Feb. 23, 2007 — An Australian lizard endures what may be the world's worst pregnancy — due to anatomical restrictions, pregnant Australian stumpies must hold a gut-busting infant weighing more than a third as much as an adult, without any swelling or extra body space.
The feat is equivalent to a woman giving birth to a seven-year-old child.
"I can't think of another animal that has such a large gestational load," said Suzy Munns, who last week experienced a veritable baby boom with mother stumpies she had collected from the south Australian desert.
Munns, a researcher in the School of Veterinary and Biomedical Sciences at James Cook University, is conducting ongoing studies on how these lizards, which can grow to over 15 inches in length, survive such a difficult pregnancy.
Munns' findings were published recently in the journal Physiological and Biochemical Zoology.
The largest members of the skink family, stumpies give birth to a single infant that is, on average, 35 percent of the mother's body weight. The growing fetus lies on top of the mother's lungs and digestive tract such that, in the latter stages of gestation, the females can no longer move much or eat.
The lizard's abdomen cannot expand because rigid scales cover most of the animal's body.
Computerized tomography (CT) scans revealed that a pregnant stumpy's lungs were compressed, or even collapsed, in certain areas, due to the embryo's weight. Analysis of the animals' oxygen consumption found that mothers were unable to take in much air, which explains their sedentary behavior.
Towards the end of the pregnancy, mother stumpies slowly drag themselves between sun and shade, but have difficulty escaping from predators.
Munns said animals use a variety of strategies to reproduce. Some have a lot of eggs or offspring, many of which die before reaching adulthood. Others, like the stumpy, produce a small number of large babies.
