British boffins have revealed a randy species of crab is able to make a marathon five day migration every year – just to mate.
The famous red land crabs of Christmas Island, which is situated in the Indian Ocean, spend the dry season lying dormant in their inland burrows.
But when the monsoon season arrives the crustaceans feel the urge to mate – and biological signals trigger ”dramatic” changes in their leg muscles.
The crabs, which usually complete just ten minutes of daily exercise, travel for 12 hours a day as they make their way towards mating grounds near the sea.
British researchers have now discovered that the incredible transformation occurs after the crabs change their weak leg muscles fibres into high-endurance tissue.
Biology professor Mark Viney, who carried out the research with a team from the University of Bristol’s School of Biological Sciences, said: ”The muscles in your body are different – the muscles in your legs are different from the muscles in your heart because they do different things.
”In the same way these crabs need to do different things, so at one point they need to go on this long migration to breed and they actually change their leg muscles to do that.
”The muscles are made of fibres that contract and there are different types of muscle fibre that require different amounts of energy as well as having different properties of how long they can carry on activity for.
”What these crabs do is change the flavour of their muscles quite dramatically in the sense of what those leg muscles can do.”
The groundbreaking project was initially led by Professor Steve Morris from the University of Bristol, who has tragically passed away since it was completed.
Dr Morris and his colleagues carried out detailed genetic analysis of samples of leg muscle taken from the crabs during their dormant and migratory periods.
They found that the crabs made ”major” physiological changes to their muscle composition to become aerobic and highly resistant to fatigue.
The changes allow the crabs to be on the move for up to 12 hours a day during the monsoon season compared with an average of ten minutes during the dry season.
Professor Viney added: ”The transformed muscle groups can then perform much greater tasks – they become high endurance muscles which the crabs need for their migration.
”People knew that the animals had to change to make this huge, sudden migration, but we’ve found out what that change is and how it happens.
”It happens over a short period of time, a matter of weeks.”
Up to 120 million red crabs live on Christmas Island and their migration often completely blocks traffic routes.
* The research has been published in the May issue of The Journal of Experimental Biology.
