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The harvester finds his way through a mossy woodland on eight rickety legs with delicate support posts that support a plump body with two small eyes. Sometimes called daddy long-legged spiders, these spiders are cousins to spiders whose outdoor lifestyle sets them apart from other creatures called daddy long-legged spiders, more commonly known as cellar spiders. They have other interesting differences: The ends of a harvester’s graceful limbs are flexible, allowing them to wrap around a branch like a monkey’s tail.
Harvestmen’s distance from spiders made them attractive to geneticists who wondered how spiders evolved. In Article published Wednesday in Proceedings of the Royal Society B, Researchers who sequenced the harvester genome reported that spiders differed significantly from spiders, explaining how certain genes tell how these trademark legs will grow.
The size of the harvester’s genome was the team’s initial focus. The ancestors of modern spiders lived off a copy of their entire genome at some point long ago, giving them more genes to work with for evolution. This may have contributed to greater diversity among spiders.
“There’s a hypothesis that when you have duplicate genomes, the retained genes might have new functions,” said Vanessa González, a computational genome scientist at the Smithsonian Institution, who is the author of the new paper.
Prashant Sharma, a professor at the University of Wisconsin at Madison and the study’s author, said some scientists wonder if such replicas could help explain some of the wild diversity of the animal kingdom. Complex genomes and more diverse organisms may seem to go together.
But despite the diversity of the harvesters — there are more than 6,000 species in the group — there are no signs of duplication in the harvester’s genome, the researchers said. And there are only a handful of species of horseshoe crabs, arachnids with at least one genome copy in their evolution.
Dr. “The Aaraknids really challenge this idea,” Sharma said. Having more genes could help organisms diversify, but only if environmental conditions and other factors lined up correctly, he speculates.
The team located a number of genes in the harvester genome that are also known to control leg development in insect species. Dr. When certain genes are suppressed in harvesters, pedipalps instead of two or more pairs of legs become tiny appendages that arachnids use to manipulate food and grasp mates, said Guilherme Gainett, a graduate student in Sharma’s lab.
Dr. The gripping ends of an ordinary harvester’s legs were found to be under the control of another gene, which Sharma compared to the extra hundred-knuckle fingers. Experimentally lowering their level resulted in just one long piece that couldn’t bend.
These transforming appendages help researchers uncover the invisible map of the creature’s development and show how its body is built with familiar genes used in the harvester’s distinctive methods.
In the future, the team hopes to use the newly acquired knowledge of the genome to understand evolution in harvesters and other arachnids. For example, the small structure near the harvester’s mouth that resembles a spider’s tooth – what tells it what to expect?
Dr. “We don’t know the first thing about what factors determine identity,” Sharma said.
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