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.     

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.     

Mate Choice and Spawning Success in the Fighting Fish Betta splendens: the Importance of Body Size, Display Behavior and Nest Size

Courtship displays should be exaggerated enough to attract mates and yet tempered so as not to deter them. We tested this hypothesis in the fighting fish Betta splendens by studying courtship displays and body size and their relationships with male parental quality and female fecundity, as well as the effects of display behavior and body size on mate choice decisions and spawning success. Because of their high degree of parental investment, males are expected to be discriminating in their choice of mates. Males who displayed more frequently built larger nests, a measure of parental quality, but larger males did not. When females were paired with males with high display rates, however, the pair had fewer eggs in their nest, even when accounting for female body mass. In a mate choice test using computer‐generated male stimuli that differed only in display behavior, females showed no preferences for displaying males vs. non‐displaying males, or for males with higher display rates vs. lower display rates. In similar tests in which the computer‐generated males differed only in size, females preferred larger males, but also preferred males that differed with respect to body size (negative assortative mating). Males preferred computer‐generated females that performed courtship displays over non‐displaying females, but showed no preferences for female body size. Neither a female's body size nor her display behavior was a significant predictor of her fecundity as estimated by the number of eggs released during spawning. Thus, our results suggest that female B. splendens must balance male parental quality (nest size) with the risk of potentially disruptive or dangerous behavior during spawning, and that females may minimize these risks through negative size‐assortative mating. Female display behavior, while unrelated to fecundity in our study, may attract males because it indicates reproductive readiness or serves a species‐recognition function.     

Fish on Prozac: a simple, noninvasive physiology laboratory investigating the mechanisms of aggressive behavior in Betta splendens

The neuromodulator serotonin is an important regulator of aggressive behavior in vertebrates. Experimentally increasing synaptic levels of serotonin with fluoxetine, a selective serotonin reuptake inhibitor, has been shown to reliably decrease the expression of aggressive behavior. Here, we describe a method by which fluoxetine can be noninvasively administered to male Betta splendens (an attractive model for the study of aggressive behavior) and describe a simple laboratory exercise that allows students to experimentally investigate the physiological mechanisms of aggressive behavior. We demonstrate that relatively short-term exposure (3 h) of male bettas to as little as 3 microg/ml of fluoxetine-treated aquarium water is sufficient to reduce the expression of specific aggressive behaviors. We emphasize the physiological concepts that can be addressed with this exercise, including the role of the serotonergic system in regulating aggression, and the interplay of environmental contaminants and physiology in regulating the expression of behavior. We also highlight important aspects of experimental design. This exercise can be flexibly altered to accommodate one or several laboratory periods. It is also low cost, is low impact to the animals, and requires minimal preparation time for instructors.