Fruit-Eating Lemurs Preform Better on Spatial Memory Tests

The Duke Lemur Center reports that lemurs preferring to eat fruit score higher on spatial memory tests than lemurs that predominantly eat leaves, insects, seeds and other plant matter.

The researchers behind the discovery said that fruit-eating lemurs such as the red-ruffed and black-and-white ruffed lemurs may preform better on spatial memory tests because their reliance on seasonally available goods requires a key cognitive skill set, such as remembering where to find something to eat, that other foraging lemur species do not need to utilize as much.

Ruffed lemurs' diet is 90 percent fruit, mostly figs. In their native Madagascar, lemurs' ability to find food from season to season requires them to know where to find trees with ripe fruit.

The study, led by Alexandra Rosati at Yale University and Kerri Rodriguez and Brian Hare of Duke University, tested five lemur species including the two aforementioned fruit-eating species, as well as leaf-eating Coquerel's sifakas, and ring-tailed and mongoose lemurs that eat a mix of fruit, leaves, seeds, flowers, nectar and insects.

Five lemur species - 64 individual lemurs - were part of the study, which appears in the journal Animal Cognition.

The researchers tested the lemurs' ability to remember the location of food items placed in mazes and boxes. The fruit-eating lemurs outperformed their foraging peers in these find-the-food tests.

One experiment tested lemurs' ability to find a food item hidden in one of two arms of a T-shaped maze. In this test, only the fruit-eating ruffed lemurs were able to find their way to the to the food source after one week had passed.

In a second experiment designed to test whether the lemurs were recalling the exact spot of the food or just recalling the turns they need to get there, the researchers placed lemurs in one wing of a symmetrical cross-shaped maze, where they set about finding hidden food. Then, after 10 minutes, the lemurs were placed in a different wing of the maze and released to find their way to the food again.

Again the ruffed lemurs were most successful at this challenge, even though new turns were introduced to the equation.

"Before they might have turned right, but now they had to turn left to get to the same spot," Rosati said. The results suggest that ruffed lemurs rely on memory of place, rather than memory of the turns they took to get there. Other lemur species seemed to rely on their knowledge of turns to return to a food location.

A third experiment tested the lemurs' ability to remember multiple locations.

As the Lemur Center reports: "In the initial session, a lemur was allowed to explore a room containing eight open boxes, each marked with a distinct visual cue. Half the boxes were baited with food and half were empty. After the lemur learned which boxes contained food and which didn't, all eight boxes were baited with food and covered with lids to keep it from view. Ten minutes later, when each lemur searched the room again, only the ruffed lemurs preferentially searched spots where they found food before."

In all experiments, the fruit-eating lemurs preformed the best.