Tarantulas are a distinct group of spiders well known for their large appearance and the hair-like setae that covers their bodies. Despite living a sedentary lifestyle where they rarely leave their underground burrows, tarantulas have managed to inhabit every continent except Antarctica, reports Peter Dockrill for Science Alert. Using spider fossils and tarantula databases, researchers may have an answer as to how tarantulas managed to crawl into most of the globe's crevices—findings they published in the April issue of the journal PeerJ.
Saoirse Foley, a bioinformatician from Carnegie Mellon University, along with her team analyzed the biogeographic spread of tarantulas by creating a family tree. The researchers built the tree by looking at clues from databases of spiders' transcriptomes—the protein coding portion of the genome in RNA, reports Mindy Weisberger for Live Science. From the databases, Foley modeled how tarantulas evolved over 120 million years, Science Alert reports.
After creating the family tree, the researchers matched it with a timeline of spider fossils to gauge where the arachnids first appeared and how they dispersed, Live Science reports. However, well-preserved tarantula fossils are rare, so the researchers also collected data from mygalomorphs, the researchers explain in a statement. That arachnid group includes tarantulas and other giant, ground-dwelling spiders, per Live Science.
From the constructed timeline and the tarantula family tree that included 29 different tarantula species and 18 other mygalomorphs, the researchers identified that ancestral tarantulas arrived in the Americas 120 million years ago during the Cretaceous period, reports Live Science. During this time, the continents were all joined together into the supercontinent of Gondwana. Before Gondwana broke apart, the tarantulas dispersed from the Americas into Australia, Africa and India—which was initially connected to Madagascar and not Asia, Live Science reports. About 55 to 35 million years ago, India separated from Madagascar and collided with Asia.
Before India collided with Asia, tarantulas there diverged into two lineages, reports Science Alert. One lineage of tarantulas lived in underground burrows, and another type preferred an arboreal lifestyle, Live Science reports. Burrowing spiders arrived in Asia first, followed by tree-dwelling spiders 20 million years later. This created two separate, "out of India" tarantula dispersals into Asia and suggests that the spiders adapted to new habitats and continued to spread after initial help from continental drift, reports Science Alert.
"Previously, we did not consider tarantulas to be good dispersers," said Foley in a statement. "While continental drift certainly played its part in their history, the two Asian colonization events encourage us to reconsider this narrative."