Climbing behavior of guarding males in the hermit crab Pagurus minutus : the effect of rivals, female size, and being we
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ARTICLE
Climbing behavior of guarding males in the hermit crab Pagurus minutus: the effect of rivals, female size, and being weaponless Takayoshi Tanaka1 · Chiaki I. Yasuda1,2 · Tsunenori Koga1 Received: 26 May 2020 / Accepted: 14 October 2020 © Japan Ethological Society 2020
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. Keywords Avoidance · Fighting ability · Male–male competition · Mating success · Resource value
Introduction Male reproductive success is often determined by the number of female mates (Bateman 1948), so males evolve specialized mating strategies, such as guarding a harem, to monopolize females (Shuster 1989). In crustaceans, precopulatory mate-guarding is typical when female receptivity is limited (Jormalainen 1998): males physically guard a receptive female and defend against conspecific solitary males (rivals) before fertilization. Previous studies of crustaceans, however, have reported that some guarders fail to defend their partner from a rival during male–male contests even when the guarders have a positional advantage (Dick and Elwood 1990; Takeshita and Henmi 2010). Therefore, for * Chiaki I. Yasuda [email protected] 1
Faculty of Education, Wakayama University, Sakaedani, Wakayama 640‑8510, Japan
Present Address: Graduate School of Fisheries Sciences, Hokkaido University, Minato‑cho, Hakodate, Hokkaido 041‑8611, Japan
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guarding males, decreasing the encounter rate with rivals would also be important to enhance mating success, along with the winning of direct contests. The intensity of such rival-avoidance might increase when the guarding males are potentially weaker contestants and/or guard a female with high value, but decrease in the ab
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