PHOTOGRAPHY: A MEDICAL TOOL MOVES ON TO ECOLOGY
by Whit Gibbons
January 22, 2006
years ago Judy Greene of the University of Georgia’s Savannah River
Ecology Laboratory (SREL) took a turtle to a nearby medical facility and
asked the staff to X-ray the animal. The turtle was not sick and did not
have a broken shell or bones. But that turtle’s X-ray photograph
had far-reaching, invaluable consequences for ecological research because
the X-ray clearly showed that the turtle was carrying eggs. X ray photography
had been used as a tool in human medicine for decades, and because of
that photograph X rays are used worldwide today to reveal highly interesting
phenomena about animals other than humans in fields other than medicine.
The animals are primarily reptiles; the fields are ecology and biology.
who study the ecology of snakes, alligators, lizards, and turtles sometimes
need information on their internal characteristics. In examination of
the "hard parts" of an organism (e.g., bones, eggs, hard stomach
contents), X-ray photography can be a useful technique. X-ray photons
are absorbed by hard, dense material like bone, and structures appear
as bright areas on the X-ray film (the radiograph). Radiographs enable
ecologists to gather pertinent data, then return the animal unharmed to
its original capture location.
feature of the X-ray technique is that the number of eggs in egg laying
reptiles can be determined from one year to the next because none need
be killed for dissection. Thus, in field studies live specimens can be
examined and released without harming them or affecting the integrity
of the population being studied. The field of ecology, not to mention
the reptiles themselves, has benefited greatly from the use of this nondestructive
sampling method by scientists who study reproduction. The advantage of
preserving individuals of rare or endangered species is particularly obvious.
For example, the reptile X-ray technique developed at SREL was eventually
used in research on an internationally endangered, one of a kind reptile
from New Zealand known as the tuatara. Because of the use of radiography,
none of the lizard looking creatures had to be dissected, and a study
to determine how many eggs a female laid added to the limited information
on reproduction in the species.
concern was whether X-rays harm the animals. In a series of experiments,
turtle eggs were X-rayed and compared to some that were not. No evidence
whatsoever of mortality or mutational effects on baby turtles was found.
Reptiles, particularly turtles, are among the least sensitive animals
in the world to radiation effects. And the brief exposure to radiation
is apparently inconsequential to a developing turtle embryo. A similar
study was done a few years ago on the eggs of tuataras, with the same
results. The effect of X-rays on a mother turtle or tuatara is more difficult
to determine, but SREL studies have kept track of frequently X-rayed female
turtles and they have continued to lay eggs year after year for decades
with no noticeable effects.
X-ray files include photographs of hundreds of turtles and thousands of
eggs. Also, in the files are X-ray photographs showing the number of eggs
in many snakes of the region. Bobby Kennamer of SREL has used the X-ray
technique to examine the eggs of birds, the unusual feature of his study
being that the eggs are inside rat snakes that have eaten them. Bobby
has been collecting data on the ecology of wood ducks for more than 20
years, capturing a total of around 200 rat snakes in the process to determine
how many wood duck eggs rat snakes eat each year. Rat snakes can get more
than seven feet long and one that was X-rayed had 11 wood duck eggs in
it. In another study, X-rays revealed a dozen eggs in a female eastern
kingsnake that were much smaller than duck eggs. Researchers discovered
that the snake held two kinds of eggs--a half dozen turtle eggs it had
eaten and another half dozen eggs of her own she would be laying.
Though some animals continue to be sacrificed in the course of ecological
research, today's ecologists avoid doing so whenever possible. X-ray technology
permits ecologists to conduct research while proceeding in the spirit
of modern day efforts to preserve natural populations of animals.
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