Evolution is rather unpredictable, but that is not the case at least with Hawaiian stick spiders that have shown the same evolution traits on different islands.
Scientists have published a study in the journal Current Biology that Hawaiian stick spiders of the Ariamnes genus have repeatedly evolved the same distinctive forms, known as ecomorphs, on different islands. The stick spiders live in the forests of the Hawaiian archipelago, over 2,000 feet above sea level, on the islands of Kauai, Oahu, Molokai, Maui, and Hawaii.
Although they’re nocturnal arthropods that can’t see well, they’re still brightly and distinctly colored. These different colorings allow the spiders to camouflage themselves against specific similarly colored surfaces in their respective habitats and avoid their major predator, birds called Hawaiian honeycreepers. But what’s remarkable is that as the spiders have moved from one island to the next during their evolutionary history, these same forms have evolved over and over again. This process produces new species that are more closely related to spiders of different forms on the same island than they are to lookalikes from other islands.
And it happens fast–at least in evolutionary time. A dark spider that hops from an old island to a new one can diversify into new species of dark, gold, and white spiders before gold and white spiders from the old island have time to reach the new one. It’s also important that these forms are the same each time.
This, she believes, suggests that the Ariamnes spiders have some sort of preprogrammed switch in their DNA that can be quickly turned on to allow them to evolve rapidly into these successful forms. But how that process might work is still unclear.