Importance of weapon size in all stages of male-male contests in the hermit crab Pagurus minutus

• Published in: Behavioral ecology and sociobiology 2016-12, Vol.70 (12), p.2175-2183
• Main Authors: Yasuda, Chiaki I., Koga, Tsunenori
• Format: Article
• Language: English
• Subjects: Animal behavior; Animal Ecology; Animals; Behavioral Sciences; Binomials; Biomedical and Life Sciences; Body size; Competition; Crabs; Crustaceans; Decapoda; Defense mechanisms; Female animals; Hermit crabs; Life Sciences; Male animals; Males; Mating behavior; Original Article; Pagurus; Size; Weapons; Zoology
• ISSN: 0340-5443; 1432-0762
• DOI: 10.1007/s00265-016-2221-0

Physical traits such as body size and weapon size typically reflect an individual's resource holding potential (RHP). During male-male contests, contestants use these traits to assess their own and their opponent's RHP. However, the advertisement of RHP does not always predict contest outcome. Here, we examined whether assessment index (body size or weapon size [major cheliped size]) and assessment tactics (self or mutual) are predictors of outcome in male-male contests of the hermit crab Pagurus minutus. In experimental contests over guarded females, intruders did not escalate the contest when their major cheliped was smaller than their opponent's, implying that intruders use mutual assessment based on weapon size when deciding whether to escalate a contest. After escalation, intruders succeeded in taking over females within a shorter period of time with increasing major cheliped size relative to their opponent's. Overall, males with a major cheliped that was larger than their opponent's were more likely to win the contest, although some intruders later stopped guarding the female they had taken over. The importance of relative weapon size after escalation indicates that mutual assessment was also used in this phase of male-male contests. Together, these results suggest that males of P. minutus use mutual assessment based on weapon size throughout malemale contests, and that weapon size is an honest index of RHP.