Discoveries On the Evolution of the Eye –Our Window on the Universe




Our eyes that scan the farthest reaches of the universe had their origin in water, in the simple hydra, a members ancient group of sea creatures that along with jellyfish, belong to the phylum cnidaria that first emerged 600 million years ago and are still flourishing.

"We determined which genetic 'gateway,' or ion channel, in the hydra is involved in light sensitivity," said Todd H. Oakley, assistant professor in UCSB's Department of Ecology, Evolution and Marine Biology author of a 2010 UC Santa Barbara study. "This is the same gateway that is used in human vision."

Oakley explained that there are many genes involved in vision, and that there is an ion channel gene responsible for starting the neural impulse of vision. This gene controls the entrance and exit of ions; i.e., it acts as a gateway. The gene, called opsin, is present in vision among vertebrate animals, and is responsible for a different way of seeing than that of animals like flies. The vision of insects emerged later than the visual machinery found in hydra and vertebrate animals.

The research challenged the misunderstanding that evolution represents a ladder-like march of progress, with humans at the pinnacle. "Instead, it illustrates how all organisms — humans included — are a complex mix of ancient and new characteristics, said Oakley."

Fast forward to today: zoologists from Cologne and Lyon announced that they have succeeded in reconstructing the structure of the eye of a predatory crustacean from the time of the dinosaurs –the internal structure of an approximately 160 million year old compound eye (sown below Dollocaris ingens van Straelen, 1923, Thylacocephala) from the Middle Jurassic period. It was discovered at the La Voulte deposit in southeastern France.



The eyes of this crustacean consist of approximately 18,000 facets, and because each of these facets contributes to the entire image as pixels contribute to a computer graphic, the eye of this crustacean belongs to the most accurate in the arthropod realm.

With the reconstruction of the eye's structure, the scientists succeeded in making the structure of soft tissue visible — which was long considered to be impossible. Together with the palaeontologist Jean Vannier and other colleagues, the zoologist Brigitte Schoenemann from the University of Cologne played a leading role in this research.

The construction of the crustacean's high-performance eye most closely resembles that of a bee or a dragonfly. Most likely it also functioned in a similar way. A physical analysis revealed that this crustacean was active during the day and lived in the light-flooded parts of the ocean. An analysis of its stomach showed that it obviously chased smaller sea organisms and fed on them.

This research work is important because up to now researchers thought that only the hard parts of an animal, such as shells or bones, could be preserved. Hence the findings of the research team on soft tissue are ground-breaking — and they describe fossil sensory cells older than those preserved in the relatively young amber.

Recently, computer-tomography has revealed that even individual sensory cells can be documented. The recent research work shows for the first time that the complete structure of a compound eye can be analysed and resolved. The team was able to open up completely new perspectives — not just for the investigation of fossilised sensory systems. It also showed that in contrast to earlier opinions, the fossil record can contribute important facts to the discussion of the evolution of visual and other internal systems.

The Daily Galaxy via UC Santa Barbara and the University of Cologne

Image credits: Cosmos –A Spacetime Odyssey and Thylacocephala


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