Hiding in Plain Sight

Sometimes the best place to hide is right under everybody's nose. If you look like you are innocuous and you belong there, every so often you can get away with trouble.

Animal mimics can resemble other species with remarkable accuracy. Many of us are most familiar with harmless mimics that resemble a different species that is toxic or poisonous. These toxic or poisonous species are often brilliantly colored and showy, relying more on predators avoiding them for their bitter taste and noxious effects than their ability to hide. And the mimics permanently resemble their toxic or poisonous counterparts so the same predators avoid them too.

Interestingly, the species that the bluestriped fangblennies mimic are not toxic or poisonous. They are downright good reef citizens! So what would fangblennies get out of an ability to look like them? It turns out, bluestriped fangblennies are not such peaceful reef citizens themselves. They eat pieces of the fins, scales or mucus of other larger fish by darting out and taking a bite before the big fish can turn around and retaliate. This sneak-up-and-bitecha strategy is most effective when the larger fish is unaware of the fangblenny's presence. A fangblenny that can look like the friendliest fish on the reef would be at an advantage.

Karen Cheney from the University of Queensland in Australia has been studying the remarkable mimicry of the bluestriped fangblenny for years. In a recent study published in Behavioral Ecology, Cheney tested just how much more mischief a fangblenny can cause when disguised as a juvenile cleaner wrasse.

A juvenile cleaner wrasse is a brilliant costume for a little fish that wants to sneak up on bigger fish. Cleaner fish eat parasites from the bodies and out of the mouths of bigger fish. Despite the fact that the much smaller cleaner fish could make a meal (or at least a good snack) for the larger client fish, the big fish don't eat or show aggression towards the cleaners. In this arrangement, the cleaner fish get a meal of parasites and are exempt from being eaten themselves while the client fish get rid of a bunch of parasites. It is a win-win situation for everyone involved.

The fish on the far left is a juvenile cleaner wrasse in the act of cleaning another fish. The two fish in the middle and on the right are both bluestriped fangblennies, one in its cleaner wrasse-mimicking coloration (middle) and the other not (right). Figure from the Cheney, 2013 article in Behavioral Ecology.

It is this arrangement that bluestriped fangblennies seem to take advantage of, particularly around predators. Karen Cheney believes that the black and blue striped coloration helps bluestriped fangblennies mimic juvenile cleaner wrasse so they can cause their feeding mischief in the presence of predators. She predicted that fangblennies that are actively mimicking juvenile cleaner wrasse would be more likely to attack (and maybe take bites out of) potential predators and be more likely to attack other fish when predators are around compared to fangblennies that are not in their mimicking coloration.

Cheney swam around the reefs of Southeast Sulawesi, Indonesia, using either snorkel or SCUBA equipment, looking for bluestriped fangblennies. When she found them, she recorded whether they were in their cleaner wrasse mimic coloration or not and then observed them for 15 minutes. During that time, she recorded the number of times the fangblenny attacked another fish, the species of the fish attacked, whether the fish attacked was a known predator or not, and how many times the fangblenny was attacked by another fish. She also recorded if there was another fish present within a meter and if that fish were a predator, a cleaner wrasse, or another species.

Cheney found that fangblennies in their mimic coloration were more likely to attack predators and more likely to attack other fish with predators around than fangblennies that were not mimicking. This effect seemed to be specific to the presence of predators: fangblenny coloration did not affect the number of times they attacked a non-predator fish when no predators were around. Predators also chased fangblennies less often when they had their mimic coloration.

In the end, fangblennies that looked like a juvenile cleaner wrasse were less likely to be attacked by predators and they took advantage of this by attacking more fish (including predators) when predators were around. This shows that sometimes an animal can take more risks and cause more mischief by hiding in plain sight.

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Further reading:
Cheney, K.L. Cleaner fish coloration decreases predation risk in aggressive fangblenny mimics, Behavioral Ecology, 24(5), 1161-1165 (2013). DOI: 10.1093/beheco/art043.

Cheney, K.L., Skogh, C., Hart, N.S., and Marshall, N.J. Mimicry, colour forms and spectral sensitivity of the bluestriped fangblenny, Plagiotremus rhinorhynchos, Proceedings of the Royal Society B, 276, 1565-1573 (2009). DOI: 10.1098/rspb.2008.1819.

Image Credits:
Plagiotremus rhinorhynchos.jpg by Jenny Huang at Wikimedia Commons.

Figure 1 from the Cheney, 2013 article in Behavioral Ecology