Understanding cephalopod regeneration: impact of sexual maturation, injury severity and general anesthesia on octopus arm restoration

Octopuses exhibit remarkable regenerative capacity, as shown by their ability to fully restore a whole arm. During this process, a complex appendage containing muscle, connective tissue, vasculature, suckers, sensory structures, peripheral nerves and the axial nerve cord (ANC) is regrown. Although the morphology of octopus regeneration is increasingly well described, the physiological variables that determine regenerative speed, including the potential contribution of ion-channel-dependent processes, remain poorly understood. In this work we examined the influence of reproductive state, injury severity, biological sex and magnesium chloride (MgCl2) anesthesia, on the rate of longitudinal arm regrowth. Reproductive stage was the strongest determinant of regenerative performance: pre-reproductive stage (pre-RS) animals showed robust regrowth, whereas reproductive stage (RS) animals regenerated significantly slower. In pre-RS animals, regeneration speed scaled strongly with injury severity, whereas this relationship was absent in RS animals. Biological sex did not independently predict regeneration speed, and MgCl2 exposure showed no long-term inhibitory effect on regeneration. Our final model explained 81.4% of variance in regeneration speed, with reproductive state and injury severity having major effects. These findings demonstrate that sexual maturation and optic-gland-mediated senescence act as an irreversible physiological block against somatic regeneration, and provide empirical support for mechanosensory and bioelectric-dependent scaling models of cephalopod limb restoration.