Friday, March 03, 2006

 

Re: [evomech] Limbs in whales and limblessness in other vertebrates: mechanisms of evolutionary and developmental transformation and loss.

From: "John Latter" <jorolat@gmail.com>
> Subject: [evomech] Limbs in whales and limblessness in other
> vertebrates: mechanisms of evolutionary and developmental
> transformation and loss. [Bejder & Hall, Evolution &
> Development, '02]
> text; http://whitelab.biology.dal.ca/lb/Bejder%20and%20Hall.pdf

> We address the developmental and evolutionary mechanisms
> underlying fore- and hindlimb development and progressive
> hindlimb reduction and skeletal loss...

There's nothing in the article about the evolutionary origin of
limbs.
That little point is glossed over in this discussion of
development
and of the evolutionary reduction of limbs.

> Limblessness in most snakes is also associated with adoption
>of a new (burrowing) lifestyle...

Were early snakes tunnelers? Or does this new burowing include
merely burrowing through surface debis? Just wondering.

> An evolutionary change in Hox gene expression--as occurs
> in snakes--or in Hox gene regulation--as occurs in some limbless
> mutants--is unlikely to have initiated loss of the hindlimbs in
> cetaceans. Selective pressures acting on a wide range of
> developmental processes and adult traits other than the
> limbs are likely to have driven the loss of hindlimbs in whales.

Are they suggesting that a change occurring via Hox genes or
their regulation can occur more quickly? Selective pressure may
drive the loss of a feature, but how do we know whether or not
Hox genes are involved?

Cliff

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