Sexual size dimorphism and male contest in wild Siamese fighting fish

Larger males of the wild Siamese fighting fish Betta splendens were more successful in male contests. There were no differences in fighting duration among treatments. Comparing agonistic behaviour between large and small males in ±1 and ±2 S.D treatments, larger males attacked, chased and performed total agonistic behaviour more than smaller males. There were no differences between larger and smaller males concerning other agonistic behaviour during fighting. Females presented with two potential mates of different sizes did not prefer larger males.     

Intra- and interspecific social and aggressive behaviour in the Siamese fighting fish, Betta splendens

Siamese fighting fish and paradise fish were operantly conditioned to swim through a cylinder to open a door allowing them to explore visually conspecifics, non-conspecifics, or inanimate objects. All stimuli significantly elevated response levels compared to control conditions, but response rate for conspecifics was not higher than for other stimuli. In experiments 2 and 3, fighting fish threatened and attacked non-conspecifics as well as conspecifics, and using a blind procedure, displays to different fish could not be easily differentiated. A final experiment with models failed to reveal any specific shape critical to the elicitation of the threat display. Discussion considers the possibility that the operant behaviour of the fighting fish may be motivated by visual exploration as well as by aggression, and that in actual fighting the social behaviour of the opponent may be more crucial than any particular visual stimulus.     

The effects of stimulus type on consistency of responses to conflicting stimuli in Siamese fighting fish

Individuals must often decide among a range of behavioral responses in a given situation and individuals will likely vary from one another in the choices they make. A rarely explored example of this is when both a male and a female are present simultaneously and a male must decide to fight or court. Consistent individual differences have been found in decision-making in Siamese fighting fish; however, dummies were used to explore this question and it is possible that individuals respond differently in this situation when faced with live stimuli as a result of feedback. Therefore, this study investigated whether males behave similarly to dummy and live stimuli by exposing them to male and female conspecifics both simultaneously and separately. Subjects were tested first with dummies and then in the same situations using live conspecifics. It was hypothesized that males would respond in the same manner to both the dummy and live fish. The results indicated that individuals behaved similarly to the dummy fish and the live fish in corresponding conditions. In addition, repeatability levels suggest that individuals behaved similarly across trials of a given treatment type while differing from one another in their responses. This study demonstrates that males are consistent in their responses even when receiving feedback from conspecifics and supports the continued use of dummy stimuli as an effective tool.     

Instrumental conditioning of choice behavior in male Siamese fighting fish (Betta splendens)

Despite the differences in the response of male Betta splendens toward various stimuli, no research has attempted to determine the preference for a live conspecific versus a mirror presentation. A submerged T-maze was used to present both stimuli to healthy male B. splendens (N=16). The results indicated that subjects' start box and swimway latencies decreased significantly over the 30 trials. Moreover, the analysis of choices demonstrated a modest, but statistically significant, preference for the live conspecific over the mirror presentation. The results are discussed in terms of the stimuli qualities that elicit an aggressive response in B. splendens and the implications for common experimental procedures.     

Type of intruder and reproductive phase influence male territorial defence in wild-caught Siamese fighting fish

This study investigated how parental care increases with offspring age by examining the level of male aggressiveness toward potential intruders during egg guarding in a natural population of Siamese fighting fish (Betta splendens Regan). The degree of aggressiveness was measured at two reproductive phases in response to three types of intruders: male, female and females that have laid eggs. The nest-holding males became more aggressive after their eggs hatched than after the eggs were laid. Nest-holding males displayed gill cover erection, biting, tail beating and attacking at the highest rate towards male intruders, intermediate towards female intruders and the least aggressive towards females, which have laid eggs.     

Timing of presentation of an audience: aggressive priming and audience effects in male displays of Siamese fighting fish (Betta splendens)

Studies of animal communication often underestimate the presence of individuals other than the signaller-receiver dyad. Signalling interactions often occur in the presence of non-participating individuals (audiences); the effect of these individuals upon the dynamics of interactions has been called the audience effect. Recent studies of fighting fish Betta splendens have shown that the presence of a male audience can increase aggression during interactions. However, in many of these studies males were allowed to see the audience prior to the interaction, thus such pre-exposure may have facilitated aggressive behaviour (aggressive priming). Here we present results of two experiments designed to examine the relative importance of priming and audience effects on the dynamics of aggressive interactions. Males that were pre-exposed showed higher levels of aggression during subsequent interactions regardless of the presence or absence of an audience. When only one of the interactants had been pre-exposed to the audience, the non-exposed male showed similar increases in aggressive behaviour, i.e. matching the level of aggression showed by his opponent. Taken together these results suggest that aggressive priming may have resulted in an over-estimation of the audience effect in previous studies. The results still highlight the importance of social environment in determining the dynamics and outcomes of aggressive contests.     

The effect of an audience on intrasexual communication in male Siamese fighting fish, Betta splendens

The evolution of signals has mainly been considered in the contextof an emitter-receiver dyadic interaction. However, communicationusually occurs in the presence of individuals (an audience)that are not directly involved in the communication interaction,and it is more realistic to assume that signal evolution occursin a network. Several types of information could be available to an audience, and, therefore, the presence of an audiencecould have effects on the behavior of the communicating animalsand on signal evolution. We investigated whether the presenceof an audience of conspecifics affected intrasexual aggressivecommunication in male fighting fish. We found that if the audiencewas a female, males increased the intensity of conspicuous displays that can be used in communication with both males andfemales and decreased highly aggressive displays that are solelydirected to males. If the audience was a male of similar size,there was no significant change in the way in which males displayed.These results suggest that the presence of an audience couldbe one reason that many long-range and conspicuous signals are often shaped to transmit information to both males and females     

Interval timing in Siamese fighting fish (Betta splendens)

The present study evaluated the temporal performance of Siamese fighting fish (Betta splendens) given short-term exposure to four fixed interval (FI) schedules of reinforcement, FI 30, 60, 120, and 240 s, during which a reinforcer (mirror image) was given for the first response (swimming through a hoop) after the interval requirement had elapsed. Response levels were generally low early in an interval and increased as the interval elapsed; wait times and break points in an interval increased with increases in the FI requirement. The results were similar to that obtained with other species and different types of responses and reinforcers, and demonstrate that the procedure is a feasible method for studying interval timing in fish.     

Prey processing in the Siamese fighting fish (Betta splendens)

We studied prey processing in the Siamese fighting fish (Betta splendens), involving slow, easily observed head-bobbing movements, which were compared with prey processing in other aquatic feeding vertebrates. We hypothesized that head-bobbing is a unique prey-processing behaviour, which alternatively could be structurally and functionally analogous with raking in basal teleosts, or with pharyngognathy in neoteleosts. Modulation of head-bobbing was elicited by prey with different motility and toughness. Head-bobbing involved sustained mouth occlusion and pronounced cranial elevation, similar to raking. However, the hyoid and pectoral girdle were protracted, and not retracted as in both raking and pharyngognathy. High-speed videofluoroscopy of hyoid movements confirmed that head-bobbing differs from other known aquatic prey-processing behaviours. Nevertheless, head-bobbing and other prey-processing behaviours converge on a recurrent functional theme in the trophic ecology of aquatic feeding vertebrates; the use of intraoral and oropharyngeal dentition surfaces to immobilize, reduce and process relatively large, tough or motile prey. Prey processing outside the pharyngeal region has not been described for neoteleosts previously, but morphological evidence suggests that relatives of Betta might use similar processing behaviours. Thus, our results suggest that pharyngognathy did not out-compete ancestral prey-processing mechanisms completely during the evolution of neoteleosts.     

Audience effect is context dependent in Siamese fighting fish, Betta splendens

Investigations of communication networks in animals have focusedprimarily on determining whether animals extract informationfrom peripheral contests (eavesdropping) or respond to the presenceof bystanders (audience effect). The possibility that an animal'sresponse to being watched might be context dependent, however,has been explored in far less detail. This study investigatedthe influence of two contexts, exposure to audiences of differentsexes and presence or absence of a nest, on the aggressive behaviorof interacting male Siamese fighting fish, Betta splendens.Males interacted in the presence (male, female) or absence ofan audience in three different nest conditions (0, 1, or 2 nests).Audience sex and territorial status influenced aggressive behaviorin the interacting males, but a strong audience x nest interactionalso was uncovered. Males were more aggressive when neithermale had a nest and a male audience was present than when afemale or no audience was present. Males also were more aggressivewhen only one male had a nest and a male audience was presentthan when a female or no audience was present. When both maleshad nests and a male audience was present, however, males wereless aggressive than when only one male or neither male hada nest. In sum, aggressive behavior was influenced by the interactionbetween audience and nest; neither nest nor audience alone wassufficient to explain the results. Male Siamese fighting fishalter their behavior based on both external cues, the sex ofthe audience, and internal cues, reproductive state and resourcepossession. Our results emphasize the importance of consideringaspects of an animal's environment when examining audience effectsand communication networks in general.     

Reproductive state, but not testosterone, reduces immune function in male house sparrows (Passer domesticus)

The immune system requires energetic and nutritional resources to optimally defend organisms against pathogens and parasites. Because resources are typically limited, immune function may require a trade-off with other physiologically demanding activities. Here, we examined whether photoperiodically induced seasonal states (breeding, molting, or nonbreeding) affected the cutaneous immune response of captive male house sparrows (Passer domesticus). To assess immune function in these birds, we injected the mitogen phytohemagglutinin (PHA) into the patagium and measured the resulting wing web swelling. Molting and nonbreeding birds had similar immune responses to PHA injection. However, males in a breeding state showed lower immune responses than both molting and nonbreeding birds even though they did not actually breed. We tested whether this decrease in the PHA swelling response in birds in a breeding state was due to elevated plasma concentrations of testosterone (T) by administering T to birds in a nonbreeding state. Contrary to some evidence in the literature, T did not suppress the response to PHA in house sparrows. Our data show that passerine birds show seasonal modulation in immune function, even in benign environmental conditions. However, even though T is often cited as a strong immunosuppressant, it is not fully responsible for this seasonal modulation.     

The influence of sex, line, and fight experience on aggressiveness of the Siamese fighting fish in intrasexual competition

We examined the influence of sex, line, i.e., broods from different parents, and previous fight experience on the aggressiveness of the Siamese fighting fish Betta splendens in intrasexual competition. The innate aggressiveness of the fish against their mirror images was measured on the day prior to the direct fight with other individuals, and it was found to be influenced by the line type but not by the sex. In the direct fight with other individuals, the males invested more effort in the fight than the females. In addition, the individuals of a particular line that exhibited a lower innate aggressiveness spent less time in the direct fight and were often losers when compared with those of other lines. After the direct fight with other individuals, the aggressiveness of the fish against their mirror images was remarkably influenced by the outcome of the direct fight, i.e., the winners exhibited more aggressive behavior, whereas the losers exhibited a lesser degree of aggressive behavior. This influence of the previous fight experience on subsequent aggressiveness was the greatest in the individuals of the line that have exhibited the lowest innate aggressiveness. However, the positive effect of the winning experience or the negative effect of the losing experience on subsequent aggressiveness decreased following several days after the previous fight increased.     

Soft songs in male ortolan buntings are used in an aggressive context but are not an aggressive signal

Many bird species produce low‐amplitude acoustic signals that have been poorly studied in comparison with loud, broadcast songs used for mate attraction and repelling rivals. In some birds, these soft signals were found to be emitted in an antagonistic context and were the most reliable predictor of a subsequent physical attack. The function of this signal is poorly understood, and several hypotheses have been proposed to explain the mechanisms and possible functions of such low‐amplitude signals. The subject of this study is the ortolan bunting, a small passerine species that produces soft songs during territorial defence. In this study, we aim to study whether the soft songs of the ortolan bunting are a signal of increased aggressiveness by testing if they meet the context, prediction and response criteria of aggressive signals. We simulated stranger male intrusion into a focal male territory with three different playback experiments. We found no significant differences in the male responses to the taxidermic model regardless of whether they were or were not producing soft songs in response. The males responded more strongly to loud songs than to soft songs during the simulated intrusions, and the males did not treat soft songs as a predictor of conflict escalation. Although soft songs clearly appeared during territorial encounters and were not present during spontaneous singing before the intrusions, our results did not support the hypothesis that soft songs indicate aggressive character. We suggest that soft songs in the ortolan bunting are intentionally used by birds to modify their intentions or target‐specific individuals within a close range.     

The pharyngeal organ in the buccal cavity of the male Siamese fighting fish, Betta splendens, supplies mucus for building bubble nests

The male Siamese fighting fish, Betta splendens, builds a bubble nest on the water surface to care for offspring during the reproductive period. To our knowledge, this study is the first to determine the composition of the bubble nest and to compare the pharyngeal organs of male and female Siamese fighting fish to determine the relationship between the pharyngeal organ and the ability to make bubble nests. Dot blots of the bubble nest probed with periodic acid-Schiff's (PAS) staining and Ponceau S solution revealed that the contents of the nest are glycoprotein rich. Dissection of the heads of Siamese fighting fish showed that the pharyngeal organ is located in the position through which inhaled air passes. The epithelial structure of the pharyngeal organ of the Siamese fighting fish, like that of other teleosts, has numerous wrinkles and papillae. Mucous goblet cells were observed on the epithelium of pharyngeal organs in male and female fish. The pharyngeal organ was found to be larger in male than in female fish. In addition, the epithelium of the pharyngeal organ in male fish has a greater number of mucous goblet cells than that in female fish. In Siamese fighting fish, this sexual dimorphism of the pharyngeal organ suggests that the male fish secretes more glycoprotein-rich mucus to build the bubble nest. Future work will focus on the type of mucous cells found in the epithelium of the pharyngeal organ that contributes to bubble formation and will determine the components of the mucus in the bubble nest.     

Reproductive success in male sunbleak, a recent invasive fish species in the U.K.

The spawning behaviour of male nest guarding sunbleak Leucaspius delineatus , a recent invasive species in southern England, was studied and quantified for the first time. In the absence of physical differences between territorial and non‐territorial males ( i.e . colour, size, etc .), the reproductive behaviour of territorial males was analysed and related to reproductive success. The results showed that females preferred high‐courting and highly aggressive males. The initial cue in female mate choice, however, was based on courtship, while aggression was the decisive behavioural trait in influencing mate choice, providing a direct signal of physical condition and 'paternal competence'. Some males picked nest sites which were subsequently preferred by other males taking over the nest of a previous male ('communal nest'), with the new territorial male adopting the eggs already present at the nest. It appears that either due to female preference for nests already containing eggs or lower rates of sired egg predation by dilution among unrelated eggs, sunbleak males have adopted the mating strategy of allopaternal care.