Convict Cichlids Research Articles

Effects of patch shape and group size on the effectiveness of defence by juvenile convict cichlids

The causes and consequences of territory size have attracted considerable attention, but there has been relatively little research on optimal territory shape. We manipulated the shape of food patches, independent of patch area (square, 13.6 × 13.6 cm; rectangular, 46.5 × 4.0 cm; elongated, 93.0 × 2.0 cm), presented to small, medium and large convict cichlids, Archocentrus nigrofasciatus , in groups of varying size (three, six, 12 fish). We used a 3 × 3 factorial design to test the predictions that the defence and monopolization of a food patch would decrease as both patch perimeter and group size increased. As predicted, with increasing patch perimeter, the ability of the large (dominant) fish to defend the patch decreased, as reflected by a decrease in the frequency of aggression and the proportion of the aggression by the dominant. Similarly, intruder success typically increased with increasing patch perimeter, as reflected by an increase in the proportion of intruders in the patch and the duration that an intruder remained in the patch. Group size also had the predicted effect on most response variables; in general, defender success decreased and intruder success increased as group size increased. Furthermore, the effects of increasing the patch perimeter and group size on measures of defensibility were largely additive.

Male size predicts the ability to defend offspring in the biparental convict cichlid Archocentrus nigrofasciatus

The data from this field study provided evidence that biparental convict cichlid Archocentrus nigrofasciatus pairs with large males had fewer intruders near their offspring compared to pairs with small males. This suggested that large males were more capable of defending their young against predators.

The dynamic nature of antipredator behavior: prey fish integrate threat-sensitive antipredator responses within background levels of predation risk

Prey animals often have to face a dynamic tradeoff between the costs of antipredator behavior and the benefits of other fitness-related activities such as foraging and reproduction. According to the threat-sensitive predator avoidance hypothesis, prey animals should match the intensity of their antipredator behavior to the degree of immediate threat posed by the predator. Moreover, longer-term temporal variability in predation risk (over days to weeks) can shape the intensity of antipredator behavior. According to the risk allocation hypothesis, changing the background level of risk for several days is often enough to change the response intensity of the prey to a given stimulus. As the background level of risk increases, the response intensity of the prey decreases. In this study, we tested for possible interactions between immediate threat-sensitive responses to varying levels of current perceived risk and temporal variability in background risk experienced over the past 3 days. Juvenile convict cichlids were preexposed to either low or high frequencies of predation risk (using conspecific chemical alarm cues) for 3 days and were then tested for a response to one of five concentrations (100, 50, 25, 12.5%, or a distilled water control). According to the threat-sensitive predator avoidance hypothesis, we found greater intensity responses to greater concentrations of alarm cues. Moreover, in accordance with the risk allocation hypothesis, we found that cichlids previously exposed to the high background level of risk exhibited a lower overall intensity response to each alarm cue concentration than those exposed to the low background level of risk. It is interesting to note that we found that the background level of risk over the past 3 days influenced the threshold level of response to varying concentrations of alarm cues. Indeed, the minimum stimulus concentration that evoked a behavioral response was lower for fish exposed to high background levels of predation than those exposed to low background levels of predation. These results illustrate a remarkable interplay between immediate (current) risk and background risk in shaping the intensity of antipredator responses.

Social interactions tune aggression and stress responsiveness in a territorial cichlid fish ( Archocentrus nigrofasciatus)

We examined the relative influences of pre-fight housing condition, contest intensity, and contest outcome in modulating post-fight stress hormone concentrations in territorial male convict cichlids ( Archocentrus nigrofasciatus). Individuals were housed either in isolation or in semi-natural communal tanks. Pairs of male cichlids that differed considerably in body mass were selected from the same housing regime. Pre-fight water-borne cortisol levels were obtained before allowing the dyad to interact until contest resolution, after which time post-fight cortisol levels were obtained from the winner and loser. There were no outcome-related differences in post-fight cortisol concentrations following escalated or non-escalated contests, a result that held true for both housing regimes. Pre-fight cortisol levels were significantly higher than post-fight cortisol levels, suggesting that initial confinement in a beaker for the water-borne hormone samples was a stressor, but that the animals acclimated quickly to confinement. Fights involving previously isolated participants were significantly more intense than those involving group-housed animals, which we explain as being a function of established relationships between social isolation, heightened acute cortisol responsiveness, and the expression of excessive aggressive behavior. Only group-housed losers demonstrated the ability to modulate aggression or hypothalamic–pituitary–interrenal (HPI) activity in a graded fashion to acute increases in cortisol or changes in contest intensity, respectively. We discuss a variety of factors that could disrupt the ability of isolates to appropriately modulate interactions between social behavior and the HPI axis, and we examine a number of functional hypotheses underlying the sensitivity of group-housed losers to changes in contest dynamics.

How does competition influence mate choice decisions for males and females in the monogamous convict cichlid fish, Archocentrus nigrofasciatus?

AbstractIt is understood that mate choice, competition, and sex differences produced by sexual selection underlie behavior, but few studies focus on their interactions within a system to understand how they shape behavior. Here, using the monogamous convict cichlid, Archocentrus nigrofasciatus, we examined the mate choice process of males and females in the presence of intrasexual competition. We compared and contrasted patterns reported in a previous study exploring this process in the absence of competition by using the same methodological paradigm. Specifically, two individuals (i.e., the competitors) were presented with a choice of two alternative, visually and tactilely isolated, mates and observed until one competitor (i.e., the primary competitor) spawned with one of the potential mates (i.e., the accepted mate). This was done for males and females separately. Both sexes spent more time with their mates while attacking and inhibiting the courtship of the other competitor (i.e., the secondary competitor). Only females expressed this time preference in the absence of competition (Santangelo & Itzkowtiz, 2004), but both sexes visited accepted mates more in the presence of competition. These results suggest competition causes the adoption of a mate guarding tactic. Males exhibited more differences than females with the addition of competition suggesting that male mate choice patterns are more labile than females. We attribute this to the ability of males to be bigamous and the adoption of different strategies based on the level of male-male competition. Courtship was not affected by competition for either sex, however the courtship of secondary individuals did appear to be influenced by primary individuals. Competition did not eliminate a searcher's continuous assessment of potential mates, yet it was conducted to a lesser degree. Thus, mate guarding is an important strategy that must be balanced with an individual's inclination to continuously assess based on present competition levels.

Effects of group size on the threat-sensitive response to varying concentrations of chemical alarm cues by juvenile convict cichlids

The threat-sensitive predator avoidance model predicts that prey should balance the intensity of antipredator responses against perceived predation risk, resulting in a graded response pattern. Recent studies have demonstrated considerable interspecific variation in the intensity of threat-sensitive response patterns, ranging from strongly graded to relatively nongraded or "hypersensitive" threat-sensitive response patterns. Here, we test for intraspecific plasticity in threat-sensitive responses by varying group size. We exposed juvenile convict cichlids, Archocentrus nigrofasciatus (Günther, 1867), as individuals or in small (groups of three) or large (groups of six) shoals to a series of dilutions of conspecific chemical alarm cues and a distilled water control. Singleton cichlids exhibited significant reductions in time spent moving and in frequency of foraging attempts (relative to distilled water controls) when exposed to a 12.5% dilution of conspecific alarm cue, with no difference in response intensity at higher stimulus concentrations, suggesting a nongraded (hypersensitive) response pattern. Small shoals exhibited a similar response pattern, but at a higher response threshold (25% dilution of stock alarm cue solution). Large shoals, however, exhibited a graded response pattern. These results suggest that group size influences the trade-off between predator avoidance and other fitness related activities, resulting in flexible threat-sensitive response patterns.

Heads up: juvenile convict cichlids switch to threat-sensitive foraging tactics based on chemosensory information

The ability to accurately assess local predation risk is crucial, as it allows prey individuals to maximize trade-offs between predator avoidance and foraging behaviour. Here, we test the hypothesis that juvenile convict cichlids, Archocentrus nigrofasciatus, rely on ambient chemosensory information to make threat-sensitive foraging decisions. In experiment 1, juvenile cichlids were exposed to conspecific chemical alarm cues above or below the threshold required to elicit an overt antipredator response and were allowed to forage on a choice of horizontal (on the substrate) or vertical (perpendicular to the substrate) food patches. Although cichlids exposed to a subthreshold alarm cue did not show an overt antipredator response, they significantly increased their use of the vertical food patch (head-up foraging posture). Cichlids exposed to a suprathreshold alarm cue significantly reduced foraging and aggressive behaviour and shifted to the head-up foraging position. In experiment 2, juvenile cichlids were exposed to the odour of an adult conspecific fed a vegetable diet, or one of two prey fish diets (juvenile cichlids or swordtails, Xiphophorus hellerii), or a distilled water control. Although we found no evidence of an overt antipredator response towards any of the stimuli, cichlids exposed to the odour of predators fed a prey fish diet significantly increased their use of the head-up foraging posture. Our results clearly show that juvenile cichlids are able to adjust their foraging patterns in a threat-sensitive fashion in response to ambient chemosensory information.

Acquired recognition of novel predator odour cocktails by juvenile glowlight tetras

Prey can learn to recognize novel predators through the association of aversive stimuli (visual or chemical) paired with a predator cue (i.e. acquired predator recognition). Previous studies have demonstrated that a variety of prey can readily learn the identity of a single predator. In this study, we examined whether predator-naive glowlight tetras, Hemigrammus erythrozonus, could simultaneously acquire recognition of three novel heterospecific odours as predation threats, and whether this simultaneous learning confers a survival benefit. Tetras were conditioned to the odours of largemouth bass, Micropterus salmoides, convict cichlids, Archocentrus nigrofasciatus, and comet goldfish, Carassius auratus, simultaneously, then subsequently tested 48 h later for learned recognition of each odour individually. Tetras were also tested for the recognition of yellow perch, Perca flavescens, a novel predator, to assess whether learned recognition is generalized. Tetras significantly increased antipredator behaviour when exposed to each of the conditioned predator odours and the nonpredator goldfish odour, but not to perch odour (i.e. not different from the distilled water control). These results demonstrate acquired recognition and not a generalization to novel predator odours. Subsequent staged encounters with live pumpkinseed sunfish, Lepomis gibbosus, predators showed that tetras conditioned to either sunfish odour alone or multiple odours increased survival over unconditioned tetras. These results are the first indication that prey possess the ability to learn the cues of multiple predators simultaneously, and that this multiple learning provides a survival benefit.

Effects of competitor-to-resource ratio on aggression and size variation within groups of convict cichlids

Resource defence theory predicts that the intensity of competitive aggression, degree of resource monopolization, and variation in fitness will be highest at intermediate levels of the spatial clumping of resources. We tested for this predicted dome-shaped relationship by manipulating the spatial clumping of food via competitor-to-resource ratio (CRR), the number of potential competitors divided by the number of resource units. Groups of 10 convict cichlids, Archocentrus nigrofasciatus, were allowed to compete for a fixed amount of food in one of five CRR treatments (1, 1.43, 2, 5 and 10), created by varying the number of patches in which the food appeared (i.e. 10, 7, 5, 2 and 1 patch, respectively). As predicted, both the frequency of aggression and the coefficient of variation of body mass (a measure of the consequences of food monopolization and variation in a component of fitness within groups) increased significantly as CRR increased from 1 to 2, and then decreased significantly at CRRs of 5 and 10. In addition, mean growth rate decreased in groups with high rates of aggression, suggesting an important cost of aggression. Our study provides the first quantitative support for the predicted dome-shaped relationship and suggests that CRR is a useful measure of the degree of spatial clumping of resources.

The roles of male size and female eavesdropping in divorce in the monogamous convict cichlid (Archocentrus nigrofasciatus, Cichlidae)

In this experiment we examined the roles of male size and female eavesdropping in divorce using the serially monogamous convict cichlid (Archocentrus nigrofasciatus) by testing predictions based upon the better option hypothesis of divorce. We tested the role of male size by exposing females to males that were 20-25% larger than their current mate or males that were similar size to their current mate. Female convict cichlids prefer larger males, therefore we predicted that the frequency of divorce would be higher when the alternate mate was larger than the current mate. We also examined the role of eavesdropping as a mechanism of female assessment of relative male quality. Females were either permitted to eavesdrop (males physically interacted) or females were unable to eavesdrop (males prevented from interacting). We predicted that female eavesdropping would result in greater frequency of divorce. We found that females chose divorce most often (50% ending in divorce) in the treatment where the alternate male was larger than the current mate and eavesdropping was permitted, whereas females never chose divorce in the treatment where the alternate male was similar in size to the current mate and the female was not permitted to eavesdrop. Although it had a mild effect, male size difference alone did not significantly increase divorce. When size difference was coupled with eavesdropping, however, females did significantly increase their divorce rates.

Juvenile convict cichlids (Archocentrus nigrofasciatus) allocate foraging and antipredator behaviour in response to temporal variation in predation risk

We examined the influence of temporal variation in predation risk on the foraging and antipredator behaviour of juvenile convict cichlids (Archocentrus nigrofasciatus). We exposed fish to one of four treatment regimes: 100% or 20% concentrations of conspecific alarm cue, given once or three times per day, for a period of three days. On the fourth day they were exposed to either 100% conspecific alarm cue or a control of 100% swordtail (Xiphophorus helleri) skin extract. There was no significant effect of concentration of alarm cue, fish previously exposed to the same frequency of risk responded in a similar manner regardless of the concentration of alarm cue previously experienced. Fish that were exposed to predation risk three times per day exhibited moderate intensities of antipredator behaviour during periods of risk and allocated significantly more foraging to periods of safety compared to those exposed to alarm cue once per day. These results demonstrate that temporal variation can influence the trade off between antipredator behaviour and foraging and that prey can use subthreshold cues to assess temporal variability in predation risk.

Biparental division of roles in the convict cichlid fish: influence of intruder numbers and locations

The convict cichlid fish (Archocentrus nigrofasciatus) has a parental division of roles in which the male spends much of his time defending the territory while the female remains near to the offspring. This division is not obligate because both parents do switch roles for brief periods and, in the absence of the mate, both sexes will perform all roles. We predicted that the division of roles depended on each parent being able to successfully complete its task. If a task could not be completed by a single parent, role specializations would be reduced resulting in a division of labor. That is, both parents would perform the same task. We modified the relative importance of the defensive role by changing the number and location of conspecific intruders. When we increased the number of distant intruders from one to two, we found that the division of roles was unaffected. Neither parent increased its defensive activities, although they did attack both intruders. Furthermore, when females did attack an intruder, it was usually the same intruder being attacked by the male. This too resembled pairs attacking single intruders. We concluded that, for distant intruders, both sexes seemed to invest a fixed amount in protecting the territory and the division of roles remained unchanged when intruder numbers changed. Placing one intruder near to the offspring greatly escalated the amount of time both parents spent attacking the intruder resulting in less time either parent spent near the offspring. A second intruder placed at a greater distance to the offspring was largely ignored by both parents. We believe we succeeded in modifying the division of roles by increasing the importance of one parental task and, in this way, the parental care in the convict cichlid resembled a division of labor around a single task.

Courtship in the monogamous convict cichlid; what are individuals saying to rejected and selected mates?

I examined the relation between courtship and mate choice in convict cichlids by presenting females with the option of courting and spawning with one of two males that were isolated from each other. I quantified the amount of courtship performed by females towards males they selected as mates and males they rejected, and the amount of courtship performed by each male towards the female. I measured courtship using two rates: (1) daily courtship rate, the total number of courtship events per number of days until spawning; and (2) contact courtship rate, the total number of courtship events per day per total time spent with a given individual. Females showed similar contact courtship rates to each male, whereas both types of courtship rates between females and only rejected males were significantly and positively correlated. Females showed a nonsignificant tendency to select larger males. Females spent significantly more time with the males they selected and therefore females' daily courtship rate towards selected males was significantly higher than that towards rejected males. Although females showed a preference early in their search for the male they eventually selected, they continued to spend time with, and court, the rejected male until spawning with the selected male, indicating that females continuously assess males throughout their search. Male courtship differed from female courtship in that while the daily courtship rates towards the females did not differ significantly between males, the contact courtship rate of rejected males was significantly higher than that of selected males. Thus, rejected males may court more because they know they are not the preferred male, or selected males may court less because they know they are the preferred male, or a combination of both.

Is the selection of sex-typical parental roles based on an assessment process? A test in the monogamous convict cichlid fish

In the biparental convict cichlid fish, Archocentrus nigrofasciatum, males and females both spend time defending their territory and their offspring, but the typically larger male parent spends more time defending the territory and the female spends more time with the offspring. Because size correlates with a convict cichlid's ability to win a fight, the larger male parent has a clear advantage in repelling intruders compared with his smaller female mate. We tested the hypothesis that male and female convict cichlids accept their parental roles as a result of their relative sizes, rather than inherent sex differences (e.g. females are more nurturing). We allowed pairs to form in which one member was smaller or larger than the other member, or of the same size (both small = 50–55 mm; both large = 70–75 mm), thus producing four pairing types. During the 5-day stationary larval stage, we subjected each breeding pair each day to a conspecific intruder that was either larger or smaller than one of the parents, or of the same size. Male and female parents adjusted their parental roles based on the size of their mates and/or the size of the intruder. Large parents displayed more defensive behaviour than small parents, regardless of sex. Male parents responded to increased threat (i.e. increasing intruder size) by increasing their defensive behaviour, but only until intruder size matched their own size, after which defensive effort decreased. Large female parents similarly responded to increased threat by increasing their defensive behaviour, but only to support their smaller mates (i.e. they did not independently attack the intruder). Larger females also showed a corresponding reduction in time spent near the offspring. Small males, in contrast, showed only a marginal increase in their time with the offspring. We conclude that the female has a more flexible parental role and, when her relative abilities change, she is more likely to expand her parental roles.

Interactions between patch size and predation risk affect competitive aggression and size variation in juvenile convict cichlids

We tested the predictions that the frequency of aggression, degree of resource monopolization and individual size variation within groups would decrease as patch size and predation risk increased. In a preliminary experiment, groups of 10 convict cichlids, Archocentrus nigrofasciatus, were allowed to compete for food presented in either small (20.7 cm2) or large (208.7 cm2) patches. As predicted, the frequency of aggression and size variation within groups decreased and the number of fish feeding at any particular time increased as patch size increased. In small, defensible patches, the increased aggression by dominant individuals apparently excluded some fish from the foraging patch, causing an increase in size variation within groups. In a second experiment, we manipulated patch size and perceived predation risk (addition of conspecific skin extract versus distilled water) in a 2 × 2 factorial design. There were significant interactions between the two main effects for all three dependent variables. In small patches, increasing the perceived predation risk caused a decrease in aggression and size variation within groups and an increase in the number of fish foraging at a time, whereas in large patches, increasing the perceived predation risk had no significant effect on aggression, but decreased the number of fish feeding, resulting in an increase in size variation within groups. In defensible patches, increasing perceived predation risk had the same effect as reducing the economic defensibility of the patch.

Disturbance chemical cues determine changes in spatial occupation by the convict cichlid Archocentrus nigrofasciatus

I studied the effect of disturbance chemical cues on fish that make trade-offs between foraging in an open area and remaining in a safe refuge. I used convict cichlids Archocentrus nigrofasciatus that were either visually exposed to a predator (n = 8) or exposed to water conditioned by chemical cues from disturbed conspecifics (n = 8). Fish visually exposed to a predator decreased their ingestion rate and spent more time in the refuge than in the foraging area, while fish receiving water from frightened conspecifics did not alter their ingestion rate or time spent in the refuge and foraging site, but increased their spatial occupation (i.e., motion). These results suggest that convict cichlids recognized the predator by visual cues. Moreover, disturbance cues are a form of threatening public information that may increase fish spatial occupation due to increased exploring behaviour; but is not sufficiently alarming to alter feeding or increase refuge use.

Distance to neighbours influences the trade-off between hiding after disturbance and defending food patches in convict cichlids (Archocentrus nigrofasciatus)

Territories are often aggregated. Because of this, distance to neighbours should influence how territory-holders balance safety from predators with the use and defence of resources. I examined the influence of distance to a neighbour on refuge use by pairs of convict cichlids (Archocentrus nigrofasciatus) faced with a conflict between hiding and defending food patches. Neighbours could reduce the rate of intrusions by strangers as a by-product of their own resource defence. This should allow fish with near neighbours to spend more time in the refuge. Neighbours could also steal from patches that are left undefended. This should lead to a reduction in use of the refuge. When one fish was confined to its refuge (so that its patch was undefended), theft by the other increased as inter-patch distance decreased. Distance between patches did not influence the rate of intrusion by non-territorial fish. When both fish defended patches, body mass influenced the effect of inter-patch distance on refuge use. Large fish rarely used the refuge, but small territory-holders spent more time in the refuge when patches were close together, as predicted. However, when one fish was dominant at both patches, distance between patches did not influence refuge use. These results suggest that, despite increased opportunity for theft, there is no realised foraging or defensive benefit to settling near neighbours that are of similar competitive ability.

Female convict cichlids (Archocentrus nigrofasciatus) prefer to consort with same-sized males

In the monogamous cichlid fish Archocentrus nigrofasciatus, the convict cichlid, males have been shown to prefer large females, even females larger than themselves. However, convict cichlids normally form male-larger assortative pairs, with males approximately 30% larger than their mates. We tested female preference for male body size by examining their allocation of visiting behavior (consorting) in a laboratory three way choice experiment. Females consorted most with the smallest of three available males, and the preferred males were usually closely matched in size to the choosing female. The most discriminating females exhibited greater concordance in preference than the least discriminating females. Female consorting behavior in the lab differs dramatically from that of males and female mate preferences may be similarly different from those of males.

Does size matter? Assessment and fighting in small and large size‐matched pairs of adult male convict cichlids

Contests between matched pairs of sexually mature convict cichlids Archocentrus nigrofasciatus were staged to determine if size alone affected the ways in which the males fought. Both small and large contests began with a period of visual displays. As fights progressed, displays diminished, and were replaced by more escalated behaviours. Small and large contests were also of similar duration. Despite these consistencies with sequential assessment, large and small contests were not entirely alike. For example, large males engaged in more lateral displays and were slower to escalate than small males. Small males displayed less and escalated to biting sooner than large males. Two possible explanations are suggested for these contrasts in contest structure: absolute opponent size and differences in the males’ ages coupled with differences in experience.

The Causes of Resource Monopolization: Interaction Between Resource Dispersion and Mode of Competition

AbstractThe degree of monopolization of resources is thought to be higher in groups that compete by interference than by exploitation. However, the monopolization of resources will presumably depend on (1) whether the dispersion of resources is economically defendable, and (2) whether some competitors have the ability to defend these resource distributions and hence capitalize on this potential. We tested for an interaction between the effects of temporal resource dispersion and aggressiveness on the degree of resource monopolization in a foraging system. Two species of fish differing markedly in aggressiveness (high: convict cichlids, Archocentrus nigrofasciatus; low: goldfish, Carrasius auratus) were allowed to compete intra‐specifically in groups of four for food that was either potentially defendable (arrived asynchronously) or not (arrived synchronously). As predicted, the monopolization of food, measured as the coefficient of variation of food eaten within groups, was significantly higher in the defendable than in the undefendable treatment for convict cichlids but not for goldfish. However, the monopolization of food was higher in the non‐aggressive goldfish than in the aggressive convict cichlids. Future studies should quantify and compare the monopolization in species that compete primarily via scramble competition to those that use primarily resource defence.