Effect of a Dummy Audience on Male–Male Interactions in Siamese Fighting Fish, Betta splendens

Recent research on Siamese fighting fish, Betta splendens, and other taxa has demonstrated that an audience can cause males to alter their behavior in aggressive interactions. One factor not taken into account in these studies is how exactly the audience influences these interactions. It is possible that a live audience may interact with the subjects, creating an active communication network rather than a signaler–receiver dyad with a passive audience. Here, we used a dummy audience to control for information exchange between the audience and the interactants that might cause them to modify their behavior. Audience treatments included dummies of male and female B. splendens, a dummy cichlid, and a control condition with no audience present. The presence of a dummy audience did not influence male–male interactions. However, males spent the most time near the audience tank when the audience was a dummy of a B. splendens. This suggests that some factor other than the physical presence of the audience is responsible for the modification of behavior found in previous audience effect studies in Siamese fighting fish. However, we cannot rule out definitively that our dummy audience is viewed as unimportant by the opponents and, thus, ignored. Further research is necessary to determine which component of the audience is important for producing audience effects.     

Agonistic Displays and the Benefits of Fighting in the Field Cricket, Gryllus bimaculatus

Fighting is often composed of discrete agonistic displays. Few studies have partitioned fighting behavior into its component agonistic displays and evaluated the relationships between the frequency of the displays and the potential benefits of fighting, particularly mating success. In this study, we quantified the frequency of male field cricket, Gryllus bimaculatus, agonistic displays. The displays were quantified under three social environments which varied in the potential benefits of fighting: males with other males only, males with other males and female scents, and males with other males and females. We found that (1) the presence of females elicited an increase in agonistic displays characteristic of intermediate levels of escalation, (2) female scents did not produce a similar increase in the frequency of agonistic displays, and (3) in the presence of females, the frequency of agonistic displays was positively correlated with mating success. Aggressive stridulation, an energetically low-cost display, was more strongly associated with mating success than were more costly displays. The results are discussed in the context of the evolutionary theory of aggression and in the context of cricket mating systems.     

Do displays and badges function in establishing the social structure of male toad-headed lizards, Phrynocephalus vlangalii?

This study addresses several basic questions relating to the roles of badges and displays in establishing social structure in male Phrynocephalus vlangalii. Significant differences in body mass and condition were found between resident and floater males of P. vlangalii, and resident males engaged in tail curling and agonistic interactions more frequently than floater males. Frequency of tail curling was correlated negatively with body mass in floater males, but was not correlated with body mass and condition in resident males. Relative tail-tip badge size, relative belly patch size and relative tail length could significantly predict an individual’s body mass, and body condition was positively correlated with relative tail length, suggesting that resident males may establish their social dominance by communicating their body mass and condition through frequent tail curling.     

Female Preferences for Sailfin and Body Size in the Sailfin Molly, Poecilia latipinna

We tested the mating preference of female sailfin mollies (Poecilia latipinna) by presenting them with pairs of dummy males differing in: (I) sailfin and body size together (holding sailfin : body size ratio constant); (II) body size alone (holding sailfin size constant); (III) sailfin size alone (holding body size constant); and (IV) sailfin : body size ratio (holding total lateral projection area constant). Females spent more time near dummies of greater sailfin or greater body size. The preference functions based on the first three sets of stimuli showed a similar pattern: the preference between any two simultaneously presented dummies increased with the magnitude of the discrepancy in lateral projection area (LPA) between them. However, when LPA was held constant in expt (IV), neither body size, sailfin size, nor any particular dummy (i.e. any particular sailfin + body size combination) was preferred. These findings suggest that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. The sailfin may therefore have evolved as a way for males to exploit this sensory bias and appear larger to prospective mates.     

The angular orientation of the black eye-bar in Haplochromis burtoni (Cichlidae,Pisces) and its relevance to aggressivity

Summary The effect of the black eye-bar in Haplochromis burtoni on the attack rate of conspecific males was found, using dummies, to depend on the angular orientation of this bar with respect to the body axis of the fish (Figs. 1, 4): The increment in attack rate increases as the black eye-bar parallels more closely the profile of the forehead and decreases as the bar approaches an orientation perpendicular to the forehead. This is valid independent of the actual body posture of the dummy bearing the black bar as could be shown by presenting dummies in a horizontal as well as in a head downward position. However, the head-down posture itself was found to cause an extra increment in attack rate, which may be considered to be additively or multiplicatively superimposed upon the increment determined by the orientation of the eye-bar with respect to the body axis (Fig. 4).Mit Unterstützung der Deutschen Forschungsgemeinschaft im Rahmen des SFB 50.We wish to thank Ann and John Thorson for their most stimulating discussion of the paper.     

Chemoreception and the Assessment of Fighting Abilities in the Lizard Liolaemus monticola

When an individual faces the risk of a conflict, its ability to make ‘correct’ decisions is crucial to its fitness. Research on decision making has focused mainly on visual and acoustic signals, while chemical signals have received much less attention, despite their relevance for many species. Chemosignals can be detected in the absence of the signaller and, in the context of fighting risk, this property confers the advantage that the receiver can avoid agonistic interactions or, if they are unavoidable, that it can prepare itself for the conflict. I studied the behaviour of males of the lizard Liolaemus monticola in the laboratory when they were confronted with chemosignals of a potential opponent. During this ‘pre‐confrontation’ stage, I tested the following predictions: (1) lizards can derive precise information from chemosignals of conspecifics, and use this to respond with precision to the perceived risk and (2) the best predictor of the receiver behaviour, and therefore the best predictor of the risk involved in the fight, is the relative fighting ability of opponents. As a measure of fighting ability, I used body size. ‘Intruders’ were placed in the terrarium of unfamiliar ‘residents’ during the absence of the latter, and their behaviours were recorded. Simple regressions were performed between the different behavioural variables and with the body sizes of intruder and resident, and with the relative difference in body sizes of opponents. The latter was the best predictor of intruder behaviour: it was negatively correlated with behaviours associated with activity (i.e. motion time), chemoexploration (i.e. number of tongue flicks) and behaviours associated with social interactions (i.e. head bobs). These results suggest that males can process information from chemosignals and decisions made during the ‘pre‐confrontation’ stage are based on the assessment of the relative fighting abilities (i.e. relative body size) of opponents.     

Birds respond similarly to taxidermic models and live cuckoos <Emphasis Type="Italic">Cuculus canorus</Emphasis>

Stuffed birds are widely used in research for identifying effects of predators and nest parasites on bird behaviour, studying levels of aggression and the size of territories. However, the fact that these models do not move or vocalize may question the results of such studies and open them to criticism. One solution would be to determine how the results of research using stuffed dummies correlate with the response of wild animals to enemies under the same environmental conditions. In a first attempt, we examined the correlation between the intensity of mobbing of a dummy cuckoo Cuculus canorus and interactions with live cuckoos in the field during the breeding season in western Poland. A total of 39 bird species mobbed cuckoo dummies; all 39 were found to attack live cuckoos, while 24 species (61.5%) did so during experiments using a dummy. The number of individual birds involved in mobbing a dummy was positively correlated with the number of individuals attacking real cuckoos in the same areas, even when the most commonly mobbing species, the barn swallow Hirundo rustica, was excluded from the analyses. However, we did not find significant differences in frequency of mobbing behaviour depending on cuckoo behaviour described as flight or sitting, or calling rather than remaining quiet. Therefore, we conclude that the use of a dummy for studying mobbing of hosts and non-hosts of the cuckoo provide results that are similar to those made in response to the behaviour of live hosts.     

Birds at the Winter Feeder do not Recognize an Artificially Coloured Predator

It is supposed that coloration may affect the recognition of predators by prey species; nevertheless, the significance of the coloration and its particular components in the recognition process remains unknown. We presented dummies of the European sparrowhawk (Accipiter nisus) with changed body coloration, but with all other typical features preserved (body size and shape, beak, eyes, legs), to great tits (Parus major) and blue tits (Cyanistes caeruleus) visiting a winter feeder. A pigeon (Columba livia f. domestica) dummy was used as a harmless control. Neither tit species showed passive avoidance in the presence of a dummy with an artificial, violet‐white chequered coloration. They obviously did not consider such an object to be a predator despite the presence of the raptor beak, eyes and talons. Sparrowhawk dummies with the coloration completely changed (altered with those of a harmless European robin) or with the typical colour feature removed (barred pattern on the underparts) were considered to be as dangerous as the unmodified sparrowhawk. We discuss the possibility that the effect of salient raptor‐like features such as beak shape, eye coloration, and leg and talons shape overwhelmed the effect of body coloration in these cases. Birds visiting the feeder probably were able to generalize the vigilance towards the sparrowhawk to other realistically coloured dummies, but not to the non‐natural dummy.     

Relationship Between Condition,Aggression, Signaling,Courtship, and Egg Laying in the Field Cricket,Gryllus assimilis

Sexual selection theory suggests males in good condition should be more successful than males in poor condition when competing with rivals for territories and mates. Understanding how condition influences the interplay between aggression, mate attraction, and courtship displays could help explain why variation is maintained in traits that confer fitness. Using laboratory‐reared Jamaican field crickets, Gryllus assimilis, we found that fine‐scale temporal components of mate attraction signals were positively correlated with body condition (residual body mass) and body size; signaling effort was positively correlated with both body condition and fine‐scale temporal signaling components; aggression was positively correlated with signaling effort; number of eggs laid was positively correlated with female body size, male body condition and aggression. Together our correlative study suggests that variation in body condition and size may drive some of the variation in cricket mate attraction signaling and aggression. Given condition and body size are influenced by foraging ability, nutrient availability and the organism’s ability to uptake and retain these essential nutrients could explain some of the persistent variation in fitness conferring traits.     

Honesty of agonistic signalling and effects of size and motivation asymmetry in contests

Game theoretical models predict that the main function of fighting behaviour is to assess the relative fighting ability of opponents. The sequential assessment game has often been used to investigate contests, while honest signalling theory has received much less attention. With the wolf spider Hygrolycosa rubrofasciata we investigated whether male agonistic signalling can reveal honest information about fighting ability, and how size and motivation asymmetries affect male fighting behaviour. We also determined whether male–male competition affects the courtship behaviour of the males. We found that agonistic drumming activity is an honest indicator of male fighting ability, and that relative size asymmetry and motivation to fight both contribute to the fighting ability. We also found that male–male competition decreases the courtship drumming rate of subdominant males, suggesting that male–male competition limits the opportunities for female choice. We conclude that sequential assessment and honest signalling may both be used in settling contests, and that they may be used simultaneously. Received: 10 December 1998 / Received in revised form: 23 June 1999 / Accepted: 5 July 1999     

Female Preference for Male Lateral Projection Area in the Shortfin Molly, Poecilia mexicana: Evidence for a Pre-existing Bias in Sexual Selection

Sailfin molly (Poecilia latipinna) males possess a large dorsal fin (sailfin) and perform an elaborate courtship display. Females prefer to associate and mate with males of greater body and sailfin size. Evidence supports a single origin for the sailfin species complex from a shortfin ancestor. Unlike sailfin species, males of the shortfin species complex are sexually monomorphic in fin size and exhibit little or no courtship behavior. In this study, we tested the pre‐existing bias and lateral projection area (LPA) hypotheses for sexual selection by examining female mating preferences in the shortfin molly, P. mexicana. Specifically, we presented females with pairs of dummy males differing in: (1) dorsal fin and body size together (holding fin:body size ratio constant); (2) body size (holding dorsal fin size constant); (3) dorsal fin size (holding body size constant); and dorsal fin:body size ratio (holding total LPA constant). Females spent more time near dummies of greater body and dorsal fin size. The preference functions based on the first three sets of stimuli showed a similar pattern: the greater the LPA difference between paired dummies, the stronger the preference for the larger of the two. However, in the fourth experiment, neither fin size, body size, nor any particular dorsal fin + body size combination was preferred. These findings support the LPA hypothesis suggesting that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. Moreover, these data are consistent with results obtained in an identical series of experiments conducted on P. latipinna. The preference for increased male dorsal fin size/LPA by both female P. latipinna and P. mexicana supports the pre‐existing bias hypothesis. Thus, a bias for increased male LPA and consequent selection for enlarged dorsal fins may have preceded the appearance of the sailfin trait within the Molliensia lineage.     

Fights at the Dinner Table: Agonistic Behavior in Pachydiplax longipennis (Odonata: Libellulidae) at Feeding Sites

Aggressive behavior of Pachydiplax longipennis during foraging was quantified by observing focal individuals on arrays of artificial perches. Pachydiplax apparently aggressively defend, for up to several hours at a time, one or a few feeding perches. Seventeen percent of all behaviors included agonistic actions, e.g., chasing or physical contact. The frequency of interactions was correlated positively with ambient temperature, solar radiation, prey density and density of other dragonflies. Both sexes initiated and responded to intra- and interspecific aggression; intraspecific interactions were more intense, however. Males had significantly higher interaction rates and fighting success than females, and intraspecific male–male contests were particularly intense. When prey were visibly localized, contest winners commonly gained perches closer to the prey swarm, and aggressive behavior was apparently correlated with feeding opportunity. Despite the frequency of aggression, these dragonflies allocated only about 19 s, on average, to agonistic behavior during 30-min observation periods. This and other costs appear small compared to foraging benefits of occupying a favorable perch, although at a very high interaction intensity high energy costs and lower intake reduce the net energy gain.     

Influence of brood size and offspring size on parental investment in a biparental cichlid fish,Neolamprologus moorii

Both males and females ofNeolamprologus moorii, a substrate-spawning cichlid fish in Lake Tanganyika, tend their eggs and fry. In this study, the influence of brood size and fry size on parental investment of this species was examined under natural conditions. Breeding parents intensively attacked fry-eating fishes that approached their broods. The attack rate by the parents against the approaching fry-eaters was positively correlated with brood size and negatively with fry size, but was much more strongly related to brood size. This suggests that the parental decision for brood defense appeared to be primarily determined by brood size. The reason for fry size being less important in the parental decision may be that even large fry have a low survival ability on their own under the high predation pressure in the study sites.     

Body color pattern and aggressiveness related to behavioral context and light intensity in an Amazonian cichlid,Laetacara fulvipinnis Staeck & Schindler, 2007

The aim of this study was to describe agonistic interaction and color patterns relative to social status and to evaluate the effects of light on aggressiveness in Laetacara fulvipinnis. Eight agonistic events were observed: frontal display, mouth fight, nipping, chase, parallel display, threat, undulation, and flight. Four body color patterns were related to the social context. Two light levels were also tested: groups of juveniles were maintained for 15 days under low (228 ± 38.60 lx) or high (1435.92 ± 481.40 lx) light. Color pattern a was mainly observed during escalating agonistic interactions. Other patterns were exhibited during flight, rest, and attack. High light decreased the latency to fighting; increased the frequency of threats, total attacks, and flight; and destabilized the social hierarchy. These findings indicate that light intensity increases aggressiveness, interferes with the stability of hierarchies, and may result in a stressful situation with negative effects on animal welfare.     

Does Male Badge Size Signal Status in Small Island Populations of House Sparrows,Passer domesticus?

The relationship between dominance and throat badge size, body size, and body condition was examined in three small island populations of house sparrows, Passer domesticus, on the coast of northern Norway. Individual dominance rank in males was determined by observation of agonistic interactions in an artificial observation cage (one replicate in Dec. and one in Mar. in two populations and one replicate in Mar. in the third population). Previous studies had indicated that badge size signals status in house sparrows. In this study, because of the small population sizes and stability in their membership, we expected that prior information about fighting ability would reduce the importance of badge size for the outcome of conflicts in favour of traits most directly associated with fighting ability. In two of five replicates, significant relationships were found between components of body size and dominance rank, but in opposite directions. The relationship between badge size and dominance rank was consistently positive, but non-significant. In a pooled sample of the three independent replicates, badge size was the best predictor of dominance, and no other variable explained any variance in dominance. However, the coefficient of determination was low and linearity of dominance hierarchies was poor. We therefore suggest that individual recognition may influence the dominance relationships.     

Trophic level scales positively with body size in fishes

Aim The existence of a body size hierarchy across trophic connections is widely accepted anecdotally and is a basic assumption of many food‐web models. Despite a strong theoretical basis, empirical evidence has been equivocal, and in general the relationship between trophic level and body size is often found to be weak or non‐existent. Location Global (aquatic). Methods Using a global dataset for fishes ( http://www.fishbase.org ), we explored the relationship between body size and trophic position for 8361 fishes in 57 orders. Results Across all species, trophic position was positively related to maximum length (r²= 0.194, b= 0.065, P < 0.0001), meaning that a one‐level increase in trophic level was associated with an increase in maximum length by a factor of 183. On average, fishes in orders that showed significantly positive trophic level–body size relations [mean = 51.6 cm ± 11.8 (95% confidence interval, CI)] were 86 cm smaller than fishes in orders that showed no relation [mean = 137.1 cm ± 50.3 (95% CI), P < 0.01]. A separate slopes model ANCOVA revealed that maximum length and trophic level were positively correlated for 47% (27 of 57) of orders, with two more orders showing marginally non‐significant positive relations; no significant negative correlations were observed. The full model (order × body size) explained 37% of the variation between body size and trophic position (P < 0.0001). Main conclusions Our results support recent models which suggest that trophic level and body size should be positively correlated, and indicate that morphological constraints associated with gape limitation may play a stronger role in determining body size in smaller fishes. Differences among orders suggest that the nature of the trophic level–body size relation may be contingent, in part, on evolutionary history.     

Deferred agonistic behavior in a long-lived scincid lizard Eumeces laticeps

Summary A laboratory experiment with the broad-headed skink (Eumeces laticeps) involving staged agonistic encounters demonstrates that larger males have an advantage over smaller ones in agonistic bouts. Field data on head wounds produced by intraspecific fighting during the breeding season show a much higher frequency of new wounds among males over 100 mm in snout-vent-length than in smaller males. The significant difference in new-wound frequency strongly suggests avoidance of fights by the small males, which is corroborated by laboratory and field observations. Access by males to reproductively active females depends on the ability to defeat other males in aggressive contests virtually always involving head biting if the males are of nearly equal size. Because the probability of winning agonistic encounters increases with size, young males avoid fights with older males. Aggressive contests with larger males and reproductive attempts other than courtship in the absence of larger males are deferred.Aggressive behavior in E. laticeps may be employed in direct defense of females, but might also be expressed in defense of specific sites and/or territories. In the laboratory, males in their home cages were significantly more likely to win encounters with males of similar size than were males fighting in the home cages of opponents. This suggests that encounter site could be important in determining encounter outcome and that field study of possible site defense or territoriality is needed.     

Decision Making and Assessment in the Fighting Behaviour of Nannacara anomala (Cichlidae,Pisces)

Predictions from ESS-theory concerning assessment of fighting ability and decision making are tested using a cichlid fish Nannacara anomala. Pairs with a pronounced difference in weight were allowed to interact. Fight duration increased when the difference in weight between the contestants decreased and the probability of an escalation from tail-beating to mouth-wrestling also increased when the weight difference decreased. Despite the fact that weight difference very well predicts the outcome of fights in this species it was found that fishes weighing less than 50 % of the opponent engaged in fighting, which suggests that visual assessment alone provides only limited information about relative fighting ability. The possible functions of various behaviour patterns are discussed in relation to assessment and escalation.     

Evolution of egg dummies in Tanganyikan cichlid fishes: the roles of parental care and sexual selection

Sexual selection has been suggested to be an important driver of speciation in cichlid fishes of the Great Lakes of Africa, and the presence of male egg dummies is proposed to have played a key role. Here, we investigate how mouthbrooding and egg dummies have evolved in Tanganyikan cichlids, the lineage which seeded the other African radiations, with a special emphasis on the egg dummies. Using modern phylogenetic comparative analyses and a phylogeny including 86% of the 200 described species, we provide formal evidence demonstrating correlated evolution between mouthbrooding and egg dummies in Tanganyikan cichlids. These results concur with existing evidence, suggesting that egg dummies have evolved through sensory exploitation. We also demonstrate that there is a strong evolutionary correlation between the presence of egg dummies and both pre‐ and post‐copulatory sexual selection. Moreover, egg dummy evolution was contingent on the intensity of pre‐ and post‐copulatory sexual selection in Tanganyikan cichlids. In sum, our results provide evidence supporting the hypothesis of egg dummies evolving through sensory exploitation and highlight the role of sexual selection in favouring the evolution and maintenance of this trait.     

Non‐sex‐biased Dominance in a Sexually Monomorphic Electric Fish: Fight Structure and Submissive Electric Signalling

Males and females commonly compete for limited resources. When interaction costs are similar for both sexes and there are no sexual differences in resource value estimation, a non‐sex‐biased dominance is expected. Moreover, only non‐sex‐biased assessment of contenders fighting ability (Resource Holding Potential, RHP) should influence contest decisions. To test these predictions, we evaluated non‐breeding agonistic intra‐ and intersexual dyadic interactions in the weakly electric fish, Gymnotus omarorum. During the non‐breeding season, resource value is not expected to depend on individuals’ reproductive status and should thus be equal for males and females. In addition, as G. omarorum presents no sexual differences in body size, interaction costs can be considered symmetric between sexes. We confirmed that body size differences, but not individuals’ gender, is the best predictor of dominance. We correlated RHP asymmetries with contest duration and evidenced that body size but not sex influences assessment in intrasexual and intersexual encounters. All dyads tested engaged in agonistic interactions (N = 33) in which a clear dominant emerged. The analysis of conflict phases evidenced the submissive role of electric displays. Electric organ discharge (EOD) interruptions appear early in the contest as an electric hiding attempt, whereas chirps are post‐resolution signals of subordinate status. Interestingly, the decision of interrupting the EOD was also influenced by RHP asymmetries, whereas chirping activity was influenced by the intensity of the attacks received. Our results confirm that body size is the best RHP proxy in non‐breeding intra‐ and intersexual contests of this monomorphic species and demonstrated a sequential pattern of submissive signalling by means of two different electric displays.