Spiders, scorpions use leg genes to grow their heads

March 26 (UPI) — Arachnids don’t need specialized genes to develop a head. According to a new study published this week in the journal PNAS, they simply use their leg genes.

University of Wisconsin-Madison researchers Emily Setton and Prashant Sharma were searching for the evolutionary origins of spinnerets, the organs that allow spiders to spin silk threads. To suss out genetic links between spinnerets and spiders’ legs, the researchers silenced leg development genes in arachnid embryos. When they did so, the tiny spiders not only failed to develop legs, they also failed to grow heads.

“Evolution doesn’t want to reinvent the wheel,” Setton said in a news release.

Followup analysis showed both spiders and scorpions use the genes Sp6-9 and Dll to manage head development. The genes code for leg development in most arthropods.

It’s not the first time scientists have found the same genes serving a variety of purposes across different species. For example, the same gene is used to code for jaw bones in reptiles and ear bones in humans.

The latest discovery is, however, a reminder of the evolutionary efficiency of the arthropod, a group that’s adapted to land, water and air. Setton and Sharma believe arthropods hold many of the secrets of genetic evolution and adaptation.

“We study spiders, scorpions and others to help build a more complete evolutionary story and look at what’s going on in the complex world of arthropods,” said Setton.

The researchers hope more of their genetic tricks will be revealed by the phylum’s many unusual members.

“We work with really difficult animals to study,” Sharma said. “A big question of the lab is how is diversity built genetically, evolutionarily? How are ancient lineages related, and what are the genetic mechanisms that underlie the differences between them?”

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