Eyespots divert attacks by fish

Abstract

Eyespots (colour patterns consisting of concentric rings) are found in a wide range of animal taxa and are often assumed to have an anti-predator function. Previous experiments have found strong evidence for an intimidating effect of eyespots against passerine birds. Some eyespots have been suggested to increase prey survival by diverting attacks towards less vital body parts or a direction that would facilitate escape. While eyespots in aquatic environments are widespread, their function is extremely understudied. Therefore, we investigated the protective function of eyespots against attacking fish. We used artificial prey and predator-naive three-spined sticklebacks (Gasterosteus aculeatus) as predators to test both the diversion (deflection) and the intimidation hypothesis. Interestingly, our results showed that eyespots smaller than the fish' own eye very effectively draw the attacks of the fish towards them. Furthermore, our experiment also showed that this was not due to the conspicuousness of the eyespot, because attack latency did not differ between prey items with and without eyespots. We found little support for an intimidating effect by larger eyespots. Even though also other markings might misdirect attacks, we can conclude that the misdirecting function may have played an important role in the evolution of eyespots in aquatic environments.

Keywords: deflection; diversion; eyespot; intimidation; predation; prey coloration.

Figure 1.

Schematic figure of the experimental aquarium. The fish was initially put in the SZ, separated by an opaque divider from the MZ and FZ. PS is the prey search area where the artificial prey item was placed.

Figure 2.

The prey items and backgrounds used in the diversion and detectability experiment (upper row), and intimidation experiment (lower row). (a) Prey type, (b) shape and (c) samples of the backgrounds are shown. Placement of the eyespot in the intimidation experiment is indicated by a circle on the folded white prey.

Figure 3.

The number of attacks directed towards the eyespot side (black bars), and towards the spotless side (white bars) in trials 1–4 of the diversion experiment.

Figure 4.

Attack times in experiment 1a and 1b. Points show the median attack latency (in seconds) in trials 1–4 of the diversion experiment (circles) and the detectability experiment (squares). Whiskers indicate the interquartile range.

Figure 5.

Attack times in the intimidation experiment. The points show the median attack latency (in seconds) for fish in the eyespot group (circles) and the spotless prey group (squares) in trials 1–4. Whiskers indicate the interquartile range.