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 protected]
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.
Speeds and variation in body form during crawling, bipedal walking, swimming and jetting by the shallow-water octopus Abdopus aculeatus were compared to explore possible interactions between defense behaviors and biomechanics of these multi-limbed organisms. General body postures and patterns were more complex and varied during the slow mode of crawling than during fast escape maneuvers such as swimming and jetting. These results may reflect a trade-off between predator deception and speed, or simply a need to reduce drag during jet-propelled locomotion. Octopuses swam faster when dorsoventrally compressed, a form that may generate lift, than when swimming in the head-raised posture. Bipedal locomotion proceeded as fast as swimming and can be considered a form of fast escape (secondary defense) that also incorporates elements of crypsis and polyphenism (primary defenses). Body postures during walking suggested the use of both static and dynamic stability. Absolute speed was not correlated with body mass in any mode. Based on these findings the implications for defense behaviors such as escape from predation, aggression, and `flatfish mimicry' performed by A. aculeatus and other octopuses are discussed.
There are about 7 species of the genus Abdopus reported worldwide and the occurrence of Abdopus horridus was observed in Andaman waters (Venkatraman et al. 2004) . The current study reports the presence of Abdopus aculeatus from Indian waters adding one more species to Abdopus genus from the intertidal habitat. The morphology of the studied specimen was found to resemble closely to Abdopus aculeatus (d’Orbigny, 1834)  described by Huffard (2007)  and Norman and Finn (2001)  but the number of suckers were found to be less (150) when compared to the specimen described by Norman and Finn (2001) .
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