Madagascar's Lemurs Eat Foods That Make No Sense—Why?

Madagascar's lemurs do a lot of things that at first glance make no sense—performing ballet-like dances across the sand; singing like a whale—but one for which scientists finally have an explanation is their odd diet. All other primates consume fruit whenever they can find it, because fruit is good for you. But on Madagascar, the lemurs have eschewed it for a diet of just leaves—why?

A new study published in the journal Scientific Reports explains how the diets of Madagascar's lemurs have evolved to contain almost no fruit at all, a phenomenon that's puzzled ecologists for a long time. The authors theorized that in certain regions, unusually low levels of nitrogen in the soil was yielding fruit correspondingly low in protein, making it too lacking in metabolic value for would-be frugivores like lemurs to bother with.

After pulling data from 79 studies spanning Africa, Asia and the Americas, the researchers found that Madagascar's soil contained the least nitrogen. It was actually the only region found to have fruit so low in protein (nitrogen is an essential building block for protein synthesis) that primates were taking their business elsewhere. Specifically, they've filled the role nutritious fruit would play in their diet with leaves, which in keeping with the lemurs' brand, isn't a particularly straightforward option, either.

Bamboo leaves can be nutritious if they're young and fresh, but lemurs have evolved to chew and digest the harder bark. This part of the plant is called the culm and essentially combines all the taste of emergency rations with all the nutritional value of wood chips, which is to say none at all. The ability of the lemurs to eat culm is impressive and strange—the only other mammal to develop the necessary specialized teeth is the giant panda—but even that won't be enough to save them. There's a reason the pandas are going extinct, too.

Lemurs are one of the most endangered primate species in the world. They're only meant to have to resort to eating culm during the dry season, but another study published last week in Current Biology describes how climate change is threatening to leave the lemurs with only dry tree bark year-round. These findings offer a potentially bleak look at how our own diets and digestive tracts might have to evolve in response to climate change. "If I was going to relate it to humans, I'd say, well, bamboo is a grass, and rice is a grass and humans eat rice, so the climate changing is going to also impact humans because of the same issues [impacting lemurs]," said primatologist Patricia Wright. "Humans just aren't critically endangered like they are."

The two studies were conducted without relation to each other, though Wright happens to be a coauthor on both. It was Wright, back in the 1980s, who discovered that the greater bamboo lemur was not, in fact, extinct as had been previously believed. Now, though, the lemurs are facing starvation—Madagascar's culm won't sustain them any more than its useless fruit will.

Anyone who has watched a giant panda for more than a few seconds has realized why massive quantities of nutritionally pointless food followed by lots of hibernating is not an exciting way to live. Fortunately, for us anyway, a key difference remaining between the greater bamboo lemur and humans is flexibility in diet.

Lemurs are specialists, which makes them more vulnerable to the effects of climate change than species like humans, which prefer to eat all kinds of things. The Current Biology researchers observed the lemurs for 18 months and found that they subsisted 95 percent of the time on the same single species of bamboo. But they're only meant to have to resort to culm in the driest part of the season, from August to November.

"But each year, the dry season gets longer by, I think, about a day," Wright said. "So by 2070, it's going to be like two months drier.… That's definitely relevant to humans."

She and her Current Biology colleagues have plans to take what they've learned and build bamboo corridors this coming January, when it'll be wetter, in the hopes of reconnecting stranded lemur populations to more fertile habitats. Continuing to observe how the lemurs' physiology and behavior adapts in the face of climate change might provide insight we could apply to humans, especially those living in the hottest and driest parts of the world—if the lemurs don't go extinct first.