Modeling Hydra Behavior Using Methods Founded in Behavior-Based Robotics

18 Chapter 5. HydraResponse to light stimulusOn exposure to strong light there is an immediate inhibition of any ongoing contraction.Following a latency, a response consisting of either contraction or locomotion is evoked.As in the case of mechanical stimulus, locomotion is more common in starved animals.The latency is inversely related to light intensity [59]. There is no habituation [53].FeedingThe feeding behavior of Hydra consists of a sequence of actions, namely prey capture,mouth opening, ingestion, digestion, and regurgitation 4 . The behavior is evoked by mechanicalstimulation of Hydra’s tentacles or by the presence of GSH, which is released byprey stung by nematocysts. The behavioral threshold is regulated by Hydra’s nutritionalstate, with starved animals exhibiting a lower threshold than recently fed ones. Also, thereis a refractory period following a feeding response, with the capacity of responding beinggradually regained [32, 33].5.1.4 Behavior coordinationAs described in the literature, feeding inhibits responses to light and mechanical stimuli.In addition, response to light inhibits response to mechanical stimuli, thus forming apriority-based relation of Hydra’s behaviors [32, 54].The behaviors and sub-behaviors of Hydra, as modeled in this project, are summarizedin Tables 5.1 and 5.2 below.Table 5.1: Behaviors shown by Hydra. Priority 1 denotes the highest priority.Label Priority DescriptionB1 4 Spontaneous actionsB2 3 Response to mechanical stimulusB3 2 Response to light stimulusB4 1 FeedingTable 5.2: Sub-behaviors of HydraLabel DescriptionB11, B21, B31 Contraction/ExtensionB12, B22, B32 Locomotion4 Through regurgitation, stomach contents is transfered back into the mouth, and in this way Hydra getsrid of undigested remains of the prey.