Fruit Eating Lemurs Score Higher on Spatial Memory Tests, Study

A new study claims that fruit eating lemurs have a better spatial memory compared to lemurs with a varied diet.

The study was conducted on five species of lemur held in captivity at the Duke Lemur Center.. It found that depending on seasonal, hard-to-get food gives a competitive edge to individuals with certain innate cognitive abilities.

The study led by researchers Alexandra Rosati at Yale University and Kerri Rodriguez and Brian Hare of Duke evaluated spatial memory skills across five species of lemurs namely the fruit loving red-ruffed and black and white ruffed lemurs, Coquerel sifakas that feed on leaves, ring-tailed and mongoose lemurs that eat a mix of fruit, leaves, seeds, flowers, nectar and insects.

The study included nearly 64 animals. The researchers measured the lemurs' ability to recall the location of food treats in mazes and boxes, in two different experiments.

In the first experiment, the researchers tested the lemurs' ability to point the location of food that was hidden in one of the two arms of a T-shaped maze. The researchers noticed that after a week, it was only the fruit eating ruffed lemurs that could successfully retain and recall the exact spot where the goodies were hidden.

In the next experiment, the researchers tested whether the lemurs remembered the exact location or they just remembered the turns they took to reach the spot. For this, they placed the mammal in one wing of symmetrical cross shaped maze where they hunted fo the hidden food. Later after a span of 10 minutes, they were again placed in a different wing of the maze and were set free to find their way to the food.

They noticed that again it were the ruffed lemurs who found the right spot in the cross maze, despite the fact that they had to venture into new turns to reach the location. This study shows that the ruffed lemurs rely primarily on a memory of the place and not on the memory of what turn they took to reach the place. The other lemur species included in the study displayed a mix of both the strategies.

They also conducted a third experiment to test the ability of the lemur to remember several locations.

The ruffed lemurs, native to Madagascar, feed 90 percent on fruits, mainly figs. It requires a good spatial skill and great recalling ability to remember when and where the food will be available in different seasons.  Coquerel's sifakas feed on leaves that are available in plenty throughout the year. The ring tailed and mongoose lemurs that ranked second and third in most of the memory tests, feed on a mix of things that are easily available at any given time.

"Animals living in captivity don't have to forage for food in the same way they do in the wild, so the differences the experiments found are probably innate, not learned," the researchers said.

The study is a part of research that aims at studying the origins of primate intelligence, and was supported by a Duke University Undergraduate Research grant to Kerri Rodriguez.