Climbing behavior of guarding males in the hermit crab Pagurus minutus: the effect of rivals, female size, and being weaponless

Abstract

Male crustaceans engage in precopulatory mate-guarding to monopolize a female. However, a conspecific rival often takes the female from the guarding males during male–male contests, so guarding males should invest in behavior to decrease the rate of encounters with rivals, especially when they are potentially weak and guard a valuable female. We examined this idea using a net-climbing (avoidance) response by precopulatory guarding males of the hermit crab Pagurus minutus. Guarding males more often climb revetment walls in the field than solitary males and females, and the guarders were larger in body size than the solitary males on the walls. Guarding males increased climbing effort in the presence of rivals compared to controls (no stimulus), but not when faced with a non-threat organism. Compared to intact guarding males, those without a major cheliped (“weaponless”) were less likely to succeed in defending their partner in direct fights, but increased climbing investment overall, rather than especially when a rival was present. Although female size positively correlates with clutch size in this species, male climbing height decreased with increasing size of the guarded female. We discuss the effectiveness and importance of climbing in this species as it relates to conditions at our study site and the general vulnerability of guarding males depending on weapon status.