lecture 18: transparency & bioluminescence

Question 1

Options for avoiding search/detection phase of visual predators?

Answer 1

• Mirrored surfaces
• like fish scales
• Counter shading/illumination
• Transparency

***these things minimize contrast

Question 2

How is transparency achieved?

Answer 2

1. Eliminate pigments
   - problems: eyes, food in gut, sunscreens
2. Thinness
3. Surface micro-bumps
   - blurs the outline of organism
4. Ultrastructural specializations

Question 3

how to fix problems w eyes, food in gut, and sunscreens?

Answer 3

fibre optic eyes

Mirrored guts or red-pigmented guts

carotenoids in copepods (pigmentation) to protect from UV

Question 4

Bioluminescence

Answer 4

Definition:
A chemical reaction within an organism that emits light

Mechanism:
Luciferin – substrate that emits light when oxidized Luciferase – enzyme that catalysis the reaction
OR
Photoprotein
- molecule with binding sites for luciferin & O2
- co-factor (usually Ca++) causes conformational
change of photoprotein allowing interaction between luciferin and O2)

***reaction needs oxygen and a co-factor which allows them to bind

• luciferase acts as catalyst
• oxygen combines with luciferin
• oxidized luciferin becomes inactive oxyluciferin

Question 5

Bioluminescence in the Ocean

Answer 5

• 80% of pelagic animals in ocean emit light
• Bioluminescence is major source of light for much of ocean (mesopelagic zone)
• Mostly blue light emission (470nm)
• Evolved minimum of 40X
• Most bioluminescent organisms do NOT get their light from symbiosis with bioluminescent bacteria
• Original evolutionary origin? Antioxidant hypothesis

Question 6

Bioluminescence - Functions (4)

Answer 6

1) communication - sexual signals

2) attraction of prey - lures

3) illumination of prey - bioluminescent flashlights

4) defense from predators

Question 7

bioluminescent functions/tactics

Answer 7

1) startle

2) counter illumination
- photophores in cephalopods

3) misdirection: smoke screen
- shrimp spews bioluminescent cloud

4) distractive body parts
- anglar fish

Question 8

Burglar alarm hypothesis

Answer 8

• Organism #1 is preyed upon by organism #2, which in turn is preyed upon by organism #3
• Organism #1 emits light when attacked by organism #2
• Light attracts organism #3, which is a predator of organism #2