Rapid regeneration of the major cheliped in relation to its function in male-male contests in the hermit crab Pagurus middendorffii

Abstract

Abstract:Most crustaceans are known to regenerate their appendages after losing them, and the pattern of regeneration may be related to its function. The pattern of regeneration of the right major cheliped was examined after experimentally induced autotomy and its behavioral function during male-male contests for mates was investigated in the hermit crab Pagurus middendorffii. Males with an autotomized major cheliped regenerated it at the first molt after autotomy and showed smaller growth in body size than in control males. The shape of the regenerated cheliped was more slender than the original, implying that the regenerated major cheliped would be less robust and weaker than previously. The length of the major cheliped of an owner male (guarding a female at the start of a dyadic contest) and the body size of an intruder affected whether or not the contest escalated, but the major cheliped length of the intruder and the body size of the owner determined the outcome of the escalated contest. The intruder used the major cheliped as an offensive weapon to take the female away from the owner by force after the contest escalated. The owner often moved the major cheliped forward, similar to a fencing weapon, before escalation. Such movement of the owner seems to be effective to prevent the intruders from approaching, and the regenerated cheliped of the owner may not require much robustness and strength as a defensive weapon before escalation. Rapid regeneration of the major cheliped in P. middendorffii would therefore be beneficial to minimize the disadvantages incurred by loss of the major cheliped.

Regeneration of major cheliped after the mating season in the hermit crab <i>Pagurus middendorffii</i>

“…R-males, moreover, molted more often than C-males, suggesting that major cheliped autotomy still facilitates the next molt. This is consistent with the prior study of P. middendorffii (Yasuda et al, 2014) as well as other studies on crustacean (Hopkins, 1982;Juanes & Smith, 1995), and our results also suggest this facilitation of molting occurs even in seasons when the molting frequency is very low.…”

“…October), we predicted that males would regenerate their major cheliped within a shorter period than a prior experiment in the non-mating season (Yasuda et al, 2014). However, the results in this study were opposite (Table 2).…”

“…However, the results in this study were opposite (Table 2). Yasuda et al (2014) found that autotomized males initiated to regenerate on the 16th day and all of the males molted with an average of 28 days. In contrast, we found that the first major cheliped regeneration occurred on the 33rd day after autotomy and the mean duration until molting was about 44 days.…”

“…The above experimental procedures were the same as our previous study (Yasuda et al, 2014) except no acclimation period was used in the present study.…”

“…middendorffii, Yasuda et al, 2012), regeneration of the major cheliped would be effective to overcome, in part, the disadvantage of loss of the major cheliped by males in this group. Yasuda et al (2014) demonstrated that males of P. middendorffii could largely regenerate their major cheliped in the first molt after autotomy requiring an average of 28 days. This study was conducted in the laboratory from late June to September.…”