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For Those Long Legs

Researchers have homed in on the genes that give daddy longlegs their characteristically long legs, New Scientist reports.

A University of Wisconsin-Madison-led team sequenced the genome of Phalangium opilio, alternatively known as daddy longlegs or harvestmen,which are spider relatives. As they report in the Proceedings of the Royal Society B, the researchers found that its genome shows no signs of having undergone a whole-genome duplication and only harbors a single Hox gene cluster. They investigated the functions of three Hox genes — Deformed (Dfd), Sex combs reduced (Scr), and a homolog of Epidermal growth factor receptor (Egfr) — through RNAi knockdown studies.

Knocking down Dfd affected the length of P. opilio's first two legs, while knocking down Dfd as well as Scr led legs one through three to develop as pedipalps, though Scr knockdown on its own had no noticeable effect. Meanwhile, Egfr knockdown affected leg segmentation, a trait that usually allows daddy longlegs to wrap their legs around objects.

"We've shown… how the combinations of these genes create a blueprint in the embryo to differentiate between what's going to be a leg that is used for walking and what is going to be a pedipalp, which can be used to manipulate food and assess the surroundings," first author Guilherme Gainett from Wisconsin-Madison tells New Scientist.