Individual boldness traits influenced by temperature in male Siamese fighting fish
Introduction
Boldness or the propensity of individuals to take risks is a fundamental axis in animal behavior that has received a great deal of attention over the past decade [1], [2]. Consistent individual differences in boldness has been identified in many taxa, including mammals [3], [4], birds [5], reptiles [6], fish [7], and crustaceans [8]. The degree to which individuals display a specific behavior in a particular situation may have significant ecological and evolutionary consequences. For example, individual differences in boldness have been shown to affect migratory propensity [9], the likelihood to become dominant [10], [11], success at foraging [12], and reproductive performance [13]. However, bold behaviors may also have fitness disadvantages, such as increased exposure to predation risk, which can reduce long-term survival [14], [15].
As one of the main abiotic factors in aquatic ecosystems, temperature has immense impact on the energy budgets, growth, respiration, behavior, and locomotion performance of aquatic ectothermic species [16], [17], [18], [19]. Fish as a major group of ectothermic animals, typically experience a wide range of temperatures across days and even within days; however, growth and reproduction only take place in a more limited temperature range [16]. Given that temperature has large direct effects on metabolic rates in fish (and indeed all ectotherms), it is likely to have large effects on physiology and behavior. For example, among year increases in temperature can lead to increases in activity and risk-taking in fish, which in turn are linked to elevated predation mortality [20]. Apart from the natural environment, fluctuating temperatures could be important in laboratory conditions, particularly when the behavioral performance of individuals should be considered [8], [15], [18], [21]. Although several studies exist which examine individual responses to temperature variation, there is still relatively few and low taxonomic breadth among these studies, which limits our ability to generalize findings about the effects on animal behavior at both the population- and individual-level.
The effects of temperature on behavioral traits are poorly studied in fish in contrast to physiological endpoints (e.g. [22], [23]). In this regard, the majority of studies on temperature dependence of the behavior of fish species have focused on swimming and foraging [24], [25], [26], which are closely related to growth and survival indices. In recent years, however, there has been a rapid growth of interest in the fitness consequences of changes in temperature in a number of aquatic organisms, especially fish (e.g. personality traits in Pomacentrus moluccensis[18], risk assessment in Pomacentrus chrysurus[27], escape ability in Daphnia[28], stability of social hierarchy in Apistogramma agassizii[29], acoustic communication in Pomatoschistus pictus[30], and Trichopsis vittata[31]).
Male Siamese fighting fish (Betta splendens) are well known for being highly territorial and aggressive towards intruder conspecifics [32]. Additionally, this fish is increasing in popularity as a model species for behavioral ecology studies (e.g. [33], [34]). Specifically, it is reported that both male and female fighting fish would be consistent in their responses within and across the different types of boldness assays [35], [36], [37]. The primary aim of this study was to determine the behaviors involved in boldness of male Siamese fighting fish as a function of temperature fluctuations which may occur in laboratory studies using different complementary behavioral assays. This may be important because studies continue to ignore small temperatures fluctuations of a few degrees or less, even though it can have substantial effects on physiology and behavior [18], [23], [27], [29], [38]. For example, in studies of fish, temperature differences of 3° [39], 4° [40], and 5 °C [41] exist during experiments but were not accounted for in analysis; however, differences in temperature of 2° [38], 2.5° [23], and 3 °C [27], [29] had significant effects on physiology and/or behavior endpoints.
Here, we studied the responses of male Siamese fighting fish to a modest temperature manipulation to test for individual and mean-level effects on behavioral traits related to boldness. Importantly, we show substantial effects of temperature that are independent of any time-related changes in behavior that could potentially confound results and interpretations. As predicted, boldness related behaviors increased with temperature in the manipulation treatment (even after 10 days of acclimation), but remained constant across trials in the control.
Section snippets
Study species
Forty sexually mature male Siamese fighting fish of the veil tail strain were purchased from a local distributor. Fish were transported to the laboratory and kept individually in opaque 0.5 L plastic containers to prevent visual contact between them. Temperature of the room used for fish keeping and experimental trials was maintained continuously at 20–24 °C. To establish conditions with higher and constant temperatures, fish containers were placed into a larger water-bath; a wide, short-wall
Latency to leave area I
There was evidence of consistent individual differences in latency for individuals within both the treatment and control groups; including these two variance parameters (one among individual variance parameter for each treatment), improved model fit (χ22 = 8.7, P = 0.013) and each parameter on its own was also significant (LR test, both P < 0.02; VARtrt1 = 0.14, se = 0.097, VARtrt2 = 0.14, se = 0.99, VARresidual = 0.70, se = 0.08).
After accounting for the repeated measures, latency responses across the two
Discussion
We found a positive effect of temperature on boldness responses of male Siamese fighting fish tested in different, complementary behavioral test assays thought to reflect boldness. Male fish showed clear changes in behavior after exposure to a 4 °C higher water temperature for a limited period of 10 days. Fish reduced their latency to leave area I, and spent more time in area III when exposed to 30 °C, showing the augmentative effect of higher temperature on boldness. Trends were also towards
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgements
We are grateful to the Aquaculture Department of University of Tehran for providing us with the laboratory space to perform these experiments. This study was funded by University of Tehran (grant no. 3120227). We thank M. Jafari for his support during the experiment. Many thanks to the Editor and the anonymous reviewers for insightful comments on the manuscript.
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2019, Science of the Total EnvironmentCitation Excerpt :In addition, the scototaxis assay tests for exploratory tendency and boldness in fish, because the white compartments represent an environment where the fish lacks camouflage and is ‘exposed’ to heightened predation risk (Maximino et al., 2010; Brodin et al., 2017). In addition to predation, warmer temperatures have often been associated with increased activity and boldness in fish (e.g. Biro et al., 2010; Ojanguren and Braña, 2000; Forsatkar et al., 2016). However, this is not always the case and more recent studies have reported that elevated temperatures can actually decrease swimming speed, activity, boldness and foraging (Johansen and Jones, 2011; Nowicki et al., 2012; Colchen et al., 2017; Davies et al., 2017).