Compared with most pregnant mums, skinks have it easy. They invest much of the energy needed to rear their young to full term when producing the egg yolk that will nourish the foetuses during development. But that doesn't mean that skink mums get off scot-free: the additional burden of carrying a litter impairs their mobility and messes with their metabolism. ‘The physiological mechanisms that underpin these gestational costs are poorly understood,’ says Suzanne Munns from James Cook University, Australia. Intrigued by the challenges faced by blotched blue-tongued skink mums-to-be, Munns and a team of scientists from the University of Tasmania, Australia, including Ashley Edwards, Stewart Nicol and Peter Frappell, measured the breathing patterns, metabolic rates, lung volumes and gas diffusion across the lungs of pregnant and non-pregnant female skinks to find out how they cope with pregnancy.
Exercising the animals, the team found that the non-pregnant females were able to rise to the challenge and increase their metabolism over 300% while breathing much deeper and faster. However, the females that were in the late stages of pregnancy were unable to alter their breathing patterns or increase their metabolism as they exercised. And when the team measured lung volume in the pregnant mums, the lung volume increased over the duration of the pregnancy, but increased even more after giving birth, suggesting that the lungs were compressed by their litter. However, gas diffusion across the lung was not affected by pregnancy. Explaining that skinks do not use the entire surface of the lung for gas exchange, the team suspects that the portion of the lung that acts as a bellows moving air around the lung is compressed during pregnancy. They say, ‘the lack of ability to respond to increased respiratory drive may be one of the mechanisms that underpin the locomotor impairments measured in pregnant lizards’.