Quick Dips

Dietary Habits and Daylight

Weddell seals may provide a better understanding of human obesity, as well as reveal information on how daily rhythms are timed.

That's the hope of a research team in Antarctica, led by Dr Graham Barrell from Lincoln University's Animal and Veterinary Sciences Group.

"We are interested in the female Weddell seal because it is an animal that suckles its young for two months without any substantial food intake," says Barrell. "Normally nutritional requirement are at their highest for any animals during the suckling process. The female seal is unusual in that it lives off its own body tissue plus delivers enough nutrients from her own body tissues to provide milk to the suckling pup."

Because of this long fasting period, the mother seals become very thin after six weeks suckling. The calf increase its weight by over 100 kilograms.

Barrell hopes that the study will provide better understanding of obesity in other animals, including humans, and changes in growth and development.

"This animal is a classic example of extremes of weight loss/weight gain in that the pup gains weight rapidly and the mother loses weight rapidly," says Barrell.

The team is collecting blood samples from both suckling and non-suckling mothers to compare biochemical changes. The group will also be covering seals with tarpaulins to simulate darkness for studies of the animals' pineal gland secretions.

"This gland is one we all use to help us time internal events and have them linked up in terms of our environment, especially the daily changes in light and darkness," says Barrell.

During the summer months, the seals are exposed to constant daylight. The team is studying how daily rhythms are maintained in the absence of darkness by taking blood samples from covered seals.

"In previous studies, we have looked at melatonin, which is secreted by the pineal gland, and found that because of the constant light, these animals don't secrete any," Barrell says.

"We know very little about the function of the pineal glands in these animals and we plan to learn more by introducing the seals to darkness to see if the gland responds by secreting melatonin."