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Killer whale evolution leads to two orca species

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Killer whale evolution leads to two orca species Empty Killer whale evolution leads to two orca species

Post  Safari Maiden Thu Sep 02, 2010 9:34 am

Extract from BBC Earth News
By Matt Walker


Orcas, commonly known as killer whales, are still evolving, and quickly.

Researchers have discovered that two distinct types of orca, a large and a pygmy form, are rapidly diverging, evolving away from each other.

The scientists' study reveals each type of orca carries a unique gene mutation that benefits its particular lifestyle.

The genetic change has occurred in the past 150,000 years, adding to evidence that the orcas are quickly evolving into two distinct species.

Details of the research are published in the journal Biology Letters by an international team of scientists led by orca expert Dr Andrew Foote of the Natural History Museum of Denmark based at the University of Copenhagen.

Energetic lifestyles

The orcas studied live in Antarctic waters, and are known as type B and type C orcas.

Type Bs are one of the largest forms of orca known and primarily feed on seals.

Type Cs, in contrast, are known as a dwarf-form of orca, and feed mainly on fish.

These differences in size and diet, as well as each type having distinct markings, has led Dr Foote and colleagues to previously propose that they could be two separate species.

Genetic evidence now backs that idea.

Dr Foote and his team analysed the mitochondrial genomes of 15 type B and 36 type C orcas, specifically looking at a gene known as cytochrome B, a gene that plays a significant role in the orca's mitochondria, the structures within cells that govern energy production and metabolism.

They found that type B and type C orcas have evolved different amino acids within this gene, that affect its performance.

All type B orcas have replaced one type of amino acid with another at a place on the gene known as site 279, and type Cs had replaced another amino acid at site 193.

"The mutation has spread throughout each type, so that all type B individuals we analysed the DNA for had the mutation and almost all of the type C individuals had the other mutation," says Dr Foote.

He explains how this mutation could be benefiting each type of orca.

"The gene under selection is important in producing energy for the body's cells, and so the mutations are probably linked to the metabolic requirements of these two types.

"Both types live in the Antarctic pack ice and therefore the low temperature of this habitat could be one selective pressure.

But the two mutations should have the opposite effect on metabolism to one another suggesting divergent evolution."

For example, type C is a dwarf killer whale morph reaching lengths of just over 6m, whereas type B is one of the largest killer whale morphs, being up to 50% larger than type C.

"So body size could also be the selective force on the gene linked to metabolism," Dr Foote told the BBC.

Neither mutation can be found in what is thought to be the mitochondrial genome of the orcas' recent ancestor.

That suggests the natural selection has fixed these mutations very quickly, and they appeared since type B and type C orcas diverged from their most recent common ancestor 150,000 years ago.
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Post  whitestarling Thu Sep 02, 2010 10:24 pm

It's amazing that they both live in the same region yet are so different I wonder if another reason for the speeding up process is the availability of food, as they take different types of prey the food scource would be greater than if they all went for the same prey. Thanks for posting SM
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Killer whale evolution leads to two orca species Empty How does it effect us?

Post  NW PERSO Sun Jul 24, 2011 7:32 pm

This is all great information and right up my ally. The question I have for you is what role do we play in this manipulation of the species? Are we at fault for the way they have changed and will continue to change? Thinking about natural selection and evolution makes me wonder if one of the species of Orca are going to get cycled out or what.....

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Post  littlewid Sun Jul 24, 2011 9:51 pm

Hello NW PERSO.

I'm interested to know why this is right up your street. Are you a scientist or biologist or someone who has an interest/love of Orcas? I would love to know.

I am not a scientist or biologist but off the top of my head I don't think man can manipulate whether one Orca will survive over the other, unless you are looking at over fishing ( which I think there are now strict rules over) which would decrease the Type C Orcas food source or the continued culling of seals is allowed to continue ( as happens in Canada) which would deplete Type B's food source. Potentially for either of these to happen man could then play a part in whether each Orca type may or may not survive.

I don't think man would meddle in the Gene pool of either Orca as it appears that their genetic makeup is completely different and from this research it would appear that they have diverged naturally over the last 150,000 years. But is that the actual case? It sounds as if this bit of research has been put out there to be challenged, as all research is, as you will know, any research is only research and is always there to be challenged so we continue learning.

One of the main things they were looking at was metabolism and different sized mammals and animals will metabolise differently. I think they were looking at whether these have always been two different types of orca or has there been a true divergance and if so how have the Mitochondrial Genomes changed within each type. Maybe they thought the variant would be minimal and only affect size but it appears that if it's a true divergance then the Mitochondrial make up is quite different , so does it pose the question again that these are two different types of orca and maybe it's the last 150,000 years that has changed them just as man has changed over time.

Just throwing thoughts out there and probably not answered your question at all.

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