X-RAY PHOTOGRAPHY: A MEDICAL TOOL MOVES ON TO ECOLOGY

by Whit Gibbons

January 22, 2006

Several 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.

Herpetologists 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.

A valuable 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.

An early 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.

The SREL 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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