Post-autotomy regeneration of chelipeds under laboratory conditions in the porcellanid crab Petrolisthes japonicus (De Haan, 1849) (Decapoda: Anomura: Porcellanidae)

Porcellanids autotomize their chelipeds rapidly when grasped, yet the regeneration of lost limbs remains poorly understood. We investigated post-autotomy cheliped regeneration in the porcellanid Petrolisthes japonicus (De Haan, 1849) under three conditions: both chelipeds intact (control), one cheliped autotomized (OCA), and both chelipeds autotomized (BCA). This species has asymmetrical chelipeds with random laterality; in the OCA group, the larger cheliped was autotomized. Regeneration patterns were similar for the original larger and smaller chelipeds in both sexes, but recovery rates of the original larger cheliped were consistently lower in the BCA group, indicating that regenerating both chelipeds imposes higher energetic costs. In the OCA group, females restored cheliped asymmetry and size within three molts, whereas males may require additional molts. In the BCA group, reversals in chela laterality occurred across successive molts, likely reflecting stochastic processes, and regenerated chelipeds showed reduced asymmetry and size. As males of P. japonicus possess larger chelipeds that contribute to mating success, cheliped loss may compromise reproductive success, even after regeneration. These findings highlight the energetic and functional constraints of regenerating paired chelipeds in this species.