Anti-predator function of eyespots and eyestripes
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-naïve
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. Further, 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 no 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.
Copperband butterflyfish with the typical eyespot pattern. It also has an "eye stripe"
running vertically through its real eye and such stripes are thought to conceal salient features such as the eye by
effectively disrupting its othewise revealing charachters. To the right: a stickleback attacking the eyespot on
an artificial prey item used in our experiments
Importance of eye mimicry for the anti-predator function of eyespots
(Ongoing project, I will reveal more about this project soon)
Background choice as an anti-predator strategy: the roles of background matching and visual complexity in the habitat choice of the least killifish (Abstract)
Because background matching improves concealment, prey animals have traditionally
been expected to prefer parts of the habitat that match their visual appearance. Yet, empirical
support for this is scarce. Moreover, this idea has recently been challenged by an alternative
hypothesis: visual complexity of the background impedes prey detection, and hence prey could
instead prefer complex parts of the habitat. We used the least killifish to test, with and without
predation threat, for the importance of the visual similarity between the fish and the background
and the level of visual complexity of the background. We observed their choice between backgrounds
patterned with elements based on the longitudinal black stripe of the fish. Predation risk was
important under some circumstances, and induced a preference for the background of matching,
horizontal stripes before the mismatching, vertical stripes. Interestingly, females under predation
threat showed a preference for the complex background of randomly-oriented and overlapping stripes
before matching stripes, whereas males did not discriminate between these two. Additionally, males
showed a preference for matching stripes before complex shapes whereas females did not discriminate
between these backgrounds. We conclude that matching is important in the choice for safe habitat,
but some aspects of visual complexity may override or act together with background-matching.
During my studies at the University of Gothenburg, I completed three theses projects:
In my first thesis I investigated whether the preference for orange color in guppies
(Poecilia reticultata) also applied on moving food objects by using coloured
daphnias (Daphnia spp.), and further I also investigated whether there was a
difference between males and females in their preference behaviour.
This was conducted in order to investigate the origin of their preference for orange colour,
i.e. whether it originated from a food context or mating context (BSc project).
I then completed a thesis on how predation risk might affect learning and memory
formation in wild caught brown trout (Salmo trutta) (MSc project).
In my third thesis project I invesigated how hunger state affected the ability
to find cryptic and conspicuous prey items in wild caught brown trout (MSc project).