Colour vision and response bias in a coral reef fish

Abstract

SUMMARYAnimals use coloured signals for a variety of communication purposes, including to attract potential mates, recognize individuals, defend territories and warn predators of secondary defences (aposematism). To understand the mechanisms that drive the evolution and design of such visual signals, it is important to understand the visual systems and potential response biases of signal receivers. Here, we provide raw data on the spectral capabilities of a coral reef fish, the Picasso triggerfish Rhinecanthus aculeatus, which is potentially trichromatic with three cone sensitivities of 413nm (single cone), 480nm (double cone, medium sensitivity) and 528nm (double cone, long sensitivity), and a rod sensitivity of 498nm. The ocular media have a 50% transmission cut off at 405nm. Behavioural experiments confirmed colour vision over their spectral range; triggerfish were significantly more likely to choose coloured stimuli over grey distractors, irrespective of luminance. We then examined whether response biases existed towards coloured and patterned stimuli to provide insight into how visual signals -in particular, aposematic colouration -may evolve. Triggerfish showed a preferential foraging response bias to red and green stimuli, in contrast to blue and yellow, irrespective of pattern. There was no response bias to patterned over monochromatic non-patterned stimuli. A foraging response bias towards red in fish differs from that of avian predators, who often avoid red food items. Red is frequently associated with warning colouration in terrestrial environments (ladybirds, snakes, frogs), whilst blue is used in aquatic environments (blueringed octopus, nudibranchs); whether the design of warning (aposematic) displays is a cause or consequence of response biases is unclear.Supplementary material available online at

Dietary carotenoids and the complex role of redness in the behavior of the firemouth cichlid Thorichthys meeki.

“…The capability of animals to perceive color can vary even within species, and some researchers have recently begun accounting for this phenomenon when conducting behavioral analyses (Cheney et al, 2013;Johnson et al, 2013). In vertebrates, variation in color vision at the individual level (Toomey & McGraw, 2012) can result from differences in carotenoids deposited in intraocular filters such as the lens, cornea or oil droplets ( Heinermann, 1984;Bowmaker, 2008;Toomey et al, 2011).…”

“…An attraction to red items could increase foraging efficiency, as well as enable individuals to quickly identify intruding neighbors or potential mates. Innate preferences for specific traits have been examined across various behaviors such as mate choice (Basolo, 1990;Fuller et al, 2005), foraging (Cheney et al, 2013), and predator avoidance (Bruce et al, 2001). Recent studies have also examined the visual properties of their focal species as a parameter of exploring their sensory bias.…”

“…Recent studies have also examined the visual properties of their focal species as a parameter of exploring their sensory bias. For example, Cheney et al (2013) explored response biases in the Picasso triggerfish. While they possessed a priori knowledge of the spectral sensitivity of their study organism, they were able to behaviorally confirm their ability to view color within the expected ranges.…”

“…Furthermore they were able to use this information to determine that these triggerfish were innately attracted to red and green stimuli. While a natural red preference has been documented in other species (Hill, 1991;Ryan & Keddy-Hector, 1992;Rodd et al, 2002;Cheney et al, 2013), it has yet to be examined in T. meeki, even though they have been documented as an honest signal in this species (Evans & Norris, 1996).…”

“…It is ideal for researchers to possess a priori information on the spectral sensitivity of their study organism (Cheney et al, 2013) before conducting behavioral trials, but the visual system of T. meeki has not been examined. Moreover, no studies to my knowledge examined whether carotenoids play a role in their color vision.…”