Neurobehavior:Lect. 5/8

Reading: There was an 8-page handout provided in lecture on Friday, May 12. It is an essay on the "Ecology of Bioluminescence" written by Dr. Case, et al. 1994.

Three excellent web sites on Bioluminescence that were developed in Dr. Case's lab, Mike Latz's lab at Scripps, or Edie Widder's lab at Harbor Branch Oceanographic are linked/listed below. I highly recommend all three as they focus on different aspects of BL and have beautiful pictures.

Bioluminescence (BL): the production of light by way of a chemical reaction that occurs inside of an organism.

Bioluminescence is NOT (see the links below for diagrams of the listed processes)

Chemistry of the BL Reaction

All BL reactions are oxidation reactions, most are catalyzed by an enzyme given the generic name, luciferase (remember molecules or proteins with names ending in "ase" are always enzymes)
The substrate, the molecule that actually is oxidized by O₂ and emits light is luciferin
This reaction is very effecient (.9 quantum effeciency), the by-product of the reaction is light
Luciferase is a mixed-function oxidase. There are many of these in your body and in all organisms. Many non-enzymatic oxidation reactions produce a very dim light. It has been hypothesized that this by-product (light) was capitalized upon for the evolution of ecologically significant light production by organisms, bioluminescence.
Some organisms have a chemical system in which there is a protein that functions as the luciferase anda binder of the luciferin. This system is activated by Ca⁺².

Color of BL

In the ocean, most BL is blue (because blue light travels furthest in water, therefore your "light signal" can be seen over the longest distance & the environment is dominated by blue light, so producing blue light helps you blend in with your environ.)
On land, most BL is greenish-yellow (yellow-green light travels furthest)
How color variations are achieved: molecular modifications of luciferases and/or "partner" fluorescent proteins (e.g., GFP), a wavelength-shifting molecule.

BL is an evolutionarily successful mechanism

Unlike visual systems, which are thought to all be evolutionarily linked (PAX-6 genes, rhodopsin molecular similarity), BL has ~ 30 independent evolutionary origins
Indicates a tremendous driving force acting on this mechanism (we’ll see by all the varied examples of uses of BL in so many diverse organisms)
There was no one common BL ancestor that all existing BL organisms had
Evidence:
- Variety of Luciferin Structures
- Random distribution of groups that possess BL within evolutionary tree: break in the flow: some bacteria and single-celled protists are BL, but no flatworms or sponges are, yet higher organisms exhibit BL.
- Biochemical control mechanisms differ widely

Another indicator of the ecological importance of BL: Animals do whatever they can to be BL

“borrowed BL” via culturing BL bacteria in special pouches
make the chemicals yourself = endogenous manufacturing
eat things that are BL “vicarious luciferins”, must obtain substrate from diet

Distribution of BL in Ocean

Predominant sources of BL changes with depth
- surface: usually dinoflagellates
- midwater: crustaceans, jellies (some fish)
- deep: fish, benthic organisms

More on the Importance of BL

Deep Sea Animals have well-developed eyes, but there is no celestial light that penetrates to that depth (>1000 m)
Why maintain vision if there is no light to see?
There must be a lot of BL to maintain eyes over millions of years of evolution

Why has BL evolved so many different times?

Because there are so many different driving forces that have caused the evolution of this mechanism.
To illustrate how adaptive BL appears to be let’s examine some of it’s many uses:

Ecological Uses or Functions of BL in organisms

There is a web site put together by a colleague of ours that has excellent short descriptions and pictures of most of the functions I list below. Go there to review functions of BL. (Also, I took the pics of the fish below from her site: Edie Widder, HBOI).

Defense (to help avoid predation)
- vision: flashlight fish
- decoy: (squirt and run) ostracods , squid, shrimp. Apparent motion in sea pens and Renilla
- burglar alarm hypothesis: Exp. with Euprymna and dinos (SLIDE)
- Counterillumination: Porichthys (SLIDES), Myctophids (Lanternfish), Sergestes, Euphausiids, Anglerfish (photophores angled towards its tail because it hangs vertically in water w/ mouth up), squid
- Startle: Jellies, Dinos(?), Retractable Sea Pens
Offense (to aid in predation)
- Vision/Light to spy by: the black dragonfish: Malacosteus, Aristostomias, Pachystomias (Deep Red photophore below eyes) (SLIDES/WEB); flashlight fish
- Counterillumination/Camouflage: Porichthys (SLIDES), Myctophids (Lanternfish), Sergestes, Euphausiids, Anglerfish (photophores angled towards its tail because it hangs vertically in water w/ mouth up), squid
- Prey Lure: deep sea fish (Angler fish), Firefly: femme fatale
- Phototaxis: New Zealand glow worm; flashlight fish
Communication (intraspecies)
- for courtship/mating: fireflies, ostracods, flashlight fish, Bermuda fireworm
Metabolic/Biochemical (light-emission may be purely coincidental, as a by-product of some adaptive reaction)
- terminal oxidase: bacteria
Other
- attract predators (bacteria, auto induction)
- deter settling: Chaetopterus
- aposematic: fireflies, brittle stars
Ecosystem Effects (see reading assignment)
- spontaneous emission of light in order to evaluate the # of same species organisms nearby
- visual organisms can watch for luminescent displays (that occur during a predator-prey interaction) and use this as a means of estimating the density of organisms in that particular region of the ocean.
- recycling of nutrients (marine snow) that might have otherwise sunken out of photic zone (it is recycled by grazers that are attracted to the dim glow of bioluminescent bacteria that have colonized the marine snow)

EEMB 160 : The Neural Basis of Behavior, "Neurobehavior"