Vision and Light Flashcards
HOw far does light penetrate ??
Most light in a visbaly wavelength to be attenuated to about 200
Blue light detectable to around 1000 m
Red wavelengths that we loose the quickest
Definition for eyes
………. ‘pigments capture photons which triggers an electrical signal. Pigments are located in the membranes of specialised receptor cells, often grouped into specialised optical structures’
What are dep sea eyes adaptated to
Deep-sea eyes need to detect small, weak light sources so sensitivity is more important than acuity
Balance maintained by the selection pressures of the light environment at different depths, time spent at each depth and task undertaken
Retinas commonly contain two types of receptor cells
RODS and CONES
CONES are capable of colour perception and have high visual acuity
Cones – colour protection and high visual acuity
RODS require a lower photon flux and are of value during dim light
What are visual pigments made up of?
Different cells contain different pigments providing broad-band spectral sensitivity Visual pigments are made up of a protein (opsins) and a chromatophore (vitamin A1 or A2) Rhodopsins (shorter λ) and porphyropsins
Receptor cells and retinal adaptations to the depe sea
- Loss of cone cells in response to low light levels
- Increased length of rod cells or multiple banks of rods
- Increase the length of the light path = increased photon absorption
- Can also be doubled by having a mirror or tapetum behind the retina
- Optical density of pigment increase photon absorption
- Absorption spectra of the pigments need to be matched to the entering light
- Deep-sea fishes have only one pigment in their rods, and only rods in the retina
Where can bioluminescne be prodiuced?
- 1.Single cells: photocytes e.g. dinoflagellates and radiolaria. Also occur in aggregates on body of holothurians, nudibranchs and amphipods
- 2.Internal glandular organs: internal photocytes produce secretion not expelled to exterior
- 3.External glandular organs: glands with photocytes that open to exterior eg Oplophorid and pandalid decapods secrete bioluminescent substance from the mouth
- open to exterior
- Escape response – shoot out jet of mucous and then swim away
- 4.Symbiont glands: luminous organs of many fish and cephalopods have glands with symbiotic bacteria. All glands open to the exterior
- Specific glands where you are hosting symbiotic bacteris – producing luciferin product
How does the structure of the pigment affect the bioluminescence?
Photocyte housed within pigmented – helps focus colour of light within a specific wavelength
Enhance directionality and focus of light with reflectors
Lenses in front of photophore
Lense attached to muscular laminealla rings
How are different filters used to direct bioluminescence light?
- Pigment absorbs bioluminescence
- Reflector reflects bioluminescence outwards
- In most fish, cephalopods and crustaceans
- Photocyte housed within pigmented – helps focus colour of light within a specific wavelength
Enhance directionality and focus of light with reflectors
Lenses in front of photophore
Lens attached to muscular laminealla rings
*
How do animals turn off bioluminescence?
Light on and off – more scope for the complexity of how you can signal Flashlight fish
Huge sub-ocular photophore
- Chromatophores expanded or dispersed
- Photophore is rotated so light is directed inwards
- An opaque shutter is drawn across the aperture
Flash Light Fish - Anomalopidae
- Nocturnal Predator
- Bacterial light organ
- illuminates prey functions as “bait
- Five genera and six species worldwide
- Two species raise skin flaps to control emission
- Two species lack skin flaps; use organ rotation
- Two species use both skin flaps and organ rotation
What produces mucous excretions?
Vargula norvegica -
Deep-sea ostracod
Give an example of light being used for defence
Meganyctiphanes norvegica -
Arctic Krill
Bioluminescence is ‘intracellular’
- produced within the photophores which are visible to the naked eye as ten prominent red spots
- One pair occurs on the eyestalks, a pair on each of the second and seventh thoracic segments, and a single organ is found ventrally on the first to fourth abdominal segments
- Each organ is made up of a light-producing element which has a lens in front and a red-pigment reflecting layer behind it
The special case of Malacosteus
Deep you go greater proportion of animals have a red pigment
Red colour becomes invisible
Blue light interact with red pigment
Red light emitted by dragonfish will illuminate (white) red coloured species
summary
- Eyes of fishes adapted for not only low light but to wavelength of biologically produced light
- Tubular eyes -loss of cone cells & banks of rods
- Bioluminescence – same reaction produced in 4 ways
- For defence and attack (lures)
- Complex reflectors and shutters to direct light
- Speciation in action!
- Target scopes – red light!
