Dynamic eye colour as an honest signal of aggression

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordAnimal eyes are some of the most widely recognisable structures in nature. Due to their salience to predators and prey, most research has focussed on how animals hide or camouflage their eyes [1]. However, across all vertebrate Classes many species actually express brightly coloured or conspicuous eyes, suggesting they may have also evolved a signalling function. Nevertheless, perhaps due to the difficulty with experimentally manipulating eye appearance, very few species beyond humans [2] have been experimentally shown to use eyes as signals [3]. Using staged behavioural trials we show that Trinidadian guppies (Poecilia reticulata), which can rapidly change their iris colour, predominantly express conspicuous eye colouration when performing aggressive behaviours towards smaller conspecifics. We then show, using a novel visually-realistic robotic system to create a mismatch between signal and relative competitive ability, that eye colour is used to honestly signal aggressive motivation. Specifically, robotic ‘cheats’, i.e. smaller and thus less-competitive robotic fish that displayed aggressive eye colouration when defending a food patch, attracted greater food competition from larger real fish. Our study suggests that eye colour may be an under-appreciated aspect of signalling in animals, shows the utility of our new biomimetic robotic system for investigations in animal behaviour, and provides rare experimental evidence that socially-mediated costs towards low-quality individuals may maintain the honesty of dynamic colour signals.This work was supported by a research grant from the Leverhulme Trust (RPG-2015-047) awarded to D.P.C. and S.K.D. D.P.C. and S.K.D. also acknowledge funding from the Danish Council for Independent Research (DFF – 1323-00105). We are very grateful to Rajendra Mahabir for assistance in the field, to Fiona Moultrie, Joah Madden, Sam Ellis, Ashley Ward, and John Endler for valuable discussion, and to Tom Houslay for advice on the R code to generate the plots

A matador-like predator diversion strategy driven by conspicuous colouration in guppies

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordUnderstanding the adaptive function of conspicuous coloration has been a major focus of evolutionary biology for much of the last century. Although considerable progress has been made in explaining how conspicuous coloration can be used in functions as diverse as sexual and social signaling, startling predators, and advertising toxicity [1], there remain a multitude of species that display conspicuous coloration that cannot be explained by existing theory. Here we detail a new “matador-like” divertive antipredator strategy based on conspicuous coloration in Trinidadian guppies (Poecilia reticulata). Guppies encountering predatory fish rapidly enhance the conspicuousness of their eyes by blackening their irises. By pitting biomimetic robotic guppies against real predatory fish, we show this conspicuous eye coloration diverts attacks away from the guppies’ center of mass to their head. To determine the function of this seemingly counterintuitive behavior, we developed a method for simulating escape probabilities when live prey interact with ballistic attacking predators, and find this diversion effect significantly benefits black-eyed guppies because they evade capture by rapidly pivoting away from the predator once it has committed to its attack. Remarkably, this antipredator strategy reverses the commonly observed negative scaling relationship between prey size and evasive ability, with larger fish benefiting most from diverting predators. Taken together, our results introduce a new antipredator divertive strategy that may be widely used by conspicuously colored prey that rely on agility to escape their predators.Leverhulme TrustDanish Research Counci