How can marine mammals survive for so long underwater?

Charlotte Hitch (Vet News Exotics Editor)

Research at the University of Liverpool into oxygen-carrying proteins in the muscles of marine mammals has recently revealed how these animals are able to hold their breath for up to 90 times longer than humans.

The protein myoglobin, which gives muscle its red colour, is responsible for supplying muscle tissue with the oxygen required for respiration. In seals and other marine mammals, muscles are often almost black in colour due to their high myoglobin content, of which the concentration is about ten times that of bovine muscle. More myoglobin means more oxygen can be stored within the muscle itself, so oxygen from the last breath before a dive can be retained in the blood and used by the vital organs, such as the brain and heart.

By storing their own oxygen, the muscle cells are still capable of carrying out respiration to produce the ATP energy needed for movement (i.e. flipper and tail motion) during the dive, so marine mammals can still be active even when they haven’t inhaled for over half an hour. This is what enables sperm whales to dive 2-3km underwater to catch giant squid, a major constituent of their diet.

The problem with having a high muscle myoglobin content is that the protein has self-associating properties when packed tightly together. When proteins stick together, their function is impaired; in this case the myoglobin would be unable to bind with oxygen properly.

To overcome this problem, marine mammals have developed a modified version of myoglobin – with an overall positive charge on the molecule. This results in repulsion between molecules, preventing self-association.

While the adaptation offers a clear advantage to marine mammals, there are risks involved. There is no problem while the myoglobin is contained in the muscle; however muscle damage from fighting or predators’ attacks may cause it to enter the bloodstream. Myoglobin is toxic to the renal tubular epithelium, so when the blood passes through the kidneys, it can lead to renal failure.

Despite the risk to the kidneys, the outcome of this adaptation has evidently contributed to the evolutionary success of marine mammals; sperm whales can hold their breath for 90 minutes and common seals for 30 minutes. Seals are even able to sleep underwater, taking refuge from land-based predators – a vital part of their survival.

References:

Picture credits:

Our Small Animal News editor, Harriet delves into the intriguing topic of canine intelligence in this month’s dose of Vet News.

SMALL ANIMALS:

Canine Intelligence

Harriet Woodhall (Vet News Small Animal News Editor)

The intelligence of domestic dogs has been a topic much in the news recently after the discovery of perhaps the “world’s cleverest dog”, Chaser the Border Collie.

One of the reasons this topic is a controversial one could be because of the limited means of testing a dog’s intelligence apart from the amount of words they are able to retain and respond to. One way scientists are trying to evaluate how intelligent the species is to look at its evolution.

It is well known that domestic dogs evolved from wolves, but how this transition came about is thought to be through humans. After a group of wolves took advantage of humans, they actually gained from the interaction and domesticated themselves naturally. It is now thought the increase in intelligence is down to their involvement with us.

Dogs have gained a social intelligence different from their wolf ancestors in which they are able to learn words in a similar way to a small child. One study has shown that dogs work things out with an inferential strategy based on the principle of exclusion: they have words that are attached to items, so when given a new word they know this belongs to a different, new item. Another quite shocking discovery was in several border collies who when shown a 2D picture were able to go and fetch the object in the picture – using something called the principle of iconicity. This was previously thought of as something that only children were able to do.

It is clear that we have much to learn about canine intelligence and are gradually uncovering new insights into their minds. One good example of a recent advance is Chaser the “world’s cleverest dog” who has been able to learn 1,200 words, more than any other non-primate and is estimated to have the intelligence of a 2 and a ½ year old child.

Even further into the field is Brian Hare from Duke University in North Carolina who has come up with a series of scientific tests covering more than just the amount of words learnt – they can also explore empathy, communication, cunning, memory and reasoning. The tests aim to prove that, like humans, dogs have different approaches to challenges. Researchers have created a profile that enables the owner to get a full overview of their dog’s traits and individual skills. The tests, through the website Dognition, are part of a study that aims to get a better understanding of how dogs think, not just for insight into dogs but also into our own intelligence evolution. As dogs learn words much like human babies it may help with our knowledge of our own learning.

Maybe the next controversial question that needs answering is: “which are smarter, dogs or cats?”

References:

http://www.newscientist.com/blogs/nstv/2013/02/canine-intelligence-tests.html

https://www.dognition.com/

http://www.smithsonianmag.com/ideas-innovations/Why-Dogs-are-More-Like-Humans-Than-Wolves-192083131.html

http://www.newscientist.com/blogs/nstv/2010/12/meet-the-dog-with-vocal-of-a-three-year-old.html

Picture Credits:

http://www.yayp.co.uk/siteimages/large_dogtraining7-453.jpg

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How can marine mammals survive for so long underwater?

Vet News – Small Animal News

SMALL ANIMALS:

Canine Intelligence