Fruit-loving lemurs are the smartest of all such animals, according to a new study.
Researchers from Duke University tested the intelligence of five lemur species. They found that the species that consume fruits as a primary staple in their diet, were smarter than those who ate a more varied diet.
The study shows lemurs who seek out fruits have a more advanced sense of spatial memory than other species of the mammal. These abilities may develop in lemurs who need to remember where fruit is growing, giving them a competitive edge over other species of the mammal.
The research was led by Alexandra Rosati from Yale University, along with Kerri Rodriguez and Brian Hare of Duke. They compared spatial memory skills in 64 animals, representing five species of lemurs. The animals are living in captivity at the Duke Lemur Center.
The species examined by the researchers included red-ruffed and black-and-white ruffed lemurs whose diet consists of over ninety percent fruits. They compared member of those species to leaf-eating Coquerel's sifakas, as well as mongoose and ring-tailed lemurs. Those species eat a diverse diet, consisting of fruit, seeds, leaves, flowers, along with bugs and insects.
The first experiment tested the ability of the animals to remember where food was located in mazes and boxes. Those who spent their time in the wild searching out fruit did better on the tests than other species. The animals were allowed to find food hidden in a T-shaped maze. After a week, only fruit-eaters were able to remember the location of the sweet treat.
In the second experiment, researchers wanted to test whether the animals were remembering the location, or just the turns they made to find the food. Ten minutes after being shown where to find food, the fruit was again placed in the same location. This time, however, the lemurs were given a different starting position.
"Before they might have turned right, but now they had to turn left to get to the same spot," Rosati said.
Again, fruit-eating lemurs did far better on the test than other species. This suggests to researchers the fruit-eating rely on memory of a place, and not just their own actions, in order to find food. Lemurs who ate a more diverse diet tended to use a combination of the two strategies.
In the final test, eight boxes were placed around a room. Each of the containers were distinctive, making them easy to identify by sight. Four of the boxes contained food. After lemurs learned which storage units contained the treats, the animals were removed from the testing room for ten minutes. During that time, fruit was placed in all eight boxes. When the animals were allowed back in, the fruit-loving ruffed lemurs first searched the same containers where they found food the first time.
Since lemurs living in captivity do not need to forage for food, researchers believe the difference in foraging technique is genetic, and not learned.
"Our results suggests that different cognitive skills might evolve for different reasons," Rosati said.
Details of the study in lemur intelligence were published in the journal Animal Cognition.