Thermo-, water motion, and chemosensory detection in the American medicinal leech, Macrobdella decora.

Abstract

Behavioral responses to heat, water movement, and chemical stimuli by Macrobdella decora (Hirudinidae) were investigated in the laboratory. A control period recording behavior was taken without the stimulus and then each stimulus was applied in a tank at three minute intervals. The angle of the leech to the test object, action mode of leech--whether swimming, stopped, head waving or inch crawling, distance traveled by leech, and distance between leech and test object were part of the recorded data measured. A paired samples t-test showed distance traveled and # of times stopped by leech in a chemical stimulus to be significant. Distance between leech and test object was important in a temperature stimulus. This implies that in the presence of a chemical in the water, a leech will travel less and stop more often to further probe out its new find. In the case of a heat source, an alerted leech will tend to stay close to this temperature change. Sensitivities to these two stimuli are important for finding food, because sensing warmth means a warm-blooded vertebrate is nearby and sensing chemcial changes mean they can choose their appropriate hosts. The combined reactions of both temperature and chemical stimuli allow leeches to recognize food and initiate feeding.