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

Amanda C Hitchcock,Allison Robbins,Arbor Quist,Janet Jeong,Tiffany Chen,Karin Darakananda,David J Ellerby,Erin Connolly

doi:10.1242/bio.201511577

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.

Highlights

Effective predator evasion is a vital component of fitness for many animals (Husak, 2006; Miles, 2004; Walker et al, 2005; Watkins, 1996)
The goals of the current study were to quantify the extent of individual variability in fish escape behaviour, place this in context with the overall scope for behavioural variability across individuals, and determine the extent to which behavioural variation and flexibility were constrained by a trade-off between variability and mechanical performance
For the composite distribution of final angles the circular variance of 0.30 was significantly greater than in individual distributions (mean 0.23, range 0.07 to 0.39; one-sample t-test, t(14)52.71, p,0.05, Figs 1, 2). This pattern of inter-individual variation is further supported by pair-wise comparisons of stage 1 and final escape angles, where of the 105 pair-wise comparisons possible with 15 individuals, 71 detected significant differences (MardiaWatson-Wheeler, p,0.02, p adjusted with Ryan’s Q; Figs 1, 2)

Summary

Introduction

Effective predator evasion is a vital component of fitness for many animals (Husak, 2006; Miles, 2004; Walker et al, 2005; Watkins, 1996). The physical and physiological features that drive escape responses. Mechanical performance is not the only predictor of escape success: theoretical models have identified optimal strategies, in terms of the escape direction relative to a predator (Arnott et al, 1999; Domenici, 2002; Weihs and Webb, 1984); escape behaviour may be modulated in response to changing environmental factors (Domenici, 2010a); and variation in behaviour may be important to avoid predictability (Domenici et al, 2008). Behavioural variation and the scope for behavioural modulation all affect escape success and organismal fitness, the interaction of these factors is poorly understood (Wainwright et al, 2008)

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Discussion

Conclusion