Polar
bears are being increasingly threatened by the effects of climate change,
but their disappearance could have far-reaching consequences. They are
uniquely adapted to the extreme conditions of the Arctic Circle, where
temperatures can reach -40°C. One reason for this is that they have up to
11 centimetres of fat underneath their skin. Humans with comparative levels
of adipose tissue would be considered obese and would be likely to suffer
from diabetes and heart disease. Yet the polar bear experiences no such
consequences.
A
2014 study by Shi Ping Liu and colleagues sheds light on this mystery. They
compared the genetic structure of polar bears with that of their closest
relatives from a warmer climate, the brown bears. This allowed them to
determine the genes that have allowed polar bears to survive in one of the
toughest environments on Earth. Liu and his colleagues found the polar
bears had a gene known as APoB, which reduces levels of low-density
lipoproteins (LDLs) – a form of ‘bad’ cholesterol. In humans, mutations of this
gene are associated with increased risk of heart disease. Polar bears may
therefore be an important study model to understand heart disease in
humans.
The
genome of the polar bear may also provide the solution for another
condition, one that particularly affects our older generation:
osteoporosis. This is a disease where bones show reduced density, usually caused
by insufficient exercise, reduced calcium intake or food starvation. Bone
tissue is constantly being remodelled, meaning that bone is added or
removed, depending on nutrient availability and the stress that the bone is
under. Female polar bears, however, undergo extreme conditions during every
pregnancy. Once autumn comes around, these females will dig maternity dens
in the snow and will remain there throughout the winter, both before and
after the birth of their cubs. This process results in about six months of
fasting, where the female bears have to keep themselves and their cubs
alive, depleting their own calcium and calorie reserves. Despite this,
their bones remain strong and dense.
Physiologists
Alanda Lennox and Allen Goodship found an explanation for this paradox in
2008. They discovered that pregnant bears were able to increase the density
of their bones before they started to build their dens. In addition, six
months later, when they finally emerged from the den with their cubs, there
was no evidence of significant loss of bone density. Hibernating brown
bears do not have this capacity and must therefore resort to major bone
reformation in the following spring. If the mechanism of bone remodelling
in polar bears can be understood, many bedridden humans, and even
astronauts, could potentially benefit.
The
medical benefits of the polar bear for humanity certainly have their
importance in our conservation efforts, but these should not be the only
factors taken into consideration. We tend to want to protect animals we
think are intelligent and possess emotions, such as elephants and primates.
Bears, on the other hand, seem to be perceived as stupid and in many cases
violent. And yet anecdotal evidence from the field challenges those
assumptions, suggesting for example that polar bears have good problem solving
abilities. A male bear called GoGo in Tennoji Zoo, Osaka, has even been
observed making use of a tool to manipulate his environment. The bear used
a tree branch on multiple occasions to dislodge a piece of meat hung out of
his reach. Problem-solving ability has also been witnessed in wild polar
bears, although not as obviously as with GoGo. A calculated move by a male
bear involved running and jumping onto barrels in an attempt to get to a
photographer standing on a platform four metres high.
In
other studies, such as one by Alison Ames in 2008, polar bears showed
deliberate and focussed manipulation. For example, Ames observed bears
putting objects in piles and then knocking them over in what appeared to be
a game. The study demonstrates that bears are capable of agile and
thought-out behaviours. These examples suggest bears have greater
creativity and problem-solving abilities than previously thought.
As
for emotions, while the evidence is once again anecdotal, many bears have
been seen to hit out at ice and snow – seemingly out of frustration – when
they have just missed out on a kill. Moreover, polar bears can form unusual
relationships with other species, including playing with the dogs used to
pull sleds in the Arctic. Remarkably, one hand-raised polar bear called
Agee has formed a close relationship with her owner Mark Dumas to the point
where they even swim together. This is even more astonishing since polar
bears are known to actively hunt humans in the wild.
If
climate change were to lead to their extinction, this would mean not only
the loss of potential breakthroughs in human medicine, but more
importantly, the disappearance of an intelligent, majestic animal.
|
No comments:
Post a Comment
thank you for visiting my blog and for your nice comments