Do weaponless males of the hermit crab Pagurus minutus give up contests without escalation? Behavior of intruders that lack their major cheliped in male–male contests

Abstract

In dyadic contests, theoretical studies have predicted that weaker contestants are less likely to engage in fights to minimize the cost of aggression. Since the major cheliped of decapod crustaceans is critically important as a weapon, contestants without a major cheliped should be more likely to give up the contests. We therefore examined whether loss of the major cheliped by the hermit crab Pagurus minutus would affect their decision to escalate male–male contests over guarded females. Intruders without a major cheliped showed no difference in the frequency of escalation compared with intact intruders, and the decision to give up was affected by the body size difference between the contestants. After escalation, compared with intact intruders, intruders without a major cheliped had significantly decreased success of takeover of a female from opponents, suggesting a strong disadvantage of losing their major cheliped. Although the decision of weaponless intruders to escalate seems irrational, several factors, such as poor accuracy of resource holding potential assessment, the influence of body size, and a high benefit to cost ratio of male–male contests, may have affected their behavior.

Males that drop a sexually selected weapon grow larger testes

“…Males without weapons are typically subordinate in male contest competition (O'Neill and Cobb ; Berzins and Caldwell ; Smith ; Abello et al. ; Taylor and Jackson ; Yasuda and Koga ; Emberts et al. in review ).…”

“…Males without weapons are typically subordinate in male contest competition (O'Neill and Cobb 1979;Berzins and Caldwell 1983;Smith 1992;Abello et al 1994;Taylor and Jackson 2003;Yasuda and Koga 2016;Emberts et al in review). Importantly, while male-male competition can limit mating for many males, it probably only rarely fully precludes males with small weapons and those without weapons from mating (e.g., Goldsmith and Alcock 1993;Emlen 1997;Simmons et al 2004).…”

“…Furthermore, after the permanent loss of a weapon, male leaf‐footed bugs rarely secure access to females in a competitive environment (Emberts, in review ). In hermit crabs (Yasuda and Koga ), jumping spiders (Taylor and Jackson ), and lobsters (O'Neill and Cobb ), males that lose a weapon are relatively unsuccessful in contest competition. Therefore, to maximize their reproductive success, theory suggests that these males should increase investment in postcopulatory traits, such as testes size (Parker et al.…”

The ecology and evolution of autotomy

“…Regarding initial stages, male fiddler crabs ( Uca mjoebergi ) that fully regenerated their major claw after autotomy were less likely to hold and defend territories than intact individuals (Reaney et al, ). Moreover, autotomy, with or without regeneration, has repeatedly been found to decrease an individual's probability of winning intraspecific fights in the context of reproduction (Smith, ; Martín & Salvador, ; Abello et al, ; Reaney et al, ; Daleo et al, ; Wada, ; Yasuda & Koga, ; Emberts et al, ). In many cases these autotomizable appendages are used directly during intraspecific interactions (e.g.…”

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

“…In contrast to other systems (Kemp & Wiklund, 2004; Pratt, McLain, & Lathrop, 2003), resident status in Pagurus might not always assure intrinsic aggressiveness and/or greater fighting ability in the males. 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).…”