How Do Hawaiian Stick Spiders Evolve?

How Do Hawaiian Stick Spiders Evolve?
Amandad / Pixabay

The subject of evolution is quite fascinating, but also, very unpredictable. Scientists have studied Hawaiian stick spiders of the Ariamnes genus and learned that the same species living on different islands managed to evolve into the same forms. A new paper looks into the mystery of this phenomenon.

Researchers from the University of California, Berkeley discovered that the stick spiders repeatedly evolved into a form known as ecomorphs, despite living at separate locations, according to the new paper published in the journal Current Biology on March 8.  The researchers are hopeful that the newly described species could help them understand the secret behind their evolutionary pattern.

Hawaiian stick spiders can be found in the forests of the Hawaiian archipelago, living 2,000 feet and more above sea level. They are spread across the different islands, Kauai, Oahu, Molokai, Maui and Hawaii. Despite being unable to see well, they are quite brightly colored.

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“You’ve got this dark one that lives in rocks or in bark, a shiny and reflective gold one that lives under leaves, and this one that’s a matte white, completely white, that lives on lichen,” Rosemary Gillespie, an evolutionary biologist at the University of California, Berkeley said in a statement.

Their different color patterns help these spiders survive against their major predator, the Hawaiian honeycreeper bird. Nevertheless, what makes them special is that the spiders moved from one island to another, at the time when they were evolving. Those same forms continued evolving over and over.

“They arrive on an island, and boom! You get independent evolution to the same set of forms,” Gillespie said. “They don’t evolve to be orange or striped. There isn’t any additional diversification.”

Researchers haven’t had time to study this phenomenon more closely before, as ecomorphs aren’t common. Gillespie’s research suggests that there are some parts of evolution that could be programmed in a predictable way, while other evolution patterns repeat themselves. For example, yellow and red stick spiders evolved independently on almost all the islands, while they are not genetically related. Also, the yellow and red stick spiders on Maui are more related to the brown spider that also lives on Maui.

“Now we’re thinking about why it’s only in these kinds of organisms that you get this sort of rapid and repeated evolution,” Gillespie said.

Gillespie is still working on answering the question on the evolution of Hawaiian stick spiders, and meanwhile the three distinctive forms of the same species live in their remote locations and successfully use their camouflaging technique that helps them combat predators. They don’t build spider webs and similarly like the lizards, they move freely, always looking for the kind of habitat that will help them camouflage more easily. Gillespie is hopeful that learning about the common traits of those groups of spiders will “provide insight into what elements of evolution are predictable, and under which circumstances we expect evolution to be predictable and under which we don’t.”

She hopes that her paper will allow the world to understand Hawaii’s forests and what they have to offer and encourage them to study them more: “Often, I hear people saying, ‘Oh, Hawaii’s so well studied. What else is there to look at?’ But there are all these unknown radiations that are just sitting there, all these weird and wonderful organisms. We need everyone to understand what’s there and how extraordinary it is. And then we need to see what we can do to protect and conserve what still waits to be described.”

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