Express yourself: bold individuals induce enhanced morphological defences

Abstract

Organisms display an impressive array of defence strategies in nature. Inducible defences (changes in morphology and/or behaviour within a prey's lifetime) allow prey to decrease vulnerability to predators and avoid unnecessary costs of expression. Many studies report considerable interindividual variation in the degree to which inducible defences are expressed, yet what underlies this variation is poorly understood. Here, we show that individuals differing in a key personality trait also differ in the magnitude of morphological defence expression. Crucian carp showing risky behaviours (bold individuals) expressed a significantly greater morphological defence response when exposed to a natural enemy when compared with shy individuals. Furthermore, we show that fish of different personality types differ in their behavioural plasticity, with shy fish exhibiting greater absolute plasticity than bold fish. Our data suggest that individuals with bold personalities may be able to compensate for their risk-prone behavioural type by expressing enhanced morphological defences.

Keywords: boldness; individual differences; inducible defence; personality trait; phenotypic plasticity; predator.

Figure 1.

(a) Relative frequency distributions of boldness scores prior to experimental treatment for trial 1 (black bars, mean = 78.6, s.d. = 170.815) and trial 2 (white bars, mean = 64.66, s.d. = 122.1), and (b) relative frequency distribution of boldness score after treatment exposure (mean = 88.1, s.d. = 202.1).

Figure 2.

Behavioural and morphological responses (mean±1 s.e.) in relative (left panel) and absolute (right, shaded panel) terms over the experimental period for bold or shy (personality) crucians held in the presence or absence of pike (predator), showing (a) change in maximum body depth, (b) change in body weight and (c) change in boldness scores.