Male crabs try to attract a female partner by using their claws to advertise the size of their home, scientists have found.
A study shows that male banana fiddler crabs try to catch a female's attention by waving their brightly coloured major claw in the air.
They then switch to a drumming signal transmitted through the ground as a series of rapid vibrations.
Males that drummed most rapidly had the largest burrows and the highest fitness, research by Anglia Ruskin University found.
In the study, researchers tested the sprint speed of crabs on a special racetrack and found crabs that had been induced to court had a poorer sprint performance.
The researchers believe the physical investment required to drum and wave allows females to select the fittest mates.
The advantage of drumming as well as waving is that male crabs can still attract females from inside their burrow when they are no longer visible.
This could also benefit female crabs because it reduces their risk of being coerced into mating when they enter a male's burrow to see how big it is.
Dr Sophie Mowles, lecturer in animal and environmental biology at Anglia Ruskin University, said: "Males frequently produce elaborate displays to attract females.
"These are often thought to demonstrate the quality of his genes, or his fitness, through a display of effort."
She said that by choosing a vigorously displaying male, a female crab could ensure she selected a good quality mate who could offer good genes for her offspring.
"Energetically costly 'signals of stamina' reflect the ability of the male to perform other demanding activities such as foraging and sprinting to avoid predators," she said. "These are attributes a choosy female should want to pass on to her offspring.
"The ability to perform a demanding display may also indicate that the male is in good condition, preventing females from mating with diseased or parasitised males."
The research is published in the journal Royal Society Open Science.