Unusual Cavefish Navigate in Darkness by the Teeth on Their Skin


COLLEGE PARK, Md., Sept. 20, 2012 (GLOBE NEWSWIRE) -- In a single cave in Ecuador, a species of cavefish has evolved to do something perhaps unique to them, navigate with their teeth.

The sensory use of these teeth, which are not in their mouths, but protrude from their skin, appears to be a previously unknown evolutionary phenomenon, one that may not exist anywhere outside this one cave, say researchers at the University of Maryland, National Institutes of Health and Pontificia Universidad Católica del Ecuador who brought to light this fascinating new adaptation to life in dark, swiftly flowing waters.

Many fish have such skin teeth (denticles), which are surrounded by dentine and capped in enamel, but most use them for cutting, protection or to reduce drag when swimming. Astroblepus pholeter, the catfish that lives in this Ecuadorian cave, developed a new use: sensing their world. University of Maryland assistant professor Daphne Soares and her colleagues found that the skin teeth of these fish evolved into environment-sensing tools, projecting hydrodynamic images that allow them to feel their way in darkness and fast currents. The teams findings were recently published in Current Biology.

"We have now a whole new sensory organ to examine when we find new species," said Soares, who works in the biology department of the University of Maryland College of Computer, Mathematical and Natural Sciences. "More importantly, we found a new way in which evolution has allowed animals to live in this challenging environment. It's not only completely dark but the world around them is also flowing fast."

Fish usually sense water flow with neuromasts, small organs in their lateral lines that share characteristics with the human ear. Most cavefish have an enlarged neuromast system to adapt to life in darkness but the A. pholeter has next to none. Instead, their skin teeth connect to the mechanosensory part of the brain, allowing them to detect the direction of water flow and the distance from the bottom as the currents deflect their teeth, the study found. The researchers observed that fish with their denticles removed could not orient in flowing water or cling to rocks along the bottom.

The fast, turbulent water where the A. pholeter live may be why their skin teeth evolved as they did, Soares believes. The current may be too strong for the neuromast system to develop as it may have. "Think of trying to hear someone talking in a rock concert--the background noise is too high," she explained.

One hypothesis is that fish live in strong currents on the surface, but there they also have eyes. Denticles are stiffer and likely less sensitive, like wearing foam ear plugs to hear the really loud band, said Soares, whose previous research includes the discovery of a major sensory ability in alligators, published in the May 2002 issue of the Journal Nature.

"We expect that the mechanosensory nature of denticles highlighted in this extreme species will uncover a widespread sensory role for these structures in other animals," Soares and her coauthors conclude in their new study.

By the teeth of their skin, cavefish find their way, Current Biology, Volume 22, Issue 16, R629-R630, 21 August 2012: Gal Haspel, NIH;, Adina Schwartz , UMD; Amy Streets, UMD;, Daniel Escobar Camacho, Universidad Católica del Ecuador; and Corresponding Author Daphne Soares, UMD. http://www.cell.com/current-biology/abstract/S0960-9822%2812%2900711-7

Contacts:

Daphne Soares, University of Maryland Assistant Professor, 301 405 8413, daph@umd.edu

or

Lee Tune, University Communications, 301 405 4679, ltune@umd.edu

301-405-4679

ltune@umd.edu

About the University of Maryland

The University of Maryland is the state's flagship university and one of the nation's preeminent public research universities. Ranked among the top 20 public universities by U.S. News & World Report for 11 straight years, it has 25 undergraduate and graduate programs in the top 10 and 72 in the top 25. The Institute of Higher Education (Jiao Tong University, Shanghai), which ranks the world's top universities based on research, puts Maryland at No. 38 in the world and No. 13 among U.S. public universities. For the fourth consecutive year, the University of Maryland ranked in the top 10 of Kiplinger's Personal Finance magazine's list of Best Values in Public Colleges for 2011-12.The university has produced six Nobel laureates, seven Pulitzer Prize winners, more than 40 members of the national academies and scores of Fulbright scholars.  The university is recognized for its diversity, with underrepresented students comprising one-third of the student population. For more information about the University of Maryland, visit www.umd.edu.

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The following pictures are available for download:

[Image] Skin teeth (denticles) protrude from the skin of Ecudarian cavefish Astroblepus pholeter.
[Image] Ecuadorian cavefish Astroblepus pholeter. Image Credit: Daphne Soares, University of Maryland
[Image] Cave in Ecuador where UMD scientists found cavefish that navigate with their teeth.

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