Time to Eat

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Science  06 Aug 2010:
Vol. 329, Issue 5992, pp. 611
DOI: 10.1126/science.329.5992.611-a

Sharks, like many other animals, are thought to track their prey by sensing differences in odor concentrations. Yet the diffusion of an odor in a freely moving fluid is unlikely to form a stable concentration gradient; rather, the odor dispersal field would look more like a river flowing over rocks—a series of chutes and eddies—making the odor plume intrinsically patchy and challenging the idea that animals could easily track food sources by detecting odor gradients. To resolve this conundrum, Gardiner and Atema fitted a small species of shark, Mustelus canis, with a device that delivered pulses of squid odor to the shark's nares. Simultaneous pulses of odor, which differed 100-fold in concentration, presented to both nares caused the sharks to turn to either side with equal frequency. When identical concentrations of odor were used, but the timing of the pulses to each naris was staggered, the sharks turned with greater frequency towards the side that received the pulse 0.1 to 0.5 s earlier. When a highly diluted odor was delivered to one naris 0.5 s ahead of a full-strength pulse to the other nostril, the sharks turned with greater frequency to the side of the dilute pulse, showing that odor arrival time, and not concentration differences, drives turning behavior.

Curr. Biol. 20, 1187 (2010).

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