The 5 fingers of our feathered friends: New research results on the evolution of bird wings

2014-01-07

(Press-News.org) Contact information: Dr. Brian Metscher
brian.metscher@univie.ac.at
43-142-775-6704
University of Vienna
The 5 fingers of our feathered friends: New research results on the evolution of bird wings

In most tetrapods (land vertebrates) the fourth (ring) finger is the first to develop in the embryo. And in birds, the finger on the outside of the hand (posterior, the pinky side) appears first, which suggests that this is the ring finger. However, it can be shown that on the thumb side (anterior) an embryonic finger begins to develop, but quickly disappears -- this would have to be digit I. These data argue for an identification of the fully-formed fingers as the index, middle, and ring fingers (II, III, IV).

However, the three fingers of the earliest known bird -- Archaeopteryx -- resemble those of the dinosaur Deinonychus, with whom Archaeopteryx was probably closely related (as was the famous Velociraptor). Successive fossils show the reduction of two fingers on the posterior side of the hand in the ancestor of Deinonychus, and thus support the thumb, index, and middle finger identification (I, II, III) of the bird fingers. Also, the genes active in first bird finger correspond with those of the developing thumb in other animals, and not those of the index finger.

To resolve this contradiction, three approaches had predominated: 1) Birds do not come from dinosaurs after all; 2) the dinosaur ancestors of birds had also the three middle fingers (II, III, IV); or 3) the three anterior fingers (I, II, III) of the birds were somehow moved to the middle three embryonic positions. In fact, none of these theories can explain all the existing data.

For the birds: Thumb, index, and middle fingers are actually index, middle, and ring fingers. "The appearance -- the so-called phenotype -- of the fingers is determined during embryonic development by the signalling protein Sonic Hedgehog, which emantes from the posterior side of the developing limb before any fingers appear. This simply means that the concentration of this protein on the little-finger side is highest and decreases toward the future thumb. Therefore each finger precursor (the cells that will develop into the finger) adjusts its gene expression -- and in consequence, its phenotype -- according to the Sonic Hedgehog concentration in its immediate environment. We have devised a hypothesis based on molecular and biomechanical mechanisms that is able to explain all the available data," said lead author Daniel Capek, who conducted research in the group of Dr. Brian Metscher and Prof. Gerd Müller in the Department for Theoretical Biology at the University of Vienna for this project and is currently a Ph.D. student at IST Austria.

According to this hypothesis, a posterior reduction in dinosaur evolution actually proceeded with the little finger being reduced and then lost, and the ring finger was partially reduced. However, it is generally much easier to reduce the outer fingers than the more central ones, as they appear later in development. Thus the first finger is reduced ("thumbs down") instead of the fourth finger, leaving an anterior area open for the early precursors of the other fingers to grow into. This would lead those developing fingers to encounter an anterior-like Sonic Hedgehog concentration and then to develop accordingly -- more like I, II, and III.

"This mechanism explains why the fingers of Archaeopteryx and modern birds have the shapes of the anterior fingers (I, II, III), even though they are actually the central fingers (II, III, IV). At the same time, this hypothesis is consistent with the fossil findings and matches the current developmental genetics results," says Brian Metscher of the Department of Theoretical Biology at the University of Vienna.

INFORMATION:

Publication in Journal of Experimental Zoology: Čapek, D., Metscher, B. D., and Müller, G. B.: Thumbs Down: A Molecular-Morphogenetic Approach to Avian Digit Homology. Journal of Experimental Zoology Part B (Molecular and Developmental Evolution), December 2013. DOI: 10.1002/jez.b.22545 http://onlinelibrary.wiley.com/doi/10.1002/jez.b.22545/pdf

Scientific Contacts Dr. Brian Metscher
Department für Theoretical Biology
University of Vienna
1090 Vienna, Althanstraße 14
T +43-1-4277-567 04
brian.metscher@univie.ac.at
http://theoretical.univie.ac.at/people/metscher/

Mag. Daniel Capek, MSc IST Austria
3400 Klosterneuburg
T +43-224-39000-7438
daniel.capek@ist.ac.at

Contact Mag. Veronika Schallhart
Press Office
University of Vienna
Research and Teaching
1010 Vienna, Universitätsring 1
T +43-1-4277-175 30
M +43-664-602 77-175 30
veronika.schallhart@univie.ac.at

ELSE PRESS RELEASES FROM THIS DATE:

Gemini Planet Imager first light

2014-01-07

Gemini Planet Imager first light World's most powerful exoplanet camera turns its eye to the sky This news release is available in Spanish. After nearly a decade of development, construction, and testing, the world's most advanced instrument for directly imaging ...

To keep their eye on the ball, batters mostly use their heads

2014-01-07

To keep their eye on the ball, batters mostly use their heads How do hitters track pitches in baseball? Study in optometry and vision science gives new insights Philadelphia, Pa. (January 7, 2014) - Baseball players at bat follow coaches' advice to "keep ...

New algorithm can dramatically streamline solutions to the 'max flow' problem

2014-01-07

New algorithm can dramatically streamline solutions to the 'max flow' problem Research could boost the efficiency even of huge networks like the Internet Finding the most efficient way to transport items across a network like the U.S. highway system or the ...

When germs attack: A lens into the molecular dance

2014-01-07

When germs attack: A lens into the molecular dance Researchers at Johns Hopkins have zoomed in on what is going on at the molecular level when the body recognizes and defends against an attack of pathogens, and the findings, they say, could influence how drugs are ...

Synthetic genetic clock checks the thermometer

2014-01-07

Synthetic genetic clock checks the thermometer Rice University leads study to counter effects of temperature on synthetic gene circuits HOUSTON – (Jan. 7, 2014) – Genetic systems run like clockwork, attuned to temperature, time of day and many other factors as they regulate ...

Dabrafenib in melanoma: Added benefit not proven

2014-01-07

Dabrafenib in melanoma: Added benefit not proven No differences could be shown for mortality, symptoms and quality of life / concerning side effects, data too uncertain Dabrafenib (trade name: Tafinlar) has been approved in Germany ...

Aflibercept in macular oedema: Added benefit not proven

2014-01-07

Aflibercept in macular oedema: Added benefit not proven Neither the new drug nor the comparator therapy was used in accordance with their approvals in the studies For the third time in one year, the German Institute for Quality ...

Increased risk of prostate cancer in African American men; implications for PSA screening

2014-01-07

Increased risk of prostate cancer in African American men; implications for PSA screening New Rochelle, NY, January 7, 2014—African American men have an increased risk of prostate cancer and are two times more likely than Caucasian American ...

Sugar-burning in the adult human brain is associated with continued growth, and remodeling

2014-01-07

Sugar-burning in the adult human brain is associated with continued growth, and remodeling Research published in the journal Cell Metabolism shows that hotspots of fuel consumption in the adult brain also show key characteristics of developing brain regions SEATTLE, ...

A CNIO research team discovers new regulators of the most prevalent liver disease

2014-01-07

A CNIO research team discovers new regulators of the most prevalent liver disease AP-1 proteins modulate fat accumulation in the liver, a disease termed fatty liver disease (FLD); the pharmacological manipulation of these proteins might help treating ...