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.
13 14Prior social experience often affects subsequent competitive interactions and their outcomes. 15 Although the effects of prior contest experience have been widely examined, effects of mating 16 experience remain less well examined. We examined, in males of the hermit crab Pagurus 17 nigrofascia, whether males successively copulated with more than one female, and whether 18 males with copulation experience differed in their subsequent contest behaviors and probability 19 of winning in male-male contests compared to males without copulation experience. The 20 copulation experience of intruders was manipulated and the contest behaviors compared 21 between mated and unmated groups. Males mated with several females regardless of the male 22 body size. Compared with unmated intruders, intruders with mating experience succeeded 23 more often in taking over females and did so within a shorter period particularly when the 24 male-male contests occurred over females with a long time to molt. These results suggest that 25 mated males of P. nigrofascia overestimate the female quality and/or enhance the competitive 26 performance similar to the 'winner effect' that is a positive feedback from prior winning 27 experience to future contests. 28 29
Pagurus hermit crabs have a well‐developed right cheliped (major cheliped) and in some species the major cheliped of males is longer than that of females. This paper describes sex‐related differences in major cheliped length and regeneration pattern of the major cheliped in the hermit crab Pagurus filholi. We also examined the function of the major cheliped in male–male competition. Major cheliped length of males was longer than that of females in P. filholi. Males regenerated larger chelipeds than females at the first molt after experimentally induced autotomy. Body size growth in males of the regeneration group was less than that in intact males of the control group while there was no significant difference in body size growth of females between regeneration and control groups. Major cheliped length was included in the best model to explain the outcome of male–male competition and thus sexual selection appears to be a causative factor in the sex‐related difference of the major cheliped length. Sex‐related differences in the regeneration pattern may reflect differences in evolutionary pressures on males for large major chelipeds and females for large body size.
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