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Bat wing digits (was Re: Tiktaalik)


Here's the paper in question, about to be published in PNAS...

http://www.pnas.org/cgi/content/abstract/0509716103v1

Sears, K.E., Behringer, R.R., Rasweiler, J.J., IV , and Niswander, L.A. (in press). Development of bat flight: Morphologic and molecular evolution of bat wing digits. Proc. Natl. Acad. Sci. USA. Published online before print April 17, 2006.

Abstract: "The earliest fossil bats resemble their modern counterparts in possessing greatly elongated digits to support the wing membrane, which is an anatomical hallmark of powered flight. To quantitatively confirm these similarities, we performed a morphometric analysis of wing bones from fossil and modern bats. We found that the lengths of the third, fourth, and fifth digits (the primary supportive elements of the wing) have remained constant relative to body size over the last 50 million years. This absence of transitional forms in the fossil record led us to look elsewhere to understand bat wing evolution. Investigating embryonic development, we found that the digits in bats (_Carollia perspicillata_) are initially similar in size to those of mice (_Mus musculus_) but that, subsequently, bat digits greatly lengthen. The developmental timing of the change in wing digit length points to a change in longitudinal cartilage growth, a process that depends on the relative proliferation and differentiation of chondrocytes. We found that bat forelimb digits exhibit relatively high rates of chondrocyte proliferation and differentiation. We show that bone morphogenetic protein 2 (Bmp2) can stimulate cartilage proliferation and differentiation and increase digit length in the bat embryonic forelimb. Also, we show that Bmp2 expression and Bmp signaling are increased in bat forelimb embryonic digits relative to mouse or bat hind limb digits. Together, our results suggest that an up-regulation of the Bmp pathway is one of the major factors in the developmental elongation of bat forelimb digits, and it is potentially a key mechanism in their evolutionary elongation as well."

(Perhaps something similar may happened in the early evolution of pterosaurs?)

Cheers

Tim

Scott Hartman wrote:

A lot happens when you're gone for a week, but anyways, that's why I said generally...also, while the number of mutations that occurred to produce the wing itself are small, it doesn't preclude a longer adaptive period of integrative selection forthe structure to be useful in the context (flight) it is used for today.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: Tim Williams <twilliams_alpha@hotmail.com>
To: dinosaur@usc.edu
Sent: Fri, 7 Apr 2006 21:24:35 -0500
Subject: Re: Tiktaalik

Scott Hartman wrote: 
 
But today biologists generally accept that large changes in body plan
>result from the accumulation of many small changes over time; there is >scant evidence for even a weak version of Goldschmidt's "Hopeful Monster" >form of phenotypic saltation. 
 
Perhaps not. Check out Karen Sears' evo-devo work on bat fingers... 
 
http://dml.cmnh.org/2004Nov/msg00242.html ;
http://dml.cmnh.org/2004Nov/msg00186.html ;
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