A female harvestman (Mitopus Morio) in a UK meadow Nick Upton/naturepl.com
A genetic study has shown that spider-like creatures can grow long legs and wrap their arms like monkey tails.
The harvestmen (or daddy-long legs) are arachnids. However, they are not spiders. They belong to an closely related group, the Opiliones. Their eight legs can be as long as 28 inches in length. They can also bend their tips to grasp and wrap around objects.
The 12 appendages are limb-like and belong to harvestmen, such as scorpions, ticks, and spiders. The four at the head develop into pincers or jaws, or shorter limbs called Pedipalps. These limbs are unique to arachnids. They can detect tastes and can be detected.
Guilherme Gainett, University of Wisconsin-Madison, and his collaborators were fascinated by the different development of these appendages. They teamed up with DNA specialists from the Smithsonian Institution Washington DC to create a sequence of the genetic code of a lab-raised harvestman (Phalangium opioido).
They identified three genes that could affect the development of legs in animals and engineered many harvestmen embryos with modified expressions of those genes.
Gainett says that some harvestmen had legs more like the first four appendages. The legs were also affected by genetic mutations that caused them to lose the ability to curl their legs around objects.
Gainett says that we have shown how these genetic combinations create a blueprint for the embryo to distinguish between whats going on in the leg that will be used for walking and whats going on in the pedipalp which can be used to assess food and manipulate the environment.
Harvestmen are unique among other arachnids. Their genome architecture may be very similar to that of older arachnids who lived over 400 million years ago. Vanessa Gonzlez, a Smithsonian Institution researcher, believes that harvestmen are ideal models for studying arachnid genes.
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2021.1168
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