In sexual selection and thermoregulation, bigger is better, at least for fiddler crabs

Sexual dimorphism in fiddler crabs. Female (A) and male (B) Uca panacea. Scale bars indicate 1 cm. From Darnell and Munguia 2011

Imagine yourself a fiddler crab. For this exercise, imagine yourself a male fiddler crab. Are you with me? Great. Check out your right claw, it’s a sleek, slender machine, perfect for picking through the sand as you sift out bacteria and other microorganisms for food. It also makes a handy shovel for digging nice deep burrows to protect you from harsh conditions. Now check out your left claw. Wow! This thing is massive. If you possess a particularly vivid mind and have place your ego within the carapace of Uca panacea, your giant claw is more than a quarter of your body weight. This comically mis-proportioned appendage is why those pesky bipeds call you and your cousins “Fiddler Crabs”.

See that female fiddler crab at the perimeter of your territory? Yes, she is checking you out. That giant claw of yours is primarily used to attract mates, signalling to interested parties that your are fit and fecund. You even have a special dance, unique to each fiddler crab species, to announce your vitality. And if some other, lesser-clawed, male tries to move in to your territory, why, you’re equipped with a serious piece of hardware to drive off that interloper.

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