RE: Tuataras are the roadrunners of molecular evolution.

[Tim Williams <twilliams_alpha@hotmail.com>]

David Marjanovic wrote:

>> On the other hand, what would hyper-variable mitochondrial control regions
>> have to do with rate of morphological (or indeed physiological) evolution?
> 
> As far as I can tell, nothing whatsoever... 


Yep, nothing at all.  The mitochondrial control region is involved in the 
replication of the mitochondrial genome (especially the 'heavy-strand', on 
which most of the mitochondrial proteins are encoded), and in the transcription 
of those genes carried on the mitochondrial genome.  Nobody is exactly sure how 
the control region does all this, although certain individual sequences within 
this region appear to be implicated (somehow).


The thing is, it is possible that animals with a 'slow' metabolism (like the 
tuatara) may be better able to tolerate mutations that have a deleterious 
effect on the performance of the control region.  If mutations accumulate to 
such a degree that it reduces the efficacy of mitochondrial replication and/or 
transcription, then it may not matter to an animal with a slow metabolism.  
Mitochondria are regarded as little 'power plants' for the cell, and rapid 
replication and transcription of the mitochondrial genome is considered 
important for overall aerobic efficiency (which is why the mitochondrial genome 
tends to be very small and compact).  However, animals with a slow metabolism 
may have an increased tolerance for reduced aerobic efficiency; it makes no 
difference to their physiology if the mitochondria are less efficient at 
producing energy.  Thus, these animals may have a higher tolerance for the 
accumulation of mutations within the control region.  Changes in the control 
region
 that are effectively neutral to the tuatara, may not be neutral to an organism 
with a fast metabolism (like us humans!), and which is dependent on the optimal 
aerobic efficiency of its mitochondria.


Long story short... the high rate of molecular change in the tuatara control 
region may be a *consequence* of a slow metabolism.


Cheers

Tim
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