Alarm Cues In Planarians

Abstract

Planarians reportedly avoid a solution prepared by pulverizing a conspecific in 1 ml of water (the full-strength test solution). This finding suggests that damaged planarians release alarm cues, but we suspect that the full-strength test solution contains compounds at concentrations higher than would be found following predation. We analyzed Dugesia sp. behavior when they were exposed to two test solutions that might be more realistic, a 10-fold dilution of the full-strength solution and a “poked” test solution in which an animal was placed in 1 ml of water and then stabbed 10 times with a pin. For testing, a planarian was placed in a hemisected, water-filled straw with cotton balls at both ends. A test solution was pipetted onto one cotton ball and a control solution onto the other. To determine preference between the solutions, the position of the flatworm was determined at 1-min intervals for 10 min. We also quantified lengthwise body contractions (scrunching) in response to the diluted test solution. Results confirmed previous findings that planarians avoid the full-strength solution, but we failed to detect a preference between the control and either the diluted or poked test solutions. Exposure to the diluted test solution, however, did lead to significantly more scrunching than exposure to the control. Scrunching could be the planarians’ equivalent to freezing, a behavior exhibited by fish when exposed to alarm signals. If so, then planarians display alarm behavior in response to a more realistic predation cue than shown previously.