The cockeyed squid has been puzzling scientists everywhere with its mismatched eyes. Now, a team of researchers from Duke University think that they have found an answer to this mystery.
Initially, Histioteuthis heteropsis is born with eyes of the same size and color. However, while it’s still young, one of the eyes of the squid grows until it bulges and it turns yellow. Scientists could not understand why this peculiar phenomenon occurs until now.
Kate Thomas is a biology graduate student at Duke University and, together with her team, she studied 161 videos of cockeyed squids filmed in Monterey Bay for over 26 years. Then, she noticed that the squid swam in a sideway position. Thus, the yellow eye was facing the surface while the black eye was facing the bottom.
This made the researcher reach the conclusion that the eyes functioned separately. The yellow eye scanned for shadows in the water above the squid, whose silhouettes were outlined by sunlight. The black eye scanned for bioluminescent creatures in the water below the squid. These creatures emit light because of some internal chemical reactions.
Scientists assumed that the separate evolution of the two eyes occurred as a reaction to the natural habitat of the squid. It lives at about half a mile below the ocean’s surface, so sunlight can barely reach these depths. This is why all creatures that dwell here have developed a series of mechanisms to help them survive in such an environment.
Therefore, the different eyes of the squid help it see different kinds of light. The larger eye is not needed to spot bioluminescent creatures, since they are brighter than the sunlight that reaches the depths. However, it can help the squid distinguish other silhouettes in the dim light.
The researchers assume that the yellow pigment found in the larger eye helps in telling the difference between bioluminescence and sunlight. In comparison, the black eye cannot distinguish silhouettes but, after all, it has no need to. Since it is only looking for bioluminescence, it doesn’t have to distinguish a clear shape but only small sparks to help it identify the kind of light it sees.
Thus, the cockeyed squid’s eyes have evolved differently for the creature to be able to cope with the harsh environment it lives in. The yellow eye grows bigger since it has a tougher job and has to search for dim shapes in the depths.
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