AbstractMale sand fiddler crabs (Uca pugilator) defend territories that consist of a breeding burrow and a display area where they wave their claw to attract females. Burrow-holding males engage in agonistic contests with both intruding males that attempt burrow take-overs and with other territory-holding neighbors that apparently attempt to limit waving or other surface activities of rivals. Contests employ one or more behavioral elements that range from no claw contact to use of the claw to push, grip, or flip an opponent. We placed each observed element into one of six groups ranked by intensity, which was based on the degree of claw contact and apparent energy expenditure. In the field, contests with intruders began at higher intensity and escalated more rapidly than did those with neighbors. Thus, U. pugilator males exhibit a dear enemy response toward neighbors. However, resident-resident contests increased in intensity when burrows were close, neighbors faced each other when exiting burrows, and neighbors were of similar size. Proximity and orientation determine the ease with which a neighbor may be engaged. Also, neighbors that are close and of similar size pose a greater threat to mating opportunities, favoring heightened intensity of contests.
Criteria for studies of dear enemy and nasty neighbor effects: a comment on Christensen and Radford
