Behav Ecol Sociobiol (2007) 61:525–531 DOI 10.1007/s00265-006-0280-3
ORIGINAL ARTICLE
Social influence on the correlation between behaviours in young-of-the-year perch Carin Magnhagen
Received: 3 March 2006 / Revised: 21 August 2006 / Accepted: 22 August 2006 / Published online: 24 October 2006 # Springer-Verlag 2006
Abstract The connection between risk-taking behaviour and exploratory behaviour in young-of-the-year perch (Perca fluviatilis) was studied in aquarium experiments to see whether individual behaviour patterns could be identified in this species and also to investigate how individual behaviour is influenced by their social environment. Risktaking was defined as the time spent foraging in an open area vs hiding in the vegetation in the presence of a piscivore. Explorative behaviour was measured as latency to enter a passage leading to an unknown area. Groups of four fish were used for the observations, and both behaviours measured were positively correlated with the mean scores of these behaviours in the other group members. Risk-taking and explorative behaviours were correlated only when data was adjusted for the behaviour of the other group members. Individuals that spent more time in the open than their companions also tended to be faster than the others to enter the passage to the unknown area and vice versa. The results indicate that there are consistent individual differences in boldness in perch, but also that behaviour could be modified according to the behaviour of group members. Keywords Behavioural syndromes . Boldness . Exploratory behaviour . Perca fluviatilis . Social influence
Communicated by J. Krause C. Magnhagen (*) Department of Aquaculture, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden e-mail:
[email protected]
Introduction Animals of the same species often show variation in individual behaviour patterns, and this is currently receiving an increasing attention. The terminology of this phenomenon is under debate and has been described as temperament (Reale et al. 2000), personality (Gosling 2001; Dingemanse and Reale 2005), coping style (Koolhaas et al. 1999), and behavioural syndrome (Sih et al. 2004). Suites of correlated behaviours are reflecting consistency in behaviour across different situations (Sih et al. 2004), for example, along a boldness/shyness gradient (Wilson et al. 1994). For example, the degree of boldness has been found to be consistent between different contexts in some studies (van Oers et al. 2004; Ward et al. 2004), but not in others (Coleman and Wilson 1998; Dingemanse and de Goede 2004). Boldness towards a predator can be correlated with other types of behaviour such as aggression and general activity (Huntingford 1976; Riechert and Hedrick 1993; Reale et al. 2000; Bell and Stamps 2004). In addition to a higher risk-taking (e.g., Brick and Jakobsson 2002), bolder individuals have been shown to move longer distances (Fraser et al. 2001; Dingemanse et al. 2003), have a lower propensity to congregate (Budaev 1997a; Armitage and Van Vuren 2003; Ward et al. 2004) and learn new tasks quicker (Dugatkin and Alfieri 2003; Sneddon 2003). Interspecific variation in behaviour patterns have been identified in organisms of several taxa, such as mammals (Svartberg and Forkman 2002; Armitage and VanVuren 2003), birds (Dingemanse et al. 2002; van Oers et al. 2004), and fish (e.g., Wilson et al. 1993; Magnhagen and Staffan 2005). The variation in behaviour could be influenced by genotype (Koolhaas et al. 1999; Dingemanse et al. 2002). Accordingly, heritability for different behavioural patterns has been found (Øverli et al. 2002; Drent et al. 2003;
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Fairbanks et al. 2004). Behaviour could also be shaped by phenotypic plasticity in response to environmental conditions (Wilson et al. 1993). In fish, antipredator behaviour can be modified by experience, even if genetic components may influence learning ability (reviewed by Kelley and Magurran 2003). Whether a genetic coupling of behaviour traits is a nonadaptive constraint is under debate (Dall et al. 2004; Neff and Sherman 2004; Sih et al. 2004; Bell 2005). For example, animals that are aggressive in one situation may be aggressive also in other contexts, when it seems to be highly nonadaptive (reviewed by Sih et al. 2004). Furthermore, the social environment can affect an individual’s behaviour patterns and potentially fitness, a question that few studies, so far, have addressed (but see Magnhagen and Staffan 2005; Sih and Watters 2005). In perch (Perca fluviatilis), we have earlier found individual differences in risk-taking behaviour both within and between populations (Westerberg et al. 2004; Magnhagen and Staffan 2005; Magnhagen 2006). Young perch live in shoals (Craig 2000), and therefore, we usually perform behaviour studies with groups of fish. Risk-taking, measured as the time spent foraging in the open in the presence of a predator, seemed to, to some extent, be influenced by the group composition (Magnhagen and Staffan 2005). In this study, I investigated whether measures of risk-taking and explorative behaviours were correlated in individual perch, to be able to identify consistency in boldness. I predicted that risk-taking individuals would be more prone to explore than risk-averse individuals. I also wanted to see in what way the behaviour of other group members influenced the observed behaviour patterns.
Materials and methods Young-of-the-year (YOY) perch were collected 24 August 2005 with a beach seine in the lake Stöcksjön close to the city of Umeå (63°47′ N; 20°17′ E) in northern Sweden. The fish were transported to Umeå Marine Research Centre, 45 km south of Umeå, where the experiments were performed. Before the experiments, the perch were kept in tanks (1×1×1 m) with continuously running water (17°C). They were fed daily with red chironomid larvae. The predators used were older perch, with a body length of 18–24 cm, caught in traps in the vicinity of the laboratory. In the experimental aquaria, they were mostly immobile, but were sometimes swimming slowly, and showed no overt signs of stress. The total length of the YOY perch was measured to the nearest millimeter (mm), and the weight, to the nearest 0.01 g. Mean length (±SD) was 55.0±4.1 mm and mean weight was 1.48±0.39 g. I divided the fish randomly into 16 groups with four individuals in each group. Within each
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group they were individually marked with Alcian blue dye on their caudal fin. Before being handled, the fish were always anaesthetized with metomidate hydrochloride (Aquacalm®). Risk-taking behaviour The experimental aquaria were 170-l (95×41×44 cm) and had continuously running water (17°C). The light regime was 13L:11D, similar to natural conditions. One-third of each aquarium was used for the predator, and the rest, for a group of YOY perch (Fig. 1a). A plastic net with a mesh size of 5 mm was placed between the predator’s space and the small perch. Between observations, an opaque plastic screen was placed next to the net to prevent the fish habituating to the predator. The water flowed in to the YOY perch section and out through the predator section to minimise olfactory cues. The aquaria had gravel on the bottom and artificial vegetation in the predator space and in the third of the space, for the YOY perch, that was farthest away from the predator. Before observations started, the perch were acclimated to the aquarium for 3 days and were fed daily with red chironomid larvae. I observed the fish for 3 consecutive days. Before each observation, the opaque screen was moved from its position next to the predator section so that the YOY perch were enclosed in the half of their section that also contained the vegetation. Chironomid larvae (approximately 60–65 larvae) were poured into the aquarium between the predator section and the screen that enclosed the YOY perch and were allowed to sink to the bottom, which took a few minutes. The opaque screen was then removed, making the large perch visible to the YOY perch through the net, and the observations started. The observations lasted for 10 min per aquarium, and once every minute, I noted the location, that is, in the vegetation or in the open area, of each individual perch. The order of observations of the 16 aquaria varied randomly between days. After each observation, the opaque screen was put back next to the net. Explorative behaviour After the 3 days of observations described above, I removed the piscivorous perch and released them at the site of capture. The artificial vegetation was also removed from the predator compartment. The mesh was, in each aquarium, replaced by an opaque plastic screen with a hole (9 cm diameter) in the centre, into which a transparent plastic cup (disposable beer mug) with a hole (4.5 cm in diameter) in the bottom was inserted (Fig. 1b). To enter the area that previously kept the predator, the perch would have to enter the cup and swim through it (depth, 13 cm) to reach the other side.
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Fig. 1 a Experimental setup for studying individual risk-taking behaviour, measured as number of observations (out of ten) in the open area (middle part) as opposed to in the vegetation, when the opaque screen is removed, showing the predator in the left section; b Setup for explorative behaviour. The area to the left of the screen was not visible to the fish, which was located on the right-hand side when observations started
The new screen with the passage was covered with another opaque screen as in the risk-taking study, and before observations, this screen was moved, as before, to enclose the group of perch in the vegetated area. Instead of placing the food in the open space, I poured the chironomid larvae into the area behind the screen with the passage. The covering screen was removed, and then, the behaviour of the fish was observed for 15 min. I noted the time for the individual fish to enter the cup and cross to the other side, to get a measure of the tendency to explore new structures, with the most explorative individuals having the shortest times. After the first 15 min, the remaining fish were checked for location every 15 min. Individuals who had not moved to the unknown section after 4 h were given the latency score 300 min.
observations in the open was subtracted with the mean number of the other three group members, giving a risktaking score relative to the rest of the group (residual number of observations in the open). Similarly, latency to enter the plastic cup to swim to the other side was subtracted by the mean latency of the other group members, giving an exploration score (residual time to unknown area). The data was tested for normality (Kolmogorov– Smirnov test), and when not normally distributed, it was log-transformed. Data used for statistical testing, thus, conformed to the requirements for the use of parametric tests.
Statistics
During the first 3 days of study (study of risk-taking), average number of observations in the open area varied between 3.0 and 9.7 per day (Fig. 2a; mean±SD=7.1±1.6). Over these 3 days, the number of observations in the open was significantly lower during the first compared to the
For the risk-taking study, the individual’s mean values over the 3 days of observation were used. To adjust for group influence, for each individual perch, the number of
Results
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Fig. 2 Distribution of a average number of observations in the vegetation (out of ten) per day, and b latency to enter the passage to the unknown area, pooled across aquaria
other days [(repeated measures ANOVA; F2,124 =6.3, p= 0.002, Tukey post hoc comparison of means; p
