Guarding males of the hermit crab climb up algae to avoid male–male competition

Abstract

Males of the hermit crab Pagurus filholi show precopulatory guarding behavior in which a male grasps the shell of a mature female with his left cheliped before copulation. Hermit crabs were most common in rocky intertidal areas with cobbles and boulders, while many guarding pairs were observed on fronds of brown algae such as Sargassum confusum in Hakodate Bay, Japan. We examined three hypotheses explaining why the guarding pairs were most common on algae; (1) aggregation place for mature males and females to find mates, (2) avoidance of male-male combat, and (3) avoidance of predators. If solitary males and females climbed up algae, then many guarding pairs were observed after pairing, but only guarding pairs climbed up the algae after removing all crabs. Experiments in aquariums showed that the disturbance rate for guarding pairs due to male-male competition was lower on the algae than in boulder and rocky flat areas, and few disturbances were observed by predatory crabs in all habitat types. These results suggest that the guarding males climb up the fronds of algae to sequester guarded females from rival males and avoid male-male combat. This behavior could be considered as a male counter tactic against indirect female choice mediated by sex pheromones in which females release sex pheromones while guarded, attracting many rival males and inducing male-male competition.

Reason for being single: some males do not guard receptive females in the hermit crab Pagurus filholi

“…When a solitary male encounters a guarding pair, a maleemale contest often occurs between the two males in Pagurus middendorffii (Wada et al, 1999; and Pagurus nigrofascia (Suzuki, Yasuda, Takeshita, & Wada, 2012;Yasuda et al, 2011), and the larger males or the guarding males are in the advantageous position in these contests Yasuda et al, 2012). Guarding males of Pagurus filholi and P. nigrofascia often climb up onto fronds of algae (Y. Hasaba, C. I. Yasuda, & S. Wada, personal observation) to sequester females from intruders and avoid maleemale contests (Kawaminami & Goshima, 2015), suggesting that guarding would be a beneficial behaviour for ensuring a mating opportunity. Almost all males immediately guard receptive females that have been guarded by other males under laboratory experiments in P. middendorffii (Wada, Arashiro, Takeshita, & Shibata, 2011) and P. nigrofascia .…”

Behavioral assay and chemical characters of female sex pheromones in the hermit crab Pagurus filholi

“…Females of the hermit crab Pagurus filholi release sex pheromones that induce males to begin assessment and guarding behavior (Imafuku 1986 ; Goshima et al 1998 ; Okamura and Goshima 2010 ; Kawaminami and Goshima 2015 ). During guarding, males grasp the shell of a mature female with their left cheliped for up to 5 days before copulation in the reproductive season, and assessment behavior is considered to be a preliminary step toward mate guarding (Goshima et al 1998 ; Minouchi and Goshima 1998 ).…”

Does prior residency interact with loss? A study of male–male contests in the hermit crab Pagurus minutus

“…Because Pagurus males guard a female with the left minor chela, guarding behavior can be conducted as usual even with a lower actual RHP due to autotomize their weapon (Yasuda & Koga, 2016a; Yasuda et al, 2011). Moreover, regardless of RHP, Pagurus males can avoid male–male contests by climbing up vertical objects such as boulders, algae, and/or banks (Kawaminami & Goshima, 2015; Yasuda et al, 2017). Our field collection and size‐matching methods might have resulted in males with a lower RHP being losers in both owner and intruder positions in trial–1.…”

“…Males of Pagurus hermit crabs have direct contests for mates during precopulatory guarding (Wada, Tanaka, & Goshima, 1999; Yasuda, Suzuki, & Wada, 2011), in which the male grasps the aperture of the gastropod shell occupied by a sexually mature female over a period of several days (Elwood & Neil, 1992; Imafuku, 1986). Females emit a sexual pheromone to induce male guarding behavior and male–male contests (Kawaminami & Goshima, 2015; Okamura & Goshima, 2010), and males can assess the females based on both size and maturity (Wada, Arashiro, Takeshita, & Shibata, 2011). Male–male contests for the female occur between a solitary male (intruder) and a guarding male (owner), and the owner continues to guard the female during the fight unless the intruder succeeds in taking over the female by physical force.…”