Males display “inverse rapping” as a mating behavior to receptive females in the hermit crab Pagurus nigrofascia

抄録

This paper describes “inverse rapping” as a characteristic mating behavior in Pagurus nigrofascia. The behavior involves one hermit crab pulling another crab’s shell towards itself causing the shells to hit against each other. This is the first evidence that males perform inverse rapping as a mating behavior in a Pagurus species. Two experiments were conducted to describe the inverse rapping in detail and to discuss its function. In Experiment A, we clarified when (mating season or non-mating season) and to whom (males or females) males displayed this behavior. A focal male that had not been guarding in the field was placed together with another crab and their interaction was observed, especially inverse rapping. Males showed inverse rapping mainly with a female that was close to copulation in the mating season, especially when the male guarded the female. In Experiment B, we examined the female’s response to male inverse rapping and tested the effect of the presence of a neighboring conspecific on the occurrence of the behavior. Most females reduced struggling and/or withdrew into their shells in response to male inverse rapping. The presence of neighboring crabs did not affect inverse rapping. Our findings suggest that inverse rapping is a mating behavior in P. nigrofascia, and that inverse rapping may benefit males in the initiation and/or continuation of precopulatory guarding because it can help to restrain struggling females. This behavior has not been observed in other sympatric Pagurus species and appears to be a characteristic mating behavior of P. nigrofascia.