Trade-offs between performance and variability in the escape responses of bluegill sunfish (Lepomis macrochirus)

Abstract

Successful predator evasion is essential to the fitness of many animals. Variation in escape behaviour may be adaptive as it reduces predictability, enhancing escape success. High escape velocities and accelerations also increase escape success, but biomechanical factors likely constrain the behavioural range over which performance can be maximized. There may therefore be a trade-off between variation and performance during escape responses. We have used bluegill sunfish (Lepomis macrochirus) escape responses to examine this potential trade-off, determining the full repertoire of escape behaviour for individual bluegill sunfish and linking this to performance as indicated by escape velocity and acceleration. Fish escapes involve an initial C-bend of the body axis, followed by variable steering movements. These generate thrust and establish the escape direction. Directional changes during the initial C-bend were less variable than the final escape angle, and the most frequent directions were associated with high escape velocity. Significant inter-individual differences in escape angles magnified the overall variation, maintaining unpredictability from a predator perspective. Steering in the latter stages of the escape to establish the final escape trajectory also affected performance, with turns away from the stimulus associated with reduced velocity. This suggests that modulation of escape behaviour by steering may also have an associated performance cost. This has important implications for understanding the scope and control of intra- and inter-individual variation in escape behaviour and the associated costs and benefits.

Escape responses of fish: a review of the diversity in motor control, kinematics and behaviour

“…Similarly high CVs (>20%) in escape traits were found in tropical damselfish (Jornod and Roche, 2015). Despite this variability among individuals, most escape response traits show a high degree of repeatability within each individual in various species, including European seabass (Marras et al, 2011), bluegill sunfish (Hitchcock et al, 2015), tropical damselfish (Jornod and Roche, 2015) and red drum larvae (Fuiman and Cowan, 2003). High repeatability in escape response traits indicates that these traits are likely to reliably represent the expected performance level of each individual, which is subject to natural selection.…”

“…While previous work clearly shows that escape performance can vary substantially depending on the behavioural context, ecologically relevant issues regarding escape performance are the variability of performance level among individuals and the repeatability of escape performance within individuals (Box 1). The assessment of repeatability is particularly relevant from an ecological and evolutionary point of view, because it is an indicator of the extent to which escape performance traits can be shaped by selection (Hitchcock et al, 2015); trait repeatability has been suggested to set the upper limit for trait heritability (Dochtermann et al, 2015). In addition, studying the effects of various environmental stressors on the diversity of escape responses may be fundamental to our understanding of escape responses in the context of climate change (Box 2).…”

Individual variation in avian avoidance behaviours in response to repeated, simulated vehicle approach

“…We compared repeatability (r), defined as the ratio of between-individual variation (i.e., the variance across random intercepts of individuals) to that of betweenand within-individual variation (i.e., residual error; Réale et al 2007;Nakagawa and Schielzeth 2010;Dingemanse and Dochtermann 2013), for nested models via -2 log likelihood ratios and non-nested models via Akaike's information criterion corrected for small sample size (AIC c ; Burnham and Anderson 2002), which is an MLbased metric (Bolker et al 2009). Values of r that approach 1 indicate consistency of behaviour for an individual or large betweenindividual differences in a behaviour (Hitchcock et al 2015). Based on published values for r in animal responses to human disturbance (e.g., Tella 2010, 2013), we considered r to be low to moderate if ≤0.50.…”

The angular position of a refuge affects escape responses in staghorn sculpin Leptocottus armatus

“…Hence, not all C-starts look the same, since there can be many modulating factors (Domenici, 2010). In addition, considerable intra and inter-individual variation occurs in escape behaviour and performance (Hitchcock et al, 2015).…”

“…This is in line with previous work on the flexibility of escape direction, which shows that walls or obstacles can modulate escape trajectories (Eaton & Emberley, 1991;Serena et al, 2009;Mirjany et al, 2011) and that in certain predator species, the direction of fast start after stimulation can be towards the stimulus itself when this is represented by a prey fallen on the water surface (Wöhl & Schuster, 2007). Flexibility here refers to the fact that the escape responses are not stereotypic as they appear to be modulated to the presence of the refuges, rather than to intra-individual variability (Hitchcock et al, 2015), which was unassessed in this work.…”