Aging leeches catch prey with ‘wave sense’

CALTECH (US) — Leeches have two distinct ways to sense prey, however, their preferred detection method changes as they age, a new study shows.

Medicinal leeches, like many aquatic animals, use water disturbances to help them find a meal. Juvenile leeches eat the blood of fish and amphibians, but adults opt for blood meals from more nutritious mammals.

Since it was known that leeches change their food sources as they develop, biologists wanted to know if the way leeches sense prey changed as well. Their findings are outlined in a paper published online in the Journal of Experimental Biology.


The group set up experiments to test how much leeches rely on each of the two sensory modalities they use to find food: hairs on their bodies that can note disturbances in the water made by prey moving through it, and simple eyes that can pick up on the passing shadows that those waves make.

Both juvenile and adult leeches were monitored 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.

“We knew that there was a developmental switch in what kind of prey they go after,” says Daniel Wagenaar, broad senior research fellow in brain circuitry at California Institute of Technology (Caltech). “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.'”

However, the team was 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 really change as the animal matures; neither does the mechanical system. What does change, however, is the integration of the visual and mechanical cues to make a final behavioral decision.

“As they mature, the animals basically start paying attention to one sense more than the other,” explains Cynthia Harley, lead author of the study and a postdoctoral scholar in biology.

The team will now focus their studies on the adult leeches to learn more about how this sensory information is processed both at the behavioral and cellular levels.

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