Due to the development of new biodiversity which is triggered when a species encounters a new environment, adaptive radiation takes place. In the case of Hawaii, because of adaptive radiation, there are 14 stick spider species that live on the different Hawaiian Islands.
Each species has their own specific traits, but the evolution of the new traits was not necessarily in response to the pressure of new environments. But the same basic forms are still there. The distinct black, white, and gold colors were retained, i4u reported.
Same physical form
No matter how far apart the stick spiders are, the researchers observed that the species has almost the same physical form on different islands. The study found that the Hawaiian stick spiders have evolved into the same basic forms over and over again.
While the black, white, and gold spiders are found on four islands, they are not closely related to each other. They independently evolved into the same physical form. The black spider lives in rocks, the gold one under the leaves, and the white species on lichen.
Rosemary Gillespie, the lead study author from the University of California Berkeley, said that the very predictable repeated evolution of the same forms is fascinating because it sheds light on how evolution actually happens. She noted that such outstanding predictability is rare and only found in a few other organisms which similarly move around the vegetation.
Charles Darwin first discovered the evolution of new species in the 19th century. His discovery helped Darwin come up with the natural selection theory, but until now, there are a lot of unanswered questions on how adaptive radiation plays out in the animal kingdom, Inquisitr noted.
He noted the phenomenon in the beaks of finches of the Galapagos Islands. The study of the finches' diversity led to Darwin's theory of evolution by natural selection, Science Blog reported. Hawaii is actually a hotbed for biological diversification compared with Galapagos which is isolated.
The conclusion reached by the researchers in the study, to be published on March 19 in the Current Biology journal, is that in the 2 million to 3 million years since the spiders arrived in Hawaii, evolution allowed for the different species to come in only the three color variants. The same scheme was repeated in multiple islands, independent of each other.
Whatever are their colors, the Hawaiian stick spider uses these to protect themselves from predators. The arachnids used their color to camouflage themselves by blending into surfaces with a similar color. The researchers were also surprised to find that the species has its own ectomorphs because of the different variants without close genetic relations that look the same.
The possible explanation is that the DNA of the spider allowed it to rapidly evolve to fit in. However, it also prevented the species from evolving into something which looks different altogether. But the opposite of the above situation also is true. There is a good chance that the white stick spider on Oahu may have closer genetic ties to brown spiders that live in the same area versus similar or identical-looking white Hawaiian stick spiders from Maui and other islands.
It was not the first time that Gillespie observed adaptive radiation in spiders. In 2004, she discovered that the Hawaiian Tetragnatha spiders – which do not spin webs – evolved their own ectomorphs since the ancestor of the species first made its way to the islands.
Conserving nature in all its form
George Roderick, a professor and chair of the Department of Environmental Science Policy and Management at Berkeley, said the study provides insights into a fundamental question about the origins of biodiversity. It also presents a remarkable story that can call attention to the need for conserving nature in all of its forms.
Because of the chronological formation of the Hawaiian Islands, the researchers were able to study the adaptive radiations of the spiders over time as the species moved from the old to the new islands. Kauai, the oldest island, was formed 5 million years ago. It was followed by Oahu, Molokai, Lanai, Maui, and the big island of Hawaii which is the youngest island in less than 1 million years.
Gillespie pointed out that the various habitat types on the Hawaiian Islands – there are cold and wet areas that are juxtaposed with hot and dry areas – provided a rich tapestry of species diversity. She noted that the opposite side of the extraordinary diversity that evolved in isolation is its vulnerability to change and to invasive species that now flood the islands caused by human traffic.
She stressed that there is a need to figure out the diversity and document it and describe what is so special about it for the people to know about it. Gillespie said it is being lost, and it is a desperate situation.
[researchpaper 리서치페이퍼= Vittorio Hernandez 기자]