Jumping spiders can see in full color, thanks to the use of a red filter in their two primary eyes, report researchers.
Roughly half a centimeter long, the Habronattus pyrrithrix jumping spiders in the study have superb visual acuity.
“The eyes of jumping spiders could not be more different from those of butterflies or birds, and yet all three tune their color sensitivities using pigments that filter light,” says Nathan Morehouse, assistant professor of biological sciences at the University of Pittsburgh.
“It’s actually a pretty clever, simple solution with a big payoff.”
The payoff, for the male of the species, is that he gets to mate. Male Habronattus are quite colorful and use their vibrant appearance to attract a female.
Scientists knew that some Habronattus pyrrithrix could see green and ultraviolet (UV) light through two of their eight eyes. It was assumed that they could also see reds and oranges—what would be the evolutionary benefit for males having red and orange coloration otherwise? But scientists had yet to figure out how the spiders could see ruby hues.
In the new study, Morehouse and colleagues find that the arachnids have red filters that sit in front of cells in their eyes that normally detect green light. The effect is similar to the gels placed in front of theater lights to get different colors on a stage.
The paper on this “spectral filtering” that the researchers discovered appears in Current Biology. It had never before been described in any spider, although similar strategies are known in birds, butterflies, and mantis shrimp. That makes this visual strategy a remarkable example of evolutionary convergence.
We see the world differently
They may have “true” color vision, but that’s not to say the spiders see the world in quite the way we do. The similarity lies in the fact that both this spider and humans have three color channels: jumping spiders have ultraviolet, green, and red channels, whereas people have blue, green, and red channels.
The difference is that humans have three different, distinct color receptors rather than making use of a filter to perceive certain hues.
“One fascinating thing about the trichromatic area in these spiders’ retinas is that it is very restricted in field of view, which means they’d have to scan scenes ‘line by line’ to accumulate color information,” says Daniel Zurek, a postdoctoral researcher in Morehouse’s lab.
With the new findings in hand, the researchers say they are about to go spider-hunting in Arizona in search of other species in this diverse Habronattus group. They hope to explore the role that color vision may have played in generating the diversity of these spiders over evolutionary time.
Source: University of Pittsburgh