Only the coolest fiddlers have big claws

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New research has discovered that male fiddler crabs use their impressive giant claws not only to attract females, but to stay cool while doing so.

Dr Zachary Darnell and Assistant Professor Pablo Munguia from the University of Texas, US discovered that crabs still in possession of the impressive pincer were able to cool themselves more rapidly than those without, demonstrating that the claw helps control temperature.

They studied the effects of heat on Gulf coast fiddler crabs (Uca panacea) by shining lamps on male crabs with and without the giant claw and measuring the crab's body temperature every 10 minutes while doing so. They found that claw-less crabs took far longer to cool.

Dr. Darnell believes this shows that the claw acts as a 'heat sink' transferring excess body heat to the claw where it can be dissipated into the air. This heat dispersing benefit would help offset the physical cost to the crab of growing such an extravagant nipper as well as the disadvantages the cumbersome claw causes males by slowing them down and hindering feeding.

Male fiddlers are risking heat stress and hunger while performing claw waving displays and searching for food in the tropical sun but it seems the big claw allows them to remain out of their burrows longer, gaining advantage over clawless rivals for food and females.

There are around 100 species of fiddler crabs in the genus Uca found living semi-terrestrial lives along coastal habitats such as beaches, lagoons and mangrove swamps. They are small, short lived creatures rarely reaching more than a few centimetres across or living more than a couple of years and are detritivores, sifting edible matter from the sediments they live upon.

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