Researchers solve mystery after examining 25 years of video footage
The animals in the deep seas comprise some of the most mysterious inhabitants of our oceans. Case in point: a squid with eyes that are of different sizes, aptly named the cockeyed squid (Histioteuthis heteropsis).
Also known as the strawberry squid, one of its eyes is large and yellow, while the other eye is small and bluish. A related species, Stigmatoteuthis dofleini, has a protruding eye on one side and a normal eye on the other side.
Although these species were discovered more than a century ago, biologists have long been puzzled over the reason of the asymmetrical qualities of the two eyes. Now, after analysing 25 years' worth of video footage of the squids taken at depths of 200 to 1,000 metres, researchers have discovered the answer. Their findings have been recently published in the journal Philosophical Transactions of the Royal Society B.
It seemed that the larger eye was always being directed upwards, while the smaller eye was directed downwards, indicating that the eyes served different functions. The larger eye, with its yellow lens, allowed the squid to detect prey against the dim down welling surface light, and makes them easier to spot. The smaller eye specialised in scanning for bright bioluminescent fashes emitted by prey in the dark waters from below.
As such, the smaller size of the downward-directed eyes enables less energy usage, thereby maximising the squid's “energy efficiency”.
Link to the study: rstb.royalsocietypublishing.org/content/372/1717/20160069