Vertebrates 5a - Colouration

Question 2

Main skin layers

Answer 2

Epidermis (stratum corneum, stratum germinativum) and dermis (stratum laxum, stratum compactum).

Question 3

Stratum germinativum

Answer 3

Epidermal stem cells and form the cells of the stratum corneum

Question 4

Stratum corneum

Answer 4

Layer of dead (often keratinized) epithelial cells. Thickness varies b/w vertebrates and within individuals, turnover (humans = constant, snakes = all at once)

Question 5

stratum laxum

Answer 5

Matrix containing glycoproteins, fibroblasts that secrete collagen, other cells and tissues. Very loose

Question 6

stratum compactum

Answer 6

Matrix containing glycoproteins, fibroblasts that secrete collagen, other cells and tissues. Compact.

Question 7

Collagen

Answer 7

Main structural component of the dermis.

Question 8

Keratin

Answer 8

Tetrapods have high levels of it, nontetrapods have less. Major structural component (hair, feathers, scales)

Question 9

Function of epithelium

Answer 9

Protection, water balance, thermoregulation (sweat glands), locomotion, gas exchange, colouration, secretion, sensory structure

Question 10

Arrector pili muscle

Answer 10

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.

Question 11

Animals without arrector pili muscles

Answer 11

Seals, it would slow them down while swimming.

Question 12

Sensory structure

Answer 12

Heat, light touch, pain, cold, strong touch

Question 13

Pigment producing cells

Answer 13

aka chromatophores, eg melanophores. Big, projections, often aromatic.

Question 14

Where are chromatophores found?

Answer 14

In mammals and birds are in epidermis. In all others are found much lower into the dermis.

Question 15

When did chromatophores develop?

Answer 15

Dinos had them, looked just like you would expect. Probably evolved as vertebrates evolved.

Question 16

Types of chromatophores and colour associated with them

Answer 16

Xanthophores (yellowish teradines; from modified bases), erythrophores (red/orange; from ß-keratin), iridophores (reflective, shiny; from nucleotide metabolism, guanine), melanophores (dark); others being discovered

Question 17

Dermal chromatophore unit

Answer 17

They work together to create the final colour as light bounces around around them

Question 18

What can affect colour?

Answer 18

Diet. If flamingoes get lots of carotenoids in diet they will have bright colours, otherwise they pale.

Question 19

Structural colouration

Answer 19

Colours refract off surface cells; certain arrangements of keratin; colours (blue, green, purple) only visible at certain angles

Question 20

When did structural colouration evolve?

Answer 20

Anciently; colour found on 40mya feather fossil; dinos might have been very coloured

Question 21

Mammalian colouration

Answer 21

Only pigment (only have melanophores), so colours not as varied.

Question 22

Mandrill

Answer 22

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

Question 23

Melanocytes

Answer 23

Produce melanin (namely eumelanin), dark brown. Black and light brown proportional to melanin and/or number of melanocytes

Question 24

Melanin production

Answer 24

Melanophores stimulated by MSH (melanocyte stimulating hormone). Pigment is produced in melanosomes (vesicles).

Question 25

MSH

Answer 25

From pituitary gland. Binds to melanocytes at Mc1r receptor (melanocortin receptor)

Question 26

Grey hair in elderly

Answer 26

Melanocytes are dying, so we lose pigment

Question 27

Pheomelanin

Answer 27

Produced when Mc1r is inactivated. It is more yellow/red. More colours from the same cell

Question 28

Mutations in Mc1r in mammals

Answer 28

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

Question 29

Spirit bear/Kermode bear

Answer 29

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

Question 30

Neanderthals

Answer 30

Some preserved specimens in ice, genome studied and looked at melanocortin receptors. Probably had varied pigment like humans

Question 31

Melatonin

Answer 31

In frogs it affects pigment; not so in humans

Question 32

Roles of skin colouration

Answer 32

Concealing/cryptic; aposematic (warning); communication (mating, silent warning (some monkeys)); thermoregulation; UV protection

Question 33

Morphological colour change

Answer 33

Gradual change in pigment over time; ex. UV radiation protection (even small amounts will cause an increase);

Question 34

Arctic hare

Answer 34

Changes colour significantly: white in winter, brown in summer. Both are cryptic.

Question 35

Whales tanning

Answer 35

Light coloured whales (like blue) actually tan seasonally; darker whales (sperm whales, etc) are pretty dark already. Data is variable since difficult to collect and pigment varies in each individual

Question 36

Physiological colour change

Answer 36

Fast. Migration of pigments within chromatophore. Some chameleons, fish, amphibians. Generally communication, some mating displays

Question 37

Flounders

Answer 37

Flat, eyes on one side, lie on floor; colour patterns match floor, some can change really fast to match substrate. They need to see the environment to match, doesn’t work if eyes are covered. Even match checkerboards.

Question 38

Mechanism of physiological colour change

Answer 38

Studied ambystoma tadpoles; can be hormonal or nervous system (faster); melanosomes migrate on cytoskeleton. If they are spread out, cell/tissue appears dark; if they move to center, it looks paler

Question 39

What stimulates physiological change (in tadpoles)?

Answer 39

MSH causes melanosome dispersion, melatonin and norepinephrine cause aggregation