Friday, 6 May 2016

Crocodile eyes are fine-tuned for lurking

By Jonathan WebbScience reporter, BBC News

4 May 2016 

A new study reveals how crocodiles' eyes are fine-tuned for lurking at the water surface to watch for prey.

The "fovea", a patch of tightly packed receptors that delivers sharp vision, forms a horizontal streak instead of the usual circular spot.

This allows the animal to scan the shoreline without moving its head, according to Australian researchers.

They also found differences in the cone cells, which sense colours, between saltwater and freshwater crocs.

Published in the Journal of Experimental Biology, the findings suggest that although the beasts have very blurry vision underwater, they do use their eyes beneath the surface.

This is because light conditions are different in salt and freshwater habitats, but only underwater - and the crocodiles' eyes show corresponding tweaks.

"There's generally more blue light in saltwater environments, and more red light in freshwater environments. Animals tend to adapt to this," explained Nicolas Nagloo, a PhD student at the University of Western Australia.

He and his colleagues studied eyeballs from juvenile "salties" and "freshies", shipped to the university from a crocodile farm in Broome.

When they measured the light absorbed by single photoreceptors in the retina, they found that those of the freshwater crocs were shifted towards longer, redder wavelengths compared with their saltwater cousins.

Finding this skewed sensitivity in crocodiles was unexpected, Mr Nagloo said, because the famous predators were only semi-aquatic and did their hunting, feeding and mating on land.

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