The importance of strength and stamina varies with ownership status in sand fiddler crab contests for breeding burrows

Abstract

Abstract: In sand fiddler crabs, Uca pugilator, contests between residents and intruders for breeding burrows often escalate to forceful pinching. In these contests, we found that winners had greater claw armature, greater claw pinching strength, and greater pinching stamina (the ability to persist in pinching at a strength close to the initial level). Winners were not superior to opponents in body size, claw length, or pinching resilience (the ability to quickly return to former pinching strength and stamina). There was also a strong resident advantage such that residents usually won when strength and claw armature were similar among contestants. A field experiment that controlled pinching strength and stamina revealed that (1) residents readily retreat into their burrows when challenged by a male of relatively high pinching strength and (2) only intruders with high stamina win contests in which residents retreat. Contests with burrow retreats are twice as long as other contests, suggesting that high stamina enables intruders to persist in engaging residents. Intruders who lost experimental contests were more likely to immediately engage another resident if they were of high resilience. The ability to engage in multiple contests in short periods of time could prove favorable to residents and may explain their relatively high resilience. This study indicates that strength is a component of RHP and that residents, by retreating into burrows, can force upon intruders the additional requirement of high stamina before they can usurp burrow ownership. Significance statement: Strength and stamina have long been associated with victory in contests between males for breeding territories. However, territory owners may utilize features of their territories to gain an advantage over rivals who possess greater fighting ability. In sand fiddler crabs, Uca pugilator Bosc, males with larger claws usually win contests for breeding burrows but there is an ownership advantage. We show that greater strength (revealed in claw pinching force) leads to victory for burrow owners but that among intruders it only leads to an additional requirement for victory, the display of stamina (revealed in the ability to persist in forceful pinching). This is because weaker owners take refuge in burrows, forcing intruders into lengthy contests. Thus, the ownership advantage derives from the need of owners to display strength but of intruders to display strength and stamina.