Describe the major anatomical developments that occured to certain species of fish during the time that the oceans cooled significantly. What anatomical developments specifically occured during the evolution of the Antarctic Icefish? How did the environment affect these changes?
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This is indeed a meaty question. Here goes...
ReplyDeleteIcefish are called such because they lack red blood cells, and therefore their blood is literally ice water. The colorless blood allows the icefish to thrive in freezing temperatures. At cold temperatures, the blood of the icefish has a very high viscosity, making it difficult to pump. The elimination of red blood cells decreases the viscosity of blood, which allows the blood to be easily pumped. Furthermore, ice water is rich with oxygen, and large gills and capillaries make up for the lack of red blood cells.
Another unique adaptation to subfreezing temperatures is the presence of "antifreeze" proteins in the plasma of these fish. Without these proteins, the icefish would freeze.
These physiological adaptations are definite selective advantages in allowing these fish to face subfreezing temperatures.
When temperatures of the ocean dropped 38 degrees and Earth's plates moved, Antarctica was completely isolated which also isolated ocean currents surrounding the continent, which led to limited migration for the fish living in the area, giving them the choice to either adapt or die off. "Necessity and opportunity" led the icefish to change certain anatomical features to adapt to the new environment. As stated in the previous comment, icefish lack red blood cells because their globin genes have gone extinct. This leads to the problem of how these fish gain oxygen. Instead of red blood cells, icefish have large gills and scaleless skin with large capillaries which allows for increased absorption of oxygen. Also the microtubules of the icefish are very stable at below freezing temperatures, unlike mammals whose microtubules are unstable below 50 degrees F. These microtubules alow for cell division, cell formation, and movement to occur in the cold environment. Changes such as these have allowed the icefish to survive despite their changing environment.
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