Fiddle-de-dee: The male fiddler crab is a fine example of how evolutionary pressure can select an exaggerated physical trait: while one claw is small and used for feeding, the other is grossly enlarged, reaching up to 2/3 of his body weight! The female has symmetrical, small claws. So, does size matter?
✤ Ornament vs. Armament: The large claw of the male fiddler crab is a sexual ornament, like the feathers of a peacock. With it, he waves flirtatiously at the susceptible female, enticing her to his sand burrow. The larger and more conspicuous his claw, the greater his chance at mating success. It is also an effective weapon, used to threaten and wage battles with competing males. But these are competing demands: large and light claws may be waved at lower energy costs, whereas heavy claws with powerful muscles are better in fights. Studies show that claws evolved to optimize fitness in both mating and fighting (REF: http://goo.gl/n00sZa)
✤ Keeping Up Appearances: In a study performed upon a beach in Zanzibar, Tanzania, scientists tethered a female crab by super-glueing a thread to her carapace and anchoring it to a spike in the sand. If she was viewed by a solo male, a friendly waving at a leisurely pace of 11.5 waves/min ensued. But in the presence of male competition, his waving became more urgent, at 16.5 waves/min! (REF: http://goo.gl/ME1wW5). Watch this little guy seemingly inspired by the Village People 🙂 YMCA crab dance with music
✤ Honesty is Not the Best Policy: When a male fiddler loses his major claw, he regenerates a new one of similar size but much weaker fighting ability. Studies have shown that the male can bluff his way through fights with the weaker claw, in a form of dishonest signaling. This unfair advantage presumably makes up for the costs of claw regeneration. (REF: http://goo.gl/OQNfB7)
✤ A Cool Tool: If you think you now know all there is about the fiddler crab claw, consider this. Scientists measured body temperature of fiddler crabs subjected to a heat lamp and showed that the large claw actually acts as a heat sink, allowing the male to cool off more quickly with it. On a hot beach, this advantage may help offset the high energy costs of his exaggerated “male ornament”. (REF: http://goo.gl/EpxrUq )
Birthday shout-out to Buddhini Samarasinghe !