Knees Evolved First in Spiders, by Duplication of “dachshund” Gene

Dr. Nikola-Michael Prpic and colleagues from Abteilung für Entwicklungsbiologie, GZMB Ernst-Caspari-Haus, Johann-Friedrich-Blumenbach-Institut für Zoologie und Anthropologie, Georg-August-Universität, Göttingen, Germany, have identified the driving force behind the evolution of a leg novelty first found in spiders: knees. They report their findings in a new study published online on October 6, 2015 in Molecular Biology and Evolution, The article is titled “Neofunctionalisation of a Duplicate dachshund Gene Underlies the Evolution of a Novel Leg Segment in Arachnids.” With eight legs and seven joints on each---that's a lot for a spider to coordinate just to take a single step. Dr. Prpic's research team homed in on a gene called dachshund (dac). This gene was first discovered in fruit flies, and humorously named for the missing leg segments and shortened legs that result from dac mutant flies. But arachnids are different from flies and other arthropods, possessing a second dac gene. And the second dac gene (dac2) is expressed only in the kneecap, or patella, during spider development. When the research group used RNA interference experiments to specifically deactivate dac2, the kneecap fuses with the tibia to form a single leg segment. The force behind knees first appearing on the spider evolutionary scene was a result of ancient gene duplication in the original dac gene that, over time, evolved into an entirely new function and way of unique way of walking about for spiders. "Species constantly adapt and evolve by inventing new body features," said Dr. Prpic. "Our work shows how a gene can be duplicated and then used during evolution to invent a new morphological feature."
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