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Feather development papers



From: Ben Creisler
bh480@scn.org


Some recent articles about feathers that might be apply to dinosaurs:

Foth, Christian (2011)
The morphology of neoptile feathers: Ancestral state reconstruction and its
phylogenetic implications.
Journal of Morphology 272 (4):387?403, April 2011
DOI: 10.1002/jmor.10916
http://onlinelibrary.wiley.com/doi/10.1002/jmor.10916/abstract

Avian neoptile feathers are defined as the first feather generation, which
covers the chick after hatching, and usually described as simple structures
consisting of numerous downy barbs which are radially symmetrically
arranged and come together in a short calamus. In contrast, in some birds
(e.g., Anas platyrhynchos, Dromaius novaehollandiae) the neoptile feathers
have a prominent rhachis, and therefore display clear bilateral symmetry.
Because the symmetrical variety found in neoptile feathers is poorly
understood, their morphology was studied in a more comprehensive and
phylogenetic approach. Neoptile body feathers from over 22 bird species
were investigated using light microscopy, SEM, and MicroCT. Characters such
as an anterior?posterior axis, a central rhachis, medullary cells, and
structure of the calamus wall were defined and mapped onto recent
phylogenetic hypotheses for extant birds. It can be shown that bilaterally
symmetric neoptile feathers (with a solid calamus wall) were already
present in the stem lineage of crown-group birds (Neornithes). In contrast,
simple radially symmetric neoptile feathers (with a fragile calamus wall)
are an apomorphic character complex for the clade Neoaves. The simple
morphology of this feather type may be the result of a reduced period of
development during embryogenesis. To date, embryogenesis of neoptile
feathers from only a few bird species was used as a model to reconstruct
feather evolution. Because this study shows that the morphology of neoptile
feathers is more diverse and even shows a clear phylogenetic signal, it is
necessary to expand the spectrum of ?model organisms? to species with
bilaterally symmetric neoptile feathers and compare differences in the
frequency of feather development from a phylogenetic point of view. 


Heller, K, (2011) How Bird Necks Get Naked. PLoS Biol 9(3): e1001029.
doi:10.1371/journal.pbio.1001029
http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.10010
29


Mou C, Pitel F, Gourichon D, Vignoles F, Tzika A, et al. (2011) Cryptic
Patterning of Avian Skin Confers a Developmental Facility for Loss of Neck
Feathering. PLoS Biol 9(3): e1001028. doi:10.1371/journal.pbio.1001028
http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.10010
28

Vertebrate skin is characterized by its patterned array of appendages,
whether feathers, hairs, or scales. In avian skin the distribution of
feathers occurs on two distinct spatial levels. Grouping of feathers within
discrete tracts, with bare skin lying between the tracts, is termed the
macropattern, while the smaller scale periodic spacing between individual
feathers is referred to as the micropattern. The degree of integration
between the patterning mechanisms that operate on these two scales during
development and the mechanisms underlying the remarkable evolvability of
skin macropatterns are unknown. A striking example of macropattern
variation is the convergent loss of neck feathering in multiple species, a
trait associated with heat tolerance in both wild and domestic birds. In
chicken, a mutation called Naked neck is characterized by a reduction of
body feathering and completely bare neck. Here we perform genetic fine
mapping of the causative region and identify a large insertion associated
with the Naked neck trait. A strong candidate gene in the critical
interval, BMP12/GDF7, displays markedly elevated expression in Naked neck
embryonic skin due to a cis-regulatory effect of the causative mutation.
BMP family members inhibit embryonic feather formation by acting in a
reaction-diffusion mechanism, and we find that selective production of
retinoic acid by neck skin potentiates BMP signaling, making neck skin more
sensitive than body skin to suppression of feather development. This
selective production of retinoic acid by neck skin constitutes a cryptic
pattern as its effects on feathering are not revealed until gross BMP
levels are altered. This developmental modularity of neck and body skin
allows simple quantitative changes in BMP levels to produce a sparsely
feathered or bare neck while maintaining robust feather patterning on the
body.







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