Lemurs eat a lot of leaves because fruit on Madagascar isn’t nutritious enough to sustain them, according to new research.
A team of 32 scientists led by Giuseppe Donati from Oxford Brookes University in the UK set out to discover why far more species of primates in the Old and New worlds eat far more fruit than their lemurid relatives.
Fruit-eating – known as frugivory – appears to have evolved independently several times among primates. Fruit it easy to digest, but because its availability is usually seasonal, only a few species eat it exclusively.
On Madagascar, some major lemur clades don’t eat it at all, opting for leaves instead, while others eat it as a relatively small proportion of their diet.
Donati and his colleagues decided to test whether the types of fruit available might be the reason for the low level of frugivory on the island.
A key component of primate diets is protein, which is made up of amino acids. These contain nitrogen, and therefore nitrogen intake can be used as a reliable proxy for protein consumption.
Previous studies had established that the nitrogen intake of primate species around the world, regardless of diet, was about the same (relative to body size), and that the feeding habits of many species appear to be predicated on consuming enough to meet metabolic demand.
Species that are primarily frugivorous, for instance, have less efficient digestive systems when it comes to optimising nitrogen intake so must compensate for this by spending comparatively more time eating.
To see how lemurs achieved adequate intake, the researchers collated the results of 79 studies that analysed the nitrogen content of fruits consumed by primates, from sites around the world.
The results were clear. “Fruit nitrogen content was higher in the New World and Old World, and lower in Madagascar,” the researchers report.
The data showed that the average percentage of nitrogen in Madagascan fruit was beneath the minimum requirements needed by primates. The researchers suggest that this situation forced lemurs to evolve non-fruit diets in order to survive.
Given that food choices drive the evolution of traits beyond those strictly concerned with diet, the finding may eventually shed light on the many unique characteristics of lemurs.
The research is published in the journal Scientific Reports.
Andrew Masterson is a former editor of Cosmos.
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