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Why Do Butterflyfish Have Spots?

Scientists study evolution of butterflyfish coloration to debunk notion that spots deter predators.

February 21, 2013

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Naso literatus

Chelmon rostratus. Photo by Scott W. Michael

Why do some coral reef fish have dazzling color patterns while others are rather drab? While some have speculated that the striking colors are to entice potential mates, others say the varying color patterns are designed to confuse or even ward off potential predators. To get a gauge on how color patterns evolved on certain fishes, scientists Jennifer L. Kelley (The University of Western Australia), John L. Fitzpatrick (University of Manchester, UK), and Sami Merilaita (Abo Akademi University, Finland) conducted a comparative analysis of  butterflyfish (of the family Chaetodontidae), and their varying color pattern diversity. They tested whether the spots and eye spots on 95 species of butterflyfish have evolved characteristics that have been claimed in the past to serve as defense mechanisms. They also attempted to find out if these spots and stripes are related to a fish's body length, dietary needs, habitat diversity and social behavior.
 
The scientists used phylogentic data that showed the evolutionary relationships among species from original research published by Prof. David Bellwood at James Cook University. They then used fish guide books, original research papers and online resources to collect data on butterflyfish color patterns and ecology. Using that data, they found little support that spots or eyespots provide protection from predators.


Click here to read about the pennant butterflyfish, which is also called the poor man's Moorish idol.

Check out the article on butterflyflish and coral compatibility here.


They conclude that the spots and eye spots have appeared only recently in butterflyfish evolution and are "evolutionarily labile," meaning that these spots probably didn't play any significant role in the evolution of these fish. They did find that striped body patterns on butterflyfish did show a correlated evolution of these fish with regard to habitat type, sociality and dietary complexity. They also found that butterflyfish that had spots and eyespots always had stripes, which they found to obscure the fish's eye, and may divert a potential predator's attention away from the actual eye and toward the spot or eyespot. The scientists also concluded that butterflyfish found in shoals had fewer stripes, and those butterflyfish that had more varied diets had more stripes.

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