Flashcards in Vertebrates 5a - Colouration Deck (38)
Main skin layers
Epidermis (stratum corneum, stratum germinativum) and dermis (stratum laxum, stratum compactum).
Epidermal stem cells and form the cells of the stratum corneum
Layer of dead (often keratinized) epithelial cells. Thickness varies b/w vertebrates and within individuals, turnover (humans = constant, snakes = all at once)
Matrix containing glycoproteins, fibroblasts that secrete collagen, other cells and tissues. Very loose
Matrix containing glycoproteins, fibroblasts that secrete collagen, other cells and tissues. Compact.
Main structural component of the dermis.
Tetrapods have high levels of it, nontetrapods have less. Major structural component (hair, feathers, scales)
Function of epithelium
Protection, water balance, thermoregulation (sweat glands), locomotion, gas exchange, colouration, secretion, sensory structure
Arrector pili muscle
Raises hair which can trap air as insulation, or to look bigger; not as useful for humans, not enough hair (vestigial reflex). Stimulated by sympathetic nervous system.
Animals without arrector pili muscles
Seals, it would slow them down while swimming.
Heat, light touch, pain, cold, strong touch
Pigment producing cells
aka chromatophores, eg melanophores. Big, projections, often aromatic.
Where are chromatophores found?
In mammals and birds are in epidermis. In all others are found much lower into the dermis.
When did chromatophores develop?
Dinos had them, looked just like you would expect. Probably evolved as vertebrates evolved.
Types of chromatophores and colour associated with them
Xanthophores (yellowish teradines; from modified bases), erythrophores (red/orange; from ß-keratin), iridophores (reflective, shiny; from nucleotide metabolism, guanine), melanophores (dark); others being discovered
Dermal chromatophore unit
They work together to create the final colour as light bounces around around them
What can affect colour?
Diet. If flamingoes get lots of carotenoids in diet they will have bright colours, otherwise they pale.
Colours refract off surface cells; certain arrangements of keratin; colours (blue, green, purple) only visible at certain angles
When did structural colouration evolve?
Anciently; colour found on 40mya feather fossil; dinos might have been very coloured
Only pigment (only have melanophores), so colours not as varied.
Males are very coloured on the skin of the snout and rump. They actually have structural colouration. Collagen organized regularly, allows for refraction of light
Produce melanin (namely eumelanin), dark brown. Black and light brown proportional to melanin and/or number of melanocytes
Melanophores stimulated by MSH (melanocyte stimulating hormone). Pigment is produced in melanosomes (vesicles).
From pituitary gland. Binds to melanocytes at Mc1r receptor (melanocortin receptor)
Grey hair in elderly
Melanocytes are dying, so we lose pigment
Produced when Mc1r is inactivated. It is more yellow/red. More colours from the same cell
Mutations in Mc1r in mammals
Mutation in the gene causes red hair. They produce less eumelanin so fair skin and they produce more pheomelanin so red hair. More prone to skin cancer
Spirit bear/Kermode bear
A type of black bear. Black bear can give birth to kermode bear. Kermode has mutation in Mc1r, much less pigment produced. Not an albino! It still has some pigment
Some preserved specimens in ice, genome studied and looked at melanocortin receptors. Probably had varied pigment like humans