Regeneration in planarians modifies behavioral switching

The planarian <i>Dugesia japonica</i> responds differently to localized stimuli: anterior regions turn, middle regions elongate, and posterior regions contract. If cut into several pieces, each piece immediately produces the same three responses. Over several days, each piece regenerates all transected body parts. This study tested how the pieces coordinate behavioral responses during regeneration. We first determined the locations of the turning/elongation and elongation/contraction behavioral switches. Immediately, all transections moved both switching sites away from the cut sites so that the worm pieces produced the same three responses as intact worms. During regeneration, the sites of behavioral switching moved progressively closer to the transection (now regeneration) sites. These results show that the immediate effects of transection (likely physiological) are coordinated with the addition of regenerating tissue (anatomical) to maintain as normal an animal as possible. Other animals that regenerate body parts, such as amphibians and reptiles, may use similar coordination mechanisms.