Leeches Use Water Disturbances to Locate a Meal
Posted on November 2, 2011
Biologists at the California Institute of Technology (Caltech) say leeches have two distinct ways of detecting dinner and their preferred method changes as they age. Leeches use water disturbances to help them find a meal. Juvenile leeches eat the blood of fish and amphibians, while adults prefer blood meals from mammals.
To find prey, leeches use two sensory modalities. Leeches have tiny hairs on their bodies that can detect disturbances in the water made by prey moving through it. They also rely on simple eyes that can pick up on the passing shadows made by the waves. The researchers set up experiments to test how much leeches rely on each of the two sensory modalities. The researchers monitored both juvenile and adult leeches as they reacted to mechanical waves in a tank of water or to passing shadows, as well as to a combination of the two stimuli. The leeches in both age groups responded in similar ways when only one stimulus was present. But when both waves and shadows existed, the adult leeches responded solely to the waves.
Daniel Wagenaar, senior author of the paper and Broad Senior Research Fellow in Brain Circuitry at Caltech, said, "We knew that there was a developmental switch in what kind of prey they go after. So when we saw a difference in the source of disturbances that the juveniles go after relative to the adults, we thought 'great-it's probably matching what we know.'"
The researchers were very surprised to see that the individual sensory modalities aren't modified during development to help decipher different types of prey. The leech's visual system doesn't change much as the animal matures and neither does the mechanical system. What does change is the integration of the visual and mechanical cues to make a final behavioral decision.
Cynthia Harley, lead author of the study and a postdoctoral scholar in biology at Caltech, says, "As they mature, the animals basically start paying attention to one sense more than the other."
The research outlined in the paper, "Developmentally regulated multisensory integration for prey localization in the medicinal leech," was funded by the Burroughs Wellcome Fund and the Broad Foundations.