The acquisition of the ability to blink may be important for the transition to a terrestrial lifestyle in vertebrates. Pennsylvania State University reports.
Animals can blink and have movable eyelids for many reasons, but primarily to keep their eyes moist and prevent injury. At the same time, the evolution of this mechanism is difficult to study, because the soft tissues of the eyelid are poorly preserved in the fossil record.
In this context, Thomas Stewart and his colleagues decided to examine the eyes of a modern fish adapted to land life – the mudskipper. These small fish live in coastal silt or sand and can stay in the air for long periods of time, provided their bodies remain moist. They move with the help of fleshy fins that work like paws.
To understand how jumpers improve their ability to blink, researchers analyzed using high-speed video, he compared the behavior and anatomy of jumpers with that of a closely related fish that doesn’t blink. Jumper’s eyes protrude overhead like a frog’s. To blink, fish momentarily retract their eyes into their sockets, where they are covered by an elastic membrane called the “skin cap”. A jumper’s blink lasts about the same time as a human’s blink.
“Blinking in mudskippers appears to have evolved as a result of the reorganization of existing muscles that changed their direction of movement, as well as the evolution of a new tissue, the dermal calyx. Scientists have found that, just like humans, mudskippers blink more frequently when faced with dry eyes,” he said.
At the same time, it is interesting that jumpers do not have lacrimal glands – instead they moisten their eyes due to the moist mucus of the body. Additionally, the analysis showed that these fish blink to clear debris from the eyeball and protect it from damage.
Based on this, the authors conclude that adapting to a terrestrial lifestyle probably led to learning to moisten eyes that do not work when dry.
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