Tarantulas, everyone’s favorite furry spiders, are found worldwide and inhabit all continents except Antarctica. But how did they become so widespread? Females rarely leave their burrows, spiders stay close to where they hatch, and adult males travel alone when looking for a mate.
To answer this question, researchers set out more than 100 million years ago to find the origin of the tarantula group, building a tarantula family tree based on molecular clues from existing databases of spider transcriptomes – the protein-coding part of it. genome, found in ribonucleic acid, or RNA.
After they created the tree, they mapped it to a spider fossil timeline, to estimate when – and where – tarantulas appeared and spread.
Related: In pictures: tarantulas show their stuff
The scientists found that tarantulas first appeared during the Cretaceous Period in what is now America. But at the time, America was part of the vast supercontinent Gondwana. Ancient tarantula relatives, even if they were now home bodies such as tarantulas, likely spread across the conjoined landmasses and spread from America to Africa, Australia, and India. Then, after Gondwana fell apart, India separated from Madagascar and collided with Asia – bringing the 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 mygalomorphs – the arachnid group that includes tarantulas and other large ground-dwelling spiders – that are better represented in the fossil record than tarantulas.
After constructing a tree for tarantulas based on transcriptome data, representing 29 bird species and 18 other mygalomorphs, the scientists calibrated the tree over time using data from fossils. This allowed the researchers to calculate the ages of tarantula lines, as well as to estimate when the ancestors of modern tarantulas spread around the world.
Tarantula timeline
According to this new timeline, tarantulas first appeared in America about 120 million years ago. There, the spiders that were ancestors of the African tarantulas emerged about 112 million to 108 million years ago. About 108 million years ago, tarantulas were settled in what is now India. India separated from Madagascar between 95 million and 84 million years ago and drifted towards Asia; That slow motion collision, which began between 58 million and 35 million years ago, brought tarantulas to the Asian continent.
Before that happened, the tarantulas of India diverged into two genera with different lifestyles: one group of tarantulas was mainly arboreal and the other preferred to live in burrows. Both sexes eventually spread to Asia, but the tree group (Ornithoctoninae, also known as “Earth Tigers”) did so 20 million years after their burrowing cousins.
This second, later wave of tarantula spread to Asia suggests the spiders were able to fill ecological niches and adapt to new habitats more effectively than ever thought.
“Previously, we didn’t consider tarantulas to be good propagators,” said lead author Saoirse Foley, an evolutionary biologist at Carnegie Mellon University in Pittsburgh. said in a statement. “While continental drift certainly played a role in their history, the two Asian colonization events encourage us to rethink this story,” Foley said.
The findings were published online April 6 in the journal PeerJ.
Originally published on Live Science.