Yesterday, I headed down to the beautiful Bell House in the Gowanus section of Brooklyn. After a 2-hour slog on the subway (a broken rail on the "6" line at Canal St had the entire Lexington Avenue corridor, 4-5-6 trains, clogged up just in time for the evening rush hour), I got to my destination to attend the latest Secret Science Club lecture, featuring Dr David Gruber of the City University of New York, the American Museum of Natural History, and the Central Caribbean Marine Institute. Dr Gruber's talk concerned biofluorescence in marine organisms, and the importance of the discovery of biofluorescent proteins.
Dr Gruber opened his lecture by noting that it was his first lecture in a bar- he was quite taken with the whole concept. He then began in earnest with a discussion of the "human visual world"- the human visible spectrum ranges from 400 to 700 nanometer wavelengths. We live in Roy G. Biv's world. Some animals are able to see into the infrared and ultraviolet portions of the spectrum. Underwater, the spectrum is reduced- water filters out non-blue light, so the underwater color world is marked by a sharply decreasing "palette".
Dr Gruber then mentioned Aequorea victoria, the crystal jelly, which produces Green Fluorescent Protein- when the animal is poked, it produces a blue light which, due to a Förster resonance energy transfer is shifted to green light. Because of water's filtering effects, blue light travels farther than green light, so many bioluminescent animals produce a blue light. The filtration effect renders white light into blue light, which is reflected back as lesser energy green light.
The talk then shifted to an overview of corals, which evolved rather suddenly about 200 million years ago. Corals are Cniadarians, as are jellyfish and sea anemones. Dr Gruber likened corals to jellyfish trapped in a calcium carbonate "rock" of their own making. Like other cnidarians, they use a single orifice as both "mouth" and "anus" and they have stinging nematocysts. Most corals have symbiotic dinoflagellates associated with them- the photosynthetic dinoflagellates, which provide much of the corals' energy, limit corals to well-lit ocean depths. The various polyps which form a coral colony are clones connected by a structure known as a coenosarc. Reef-building corals largely occur in two geographic zones, the Caribbean and the Indo-Pacific. Since corals are cnidarians, it was probable that they would also be fluorescent (this was borne out as these beautiful images attest.
Why would sessile corals fluoresce? It is possible that corals fluoresce green in order to cause a phototaxis to attract their dinoflagellate symbionts. Dr Gruber made a parenthetical note that dinoflagellates tend to have huge chromosome counts, with up to twenty-five times the amount of DNA that humans have.
Dr Gruber then went off on a brief tangent that he called the "Electric Kool-Aid Coral Acid Test". In an experiment performed to determine the effects of ocean acidification on corals, a specimen of the Oculina patagonica coral was subjected to a water with a decreasing pH level (from 8.1 to 7.4). As the pH level decreased, the coral polyps became increasingly disconnected from their calcium carbonate matrix and took on the appearance of sea anemones (Dr Gruber showed a time-lapse video of the experiment, but I have been unable to locate it yet). He then brought up the "Naked Coral Hypothesis", which posits that the "overnight" appearance of coral in the Triassic fossil record was probably due to increasing pH levels which allowed coral polyps to form their calcium carbonate "rocks". Because many corals can revert to anemone-like polyps, they have an "escape hatch" in conditions of increasing acidity. Dr Gruber wryly quipped that, in the case of increasing ocean acidification, "worry about your own shit, you can't turn into a polyp."
Dr Gruber then moved on from corals to the discovery of biofluorescence in vertebrates, - on one particular dive to photograph fluorescent corals, a bright-green fluorescent eel, a false moray Kaupichthys hyoproroides stood out in the foreground of one photograph... it was the first fluorescent vertebrate ever found.
Dr Gruber described his research as taking place in three "generations"- the first generation involved using lights with filters duct-taped to them (he praised the uses of duct tape during his lecture). The second generation involved the use of better lights powered with motorcycle batteries- he assured us that the lights were "perfectly safe". The second generation equipment was taken to Shark Point in the Solomon Islands. While diving in the Solomons, the researchers found two hundred new species of fluorescent fish. Many of the fish had a yellow intraocular filter which allowed them to perceive biofluorescent organisms. Dr Gruber observed that the fluorescence may serve as camouflage, with red fluorescent organisms preferring red backgrounds and green fluorescent organisms preferring green backgrounds. This portion of the lecture was accompanied by gorgeous photographs and videos. In the case of some biofluorescent fish, they appeared identical to closely related species under normal light conditions, but they fluoresced in different patterns, which may facilitate spawning in the light of the full moon.
On one particular dive, a fluorescent ray was spotted, which raised the possibility that certain sharks may be fluorescent. Regarding the prospect of diving in search of fluorescent sharks, Dr Gruber noted that he had spent six years of his life working on his PhD in windowless rooms and now he is wearing a helmet and a shark suit to work. He went on a brief tangent about diving at night and told us that the shark wrangler that accompanied the expedition had never "wrangled" at night. The first shark discovered to be fluorescent was a swell shark (Cephaloscyllium ventriosum) and a chain shark (Scyliorhinus retifer) was found to be fluorescent soon afterwards. He went on a brief tangent about shark vision, with especial attention drawn to the bigeye thresher shark )Alopias superciliosus), noting that the sharks' eyes may have evolved to seek bioluminescent animals. He also noted that shark's acute sensory arrays also included the electroreceptors known as ampullae of Lorenzini and a sense of smell that isn't tuned to sense blood per se, but amino acids.
Dr Gruber described the third generation of his research as involving the use of a submarine with movie-projector quality LED lights and fiber optics (a big step up from duct tape) and showed us a picture of himself in a deep-sea diving suit that had been modified to accommodate the special light and photographic equipment. Using the deep-diving apparatus, the team discovered that there was a plethora of biofluorescent organisms at depths below 500 meters.
Dr Gruber finished his talk with a discussion of the importance of Green Fluorescent Protein in research- the discoverers of GFP were awarded the 2008 Nobel Prize in Chemistry. Green Fluorescent Protein can be "attached" to "proteins of interest". Beta tubilin can be tagged with GFP to help researchers study mitosis. Tagging kinases with GFP can assist in the development of cancer drugs (this particular topic is reminiscent of last month's lecture.
Finally, GFP offers a window into human consciousness- neurons can be tagged with GFP, a change in the intensity of fluorescence occurs when the neurons fire- Dr Gruber likened this to observing "consciousness in real time".
Dr Gruber finished his lecture by underscoring the importance of further research in conservation efforts, noting that it is estimated that only 10% of the species associated with coral reefs are believed to be known, and that you can't protect what you don't love.
Once again, the Secret Science Club offered up a spectacular lecture. Dr Gruber's talk hit that sweet spot at the intersection of hard science, adventure narrative, and humorous anecdotes from a life well-lived, plus some incredibly gorgeous photography and video footage. As I listened to Dr Gruber, I continually thought, "This is a person who is utterly enamored with his life's work." The man clearly loves what he is doing and he loves to share his work with others. In the Q&A some bastard in the audience asked about the number of taxa that exhibit biofluorescence, and what inferences can be drawn about the evolution of this phenomenon. Dr Gruber noted that it's clearly a case of convergent evolution, with fluorescence evolving multiple times- he noted that no fluorescent bacteria have been discovered, so this is not a case of the involvement of bacterial symbionts.
The research team to which Dr Gruber belongs has a beautiful website- seriously, you can become lost in the utter beauty of the images on the site, while reading about the methodology they employ.