| So! Continuing our discussions of environmental adaptation, |
| today I want to focus on a species of fish, called the Notothenioids. |
| A bit of a mouthful, I know. |
| Scientists have documented over 90 species of Notothenioids, in both deep and shallow waters. |
| If you're getting creeped out by the powerpoint slide, don't worry, |
| they really only live around Antarctica. |
| Most of them are pretty small. |
| However, a few species can weigh up to 150 kilograms. |
| These fish can be identified by their huge eyes, |
| insulated with a layer of thick transparent protective tissue. |
| This kind of tissue protects the fluid in their eyeballs from freezing in the incredibly cold seawater. |
| Remember, saltwater has a lower freezing point than freshwater, |
| so moisture in an animal's tissue would be particularly vulnerable to freezing and causing cell death. |
| So while the cold ocean of Antarctica could freeze and kill most fish, |
| the Notothenioids end up thriving in these icy waters. |
| They actually make up nearly 95% of all fish species |
| in the southern ocean around that cold continent. |
| That kind of thing is a stark contrast to tropical oceans, |
| where the biodiversity is extremely high. |
| When you think of a tropical reef, for instance, |
| you probably imagine a plethora of different types of fish and sea creatures |
| living together and preying on each other. |
| The average coral reef supports over four thousand types of fish, sponges, crustaceans, and others. |
| To have one species of fish in an entire section of the ocean? |
| Pretty impressive. |
| Yes! Amy? |
| When did the Notothenioids end up taking over the southern ocean? |
| I'm glad you asked. |
| That was actually my next point of interest. |
| So, about thirty million years ago, |
| the water in that area was a lot warmer than it is today. |
| Way back then, South America and Antarctica were actually connected. |
| The air from around the equator could travel south to heat up the chilly Antarctic waters. |
| The warm tropical waters could also flow southwards, |
| bringing the rich biodiversity along with it. |
| Because Antarctica's waters were relatively warm back then, |
| it could support a lot of different types of animals. |
| We confirmed this by looking at the fossil record, |
| even finding out that 90 or so of the Notothenioids even existed back then. |
| Historians think that somewhere between five and fourteen million years ago, |
| two huge changes occurred. |
| First of all, a chance mutation allowed the Notothenioids to develop a special protein |
| that now flows through their body. |
| Umm, this special protein is actually a type of antifreeze. |
| It works by bonding to an ice crystal that formed inside their flesh, |
| preventing it from growing any larger. |
| So! At the time, the waters they swam in were still decently warm, |
| and the protein didn't do much for their overall survival rates. |
| Still, somewhere around this time period, |
| there are records of a colossal shift that moved around the Earth's tectonic plates. |
| This movement is now known as Continental drift. |
| It pushed Antarctica away from South America |
| and down toward the chilly southern end of the earth. |
| This caused a current to swirl up and form, |
| encircling the cooling continent with a rush of cold water. |
| This cold water prevented warmer tides from intermingling. |
| It eventually dropped to the sub-zero icy landscape we know today. |
| As you may have guessed, |
| the tropical fish didn't do so well in the sudden drop of environmental temperatures, |
| and many species went extinct. |
| Luckily for the Notothenioids, |
| they had a handy dandy gene mutation that let them produce this antifreeze protein. |
| Now the only type of fish that could survive the cold waters, |
| it had virtually no competition for food or resources and went wild. |
| So! As its population increased dramatically, |
| they migrated into different parts of oceans. |
| Over time they developed different physical adaptations to survive in their particular environment. |
| Eventually they split off into subspecies, mutated a bit more, |
| had a bit of geologic morphology going on, very cool stuff. |
| We call this kind of physical differentiation: process of Adaptive Radiation. |
| It really only happens when a species rapidly changes, |
| and ends up with quite a few new species to fill empty niches |
| that either didn't exist before, or weren't available. |
| So now we have about 90 species of Notothenioids, kicking it in the southern ocean. |