Relying almost exclusively on one food source typically requires resourcefulness and strong spatial memory for the foraging animal to survive -- especially when that source is fruit, ripe only at certain times and available only at certain locations. Comparing five different species of lemur (red ruffed, black-and-white ruffed, Coquerel's sifakas, ring-tailed, and mongoose), researchers at the Duke University Lemur Center (all the more reason to attend Duke, they have lemurs!) found those that depended the most on a single source of food (in this case, fruit) had the best spatial memory. Their study was published recently in the journal, Animal Cognition, Laboratory Equpiment reported.

"Our results suggest that different cognitive skills might evolve for different reasons," lexandra Rosati, one of the lead researchers, said in a press release.

Ninety percent of ruffed lemurs' diets consist of fruit, while the other lemurs studied relied on either more widely available food (leaves for the Coquerel's sifakas) or more varied food (fruit, leaves, seeds, flowers, nectar and insects for the ring-tailed and mongoose lemurs), according to the study. To confirm that ruffled lemurs evolved superior spatial memory to remember key locations and sustain their fruit-heavy diet, researchers put the five kinds of lemurs through three memory tests.

The first test was a maze. First, the lemurs were shown the correct route to their preferred food. A week later, they were placed at the start and left to find it. As expected, fruit-seeking lemurs performed the best.

Scientists were unsure, however, if the fruit-eaters were remembering the turns they took or the exact spot so they set up a second experiment in which they switched the lemurs' starting position. Once again, the ruffed lemurs were the first to the finish, demonstrating that they were remembering location over a specific route.

"Before they might have turned right, but now they had to turn left to get to the same spot," Rosati said.

The last experiment asked the lemurs to remember -- or not remember -- multiple locations. For ten minutes, the five species explored a room with eight boxes, half which contained food and half which were empty. Later, when they were put back into the room (and all the boxes were filled with food, to presumably control for smell), only the ruffed lemurs sought out the same boxes that had previously contained food.

Since animals bred in captivity -- such as those in this experiment -- don't need to find their own food, the ruffed lemurs' superior spatial memory is likely an innate ability, according to the researchers.