Hidden evolution: How the mammoth kept its cool

Last weekend I went to see an exhibition on mammoths in the Natural History Museum in London (unfortunately now closed). The descriptions and posters did a very good job of explaining our current knowledge of mammoths and how that knowledge had been gained. In particular, the curators were very keen to highlight the evolutionary relationships between different mammoth species and modern elephants.

A lot of the differences between the woolly mammoths and modern elephants are quickly apparent. The woolly mammoths are larger, hairier, and of course there are the tusks.

The tusks can be a big giveaway for a mammoth

The tusks can be a big giveaway for a mammoth

But one little sign caught my eye. It said that from the genetic material gathered from mammoth remains (we’ve recorded about 70% of their genome, so maybe not too far off until we can clone mammoths back into existence!), we can tell that woolly mammoths had a mutated form of haemoglobin that worked better in cold temperatures.

This haemoglobin discovery was published in 2010, so it isn’t anything new. But for me, this is evolution at its most interesting – not apes walking upright or fish breathing on land, but the tiny internal changes that adapt the body’s complex machinery.

Haemoglobin has a difficult balancing act to achieve – it needs to grab hold of oxygen from the lungs and it needs to release it around the body. If it holds the oxygen too tightly, the muscles can’t receive enough. If the haemoglobin holds on too weakly, it won’t be able to carry enough oxygen to where it is needed.

Elephant haemoglobin, like the human form, more readily releases oxygen at higher temperatures. That comes down to the energetics of breaking its hold, but it also means that harder-working (and therefore warm) muscles can take a greater share. This can be a serious issue if body-parts get too cold – they can suffocate to death. This is a danger for trekking around Siberia, even if you are large and hairy.

Researchers from the University of Manitoba, Canada, compared the haemoglobin genes of woolly mammoths to those of an Asian elephant from a nearby zoo. They noticed that there were four mutations that led to changes in the amino acid chains of the haemoglobin proteins.

Without any mammoth blood to hand, it can be very difficult to work out the effect of these changes. Fortunately, although we can’t resurrect a full mammoth now, we can insert the haemoglobin DNA into bacteria and resurrect one small part of them.

With the bacterium-produced mammoth haemoglobin, the researchers could run the tests needed to confirm that it was indeed adapted to the cold. Rather than the strong link to temperature seen in elephants, the mammoths’ haemoglobin can release oxygen at a similar level over a wide range of temperatures.

The structure of haemoglobin, with the blue regions showing where the mammoth mutations are

The structure of haemoglobin, with the blue regions showing where the mammoth mutations are (Credit: K Campbell et al, 2010)

The blue regions in the picture above show where the changes are in the structure of haemoglobin. These changes don’t appear to make any direct contact with the heme group (the part that carries the oxygen, shown in orange sticks), but they alter the shape of the protein subtly. This change in shape is enough to give mammoths a better chance of surviving freezing cold environments.

Mutations in haemoglobin are also seen in other animals adapted to cold environments, such as the arctic fox. The mutations seen in these animals are all different but lead to similar effects – an example of convergent evolution.

Just last year, the same researchers who made this discovery started work on an exciting new find: well-preserved mammoth blood. This could give them the chance to test the same idea on haemoglobin straight from a mammoth. There is even a (very small) chance that intact cells could be found in the sample, which would make cloning a full mammoth a lot easier.

So before long we might find out a lot more about these legendary creatures.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s