Story URL: http://news.medill.northwestern.edu/chicago/news.aspx?id=217273
Story Retrieval Date: 3/28/2015 9:21:12 AM CST
"Let there be light" sets foundations for religion, science and art. And there is light, even in the darkest of places – the ocean’s depths. The illumination is fed through the power grid of a little-known phenomenon called bioluminescence.
The dazzling visual displays remain largely unexplored and even less understood. Yet, most of us are aware of it. Bioluminescence made a grand guest appearance in the Oscar winning movie Life of Pi. The scene shows the ocean glowing with life one night.
In the real world, bioluminescence is at the heart of humanity’s search for the giant squid and even efforts to target cancer drugs.
In an illuminating recent lecture, Harvard professor and photobiology expert Woodland Hastings attempted to shed some light on the topic. The Chicago Council on Science and Technology organized the event, and, afterwards, Hastings sat down with Medill News Service reporter Ajai Sreevatsan to answer a few questions.
Q. What is bioluminescence?
A. It is the property that causes living organisms to emit light. Though the most well-known example would be the firefly, the true breath and diversity of bioluminescence is found in the seas. There are places in Puerto Rico and Australia where swaths of the coastline start glowing at night. Some of these phosphorescent bays can even be seen from space.
Q. What is the point of this visual display? Why do these organisms spend so much energy creating light?
A. There is no clear answer to that question. Some of them use it as a mating display. Some fish such as the Angler use it as a decoy to attract prey. But bioluminescence is spread widely across the tree of life. You can find it in fungi as well as fish. There are mushrooms that glow at night. In many cases, different genes are involved, which means the underlying chemistry is different. That's remarkable. That means bioluminescence evolved independently in different phyla, instead of from a common ancestor. That makes it difficult for evolutionists to explain the phenomenon. The evolutionary advantage of luminescence is also unclear and requires further study.
Q. So, do you mean to say bioluminescence defies the logic of natural selection?
A. No. I think bioluminescence evolved not as a selection for light emission, but as a selection for removal of oxygen. I am proposing that the spectacular light display is just incidental. About 3.6 billion years ago, when the earliest known life forms were beginning to make an appearance, our planet was going through a transformation. The oxygen content in the atmosphere was slowly rising. These organisms would have never experienced oxygen before. And like present day anaerobic organisms, they would have been killed by oxygen. Bioluminescent systems must have arisen during early evolution as a way to detoxify oxygen. Luciferase, the enzyme used to produce light, could have been the earliest anti-oxidant.
Q. Was light emission enough to get rid of the excess oxygen in cells, to allow early life to survive and evolve survival mechanisms beyond bioluminescence?
A. Every calculation would indicate there was only a small amount of oxygen at the very beginning. Oxygen would have accounted for around 2 percent of the atmosphere. As the oxygen levels rose, luminescence was not enough and many of these early life forms went extinct. Those that survived adapted their bioluminescent systems to satisfy new needs.
Q. In today's organisms, how important is bioluminescence? And how widespread is it?
A. It's very widespread across the tree of life. But it's limited to very few individual species. However, those species could teach us certain things about basic biology and evolution in a way that has not been heavily explored by scientists. For example, the protein of our eye is coded for by a gene that is an enzyme. And it has no enzyme function in the eye. Lens protein is derived from some other enzyme. Today, we study a lot about relationships between genes. But we never ask what the first one was. When did that gene first arise? And what caused it. The search for the origins of bioluminescence could offer us a way to ask many of these other questions.
Q. In your book Living Lights, you write about the threats many bioluminescent organisms face. Can you elaborate?
A. One of the environmental factors that will cause bioluminescence to become extinct is artificial illumination. If you are using light to survive and there is a competing light source, then your light is not going to be seen. Light pollution is a major threat, which is perhaps why most of the luminescent organisms that we know of exist in the deep seas.
Q. What is your favorite bioluminescent organism?
A. I do not have favorites among my children.