In the animal kingdom it pays to look more dangerous and less tasty. It also helps if harmful species resemble one another so that predators might "learn" more easily to avoid both.

A new example of this form of mimicry has been discovered among catfish that live in the Amazonian basin, where a school of spiny, armored catfish (from the subfamily Corydoradinae) might contain three distinct species. The findings were described online January 5 in Nature (Scientific American is part of Nature Publishing Group).

"This research highlights the hidden diversity and complexity found within neotropical freshwater ecosystems," Martin Taylor, of Bangor University's Environment Centre Wales and co-author of the new study, said in a prepared statement. In addition to this semi-hidden biodiversity, species that were of closer genetic relation but lived farther apart had developed different patterning to look more like other local species. These details suggest not only convergent evolution, but also another selective force acting on the fish species.

The trouble with this sort of mimicry, first described by Fritz Müller in the 19th century, is that if co-benefiting mimics are competing for the same resources, the shared habitat loses some of its luster. For these Amazonian catfish, however, the researchers discovered that even though the fish swam the same waters, similar-looking species had slightly different lifestyles.

"Although appearing identical in terms of color pattern, our in-depth assessments of genetic relationships, diet, body shape and color patterns of the fish revealed that 92 percent of the communities we sampled comprised species that do not compete for resources," Markos Alexandrou, also of Bangor University and co-author of the study, said in a prepared statement. And as James Mallet and Kanchon Dasmahapatra, both of University College London, pointed out in an essay accompanying the new study in the same issue of Nature, "closely related catfish, by contrast, are usually similar in terms of snout morphology and diet, and tend not to be co-mimics," Mallet and Dasmahapatra noted in their essay.

In addition to highlighting additional biodiversity in the threatened Amazonian region, the new analysis also demonstrates how "mimicry is still contributing fundamental ideas to ecological and evolutionary biology, 150 years after its discovery," concluded Mallet and Dasmahapatra.

Image of Corydoras haraldshultzi courtesy of Martin Taylor; image of two different catfish species (Corydoras sp. C68 and Corydoras maculifer) courtesy of Markos Alexandrou