382
Marine Bird Keratins Marine birds are defi nitively related to marine vertebrates
as described in chapters above, however, I take the liberty not to analyse the feather
keratins here in detail due to the existing literature. Both the structural biology of
feathers (Fraser and Parry 2008 ; Lingham-Soliar et al. 2010 ) and their mechanical
properties (Bonser 1996 , 2001 ; Bonser and Purslow 1995 ; Cameron et al. 2003 ;
Bonser et al. 2004 ) are well described. However, I would like to note here that today
much attention is paid to the photonic properties of bird feathers, because of the
specifi c nanostructural organization of their keratins.
One of the intriguing topics concerning bird keratins is based on identifi cation of
the colour-producing intracellular β-keratin nanostructures observed in more than
20 different families of birds (Prum 2006 ). Many birds, including marine species,
show broad variety of structural colours of their feathers. Note, that these colours
are non-iridescent! Air nanostructures localized within the medullary cells of feather
barbs and 3D sponge-like amorphous (or quasi-ordered) β-keratin are responsible
for production of these colours (see for details Prum et al. 2009 ; Clarke et al. 2010 ;
Stavenga et al. 2011 ; Shawkey et al. 2011 ; Maia et al. 2011 , 2012 ; D’Alba et al. 2012 ).
Two main classes of three-dimensional barb nanostructures are known, characterized
by a tortuous network of air channels or a close packing of spheroidal air cavities
(Saranathan et al. 2012 ). For example, the non-iridescent blue feather barbs of blue
penguins ( Eudyptula minor ) contain a some kind of biophotonic nanostructure
(D’Alba et al. 2011 ). “It is composed of parallel β-keratin nanofi bres organized into
densely packed bundles. Synchrotron small angle X-ray scattering and twodimensional Fourier analysis of electron micrographs of the barb nanostructure
revealed short-range order in the organization of fi bres at the appropriate size
scale needed to produce the observed colour by coherent scattering. These twodimensional quasi-ordered penguin nanostructures are convergent with similar
arrays of parallel collagen fi bres in avian and mammalian skin, but constitute a
novel morphology for feathers. The identifi cation of a new class of β-keratin nanostructures adds signifi cantly to the known mechanisms of colour production in
birds, and suggests additional complexity in their self-assembly,” (D’Alba et al. 2011 ).
Eliason and Shawkey ( 2012 ) investigated Dabbling ducks (Anatinae), which are
“a speciose clade with substantial interspecifi c variation in the iridescent coloration
of their wing patches (specula). In all species examined, speculum colour is produced
by a photonic heterostructure. This consists of both a single thin-fi lm of keratin and
a two-dimensional hexagonal lattice of melanosomes in feather barbules. Although
the range of possible variations of this heterostructure is theoretically broad, only
relatively close-packed, energetically stable variants producing more saturated
colours were observed, suggesting that ducks are either physically constrained to
these confi gurations or are under selection for the colours that they produce,”
(Eliason and Shawkey 2012 ).
Recently, it was found that the sponge in the feather barbs of scarlet macaw ( Ara
macao ) “is an amorphous diamond-structured photonic crystal with only short- range
order. It possesses an isotropic photonic pseudogap that is ultimately responsible for
the brilliant noniridescent coloration. The researchers further unravel an ingenious
11 Marine Keratins
Marine Bird Keratins Marine birds are defi nitively related to marine vertebrates
as described in chapters above, however, I take the liberty not to analyse the feather
keratins here in detail due to the existing literature. Both the structural biology of
feathers (Fraser and Parry 2008 ; Lingham-Soliar et al. 2010 ) and their mechanical
properties (Bonser 1996 , 2001 ; Bonser and Purslow 1995 ; Cameron et al. 2003 ;
Bonser et al. 2004 ) are well described. However, I would like to note here that today
much attention is paid to the photonic properties of bird feathers, because of the
specifi c nanostructural organization of their keratins.
One of the intriguing topics concerning bird keratins is based on identifi cation of
the colour-producing intracellular β-keratin nanostructures observed in more than
20 different families of birds (Prum 2006 ). Many birds, including marine species,
show broad variety of structural colours of their feathers. Note, that these colours
are non-iridescent! Air nanostructures localized within the medullary cells of feather
barbs and 3D sponge-like amorphous (or quasi-ordered) β-keratin are responsible
for production of these colours (see for details Prum et al. 2009 ; Clarke et al. 2010 ;
Stavenga et al. 2011 ; Shawkey et al. 2011 ; Maia et al. 2011 , 2012 ; D’Alba et al. 2012 ).
Two main classes of three-dimensional barb nanostructures are known, characterized
by a tortuous network of air channels or a close packing of spheroidal air cavities
(Saranathan et al. 2012 ). For example, the non-iridescent blue feather barbs of blue
penguins ( Eudyptula minor ) contain a some kind of biophotonic nanostructure
(D’Alba et al. 2011 ). “It is composed of parallel β-keratin nanofi bres organized into
densely packed bundles. Synchrotron small angle X-ray scattering and twodimensional Fourier analysis of electron micrographs of the barb nanostructure
revealed short-range order in the organization of fi bres at the appropriate size
scale needed to produce the observed colour by coherent scattering. These twodimensional quasi-ordered penguin nanostructures are convergent with similar
arrays of parallel collagen fi bres in avian and mammalian skin, but constitute a
novel morphology for feathers. The identifi cation of a new class of β-keratin nanostructures adds signifi cantly to the known mechanisms of colour production in
birds, and suggests additional complexity in their self-assembly,” (D’Alba et al. 2011 ).
Eliason and Shawkey ( 2012 ) investigated Dabbling ducks (Anatinae), which are
“a speciose clade with substantial interspecifi c variation in the iridescent coloration
of their wing patches (specula). In all species examined, speculum colour is produced
by a photonic heterostructure. This consists of both a single thin-fi lm of keratin and
a two-dimensional hexagonal lattice of melanosomes in feather barbules. Although
the range of possible variations of this heterostructure is theoretically broad, only
relatively close-packed, energetically stable variants producing more saturated
colours were observed, suggesting that ducks are either physically constrained to
these confi gurations or are under selection for the colours that they produce,”
(Eliason and Shawkey 2012 ).
Recently, it was found that the sponge in the feather barbs of scarlet macaw ( Ara
macao ) “is an amorphous diamond-structured photonic crystal with only short- range
order. It possesses an isotropic photonic pseudogap that is ultimately responsible for
the brilliant noniridescent coloration. The researchers further unravel an ingenious
11 Marine Keratins