Colorful Hawaiian Spiders On Separate Islands Share Common Ancestors

Thursday, 08 March 2018 - 7:56PM
Thursday, 08 March 2018 - 7:56PM
Colorful Hawaiian Spiders On Separate Islands Share Common Ancestors
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Spiders often get a bad rap just because some species are venomous to the point of being deadly.

If you're able to look past the tiny little issue of the threat of death, many of these creatures are absolutely fascinating in their own right. Especially when they're dressed up in some of the coolest camouflage in the animal kingdom.

A new paper, shortly to be published in Current Biology, details the evolutionary journey of fourteen different spider species that live on various Hawaiian islands. While these spiders are very distinct in their appearance and hunting methods, they're actually all related, sharing a single ancestor species that arrived on the islands before rapidly evolving into over a dozen different kinds of arachnids.

It's believed that the original spiders from this family that arrived in Hawaii were blown to the Pacific Islands by accident thanks to heavy winds and a form of makeshift sales or flying contraptions created from strands of web. These spiders were thieves; they fed themselves by stealing flies and insects that got stuck in the webs of other spiders.

Upon arrival in Hawaii, these spiders quickly discovered that there weren't enough web-making spiders on the island that they could steal from. In the absence of spiders to steal from, these first generation immigrants quickly adapted to munch on a different food source instead: each other.

Thus was born a species of spiders that rapidly evolved the tools necessary to hunt and kill other spiders. They developed the ability to hide under rocks, and from there, the species exploded in many different directions as the spiders evolved to fit various niches within the food chain.

This process, known as adaptive radiation, was first observed by Charles Darwin in the beaks of finches living in the Galapagos islands and ultimately led to the initial theory of natural selection. Despite being commonly accepted by the scientific community, it's rare for scientists to get a really good example of adaptive radiation, as this phenomenon requires a habitat that's somewhat isolated until a few lucky animals turn up and start breeding rapidly as they evolve in order to fill a void.

The study of these spiders has shown some interesting elements of adaptive radiation at play. For example, various islands across Hawaii feature spiders that, much like stick insects, have camouflage that makes them look like standard twigs or leaves.

These spiders aren't the result of a single species spreading across the islands, but rather, different spiders on different islands all ended up developing the same camouflage independently of each others - clearly there was a benefit to this appearance, and as the spider families branched out, they inadvertently ended up gaining a family resemblance again as a happy accident.

This research helps us to better understand what evolution looks like in practice, and how one species, given an ideal environment in which to develop, will rapidly transform and adapt in order to fill various different niche roles.

There is, however, a downside to this process. These spiders have become so specialized thanks to years of evolution, that they're no longer capable of the quick adaptation that was the secret to their ancestors' success. When a new species or environmental factor is introduced to the Hawaiian islands, by, say, unwitting tourists traveling from other parts of the world, these spiders have a difficult time changing their ways to better fit the new environmental paradigm.

While we often think of evolution as being defined by the mantra "survival of the fittest", it's often more accurate to refer to this as "survival of the most flexible". Because these species of spiders have become so specialized over millennia of evolution, they're now so rigidly set in their ways that they can't cope with the exact experience that helped their immigrant ancestors to thrive.
Science News