Effects of cheliped autotomy on male reproductive success in the porcellanid crab Petrolisthes japonicus

Porcellanid crabs avoid predation by autotomizing their chelipeds, a strategy that enhances immediate survival. In decapod crustaceans, males with larger bodies and chelipeds often outcompete rivals for access to receptive females, suggesting that cheliped loss may reduce reproductive success. We tested this hypothesis in the porcellanid crab Petrolisthes japonicus, a gregarious species inhabiting intertidal cobble and boulder shores, under three autotomy conditions: both chelipeds intact (control), one cheliped autotomized (OCA), and both chelipeds autotomized (BCA). Mating behavior was observed, and female reproductive traits — including spawning, egg number, egg size, and fertilization rate — were assessed, as these factors influence male reproductive success. Two mating experiments were conducted. In experiment 1, a female was presented with two males of different autotomy conditions (control vs OCA, control vs BCA, and OCA vs BCA). In experiment 2, each pair consisted of a female and a male from one of the three groups. Male cheliped loss did not affect mating behavior or the reproductive traits of female partners. In experiment 1, BCA males showed reduced mating success only when competing with control males. In experiment 2, copulation frequency did not differ significantly among groups. These results indicate that the impact of male cheliped loss on reproductive success depends on both the number of chelipeds lost and the competitive context. However, the loss of both chelipeds may severely reduce male reproductive success in P. japonicus under natural conditions.