Magazine article Science News

Famine Reveals Incredible Shrinking Iguanas

Magazine article Science News

Famine Reveals Incredible Shrinking Iguanas

Article excerpt

Marine iguanas in the Galapagos Islands are the first vertebrates shown to shorten and then regrow, say researchers in the United States and Germany.

The seagoing reptiles shrank by as much as 20 percent during a 2-year food shortage inflicted by El Nino, says Martin Wikelski of the University of Illinois at Urbana-Champaign. In the Jan. 6 NATURE, he and Corinna Thom of the University of Wurzburg in Germany describe observations of some 6,000 Amblyrhynchus cristatus during four El Ninos. They report reversible shortening in more than 100 individuals.

People certainly shrink as aging bones lose calcium, and doctors would love to reverse this symptom of osteoporosis. Iguanas might hold that secret, according to Wikelski. The size of the reptilian changes that he observed requires that the bones themselves shrink and then lengthen, he calculates. If connective tissue alone shriveled, the animals could shorten only by about 10 percent.

He first dismissed the apparent shrinkage as goofs in measurement. "We didn't believe our own data for 18 years," Wikelski says. He reconsidered his position when the researchers noticed that the length decreases correlated with El Ninos, ocean warmings that thin out marine algal beds where the iguanas swim and graze. Moreover, the length of some iguanas' bodies, the herpetologists' traditional "snout-to-vent length," dropped as much as 6.8 centimeters. "That is way beyond any measurement error," Wikelski claims.

The risk of error has stymied other researchers who have wondered whether animals shrink, according to Judy Stamps of the University of California, Davis. She recalls data on lizards and salamanders that seemed to suggest shrinkage. "Most people have seen it, and most people have ignored it as a measurement mistake," she says. However, the iguana changes look too big to ignore, she adds.

Ken Nagy of the University of California, Los Angeles echoes Stamps. …

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