P3.1 Thursday, Jan. 6 Characterizing arm autotomy: an octopus mode of defense ALUPAY, Jean S.*; CALDWELL, Roy L.; Univ. of California, Berkeley; Univ. of California, Berkeley email@example.com
Animals have evolved a diversity of defense mechanisms including cryptic and startling displays, flight response, and inking. Arguably one of the most extreme tactics is autotomy, the voluntary shedding of a limb or body part at a specific cleavage plane, often under neural control. This behavior provides immediate benefits that allow the organism to escape from predators, while simultaneously incurring long-term costs including energetically expensive regeneration. Many studies in reptiles, echinoderms, and crustaceans provide evidence for increased survival in autotomizing individuals. There have only been anecdotal reports of autotomy in various unrelated species of octopus, which have many arms susceptible to loss. We studied one species, Abdopus aculeatus, by stimulating arm loss, preserving them for histological sections, and measuring regeneration. In addition, longitudinal histological sections were performed on the arms of various octopus species to locate the presence of cleavage planes. We found that in A. aculeatus, autotomy often occurs at the base of the arm, where the cleaved ends displayed a clean break and minimal blood loss indicative of voluntary dropping. The time required to stimulate autotomy varied between individuals, but once triggered, cleavage was almost instantaneous. Thrashing and sucker attachment of the newly autotomized limb persisted for nearly an hour, likely functioning as predator distraction. Signs of arm regeneration were evident as early as three weeks after the arm was lost. These results correlated with studies of other arm autotomizing cephalopods. With these data, more quantitative analyses of the costs and benefits of autotomy may be determined along with the evolution of this extreme tactic among cephalopods.