Chapter 4: Part 2 Flashcards
Describe how activation of genes Bmp2 and Shh account for the evolutionary development of feathers
- signaling of molecules reployed after the placode forms
- their domains of expression overlap, stimulating growth of an elongated epidermal tube
- both genes are re-deployed again to the sides of the shaft of growing feather; they mark tissue to be removed to form the barbs of a feather
- the pattern of the 2 genes change from vertical building; strips are forming on one side and stop on the other
- the side without formation forms the rachis rather than barbs
2 types of feather color
- pigments and structural coloration
Pigments
- in feather tissue itself
- proteins of colors
- includes melanins, carotenoids, pterin, porphyrins, and Psittacofulvins
Melanins
- most common
- earth tones
- eumelanin(black and gray)
- Pheomelanin(red brown, rufous, and buff tan)
Melanosomes
- melanin-containing bodies within skin cells and feathers
- shapes can often point to coloration with these
Carotenoids
- yellow, orange, or red pigments
- zeaxanthin is yellow dietary example
How do they produce different carotenoid plumage colors?
- they are produced by different pigment molecules, which vary in the length of the central chain of alternating carbon double bonds
- the birds can ingest pigment to modify their own pigment metabolically; pigments with longer or shorter chains of double bonds
- the longer the chain, the longer the wavelength of color
Pigment Psittacofulvins
- bright yellow, orange, and red feathers in parrots
- tetradecahexanal
Pigment Porphyrins
- chemically related to iron-containing red hemoglobin and to the manganese-containing green chlorophyll pigments of plants
-turacin
(however, most greens are NOT pigments)
Pigment Pterin
- the golden yellow crest and facial feathers of penguins
Structural Colors
- produced by the structure of the feather instead of pigments
- deals with nanostructure (orientation and structure reflects certain wavelengths of light)
Name the four types of structural colors
- Constructive interference
- Destructive interference
- Coherent Scattering
- Incoherent Scattering
Constructive Interference
Occurs when the maxima of two waves add together (the two waves are in phase), so that the amplitude of the resulting wave is equal to the sum of the individual amplitudes
2 wavelengths add up to create a 3rd
Destructive Interference
If the crests of one wave coincide with the troughs of the other wave, the resulting amplitude is decreased or may even be completely canceled
Coherent Scattering
A form of electromagnetic wave in which photons share the same frequency and wavelengths are in phase with one another
Incoherent Scattering
Photons are in different frequencies and are out of phase
Examples of Constructive Interference
- iridescence: change in hue with angle of observation or illumination
(from arrays of melanosomes in the beta-keratin of feather barbules) - iridescent plumage colors are produced by constructive interference from arrays of melanin granules in the feather barbules
(Violet-backed starling, Bird-of-paradise)
example of Incoherent reflectance
- produces white, Rock ptarmigan
Describe Non-iridescent colors
- they are produced by spongy nanostructures made of air bubbles and beta-keratin inside of the medullary cells of feather barb rami
- light goes through spongy layer keratin/air matrix and bounces back desired color to bird(through color-producing cells that contain light scattering vacuoles), other wavelengths collected by a bottom black melanin layer
(ex: bluebird, Red-legged honeycreeper)
Describe a bird with structural and pigmentary color
- Paradise Tanager (blue belly and neon green crown feathers)
- has identical feather nanostructures, but green crown contains yellow carotenoid pigments(zeaxanthin and lutein)
- yellow pigments absorb blue and ultraviolet wavelength to created a neon green color
What are Pterylae?
- feather tracts
What is Apteria?
few or no contour feathers
Describe feather erector muscles
- runs between follicles of neighboring feathers within a feather tract
- contraction of erector muscles rotates the feathers upwards
Depressor muscles
- run between the follicles of neighboring feathers within a feather tract
What is the location of the uropygial gland?
- located at the base of tail, lower back of most bird
What is the function of the uropygial gland?
- produces a rich oil of waxes, fatty acids, fat, and water
- Cleans feathers and preserves feather moistness and flexibility
- Functions as an insulating and waterproofing layer
- Helps to regulate the parasitic bacteria and fungi that grow on feathers
