Meeting Abstract
68.1 Monday, Jan. 6 08:00 Bioelectric crypsis in cephalopods reduces detection by shark predators BEDORE, CN*; KAJIURA, SM; JOHNSEN, SJ; Duke University; Florida Atlantic University; Duke University christine.bedore@duke.edu
The ability of cephalopods to camouflage themselves is well documented as a defense against predation. However, visual camouflage is only effective against primarily visual predators. For example, bioelectric cues that arise from the rhythmic exposure of mucous membranes, such as gills, may make certain animals vulnerable to detection by electroreceptive predators, such as elasmobranchs and some teleosts. Thus, modulation of an organism’s own bioelectric field in response to predator stimuli may decrease the risk of predation, which has been suggested for egg-encapsulated elasmobranchs that suspend their ventilatory movements in the presence of predator-simulating electric fields. We used behavioral and physiological assays to assess the freeze response in the cuttlefish, Sepia officinalis, and its effect on detection by sharks. Sepia officinalis ceased ventilation for a period of 2-37s in response to a video simulation of a looming fish predator. The freeze response resulted in a 45±17% decrease in voltage at the mantle opening relative to the surrounding seawater (N=15, P=0.015). Escape by jetting was also observed, and resulted in a 420±240% increase in voltage relative to seawater. Dipole electric fields that simulated S. officinalis resting, freezing, and jetting DC fields were produced with underwater electrodes in a behavioral assay to quantify the detectability by shark predators. Blacktip sharks, Carcharhinus limbatus, and bonnethead sharks, Sphyrna tiburo, responded to freeze stimuli less frequently than resting and jetting and they responded to jetting stimuli most often (N=534 responses; P<0.001). These results suggest the freeze response facilitates predator avoidance via reduction of sensory stimuli, including bioelectric fields, and future work should examine the extent to which other cues are modulated during this behavior.
