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May 18, 2015

Jumping spiders master color vision

Chuck Bednar for redOrbit.com - @BednarChuck

When most people encounter a spider, they probably don’t stop to think about how amazing their eyes are before they crush the living daylights out of it, but researchers from the University of Pittsburgh have discovered an unusual mechanism that has never been observed in any other type of arachnid.

As reported by the team in Monday’s edition of the journal Current Biology, jumping spiders (or members of the genus Habronattus) see things in three color “channels” like most humans, and although they tune the color sensitivities using light-filtering pigments similar to butterflies and birds, the mechanics of their eyes are vastly different.

In an email sent to redOrbit, study author and postdoctoral researcher Daniel Zurek said that the findings “represent a significant advance for our understanding of one of the most sophisticated visual systems on the planet.” Unlike dogs or deer that have two color channels in their retinas, the jumping spiders have a third that enables them to use “spectral filtering” – using a red filter that shifts a set of green sensitive cells to being red sensitive.

Spectral filtering had never been found in an arachnid species before, he added, and while these creatures may have “true” color vision, the trichromatic area in their retinas is rather restricted in field of view, meaning that they have to scan scenes “line-by-line” to accumulate color data.

Studying spiders in the desert

The Pitt researcher explained that most spiders have poor vision, but jumping spiders can see very well and have extremely high resolution in their eight single-lens eyes. Their sophisticated vision allows them to perform complex behaviors not unlike those observed in vertebrates, such as plotting indirect route to their prey and using complex visual signals to communicate.

“The discovery that these colorful jumping spiders can see color may not seem surprising, but it offers an important clue into why this particular group of jumping spiders is so vibrantly colored whereas many other spiders are so drab,” Zurek’s colleague, Nathan Morehouse, told redOrbit via email.

“Our preliminary research suggests that the filter-based trichromatic vision that we uncovered may be restricted to the genus Habronattus, a jumping spider group known for its colorful courtship dances and rapid rates of speciation,” he said, adding that he was preparing to travel to the southwestern US to study other up to 20 other species of Habronattus spiders and learn more about how colors appear in their natural habitats.

“While their ability to see color helps us to understand why these animals are so colorful, our next step is to understand why different species have evolved to be so differently colored,” he told redOrbit. “We hope that aspects of their natural environments, such as the color, pattern, or movement of background objects may help us to understand why some displays differ from others.”

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