Among the tarantulas sit some of Earth’s largest and fuzziest species of spider. That they can be found on six of the planet’s seven continents has proven puzzling for scientists, as these lumbering giants aren’t known for having nomadic lifestyles. In fact, they’re one of the most sedentary groups of spiders with only the males having to go out on the prowl for a mate while females kick back in their burrows. So, how did they take over the world?
New research published in the journal PeerJ believes to have found the answer, which centers around how long ago these eight-legged beasts first emerged. Carried out by an international team of researchers, the study looked at the transcriptomes (the mRNA expressed by an organism) from a wide range of tarantula species that hailed from different periods in Earth’s history. From this, they were able to create a genetic tree of tarantula species that could be cross-referenced with specimens from the fossil record.
It turns out these fuzzy critters are ancient and were actually scuttling around what’s now known as the Americas around 120 million years ago. This puts them on Earth while the dinosaurs were still roaming, forging what would be the most metal duo of the natural world if they hung out as some frogs and spiders do. They would have been residents of Gondwana, a supercontinent that joined South America, Africa, India, and Australia. It figures, then, that they were able to stretch to these (now far-reaching) corners of the globe thanks to continental drift, but it seems their reach goes beyond just dumb luck.
The researchers found something interesting as they looked at two tarantula lineages' colonization of Asia, which indicates tarantulas are better dispersers than we give them credit for. Both emerged on the Indian subcontinent before it joined Asia, one navigating the treetops while the other ran about on land. The first of the two to reach Asia (the second made ground around 20 million years later) did something particularly surprising, skipping its way down to and over the Wallace Line, the "boundary" line that seems to separates the biogeographical realms of Asia and Australia. Normally species are expected to thrive on one side or the other, but it seems this lineage of tarantulas successfully made camp on either side.
“Previously, we did not consider tarantulas to be good dispersers,” said Saoirse Foley of Carnegie Mellon University in a statement. “While continental drift certainly played its part in their history, the two Asian colonization events encourage us to reconsider this narrative. The microhabitat differences between those two lineages also suggest that tarantulas are experts at exploiting ecological niches, while simultaneously displaying signs of niche conservation.”
1