As any diver knows, hungry fish roaming the oceans display an astonishing array of ways to fill their stomachs. `How can we explain the tremendous variation we see in the oceans?' Aaron Rice at the University of Chicago wondered. He decided to take a closer look at the dining habits of two vegetarian parrotfish species, the bucktooth parrotfish (Sparisoma radians) and Quoy's parrotfish (Scarus quoyi). Working with Mark Westneat, Rice investigated how parrotfish coordinate the movements of their jaws, fins and eyes as they munch on their dinners(p. 3503).
We know a lot about visual, locomotor and feeding systems in isolation,Rice explains, but a fish really needs to coordinate all three systems to ensure that it doesn't go hungry. `You need jaws to eat your food,' Rice says,`but a set of jaws can't get to food on its own.' To understand how a fish feeds, we need to understand how its jaws, fins and eyes operate in relation to each other.
So Rice and Westneat set out to study how parrotfish coordinate these systems.
Luckily, parrotfish aren't too fussy about eating in the lab. Bucktooth parrotfish found the small lettuce pieces Rice anchored to the bottom of their tanks a tasty enough substitute for their usual fare of sea grasses. And Quoy's parrotfish happily feasted on algae that Rice spread onto a coral skeleton dinner plate, as they are accustomed to in the ocean.
Satisfied that the fish would eat in the lab, Rice and Westneat prepared to film them. But they hadn't counted on parrotfishes' bashful nature. The fish were `perpetually nervous', Rice recalls, especially with bright lights and the large eye of a high-speed digital camera trained on them. It took Rice months to coax the fish to eat in front of the camera. When they finally had some good footage, Rice traced the exact movements of each fish's jaws, fins and eyes as it lunged towards its meal by plotting 19 landmarks onto a frame of the video and meticulously recording the landmarks' positions in successive frames.
What Rice and Westneat found surprised them. Despite both being herbivores,the two species had quite different coordination patterns. Quoy's parrotfish showed much earlier cranial elevation and a lot more jaw protrusion as they approached their food than bucktooth parrotfish did. The pair suspects that these differences reflect the algae-munching habit of Quoy's parrotfish;scraping algae off coral may require more force than grazing on sea grass, and perhaps these differences help Quoy's parrotfish generate a more powerful bite. But they also spotted similarities; both species peered down at their food as they approached it, and glanced upwards just before taking a bite. Rice isn't sure why they do this, but it might be to spot lurking predators. Both species also braked sharply just before reaching their mouthful. This makes a lot of sense for Quoy's parrotfish; if your head is on a collision course with an unforgiving lump of coral, you'd better make sure that you slam on the brakes fast enough to avoid a concussion.
The complex feeding kinematics that Rice and Westneat describe for these herbivores illustrate how important it is to consider both what an animal sees and how it moves. `The future of feeding ecology lies in understanding how these different systems operate together', Rice concludes.