Moment egg sack spews HUNDREDS of spiders
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The genetically altered mutant was created by a team of researchers at the University of Wisconsin–Madison in the US using a technique known as “RNA interference”. The researchers sequenced the world’s first genome of the daddy longlegs – a spider-like member of the Opiliones family. These gangly creepy crawlies, which are sometimes known as harvestmen, are a close relative of the spider.
Daddy longlegs move very differently to their eight-legged cousins, however, and that made them a perfect candidate to study arachnid evolution.
Guilherme Gainett, a UW–Madison graduate student and lead author of the study, said: “The true spiders in the order Araneae, the group that most people are familiar with, they usually use all those legs for walking.
“If you watch a daddy longlegs move, it will effectively walk on just three pairs of its legs.
“The remaining pair, the longest, they wave and touch around like a blind man.”
In the case of the Phalangium opilio, the critter’s longest legs, which are the second pair from the front, are covered in tiny hair-like structures that act like sensory organs.
The longest legs are also divided like fingers with multiple knuckles into structures known as tarsomeres.
According to Prashant Sharma, a Professor of Integrative Biology, tarsomeres are used in a wide variety of behaviours such as courting, fighting, sensing and climbing.
To better understand why daddy longlegs have such articulate and unique legs, they used the RNA interference technique to “knock off” or shut off certain genes in the critter’s genome – and the result was truly horrifying.
Mr Gainett said: “What we have been able to show is that two Hox genes acting in combination are sufficient to specify the identity of the first three pairs of legs.
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“They tell them, ‘You’re going to be a walking leg,’ and, ‘You’re not going to be a pedipalp,’ which is the small food-manipulating appendage.”
The researchers used their RNA technique to shut off two Hox genes – “Deformed” and “Sex combs reduced” – in Phalangium opilio eggs.
The resulting critters were born with mutated limbs that were transformed into much shorter appendages used to gather food.
And by altering another set of genes that are associated with the development of legs in fruit flies and other insects, the scientists were able to completely take away the daddy longlegs’ tarsomeres.
The study’s bizarre findings were published in the journal Proceedings of the Royal Society.
Professor Sharma said: “This is the first data outside of insects that points to how it is that these structures are made.
“And we see that evolution is not really coming up with new solutions here.
“It’s recycling the same genetic platform to make these organs even as they evolve independently in different species.”
The UW–Madison researchers collected the critters they experimented on around their campus buildings.
The Phalangium opilio is one of the most widespread species of daddy longlegs, which are found across Europe, Asia, North America, Africa and New Zealand.
Professor Sharma added: “There’s a very tight correlation to having a large number of tarsomeres and being able to climb, and climbing groups also tend to be much more diverse.
“The most diverse family of harvestmen by far happens to be the one that has the most tarsomeres.
“So, it’s providing some sort of ecological advantage.”
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