Crabs spy on competitors to detect female mates

Melbourne, June 2 (ANI): Male fiddler crabs keep a check on other males waving their 'love claw' to detect the presence of a female, Australian researchers have found.

Male fiddler crabs have a large specialised claw that they use to fight and wave around to attract mates.

And thus, crabs spy on their competitors to look for potential female mates.

"Males will use other males as female detectors," ABC Science quoted behavioural ecologist Richard Milner of the Australian National University in Canberra, as saying.

"They'll eavesdrop on other males' courtship displays to detect the presence of a female," he added.

"When a female approaches a group of males they'll all start waving in synchrony and they'll all start trying to attract her," said Milner.

But knowing when females are around in the first place can be tricky because females are well camouflaged.

"The males are ridiculously conspicuous but the females look very bland," said Milner.

For the study, Milner wanted to see if males would use waving by other males as a sign there was a female around and start waving before they could actually see the female.

This would enable them to detect the presence of a female earlier than they otherwise would.

Milner set up a field experiment involving a group of four or five male crabs.

Milner then measured the number times per minute a particular "focal male" waved his love claw, under three different conditions.

When there was a female around, the focal male waved his claw 20 times a minute.

This compared to a base rate of once a minute when there were no females around.

Interestingly, though, when the focal male could not see the female (but the other males could), he waved his claw 12 times a minute.

"Eavesdropping males wave 12 times faster than non-courting males, but only 1.7 times slower than males in full visual contact with the female," said Milner.

Milner repeated the experiment with different 50 focal males.

"That's how I worked out that they do use other males as female detectors," said Milner.

The findings are reported in Biology Letters. (ANI)