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Scientists Trace Origins of Animal Vision


What do we have in common with an animal found in pond scum?


The hydra, a star in the high school biology textbook scene, where it’s known for its ability to regenerate, is once again the darling of some scientific circles. This time it’s for what it reveals about our own eyes.

"We wanted to study a group of animals that has been around for a long time," said UCSB biology professor Todd Oakley. He, graduate student David Plachetski and their colleagues were looking for the presence of these vision genes, called opsins, in different animal groups. They settled on the hydra, an ancient member of the phylum Cnidaria, the group that also contains corals, sea anemones and jellyfish. The hydra genome has been fully sequenced.

"Not only are we the first to analyze these vision genes in these early animals, but because we don’t find them in earlier evolving animals like sponges, we can put a date on the evolution of light sensitivity in animals," said Plachetzki, a graduate student and first author of the paper, which was published in the scientific journal PLoS ONE.

According to their research, animals began sensing light about 600 million yeas ago. That discovery, said Oakley, is one of only a few cases where scientists have pinpointed specific mutational events that have given rise to new features during evolution.

This idea of new features being produced through evolution may sound like fighting words to some anti-evolutionists who, Oakley said, often argue that mutations onlydestroy features, not create them.

"Our paper shows that such claims are simply wrong. We show very clearly that specific mutational changes in a particular duplicated gene allowed the new genes to interact with different proteins in new ways,” Oakley said.

The opsin genes in hydras, speculate the researchers, allowed the animal to sense when a potential prey cast a shadow on them. Most of the opsins they found are concentrated near the animal’s mouth.

This mechanism of genes interacting with different proteins, said Oakley, is what eventually produced human vision. Humans have multiple different genes for vision, which enable us to see colors, or sense day from night. According to evolution, which asserts that all organisms share a common ancestry, an animal related to the hydra evolved another set of opsins, and so on until different animal eyes were produced, including ours.

"Mutations are random," said Oakley. Whether they are maintained, according to the theory of natural selection, depends on their ability to pass themselves on into future generations.

Funding for the research came from a prestigious National Science Foundation  dissertation improvement grant. Co-author Bernie M. Degnan  from the University of Queensland in Brisbane, Australia, provided computational tools to complete the study.

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