GERALD, Gary W.*; KOTCHER, John E.; STONE, Caitlin; CLAUSSEN, Dennis L.; Miami University, Oxford, OH; Miami University, Oxford, OH; Miami University, Oxford, OH; Miami University, Oxford, OH: Effects of incline and substrate on the costs of locomotion in male fiddler crabs (Uca pugilator)

Sexual selection occurs when females preferentially produce offspring with males possessing exaggerated traits. However, sexually-selected traits may simultaneously reduce male fitness by hindering other characteristics, such as locomotor performance. The male fiddler crab (Uca pugilator) is a prime example of an animal with an enhanced sexually-selected trait (i.e. one enlarged claw used to attract females) that could impede locomotion. We hypothesized that the possession of a major claw by males would reduce their locomotor performance and, more specifically, that the negative impact would be greatest for animals moving on steeper inclines and on more compliant substrates. We measured the mean and maximum speeds, stride lengths, and stride frequencies of male and female fiddler crabs moving on two substrates (dry and wet sand) and at three different inclines (0&deg, 15&deg, 30&deg). Performance was measured before and after the major claw was removed from the males. Crabs of both sexes exhibited significant decreases in velocity when moving on the more compliant substrate (dry sand) and on steeper inclines. The removal of the claw did not significantly increase the speeds of males moving horizontally on either substrate. However, claw removal did significantly increase speeds on both 15&deg and 30&deg inclines (by 26% and 32% respectively). These results suggest that the costs of carrying an exaggerated claw are incline dependent, or, more generally, that habitat characteristics may play a crucial role in the evolution of sexually-selected traits.