Ecology shapes the evolutionary trade‐off between predator avoidance and defence in coral reef butterflyfishes

Abstract

Antipredator defensive traits are thought to trade-off evolutionarily with traits that facilitate predator avoidance. However, complexity and scale have precluded tests of this prediction in many groups, including fishes. Using a macroevolutionary approach, we test this prediction in butterflyfishes, an iconic group of coral reef inhabitants with diverse social behaviours, foraging strategies and antipredator adaptations. We find that several antipredator traits have evolved adaptively, dependent primarily on foraging strategy. We identify a previously unrecognised axis of diversity in butterflyfishes where species with robust morphological defences have riskier foraging strategies and lack sociality, while species with reduced morphological defences feed in familiar territories, have adaptations for quick escapes and benefit from the vigilance provided by sociality. Furthermore, we find evidence for the constrained evolution of fin spines among species that graze solely on corals, highlighting the importance of corals, as both prey and structural refuge, in shaping fish morphology.

A meta‐analysis of fish behavioural reaction to underwater human presence

“…Shoaling and habitat preferences were recently recognized as two major ecological traits that balance the evolutionary trade‐offs in antipredator morphological adaptations in fishes (Hodge et al, ). Here, we also show that shoaling behaviour is of primary importance to explain the strength of the relationship between individual body size and FID, while habitat preference is a relatively minor factor in explaining this relationship.…”

“…Therefore, even if vigilance adds just a small contribution to survival, during an individual's life span, it becomes quite important, contributing to safety perception (Dehn, ). Solitary or paired species often rely on morphological defences, such as seen in butterflyfishes (Hodge et al, ). Hence, it is likely that regardless of their size, solitary species evolved a number of morphological adaptations that shoaling species lack, to compensate for predatory threats and the lack of “many eyes” to detect them.…”

“…The positive relationship between body size and FID has been reported in birds (Møller, Samia, Weston, Guay, & Blumstein, 2014;Møller, Stokke, & Samia, 2015;Samia, Nakagawa, et al, 2015a) and lizards (Samia et al, 2016), particularly in unexploited or undisturbed populations (Samia, Nakagawa, et al, 2015a). Yet it is important to realize that predator avoidance strategy is highly species-specific (Domenici, 2010;Hodge et al, 2018), and while fish size is a reasonably good predictor of FID, various confounding factors can influence escape abilities. While experience accumulated with age (i.e.…”

Colour pattern divergence in reef fish species is rapid and driven by both range overlap and symmetry

“…Interestingly, defensive morphological traits in chaetodontids, like the dorsal and anal fin spines, have been show to follow axes driven by their pairing tendency and foraging strategies (Hodge et al . ). It appears that colour patterns may be reflecting a similar relationship.…”

“…Together, the use of these specific colours, and the strength of social/territorial structure, puts the divergence of these signals into perspective. Interestingly, defensive morphological traits in chaetodontids, like the dorsal and anal fin spines, have been show to follow axes driven by their pairing tendency and foraging strategies (Hodge et al 2018). It appears that colour patterns may be reflecting a similar relationship.…”