For Your Eyes Only: The Ophthalmic Advantage

Posted: Nov 21 2015, 10:50am CST | by , in News | Latest Science News

For Your Eyes Only: The Ophthalmic Advantage
In the freshwater crustacean Daphnia obtusa Kurz, larger eye size was shown to be the source of a sizable reproductive advantage. Credit: University of South Carolina

As the James Bond movie said it so well “For Your Eyes Only”. The ophthalmic advantage holds true down to the microlevel in organisms.

A microcrustacean known as Daphnia has higher reproductive chances depending on the size of its eyes. Eyes are indeed windows to the soul or should we say inner libido. Biologists have long known that the delicate and balanced system that forms the eyes and their function (that would be eyesight) hold the key to reproductive success.

The evolutionary ladder from simple organisms with a light-sensitive cell all the way to eagles with the sharpest eyes on the planet shows that Nature sure knows how to build on its basic components.

A research team led by biology professor Jeff Dudycha recently published a paper in the Journal of Evolutionary Biology showing that larger eye size lends a sizable reproductive advantage to individuals of a particular species.

"What also turned out to be interesting is that we were also able to measure the effect of variation in body size, and it turns out that the effect of eye size was greater than the effect of body size," Dudycha says.

"Within ecology and evolution, everybody understands that body size is related to reproductive output. Larger individuals can produce more offspring, and that's true over a wide variety of organisms. So here was something that everybody knew and understood affected reproductive success, and we have data that said that eye size, which nobody had looked at anywhere as far as we can tell, had a bigger effect."

The story of eye structure in each individual organism has had its proof discovered just now though. It appears to be the case that a large eye size lends reproductive advantage to the animal.

Furthermore, it was not body size but eye size that matters in the end. While body size was related to reproductive strategy, in the microlevel case, it was eye size. Larger animals tend to produce more children. But eye size was the real deal-maker.

The tiny crustacean known as the Daphne is just a millimeter or two in length. But its black eye is so large that it gets spotted in a jiffy thanks to this one prominent feature. An eye is neurologically costly to maintain.

The amount of energy it takes for its upkeep is simply too much. Thus it must serve a function or two other than sight. There are fish that lose their eyes and migrate into the depths of the ocean. Thus there seems to be a cost to losing eyes as well as maintaining them.

"A big eye is costly to maintain, because any kind of neurological tissue, including retinal tissue, is energetically demanding relative to other kinds of tissue," Dudycha says.

"And we also know there are organisms, like blind cave fish, that once had eyes and have moved into environments without any light at all, and they lose their eyes, which wouldn't happen unless there was a cost to having an eye. So if there is a cost to keep having eyes, there needs to be some kind of benefit, and we were wondering if we could measure that benefit."

Over 200 female Daphnia individuals were studied by a team of researchers. Both eye size and number of eggs per organizms were noted down. An increase in eye size meant more eggs. Thus there was a clear reproductive advantage.

The eyes definitely have it. It is as if the most beautiful of the senses also serves as an aesthetic advantage lender in the reproductive stratagems that go on in the animal kingdom.

As the larger eyes see clearer and give off signals that make the mating game more pleasurable, so the fecundity of the female of the species increases in accordance. And the virility of the male also depends on this key feature.

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<a href="/latest_stories/all/all/20" rel="author">Sumayah Aamir</a>
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