Robot crab ‘killed' by rivals in mating rituals

Telegraph

3 days ago

When scientists deposited 'Wavy Dave' the robot crab on a mudflat in Portugal, they hoped to learn more about how males compete for mates by waving their huge claws.
But the little machine was thwarted by an altogether different kind of pincer movement after being attacked by furious rivals, unhappy with the interloper.
'The females realised he was a bit odd, and some of the males tried to fight him,' admitted Dr Joe Wilde, who carried out the study while working for the University of Exeter.
'One male broke Wavy Dave by pulling off his claw. We had to abandon that trial and reboot the robot.'
The Exeter team were studying the mating habits of male fiddler crabs, who have one oversized claw, and attract females by standing outside their burrow and waving it.
Female fiddler crabs prefer males with a larger claw, and those that wave their jumbo pincher more quickly. The outsized claw is so big it can be 30 per cent of their body weight and takes a lot of effort to continually wave.
Once a male crab has impressed a female with his laborious claw waving, she will lay eggs in his burrow which he will then fertilise. Once the eggs have hatched, the larvae float away to sea.
Thousands of crabs live on the mudflats in Southern Portugal where the study was conducted, and Wavy Dave was set up 12 inches from a real male's burrow to find out how males adjust their behaviour in the presence of a rival.
The team discovered that the males did not appreciate the extra competition and stayed outside their burrows, waving for longer, to make sure they won the female's attention.
The study – led by the Centre for Research in Animal Behaviour (CRAB) at Exeter – suggests male crabs notice the behaviour of rivals and can adjust their courtship in response.
'If you own a shop and your rivals start selling things really cheaply, you might have to change how you run your business,' added Dr Wilde.
'The same might be true for males signalling to attract females – and our study suggests males do indeed respond to competition.
'Our findings reveal the subtle ways in which these crabs adjust their behaviour to compete in a dynamic environment, investing more in signalling when it is likely to be most profitable.'
The scientists said they observed multiple males 'aggressively challenging and physically attacking' the robot during trials, saying they were confident they saw Wavy Dave as a rival.
However, when a larger claw was fitted, the crabs grew more fearful and less willing to throw their hat into the ring for the females.
They retreated back into the burrow for longer periods, which researchers said was potentially to avoid attack and prevent their homes being stolen. Scientists believe crabs use the size of claws to assess fighting ability.
Dr Wilde said Wavy Dave began as a 'pipedream' during the Covid lockdown.
At the time, Dr Wilde was learning about 3D printing, and he happened to see that someone had created 3D scans of fiddler crabs and made them freely available.
He found a 3D printer to make a model, and taught himself enough robotics to make a crab that waved its claw. He then developed an app to control the crab via Bluetooth signals.
The new research was published in the journal Proceedings of the Royal Society B.