Friday 25th November comments: Yesterday seal expert Kimberley Bennett started answering the question ‘how do seal pups stay warm in winter?’ Today we look at further reasons on how seal pups keep warm as not all Seal pups are born fat, some are born wet and skinny so how do they stay warm? Kimberley explains…
Make more heat! When the newborn gets cold, it can shiver, just like we do, and this uncoordinated muscle contraction makes more heat. But there’s another trick that all mammals have up their sleeves: they turn up the heat some more. In newborns there are specialised areas of fat that look different from normal white fat, called brown fat. Brown fat has lots of mitochondria, the energy generating centres in the cells, which contain a protein called thermogenin, or UCP1. When UCP1 is switched on, brown fat cells make heat without the need for shivering.
Be clever with blood flow! It’s no good generating heat if you can’t keep it inside because that just wastes energy, so the faster the pups can dry off (not easy on a cold rainy night) and put on fat the better. But there are a couple more anatomical adaptations that seals have to help them retain body heat. The flippers and the nose are not very well insulated. To avoid heat loss from these parts of the body, seals have a special arrangement of their blood vessels. Warm blood flows from the core of the body to the flippers in arterioles. The blood coming back from the flippers, which has been cooled a little, flows in the opposite direction in veins that run right alongside the warm arterioles. That means the cool blood gets warmed up as it returns to the body and avoids a drop in core temperature. It also means the warm blood going out to the flippers gets cooled down and less heat it lost once it reaches the flippers. Very clever! This is called a counter current exchanger. A counter current exchanger is also found in the nose. If you look in the nose of the skull photo you will see a complicated set of very delicate bones. These are called turbinates and they help the seal to retain body heat. As blood enters the delicate skin that covers the turbinates it slows down and warms the air in the nose before it can chill the lungs deep inside. Blood returning to the body core from the nose get rewarmed by that clever counter current system, so breathing cold air doesn’t cool the seal down.
The range of outside temperatures over which an animal can maintain its internal body temperature without having to sweat or shiver is called its thermoneutral zone. The thermoneutral zone of a weaned seal pup goes from 23 °C all the way down to -7°C. In fact, it’s been estimated that they can survive temperatures down to as low as -85°C! So all these adaptations mean that seals can still have a comfy night’s sleep in the teeth of a gale, the pouring rain, in a frosty hollow on the Isle of May or on the ice floes of the Arctic.
So there you have it, four reasons on how seal pups keep themselves warm! Its all in the science.