of the larger iguanas, Amblyrhynchus cristatus is the only
iguana that depends on a marine environment, diving for algae.
This one is roughly one foot long from snout to anus. (Martin
Wikelski/University of Illinois)
When at least one species of iguana goes hungry, it doesnt
just become skinny. It gets shorter, too.
Much to his
surprise, a biologist has found that in times of El Niño-induced
famine, iguanas in the Galápagos Islands shrink in length
then regrow when food becomes plentiful again.
reported in this weeks issue of the journal Nature, is the
first of a shrinking adult vertebrate animal.
really believed it, and we didnt know what to do about it,
says Martin Wikelski, the articles lead author. You
think its a measurement error.
when biologists found data indicating a shrinking animal, they
generally fudged the growth rate to zero.
in waters around the Galápagos Islands, located off Ecuador,
rise considerably during El Niño years, changing the ecological
balance. ABCNEWS.com/Magellan Geographix)
its sort of a dogma [that they dont shrink],
says Wikelski, who says he believes closer observations will reveal
other shrinking animals.
Wikelski, a professor at of ecology, ethology and evolution at
University of Illinois at Urbana-Champaign, has been flipping
over Galápagos marine iguanas, stretching them out on their
backs and measuring their snout-to-anus length. By branding the
iguanas, Wikelski tracks individuals through many years.
On one island,
iguanas grew up to 16 inches long not including their tails
and 7½ pounds. When the warm waters of the 1997-98
El Niño arrived, the red and green algae the iguanas eat
disappeared. In those two years, some of the iguanas shed more
than one-third of their weight and shrank in length by
up to 20 percent.
male and female pair of Galápagos marine iguanas. (Martin
Wikelski/University of Illinois)
the equivalent of a hungry Shaquille ONeal dwindling from
7 foot 1 to 5 foot 8.
Ones Own Skeleton
way beyond any measurement error, Wikelski says.
also too much to be explained by the shrinking of just cartilage
and connective tissue. Wikelski hypothesizes the iguanas literally
digest part of their bones. Were not entirely sure
about the mechanism yet, he says.
miniaturized iguanas forage more efficiently, Wikelski says, and
the smaller size also allows the cold-blooded lizards to be warmed
more easily by the sun. The animals that are most prone
to starvation are the large animals, he says.
El Niño goes away and the algae return, the iguanas grow
again. In times when food is bountiful, being the big lizard on
the island is an advantage.
They fight for territories, Wikelski says. Those that
are largest get those territories more easily. Its a reproductive
advantage. You want to be the largest one during the non-El Niño
years, and then you want to be the smallest one during the El Niño
puzzle out how the iguanas do their shrinking trick, Wikelski will bring
along a portable X-ray machine during his next trip to the Galápagos
And if the
iguanas look any bigger or smaller than the last time he saw them, hell
know it isnt just an illusion.
Wikelski is now teaching at Princeton. Check his website
for information on current projects and publications.
more information on Galápagos iguanas
shrink to survive on less food resulting from weather change - UIUC
Dragons of the Galápagos - Martin Wikelski
Galápagos Marine Iguana:.a model system for the evolution of body
size - Martin Wikelski
Iguanas - Cornell University
Spill Starves Iguanas: Ecologist Sues
iguanas: The first known animals with backbones that grow shorter when
food is scarce
This article from WorldBookOnline has links to lots of related information
- great site for students researching material for school projects.