New research on Hawaiian stick spiders suggests that the creatures offer an example of adaptive radiation, with the main species’ many variants being among the very few examples of ecomorphs – animals that live in similar habitats and look practically the same as each other, but are not as closely related as one would think.
As explained by Phys.org, adaptive radiation, or the evolution of new species that could adjust to different environments and circumstances, was first discovered by Charles Darwin in the 19th century. While this discovery of his phenomenon helped Darwin as he eventually came up with his natural selection theory, there are still a lot of unanswered questions about how adaptive radiation plays out in the animal kingdom, though recent observations on Hawaiian Ariamnes stick spiders could offer some clues going forward.
In a study set to be published on March 19 in the journal Current Biology, a team of researchers at the University of California, Berkeley detailed how Hawaiian stick spiders evolved into 14 different species that can now be found throughout Hawaii. Despite the seemingly diverse variety of individual species, the spiders can only be found in three color schemes, namely red and yellow, black, and matte white, according to Newsweek. The researchers concluded that in the two to three million years since the creatures first arrived on what is now known as Hawaii, evolution had allowed for the different Hawaiian stick spider species to come in only those three color variants, and for the same schemes to be repeated in multiple islands, independent of each other.
“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,” commented University of California, Berkeley evolutionary biologist and study lead author Rosemary Gillespie, as quoted by EurekAlert.
Regardless of the color scheme or individual species, Hawaiian Ariamnes stick spiders use their colorings as a tool to protect themselves from predators, as they camouflage themselves by blending into surfaces with a similar color. But what surprised the scientists was how the species turned out to have its own ecomorphs, due to the fact that different variants without close genetic relations look the same, as they evolved separately on their respective islands. According to Newsweek, this could be because of the spiders’ DNA allowing them to rapidly evolve to fit in, but also preventing them from evolving into something that looks different altogether.
Conversely, Phys.org also cited an example of how the opposite of the above situation holds true – there’s a good chance white stick spiders on Oahu may have closer genetic ties to brown spiders that live in the same area, as opposed to similar or identical looking white Hawaiian stick spiders from Maui, or other islands.
“This very predictable repeated evolution of the same forms is fascinating because it sheds light on how evolution actually happens,” Gillespie continued, while emphasizing how rare such a phenomenon is in the animal kingdom.
“Such outstanding predictability is rare and is only found in a few other organisms that similarly move around the vegetation.”
Phys.org also noted that the new study on Hawaiian stick spiders is not the first time Gillespie has observed adaptive radiation in arachnids. Fourteen years ago, Gillespie found that Hawaiian Tetragnatha spiders, which are known for the fact that they do not spin webs, also evolved their own ecomorphs since the species’ ancestor first made its way to the islands.