As I mentioned in a previous article, scientists recently sequenced the Coelacanth genome, analyzed it a bit, and published the resultsin Nature magazine. The Coelacanth is a fish - not even an edible fish, by human standards - yet particular scientists are quite excited about this genome becoming available for their use. What makes a fish so exciting?
Just for a moment, imagine that you are Professor Smith at Rhodes University in South Africa. It’s the late 1930’s. Some 50 miles to the north of you is a town called East London, South Africa, where a museum curator collects her fish specimens from the local catch. She sends you a sketch and a description of a fish she found. She says that she has only found its like in the fossil record, and she thinks it might be a significant find: a Coelacanth.
You see: amphibians are fish with legs. It’s not really that simple, but legs are the easiest way to tell them apart in the fossil record. By 1939, paleontologists had observed a particular fish with peculiar fins. These fins contained more than just the simple ray-bones of fish like the barracuda and salmon. The fossil fins had additional joints. The joints caused the fins to start narrow before spreading out into something that could push water. They looked more like lobes. These lobes seem to be very primitive fish legs.
This set of fossils blurs the line between fish and amphibians.
This blurring of the line between groups of living things is caused by change over time. Every living thing mutates, usually just a little bit. Your DNA is different now, in some part of your body, than it was when you were one living cell just starting to grow into one living being. Some of an organism’s mutations get passed on to offspring, but most only change the individual.
Get enough living things together for long enough, and tiny changes add up to huge changes. For instance, fish can grow legs if there are millions of fish mutating and reproducing for millions of years. The catch is that stages between fins and legs have to be useful for something. Each stage must help the fish pass on these cool new mutations to the next generation.
Scientists interested in this subject might spend hours studying the bones, especially in comparison with other animals, and imagining what these creatures did with their fins. What did they look like when they were alive? Did they crawl along the bottom of the sea? It appeared that scientists would never know the answer for sure, but they came up with ideas and bounced them off each other to try to make the ideas better.
Suddenly, in 1938, a fleshed-out Coelacanth specimen was found. Although this was a new species compared to any of the previous fossils, the potential was enormous. Scientists could find a living specimen and study its habits and its use of its unusual lobed fins. They might one day study the habits, diet, and environment of a modern Coelacanth, which would inform them about ancient ones. It's this promise that made the first specimen from East London, South Africa, famous.
Fast forward again to today. The potentials of 1938 are exceeded.
We’ve learned about their diet. In the gut of those fish that have been collected, scientists have found tentacled swimmers and small ray-finned fish. How do these fish fall prey?
Scientists haven’t slacked in their Coelacanth-stalking responsibilities. Coelacanths have been discovered in several locations in the Indian Ocean. In following live Coelacanths, we’ve learned that these large fish are ambush hunters, though no one has seen exactly how the prey is caught. We know that they move very slowly. When prey comes within range, they might use a combination of strange sensory organs, bursts of speed, and synchronized swimming techniques to catch food. That’s right, swimming. It ends up Coelacanth don't crawl, they scull.
The slow movement and low-energy hunting techniques allow Coelacanths to survive with a very low metabolism in an environment that doesn’t have very much food. Another important set of survival techniques involves their young. Coelacanth eggs are enormous and mostly made of nutrients. Gestation seems to be very long, perhaps lasting several years. When you combine these features with the detail that modern Coelacanths give birth to live young rather than laying eggs, you get a reproduction strategy that involves a lot of energy invested over a long time to ensure that the young survive. Unfortunately, this strategy could contribute to Coelacanth decline, if the populations ever experience heavy fishing. For this reason, Coelacanths have been declared endangered to help protect the fish from more than accidental fishing. Of course, their inedibility helps with this, too.
Another brick in the monument of knowledge built because of the 1938 discovery was put into place just last month. The Coelacanth genome has been sequenced, and it has been placed on the continuum of relatives to humans and every other living thing. Sign up for my RSS or Twitter feed for more detail in the coming days.