Effects of cheliped autotomy on molting and growth in the porcellanid crab <i>Petrolisthes japonicus</i> (Decapoda: Anomura: Porcellanidae) under laboratory conditions

Porcellanids avoid predation by autotomizing a cheliped, a strategy that enhances immediate survival but incurs costs. Previous research that did not consider sex differences has suggested that cheliped loss accelerates molting and reduces growth at molt. As female decapods typically allocate more energy to reproduction than males do, molting and growth patterns may vary between sexes. This study investigated the effects of cheliped autotomy on molting and growth in the porcellanid crab Petrolisthes japonicus. Male and female crabs were cultured under three autotomy conditions: both chelipeds intact, the larger cheliped autotomized, and both chelipeds autotomized. Loss of both chelipeds reduced growth at the first molt in both sexes, but this effect disappeared in subsequent molts for females, likely due to energy allocation to reproduction in all groups. Sex-specific differences emerged in crabs with intact or single-cheliped loss, with males exhibiting longer molt cycles and fewer molts than females, potentially enhancing male mating opportunities and female reproductive output. However, autotomizing both chelipeds increased the molting frequency in males, counteracting these patterns. These findings highlight the interplay between autotomy, molting, and sex-specific energy allocation, suggesting that cheliped loss affects growth and reproduction differently in males and females, with potential fitness trade-offs.