Tuesday, October 20, 2009

Selecting for Mutation: The Bull Terrier

The pictures, above, show what happened to the Bull Terrier between 1930, 1950 and 1980, as breeders selected for clinorhynchy, or dorsoventral nose bend -- a downward nose droop.

Bull terriers have purposefully selected for this genetic mutation, creating a dramatic case of evolution visible in the short time we have had modern photography. As Fondon and Garner note,

"The dramatic changes that have occurred in domestic dog breeds in response to breeders’ selection toward breed standards over the last 150 years demonstrate the potential of the mammalian genome to effect rapid morphological change in response to strong selection, even with small, closed gene pools."

To see more dramatic pictures of dog skull evolution, see >> Molecular origins of rapid and continuous morphological evolution by John W. Fondon III and Harold R. Garner

To put these changes to the dog within context of working terriers, see >> Rosettes to Ruin.


Viatecio said...

The PDF of the study isn't linking. Just FYI.

PBurns said...

Thanks -- fixed the link. I wrote this piece back in 2004 or 2005 (it's a recycle) and did not check the link. I put in on my own server now, so it should be stable.

For those interested in canine morphology, the place is the Albert Heim Foundation for Canine Research, Basil, Switzerland which is who actually owns the skulls pictured here.


dp said...

The skull of the Bullterrier was achieved not through selecting for a mutation, as there was no "mutation".

It was progressive selection for this shape that formed it.

I have many photos which show the change in the Bullterrier over the years---not just its skull shape.

PBurns said...

DP, you may not know what mutation means. It's not the X-men! See the dictionary at >> http://www.answers.com/topic/mutation

The Bull terrier did not start off with clinorhynchy (or Klinorhynchy, it's spelled both ways).

It appeared in a dog, and then it was selectively bred for, same as dwarfism (achondroplasia) or a flat-face (brachycephalic), or hairlessness.

Read the full article linked to at >> http://www.terrierman.com/morphological-evolution-dogs-pdf.pdf


PBurns said...

DP -- more here about tandem repeats (what causes the dipped nose on the bull terrier) here >> http://pharyngula.org/index/weblog/comments/tandem_repeats_and_morphological_variation/

As they note:

"That there would be this substantial amount of genetic variation in tandem repeat number isn't at all surprising. Tandem repeats are subject to very high mutation rates, up to 100,000 times greater probability than a point mutation, because they are prone to a kind of error called slipped-strand mispairing."


dp said...

Thank you for the lessons.

I do know what a mutation is and I agree that the Bullterrier head was achieved through selective breeding.

PBurns said...

It is the selective breeding of dogs with TANDEM REPEAT MUTATIONS of the gene that causes that crooked nose!

Understanding mutation is basic to understanding evolution -- see Darwin or this video at >> http://videos.howstuffworks.com/discovery/28755-assignment-discovery-darwin-and-mutation-video.htm

What dog breeders do is find a mutation (an odd color variation, an odd coat variation, a deformed head, crooked legs, a flat face) and try to breed for it. The concentration of mutation is what "selective breeding" is all about, but in the case of dog breeders it is UN-natural selection rather than natural selection.

Dog breeders are generally selecting for FAIL -- the thing that is rare in nature because it is maladaptive in natural dogs (i.e. it causes them to die or fail to thrive). The shape of the head of the Bull Terrier is such that is could not actually hunt in the wild -- it a UN-natural selection to preserve a mutation (the tandem genetics repeats that cause the crooked nose).


Katrina van Grouw said...

Dear All,
Thought you might be interested to know that this is the very subject of a book I'm writing and illustrating for Princeton University Press - and it's actually called 'Unnatural Selection'. It deals with the skeletal structure of all domesticated animals, including birds and commercial livestock, and will compare changes caused by selective breeding as well as showing complete skeletons in lifelike positions. It will be published in 2015, but meanwhile I have a book on bird anatomy, 'The Unfeathered Bird' coming out in November. I'm visiting the Albert-Heim Foundation shortly. Incidentally it's in Berne, not Basle.
Katrina van Grouw

PBurns said...

Excellent. Will correct location.

I used to work for the National Audubon Society so I have looked at what has been done to pigeons and chickens (and a little at ducks). See this post on pigeons, for example >> http://terriermandotcom.blogspot.com/2010/02/maladaptive-pigeons-at-hand-of-man.html Of course the real story is inside with the Rollers and Homers.

I put together a poster and T-shirt for what has happend to dogs >> http://www.terrierman.com/DarwinDogfinal.jpg and http://www.cafepress.com/darwindogs