tarantulas, everyone’s favorite hair spiders, are found all over the world, living on all continents except Antarctica. But how did they become so widespread? Females rarely leave their burrows, spiders stay close to where they hatch, and mature males travel only when looking for a mate.
To answer this question, researchers traced the origins of the tarantula group more than 100 million years ago, building a tarantula family tree based on molecular clues from existing spider transcriptome databases – the portion of the genome that encodes proteins. . ribonucleic acid or RNA.
Once they created the tree, they mapped it on a chronological line of spider fossils to estimate when and where the tarantulas appeared and dispersed.
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Scientists have discovered that tarantulas first appeared during the Cretaceous in what is now America. But at the time, America was part of the massive supercontinent Gondwana. The ancient relatives of the tarantula, even if today they were household bodies like the tarantulas today, probably spread on the united earth masses, dispersing from America to Africa, Australia and India. Then, after Gondwana broke up, India separated from Madagascar and clashed with Asia – and brought hairy spiders to that continent as well, the researchers reported.
There are only two known tarantula fossils, both preserved in amber: one is from Mexico and is believed to be about 16 million years old, and the other is from Myanmar and is about 100 million years old, the study authors reported. Because tarantula fossils are so rare, the researchers also collected data from related myalomorphs – the group of arachnids that includes tarantulas and other large spiders that live on the ground – that are better represented in the fossil record than tarantulas.
After constructing a family tree for tarantulas from transcriptome data, representing 29 species of tarantulas and another 18 myalomorphs, the scientists calibrated the tree using fossil data. This allowed researchers to calculate the ages of the tarantula’s offspring and to approximate when the ancestors of modern tarantulas spread around the world.
Tarantula Chronology
According to this new chronology, tarantulas first appeared in America about 120 million years ago. There, the ancestral spiders of African tarantulas appeared about 112 million to 108 million years ago. About 108 million years ago, tarantulas were established in what is now India. India separated from Madagascar between 95 and 84 million years ago and headed for Asia; that slow-moving collision, which began between 58 and 35 million years ago, brought tarantulas to the Asian continent.
However, before this happened, Indian tarantulas were divided into two descendants with different lifestyles: One group of tarantulas was predominantly tree dwellers, and the other mostly preferred life in burrows. Both offspring eventually spread to Asia, but the tree group (Ornithoctoninae, also known as the “tigers of the earth”) did so 20 million years after their cousins.
This second subsequent wave of tarantula dispersal in Asia suggests that spiders have managed to fill ecological niches and adapt to new habitats more efficiently than previously thought.
“Previously, we didn’t consider tarantulas to be good dispersers,” wrote study author Saoirse Foley, an evolutionary biologist at Carnegie Mellon University in Pittsburgh. he said in a statement. “While continental drift has certainly played its part in their history, the two events of Asian colonization encourage us to reconsider this narrative,” Foley said.
The findings were published online on April 6 in the journal PeerJ.
Originally published on Live Science.