Tarantulas Almost Everywhere Because of the Continental Drift

Seeing a tarantula is not new to many people. Perhaps the most popular species of spiders are the brightly-colored, hairy tarantulas - and a new study might finally explain how these eight-legged creatures exist virtually everywhere on the planet.

With more than 1,000 species identified under the Theraphosidae (tarantula) family, it should not be surprising that their global footprint is also unusually large. However, what makes this puzzling is that tarantulas are particularly sedentary - they don't really move away from their homes if they even do at all.

Regardless, tarantulas can be found almost everywhere. They live in all of the continents except for the icy wastelands of Antarctica.

Now, a new study appearing in the peer-reviewed journal Biodiversity and Conservation, titled "Phylogenomic analyses reveal a Gondwanan origin and repeated out of India colonizations into Asia by tarantulas (Araneae: Theraphosidae)," proposes a sound explanation on how such sedentary spiders covered a large part of the planet.

(Photo: Photo by Stefan Zaklin/Getty Images)
WASHINGTON - MARCH 29: Children watch a tarantula climb its tank on March 29, 2003, at the Smithsonian's National Museum of Natural History in Washington, D.C. The museum hosted its Insect Expo and invited visitors to hold selected insects and to watch tarantulas get fed crickets by volunteers.

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Finding Tarantulas (Almost) Everywhere

The researchers explained in their paper that tarantulas are quite widespread and are found throughout the subtropical regions of every continent. The international team was led by Saoirse Foley from Carnegie Mellon University together with members from the National University of Singapore and Universität Trier in Germany.

Researchers additionally note that the spiders' behavior is not consistent with those found in "successful dispersers." However, tarantulas still managed to spread across the Earth and have "colonized strikingly different ecological niches."

So, how did the tarantulas do it?

As reported on Science Alert, to answer the puzzling question of these spiders' global footprint, researchers turned to investigate the biogeographic patterns of tarantulas across history. They examined messenger RNA logged in tarantula transcriptome databases - the complete set of these spiders' transcripts, usually used for comparative studies of genes of the same species in different environmental conditions.

Researchers then created modeling of the tarantula family tree developing over a hypothetical evolution over 120 million years.

Created by the Continental Drift

The tarantulas' ancestry might be the key to their global presence, with their earlier ancestors establishing themselves in the now-separated continents through the continental drift - the gradual movement of the world's largest landmasses, separating and colliding for millions of years after the breakup of the supercontinent Gondwana, which began splitting during the Jurassic period some 180 million years ago.

Researchers noted in their paper that previous studies estimate that tarantulas emerged between 150 Ma-71 Ma or ~107 Ma, which is compatible with a Gondwanan origin. Furthermore, this model supports how some tarantulas under the subfamily Selenocosmiinae have been suggested to be North Gondwanan taxa.

In their studies, they also presented evidence for the existence of two separate "out of India" expansions of the tarantulas' forefathers deep into Asia, traced back to the time when the Indian subcontinent collided with mainland Asia some 55 to 35 million years ago.

This led the researchers to note that despite their earlier analysis suggesting a Gondwanan origin for the tarantulas, this pattern observed from the Indian subcontinent suggests otherwise. Theraphosidae might not have been always present in Oceania, and supports the theory of Selenocosmiinae diversifying over Asia, crossing the Wallace Line - the boundary line between Asia and Australia - while their terrestrial cousins, Thrigmopoeinae remained in India.