I had to post on this one not only for its behavioral ecology significance, but also because I had my first start in science experimenting with fiddler crab circadian rhythms and pigmentation, back in high school. The advantage of having a left claw, they find, probably has to do with something other than a frequency dependent advantage in fighting ability. I like the straightforward question as posed in the title, although they should have included that they were asking the question in reference to fighting.
This is also interesting in the context of that recent paper on the left-handedness gene. Maybe they could check out that gene in the crab. In that paper they also went through an evolutionary explanation for left-handedness in humans.. sorry, don't have link to that paper. I think it was in Molecular Psychiatry.
What are the consequences of being left-clawed in a predominantly right-clawed fiddler crab?
P.R.Y. Backwell, M. Matsumasa, M. Double, A. Roberts, M. Murai, J.S. Keogh, M.D. Jennions
Proceedings Royal Society, B Online: Tuesday, August 21, 2007
Abstract: Male fiddler crabs (genus Uca) have an enlarged major claw that is used during fights. In most species, 50% of males have a major claw on the left and 50% on the right. In Uca vocans vomeris, however, less than 1.4% of males are left-clawed. Fights between opponents with claws on the same or opposite side result in different physical alignment of claws, which affects fighting tactics. Left-clawed males mainly fight opposite-clawed opponents, so we predicted that they would be better fighters due to their relatively greater experience in fighting opposite-clawed opponents. We found, however, that (i) a left-clawed male retains a burrow for a significantly shorter period than a size-matched right-clawed male, (ii) when experimentally displaced from their burrow, there is no difference in the tactics used by left- and right-clawed males to obtain a new burrow; however, right-clawed males are significantly more likely to initiate fights with resident males, and (iii) right-clawed residents engage in significantly more fights than left-clawed residents. It appears that left-clawed males are actually less likely to fight, and when they do fight they are less likely to win, than right-clawed males. The low-level persistence of left-clawed males is therefore unlikely to involve a frequency-dependent advantage associated with fighting experience.