On Antarctica and its divergence from other continents

Photos from UAB in Antarctica group on Flickr, related to this post
By Kate
Posted on 04/20/10

"An ocean without its unnamed monsters would be like a completely dreamless sleep." - John Steinbeck, The Log from the Sea of Cortez

    This is what draws people to the deeps of the sea and all across the globe. It haunts us in our dreams, our movies and sometimes in real life.  The ocean has been fascinating people for hundreds and thousands of years and this is what brings us to Antarctica. We come here to dream up ways of evaluating ecological relationships that are accentuated on this remote continent, do drug discovery with the chemicals some of these organisms produce, and more. Why is it that we have to come so far to do this?

    First and foremost, evolution and continental divergence apply because they are the driving forces that create unique organisms such as those found in Antarctica. Much of evolution was first discovered through something referred to as island biogeography, by biologists such as Wallace and Darwin. Speciation occurs when populations of one species become isolated in separate areas, for instance on two different islands. Suppose these areas are subject to different weather patterns and one is also home to a large predator. Each population will survive in the way that best protects it in its habitat and eventually they will adapt and become so different that they won't belong to the same species anymore.

    Genetic mutation of traits facilitates species adaptation or survival in their habitat. If you have heard of the 19th century Austrian monk Gregor Mendel and his peas, you probably remember that, genetic mutation is occurring with specific traits which can physically be seen in the color or texture of the pea. For humans an example of a trait would be eye color, for algae it could be a specific photoreceptor or chemical compound. The selection for a trait in nature is not done consciously, but because it allows or is associated with a trait that allows the species to survive in its habitat.

    The continent of Antarctica was created with others by diverging from the supercontinent Gondwana during the Devonian period. It was a warm continent with conifer forests and swamps, home to few dinosaurs and marsupials.

    Approximately 23 million years ago the Drake Passage opened at the tip of South America and the Antarctic Circumpolar Current (or ACC) was created. This isolated the continent from the other world oceans and began its cooling. The cooling disallowed the forests and animals to persist, whereas on the neighboring continent of Australia, forests and marsupials still exist.  The ACC currents and the associated winds prevent movement of marine and terrestrial organisms in and out of the Southern Ocean, save few sea birds such as the Wandering Albatross.

    Isolation has allowed Antarctic species to evolve without introduction of new predators or competitors, and has led to a very interesting marine system. This is a system devoid of the abundance and diversity of mobile invertebrate fauna and fish usually found in temperate and tropical marine systems. There are no crabs, few fish, and definitely no sharks. The behavior of many of the common fish is exemplary of this absence of predators. They hide from seals in the dense seaweeds but can be caught easily in hand and have even snuggled with me on dives. 

    Most interesting for my research is the effect this has had on the density and diversity of the amphipod population in Antarctica. Maggie has already written an entry introducing you to amphipods.  These small but incredibly numerous crustaceans exert the most grazing pressure on marine algae here, which in turn may account for the prevalent populations of endophyte within many of the macro algae. This has been seen in other marine systems but here it is very extensive. It also may account for the prevalence of secondary metabolites, or defensive chemicals, that we find in the algae and invertebrates here.

    Lastly, present day Antarctica has distinguishing species which are found only here, we call these endemic species. These include some sea birds, seals, ice fish, species of algae and invertebrate. But as for the monsters of our dreams (leopard seals excluded)? This ocean is a new frontier that we have barely begun exploring. There are a myriad of organisms we have yet to find, nonetheless explore their specific properties (such as chemicals) and adaptations. Antarctica is a long way to travel, but if we were to select for a location that has been allowed to evolve without human disturbance, we couldn't find a more perfect place.

 

Comments

  1. Re: On Antarctica and its divergence from other continents
    Posted by Samson on 04/22/10

    This is really nervising!

  2. Re: On Antarctica and its divergence from other continents
    Posted by Terri Schoenrock on 04/24/10

    Oh Kate. What can I say. You hit my buttons: Steinbeck and Wallace. An essay by Dr. Ricketts might start with a beer milkshake and a trip across the street, and an essay by Ms. Kate starts with sea monsters and leopard seals. You are a lovely writer my sweet. You stir my imagination and make me think.

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