Tarantulas are one of the most notorious spiders, in part because of their size, vibrant colors and appearance around the world. But one thing most people do not know is that tarantulas are home bodies. Females and their young rarely leave their holes and only adult males will wander to find a mate. How did such a seated spider inhabit six out of seven continents?
An international team of researchers, including Carnegie Mellon University’s Saoirse Foley University, has embarked on an ancestry.com-like investigation to find the answer to this question. They looked at the transcripts, the sum of all the transcripts of the mRNA, of many tarantulas and other spiders from different periods. Their findings were published online by PeerJ on April 6, 2021.
They used the transcriptomes to build a genetic tree from spiders and then calibrated their tree with the fossil data. Tarantula fossils are extremely rare, but the software used in the study was able to estimate the ages of older tarantula relative to the ages of fossils of other spiders.
Two independent tarantula descendants originated from India. Credit: https://dinosaurpictures.org/, 2021
They found that tarantulas are old, and the first time in the piece of land that is now considered the Americas about 120 million years ago, Chalk period. At that time, South America would have been attached to Africa, India and Australia as part of the Gondwana supercontinent. The spiders have finally reached their current destinations due to continental drift, with some interesting points of departure.
The nature of their entry into Asia, for example, suggests that tarantulas may also be surprisingly skilled distributors. The researchers were able to determine two separate lines of tarantula that set out on the Indian subcontinent before it crashed in Asia, with one generation mainly land dwellers and the other mainly in the country. They found that these generations colonized Asia about 20 million years apart. Surprisingly, the first group to reach Asia was also able to cross the Wallace line, a border between Australia and the Asian islands where many species abound on the one hand and rarely or not at all on the other.
Ancestor series of tarantulas estimated by researchers. Credit: https://mapchart.net/, 2021 (CC BY SA 4.0)
“Before, we did not consider tarantula to be good distributors. Although continental drift has certainly played a role in their history, the two Asian colonization opportunities encourage us to reconsider this narrative. “The microhabitat differences between the two sex lists also indicate that tarantulas are experts at exploiting ecological niches, while at the same time showing signs of niche conservation,” Foley said.
Reference: “Philogenomic Analyzes Reveal a Gondwanan Origin and Repeat from India Colonizations in Asia by Tarantulas (Araneae: Theraphosidae)” by Saoirse Foley, Henrik Krehenwinkel, Dong-Qiang Cheng and William H. Piel, April 6, 2021 PeerJ.
DOI: 10.7717 / peerj.11162
Additional study authors include Willam H. Piel and Dong-Qiang Cheng of Yale-NUS College in Singapore and Henrik Krehenwinkel of the University of Trier in Germany.