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Origin of feathers and hair + alula function (free pdfs)

Ben Creisler

Two recent open-access papers that may be of interest:

Bettina Strasser, Veronika Mlitz, Marcela Hermann, Erwin Tschachler &
Leopold Eckhart (2015)
Convergent evolution of cysteine-rich proteins in feathers and hair.
BMC Evolutionary Biology (advance online publication)
DOI: 10.1186/s12862-015-0360-y

Feathers and hair consist of cornified epidermal keratinocytes in
which proteins are crosslinked via disulfide bonds between cysteine
residues of structural proteins to establish mechanical resilience.
Cysteine-rich keratin-associated proteins (KRTAPs) are important
components of hair whereas the molecular components of feathers have
remained incompletely known. Recently, we have identified a chicken
gene, named epidermal differentiation cysteine-rich protein (EDCRP),
that encodes a protein with a cysteine content of 36%. Here we have
investigated the putative role of EDCRP in the molecular architecture
and evolution of feathers.

Comparative genomics showed that the presence of an EDCRP gene and the
high cysteine content of the encoded proteins are conserved among
birds. Avian EDCRPs contain a species-specific number of sequence
repeats with the consensus sequence CCDPCQ(K/Q)(S/P)V, thus resembling
mammalian cysteine-rich KRTAPs which also contain sequence repeats of
similar sequence. However, differences in gene loci and exon-intron
structures suggest that EDCRP and KRTAPs have not evolved from a
common gene ancestor but represent the products of convergent sequence
evolution. mRNA in situ hybridization demonstrated that chicken EDCRP
is expressed in the subperiderm layer of the embryonic epidermis and
in the barbule cells of growing feathers. This expression pattern
supports the hypothesis that feathers are evolutionarily derived from
the subperiderm.

The results of this study suggest that convergent sequence evolution
of avian EDCRP and mammalian KRTAPs has contributed to independent
evolution of feathers and hair, respectively


Sang-im Lee, Jooha Kim, Hyungmin Park, Piotr G. Jabłoński & Haecheon Choi (2015)
The Function of the Alula in Avian Flight.
Scientific Reports 5, Article number: 9914

The alula is a small structure located at the joint between the
hand-wing and arm-wing of birds and is known to be used in slow flight
with high angles of attack such as landing. It is assumed to function
similarly to a leading-edge slat that increases lift and delays stall.
However, in spite of its universal presence in flying birds and the
wide acceptance of stall delay as its main function, how the alula
delays the stall and aids the flight of birds remains unclear. Here,
we investigated the function of alula on the aerodynamic performance
of avian wings based on data from flight tasks and wind-tunnel
experiments. With the alula, the birds performed steeper descending
flights with greater changes in body orientation. Force measurements
revealed that the alula increases the lift and often delays the stall.
Digital particle image velocimetry showed that these effects are
caused by the streamwise vortex, formed at the tip of the alula, that
induces strong downwash and suppresses the flow separation over the
wing surface. This is the first experimental evidence that the alula
functions as a vortex generator that increases the lift force and
enhances manoeuvrability in flights at high angles of attack.