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colors



Mickey Rowe asked several questions regarding the use of carotenoid
pigments in structures other than feathers in birds. Note  that most,
but not all. of the feather reds/yellow/orange/gold etc are due to
carotenoids.
  1. carotenoids can be deposited in other areas. Conspecious examples
include feet and beaks (all pigeons have red feet). An example in humans
is the subcutaneous fat of people who consume lots of carrots and leafy
greens. (Bell pepers are an excellent source of carotenoids). However,
in birds red structures such as combs and wattles are not colored by carotenoid
s. It's a transparent skin exposive the blood underneath--just like some
folks noses.  Mammals also produce a corpra luteum, well at least females,
that contains carotenoids.
   2. carotenoids have been recovered from reptiles and may even paly a role
in some integumentary structures. Topic not very well studied.
   3.In answer to the question as to when birds began to use carotenoids
I will assume that he means in feathers (afterall the yellow of the yoke
is carotenoid.  Because carotenoids can be found in feathers of most (?)
orders it is relatively primitive. Remember it is a secondary metabolite
and by themselves contain no usable genetic information and therefore no
phylogenetic information.  However, the pathways that lead to carotenoid modifi
cation and the mechanisms that allow absorption and selective deposition
 are likely derived, and possible polyphyletic within birds. In other words
the distribution and the nature of the pathways and capacities is not highly
 information. On the other hand, they can be wonderfully informative  in
regard to the physiology of the pigments and their relationships to the
general biology of birds.
   I might also point out that the pigments that produce the feather colors in
parrots and their relatives are probably not carotenoids. Their nature and
origin is currently unknown (my lab had wroked on this problem for several
years).

  VICKI ROSENZWEIG may be confusing colors produced by carotenoids and those
produced by melanins. Melanins are essentially polymerized molecules derived
from the amino acid tyrosine. A single enzyme is involved in the pathway
(which includes DOPA) and the colors are determined by extent of polymerization
and , in the case of some of the redder molecules the amount of iron involved.
Yes, we do refer to the kid with red hair as Rusty for good reason. The
enzymes involved here are very wide spead in all organisms. Even mushrooms
have them.
  Carotenoids are produced by plants, including single celled ones in the
ocean. Those that are included in animals are obtained from the diet and
may or may not be modified prior to being deposited.
  By the way, no higher vertebrate produce blue pigments for deposition in the
skin. These are almost always structural colors that may involve melaanins as
well. For example, the common Blue Jay on a single feather may have all
three  colors:white, blue, and black. Blue for the same reason that the sky
is blue.
   It is my understanding that in bats (and most other mammals--consider the
colors of dogs) the colors black/gray/orange yellow etc of the pelage sre
all produced by melanins. Yes, they are that varialbe! No special case for
skunks, just balck (melanin) and white (no pigment).
             Cheers,
                  Alan Brush
 Physiology & Neurobiology, University of Connecticut, Storrs