawners is a result of first-spawners aggres- sively defending a territory during the time that second- spawner data were recorded, so the second-spawners were prevented from using some portion of the pool. Because the

AA declined on day 0, and remained low during the PC period when a territory around the eggs existed, we conclude that the larger AAs observed before day 0 indicate that territories had not yet been firmly established.

Both sexes also showed an equal and constant AP within the AA until day 0 (Fig. 6C). Meral (1973) observed that females sometimes used a potential spawning site as a centre of activity while courting passing males. This was not true in our study because the low AP values on the days before spawning indi- cate a relatively even distribution of observed location points for both sexes within the large AA. In contrast, the increased AP value on the day of spawning, particularly for females, reflects a concentration of activity around the spawning site.

Pair formation, as mentioned above, generally occurred first between the most aggressive individuals. There was no indica- tion that either sex initiated pair formation by courting a poten- tial mate. The frequency of courtship was low on all days and there was no difference between the sexes. A better indicator of pair-bond development was the frequency of occurrence with the fish's eventual mate. From day -2 to day 0 there was a significant increase in the amount of time the members of the pair spent together (Fig. 4A). Meral (1973) reported that female convict cichlids initiated courtship by approaching passing males and performing courtship behaviours. In our study, we observed that females approached and followed a male, and chased other females away from him, much more often than males approached and followed a female.

The other potentially important component of prefertiliza- tion PI for convicts is nest preparation. There was, however,

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966 CAN. J . ZOOL. VOL. 71. 1993

a low frequency of nest preparation behaviour (Fig. 5A). Pairs tended to spawn on the exposed surfaces of the rock clumps in the central area of the pool and did not do much digging around the rocks. This result is in contrast with free-living convict cichlids, which usually spawn in caves excavated under rocks (Meral 1973; McKaye 1977; Keenleyside et al. 1990). The low frequency of cave spawning in our study may be due to a relatively low density of egg predators compared with that in nature.

The results of experiment 1 suggest that prefertilization investment is a minor component of the overall PI of convict cichlids because neither sex was involved in high levels of territory establishment or nest preparation. However, this may have been influenced by the experimental conditions. Because potential nest sites were abundant, there may have been no advantage to investing a large amount of energy in defending one until spawning occurred. Studies of male pupfish (Cyprino- don nevadensis amargosae), which defend territories and attract females, have shown that the energetic cost of defend- ing a territory may be almost double the cost of resting metabolism (Feldmeth 1983). In order for territoriality to be advantageous, the cost of defending the area must be balanced by a benefit in terms of controlling food resources or increas- ing reproductive success (Davies and Houston 1984). In a sys- tem where spawning sites are abundant and food is regularly provided, there is probably little benefit derived from defend- ing one site until spawning.

Experiment 2 examined the effect of limiting the number of potential spawning sites to one site for three potential pairs of fish. By limiting spawning sites we hoped to increase the benefit to an individual or a pair of defending a territory before spawning because the pair would need to control the site to

brood to survive (Barlow 1974; Keenley side 199 1). For con- vict cichlids, the number of competitors for high-quality spawning sites may also be high and both members of the pair may be needed to defend the territory before spawning (McKaye 1977). However, there is likely a high energetic cost to defending a territory and it may be advantageous for each sex to minimize the time the territory is defended before spawn- ing. The female may concentrate her energy in egg production and find a mate only when she is ready to spawn. Males may attract gravid females by being dominant over other males rather than investing in defending a territory alone. Once the pair has formed and found a suitable spawning location, they can quickly establish a territory, prepare the spawning site, and spawn; the cost of territoriality then becomes necessary to ensure survival of the eggs.

In conclusion, the prespawning behaviour of convict cich- lids appeared to follow a consistent pattern. Prespawning events were initiated when the female demonstrated her readi- ness to spawn by following the male, exchanging courtship displays with him, and behaving aggressively towards other females that approached the male. The pair bond formed several days before spawning and the pair travelled together investigating potential spawning sites. Neither sex appeared to invest a large amount of energy in preparing the spawning site. On the day of spawning, the pair became territorial and focused their activity around the spawning site. The pattern of prespawning events was not altered by limiting the number of potential nest sites. The results suggest that, although pre- spawning behaviour is variable, the overall pattern does not change in response to variation in spawning site availability.

Acknowledgements reproduce successfully .- There was, however, little difference we thank R. c Bailey, S. G. ~ i ~ ~ h , T. M. Laverty, R. J. in observed behaviour between experiments 1 and 2. At first, L ~ ~ ~ ~ ~ , M. J. ~ ~ ~ k ~ ~ ~ ~ h , D. R. c Robilliard, B. D. the fish in experiment 2 wandered as a group and Wisenden, and two anonymous reviewers for their help and mainly intrasexual aggression. As in experiment 1, the most comments on the study. Financial support was provided by a aggressive fish (which appeared dominant) were generally the Natural Sciences and Engineering Research Council of first to form a pair bond. Pairs in experiment 2 reduced their canada grant to M.H.A.K. AA and increased their AP sooner than in experiment 1, prob- ably because did not need investigate a number Baerends, G. P.. and Baerends-van Roon. J. M. 1950. An introduc- different possible sites. Even with the smaller AA, the pair did tion to the study of the ethology of cichlid fishes. Behaviour not aggressively defend or focus their activity around the one (Suppl.), 1: 1-243. possible spawning site until the day of spawning, suggesting Barlow, G. W. 1974. Contrasts in social behavior between Central that the territory was not established sooner than in experi- American cichlid fishes and coral-reef surgeon fishes. Am. Zool. ment 1. 14: 9-34.

The low level of prefertilization PI observed in experiment Davies. N. B.. and Houston. A. 1. 1984. Territory economics. In

1 was therefore not due to an abundance of spawning sites. Behavioural ecology: an evolutionary approach. Edited by J. R. Krebs and N. B. Davis. 2nd ed. Blackwell Scientific Publications Even in experiment 2, where the only chance of successfully Ltd., London. pp. 148 - 169.

'pawning was to a the fish waited the Feldmeth, C. R. 1983. Costs of aggression i n trout and pupfish. In The for this is Behavioral energetics: the cost of survival in vertebrates. Edited by

probably that convicts have a 10% breeding Season in which W. P. Aspey and S. I. Lustick. Ohio State University Press, they may spawn several times (McKaye 1977). Between Columbus. pp. 117-140. broods, the female must acquire energy to produce more eggs. Because there is probably some variability in unpaired females' gravidness, it may be advantageous for males to wait until a female indicates her readiness to spawn before begin- ning courtship. Furthermore, female convict cichlids are the more brightly coloured sex, and a female's colours are usually brightest when she is ready to spawn, which may serve to advertise her gravidness (Barlow 1974; Loiselle 1985).

In nature, predation on the young of biparental cichlid species is high and it has been suggested that the reason they are biparental is that both parents are needed in order for the

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