http://phys.org/news/2015-01-perspective-snake-evolution.html
Nature Journal
January 5, 2015
Jason Head's and P. David Polly's recent study of the snake skeleton has revealed new information on how they may have evolved. We previously believed that snakes evolved from their lizard ancestors to a more simplified form. Now, it is becoming considered that other animals and lizards gained a more complex skeleton instead. This is due to the finding of distinctions among vertebral bones in the snake's skeleton identical to those of four-legged lizards. This ties to the function of Hox genes in the snakes. Hox genes regulate growth of the neck, trunk, lumbar, sacral and tail regions of limbed animals. Before, it was thought that the function of these genes was disrupted in snakes, resulting in no limbs and a simplified skeleton. It was then thought that the absence of limbs resulted in the loss of the distinction between the shape of the vertebrae in their backbones and neck, trunk, and lumbar regions. However, Head's and Polly's study revealed distinctions in the snake skeleton's vertebrae similar to the ones in lizards and mice. If the Hox genes were really disrupted in snakes, then their vertebrae would all be similar shapes and sizes, but they were not. Further investigation showed that the regions with Hox genes in snakes matched those in lizards, revealing that these genes in snakes simply control more simple and gradient changes in shape instead of the complex patterned ones in mice and lizard skeletons. It isn't that snakes simplified, it's that mammals and birds have gained more complex skeletal and Hox regions. This completely contrasts what was originally believed about snake evolution.
This new discovery is very important to science and directly relates to what we have been learning in the evolution unit. Scientists now have a better understanding of how reptiles may have evolved, which could lead to further investigation and discovery of the evolution of different animals and/or species. Although their evolution isn't what we had expected and originally predicted, snakes did change over the course of a long time from their lizard ancestors. This evolution was likely due to the need to survive in a different environment from the one lizards lived in. This new body shape for the snakes could help them catch food, escape predators, and blend in to different surroundings, and has evidently been working for them, as they have thrived in many areas. This also relates to how the study of bones and fossils can lead to great evolutionary discoveries, as we have learned in class. Overall, it is a great new point of view that helps us as students as well as other scientists learn more about evolution.
Why did mammals and birds gain more complex Hox regions?
ReplyDeleteThere is no definite answer, but it is likely due to their environment and how they adapted to it. Their structure would have to develop differently based on the different functions that their environment demanded. For example, the snake has less complex Hox regions because it adapted to a lifestyle in which it slithers on the ground instead of walking on legs. This adaptation likely stemmed from the prey it wants to catch, the predators it needs to escape from, and other factors in the environment. The same could be said for any mammal or bird. Considering that birds fly, you could imagine that they need more complex Hox regions for that, which likely resulted from an adaptation.
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