By Barbara Cloud
In mythic lore, the dragon is a huge, ferocious, terrifying creature. In real life, the dragon is a huge, ferocious, terrifying creature.
And if you didn't believe there was a real-life dragon, you haven't met Varanus komodoensis, the Komodo dragon, a beast that may not actually breathe fire, but that otherwise lives up to its "dragonian" reputation.
"Komodo dragons thoroughly enjoy eating people," says Carl Reiber, a physiologist in UNLV's department of biological sciences who studies the world's largest lizards. "They are predators, bar none. They tend not to be able to eat full-grown adults, but there are numerous occasions reported when these animals have attacked children."
Komodos, which are found in nature on the hilly island of Komodo in Indonesia, stalk and ambush their prey- usually goats, sheep, and other small animals, but sometimes humans.
"They don't usually take them down immediately; it's not like a lion that stalks his prey and grabs it by the throat, suffocating it or destroying blood vessels so that it bleeds to death. Komodos bite their victims, and these animals have foul mouths. They have a bacterial and fungal population in their mouths that is absolutely horrible." So when a Komodo bites its prey, it infects the animal, rendering it greatly weakened within 24 hours.
"All this time the animal has been running around, and the Komodo is following, tracking him, ready to move in when he drops."
Despite the dragon's colorful-albeit anti-social-style, Reiber, who has been studying the endangered reptile for the past three years, is more interested in its eggs than its predatory behavior.
Thirteen healthy Komodo dragons, each weighing about three and a
half ounces, hatched from their leathery eggs under the care of UNLV
physiologist Carl Reiber and his colleagues. Komodo dragon photos by
Jessie Cohen of the National Zoo.
Now in his third year at UNLV, Reiber formerly taught part time at George Mason University in Virginia, where he began a collaborative study of the dragons with another physiologist, Geoffrey Birchard. The two scientists have been working with the National Zoological Park in Washington, D.C., since 1992 in its effort to produce healthy offspring from the only two Komodos to have been bred in captivity-Friendty, a male, and Sobat, a female, both given to the zoo by Indonesia in 1988.
Since 1934 the National Zoo has exhibited seven Komodo dragons. The captured reptiles never lived more than a few years, even though in the wild they are thought to live as long as 100 years.
Early specimens were the largest animals that collectors could capture. (Komodos have been recorded at just over 10 feet and more than 350 pounds.) However, modern zoo curators realized that the very large, old dragons were stressed by capture, travel, and their new surroundings and that this undoubtedly hastened their demise. Hence, curators began seeking younger and smaller specimens, such as Friendty and Sobat, who have grown since arriving at the National Zoo, but still measure only about 6-7 feet and weigh 50-115 pounds. They have already lived longer than any previous Komodo in captivity.
Modern zoos also offer animals more natural surroundings than were common 60 years ago, and the National Zoo's Komodos have warm conditions and deep soil in which they can burrow as they do in the wild. Their diet, too, has been improved. In 1934, one specialist advised feeding the Komodos chicken, beef, lobster, pheasants, and pigs three times a day; Friendty and Sobat get a more austere, yet realistic, diet: a feast of rats once a week.
As the zoo staff continued to improve the dragons-living and breeding-conditions, they began to wonder what might happen if their efforts at matchmaking paid off. What if the Komodos did breed and the female laid a clutch of eggs? What could they do to increase the likelihood that the eggs would hatch?
That's when Reiber and his colleague entered the picture. As experts on the cardiovascular development of reptile eggs, they were called in to help.
"The zoo decided it didn't want to put all of its eggs in one basket," Reiber says with a straight face. "So when 26 eggs were discovered in the female's burrow, the zoo gave 10 of them to us for hatching and for study."
The first two komodo dragons to be bred in captivity, Sobat and
Friendty, share an intimate moment.The first problem for the physiologists was to determine optimum hatching conditions. Because Komodo dragons are not the kind of creatures that invite scientists to poke around in their burrows, little was known about conditions in their nests. And since the climate in the Komodo's natural habitat can vary greatly, Reiber and Birchard faced added uncertainty in determining the right incubation temperatures.
"In the wild these animals can be exposed to temperatures of 100 degrees plus, and it doesn't rain for long periods of time. Then they are inundated with monsoon rains," Reiber says.
The limited previous observations of the Komodos' natural environment suggested the appropriate temperature was about 84 degrees. As with the eggs of birds and other reptiles, Reiber says, moisture content of the surrounding soil was also a critical concern.
"If you take a chicken egg and stick it out in the air here, you can incubate it at the proper temperature, turn it, and do everything else right, but it will die because it loses all its water."
But there was nothing to indicate how soil moisture might affect the Komodos' large, leathery eggs. So Reiber and Birchard began to experiment with varying the moisture levels in the soil in which the dragon eggs were incubating. Initially, this included moisture levels up to four parts water to one part vermiculite, a lightweight, highly water-absorbent material. But they soon discovered that the eggs absorbed too much water on that combination.
"They looked like they were going to burst, just like water balloons," Reiber recalls, "so we had to dehydrate them back down and let them lose weight." However, once the researchers controlled for excessive water absorption, Reiber says, "it didn't seem to matter which of the lower moisture levels was used for incubation." From their study of the 10 eggs from the first clutch and eight more the next year, they found no significant difference in weight or incubation time for the hatch-lings if the incubation material was dry as a desert or as damp as a rainforest. That finding was one in a series that would perplex the researchers. "With other reptile eggs, you usually see a much heavier animal if it has more water," he says.
Another area they studied intensively was the length of incubation of the Komodo eggs. More specifically, they examined what they call the "cost of development" - the total amount of energy required to go from one point in development to the next.
Temperature and moisture content of the soil surrounding the incubating
eggs were critical concerns for Reiber and his colleagues. One of
Reiber's eggs was the first to hatch.Komodo dragons have an unusually long incubation period-about eight months, which is not only longer than any other reptile, but also longer than one would expect for the size of their eggs.
Reiber points out that the long incubation time suggests a high cost of development, but by reptilian standards, the energy source-the yolk of the egg-is not large enough to provide enough food for such a lengthy period.
Because the zoo badly wanted the eggs to hatch, Reiber and his colleague could not break them open and analyze the yolk to see what it contained. So Reiber's skill in noninvasive measurement, honed in his study of invertebrates, provided the solution.
He explains that one of the ways they measure energy consumption of an embryo is to determine how much oxygen is being used by the egg in which it grows. So they put a Komodo egg in a closed jar with a substance that absorbs carbon dioxide. As the egg would "breathe," it would take up oxygen and give off CO2. As the absorbent substance sucked in the CO2, the pressure in the jar decreased. Then, calculations based on the reduced pressure showed how much oxygen was being used.
Typically for reptiles, Reiber says, the larger the egg, the higher the oxygen consumption and metabolic rate. However, both the Komodos' oxygen consumption and metabolic rate were significantly lower than expected, Reiber says.
"The Komodos have a lower-than-predicted metabolic rate and a longer-than-predicted incubation time," Reiber says, "and we want to know why."Clearly, something is happening to the Komodo that doesnÍt fit typical reptile patterns."
Part of the explanation appears to lie in the gas exchange process, Reiber notes, explaining that like the chicken egg, the Komodo egg has a chorioallantoic membrane that lines the shell. "We just call it the `cam,'" he says.
The cam develops blood vessels that expand as the animal grows, and these blood vessels provide the embryo's link to the outside world. The animal's heart pumps blood to the cam at the surface of the eggshell, the CO2 is released, oxygen is absorbed, and the oxygen-rich blood is pumped back to the animal.
Late in the development of the Komodo embryo, its metabolism plateaus. One of Reiber's hypotheses is that for some reason the cam has gotten as large as it can and can no longer exchange gases efficiently. This may be what triggers hatching, Reiber says.
"This is analogous to what happens when a human baby goes beyond term. One of the reasons doctors will induce labor after a baby is a week or two overdue is that the placenta begins to break down, and the baby begins to become starved for oxygen. We see theæsame things happening here with the cam."
Why the cam breaks down remains something of a mystery, Reiber says, acknowledging that much of his work on the Komodos has presented more questions than answers.
But identifying the enigmas of Komodo development is only part of their work: Reiber proudly reports that their role as surrogate parents paid off when one of the eggs under their tender care was the first to hatch-even before those under the zoo's care. The zoo eventually had 13 healthy baby lizards, each approximately 16 inches long and weighing about 31/2 ounces. The next year Sobat was successfully mated with a male in the Cincinnati Zoo and another clutch of eggs was hatched.
The success in getting Komodo dragon eggs to hatch has meant the scientists can use invasive procedures to study the reptile's embryo and perhaps find answers to more of the questions about its development. Eggs for such study are available because Sobat and her two partners are responsible for almost all of the Komodos now in the United States; as a result, they are no longer genetically viable. Further breeding is not desirable because of the lack of diversity in the gene pool and the consequent dangers of inbreeding.
Reiber and his colleague are taking advantage of the fact that the zoo insists that the eggs not be allowed to hatch. The scientists are now able to peel back the leathery external layer of the shell, count the number of blood vessels present in the cam, and compare their findings with what is known about other reptiles. Reiber says the findings so far are surprising.
In his research on the Komodo eggs, Reiber, left, had to start from
scratch in determining optimum hatching conditions because, not surprisingly,
little was known about the dragon's nest."We expected because of the metabolism of the animal that it would have looked much more like birds, that it would have had a lot more blood vessels than it has. [That was not the case] so there's obviously something else going on here." Analysis of the data is continuing.
The dragon egg studies have been conducted in a laboratory at George Mason University, and Reiber spends two or three months a year there. Meanwhile, if he wants to observe a Komodo closer to home, he must travel to the San Diego Zoo.
But Reiber doesn't keep all of his eggs in one basket either. His studies of the Komodo dragon have led quite naturally into his research on another reptile, one indigenous to the Las Vegas area: the endangered desert tortoise.
"The reason for working on them really stems from the Komodo dragon work in that they are such different eggs," he says, comparing the leathery shells of the Komodo eggs to the more brittle eggshells of the tortoise, which are similar to chicken eggs. And, while the dragon eggs apparently can tolerate considerable extremes in conditions, they would have a hard time in Southern Nevada's exceptionally arid climate in which the tortoise eggs thrive.
"If you took a Komodo dragon egg and put it in a Las Vegas environment, it would not hatch," Reiber says. "It would dry up and blow away. If you put a snapping turtle egg [the subject of one of Reiber's earlier studies] in the Las Vegas environment, it wouldn't hatch. Yet these desert tortoises-their eggs sit in the air, and they don't lose water. This capability to conserve water is unique."
As with the dragons, Reiber is trying to discover how the tortoise egg's cardiovascular system handles incubation conditions. "We are looking for optimal hatching conditions, but also how the cardiovascular system deals with such a dry environment. Is the egg dehydrated proportionately to other reptiles' eggs, and if so, does it have an effect?"
Yet another subject of Reiber's research is the crayfish, specimens of which he collects in the Flamingo Wash, not far from the UNLV campus. Reiber focuses on newly hatched crayfish, so tiny and transparent they are barely visible in the tanks that line his lab in the Juanita Greer White Lifesciences building.
Although the techniques for studying the crayfish hatchlings differ from those used to analyze reptile eggs, Reiber's objective is still to measure cardiovascular pressures and flow rates in an effort to discover how the system works. When does the heart start to beat? What effect does the oxygen supply have on the developing system? What role does the cardiovascular system play in regulating development?
Reiber would be the first to acknowledge that while he might find a greater number of subjects nearby for his work on the crayfish and the tortoise, they can't compete with the Komodo dragon when it comes to generating interest in his research. The dragon would win hands down every time in a contest gauging public appeal, he notes.
That is, of course, unless the contest were held on the island of Komodo.
