Tarantula’s, everyone’s favorite hairy spiders, is found worldwide and inhabits all continents except Antarctica. But how did they become so widespread? Females rarely leave their holes, spiders stay close to where they hatch, and adult males travel only when searching for a mate.
To answer this question, more than 100 million years ago, researchers went to search for the origin of the tarantula group and built a tarantula family tree based on molecular clues from existing databases of spider transcripts – the protein-coding part of the genome, found in ribonucleic acid, or RNA.
After creating the tree, they mapped it on a timeline of spider fossils to estimate when – and where – tarantulas appear and spread.
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The scientists discovered that tarantulas first appeared in the Cretaceous in what is now the Americas. But at the time, the Americas were part of the massive supercontinent Gondwana. Ancient relatives of the tarantula, even though they were home lists today, were probably scattered over the amalgamated land masses and spread from the Americas to Africa, Australia, and India. After Gondwana broke up, India separated from Madagascar and clashed with Asia – and also brought the hairy spiders to that continent, researchers report.
Only two tarantula fossils are known, both preserved in amber: one is from Mexico and is thought to be about 16 million years old, and the other is from Myanmar and is about 100 million years old, the authors of the study reported. Because tarantula fossils are so rare, the researchers also have data from related mygalomorphs – the arachnid group that includes tarantulas and other large, terrestrial spiders – which are better represented in the fossil record than tarantula.
After constructing a pedigree for tarantulas from transcriptome data, representing 29 tarantula species and 18 other mygalomorphs, the scientists calibrated the tree using data from fossils. This enabled the researchers to calculate the ages of tarantula lines, and to approximate when the ancestors of modern tarantula spread around the world.
Tarantula timeline
According to this new timeline, tarantula appeared in the Americas about 120 million years ago. There, the spiders that were ancestors of the tarantulas of Africa emerged about 112 million to 108 million years ago. About 108 million years ago, tarantula was established in what is now India. India separated from Madagascar between 95 and 84 million years ago and drifted to Asia; that slow motion collision, which began between 58 million and 35 million years ago, brought tarantulas to the Asian continent.
Before this happened, however, India’s tarantulas were divided into two generations with different lifestyles: one group of tarantulas were mainly tree dwellers, and the other mostly preferred life in holes. Both sexes eventually spread to Asia, but the tree group (Ornithoctoninae, also known as “Earth Tigers”) did so 20 million years after their buried cousins.
This second wave of tarantula distribution in Asia suggests that the spiders were able to fill ecological niches and adapt more effectively than they ever thought.
“Previously, we did not consider tarantulas to be good distributors,” said Saoirse Foley, an evolutionary biologist at Carnegie Mellon University in Pittsburgh, lead study author. said in a statement. “While continental drift has certainly played its part in their history, the two Asian colonization events encourage us to reconsider this narrative,” Foley said.
The findings were published online in the journal on April 6. PeerJ.
Originally published on Live Science.