DNA 'metabarcoding' on 20-year-old elephant dung solves foraging puzzle
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Elephants seek variety in their diets, even varying what they eat for dinner every night, according to a study that used cutting-edge genetic techniques published in Royal Society Open Science on July 4.
Significantly, the findings shed light on why elephants forage in groups: they adjust their diets based not only on availability but on preferences and physiological needs to avoid food-related conflicts. In this way, they can stay together.
"Each elephant needs variety, a little bit of spice — not literally in their food, but in their dietary habits," said study author Tyler Kartzinel, an assistant professor of environmental studies and ecology, evolution, and organismal biology at Brown University, in a press release.
Using DNA metabarcoding to unveil elephants' food choices
Previous research conducted by two of the study's authors, George Wittemyer from Colorado State University and Thure Cerling from the University of Utah, revealed that elephants change their diet from fresh grasses to trees depending on the rainy or dry seasons.
However, their study was more focused on broad-scale dietary patterns and couldn't identify the specific types of plants consumed by elephants.
Scientists in the new study addressed this gap by using a modern genetic method called DNA metabarcoding to study how social groups, like families, choose what to eat. Researchers could identify the makeup of biological samples by comparing DNA fragments from an elephant's food to a plant DNA library.
According to Kartzinel, this study marks the first time DNA metabarcoding has been used to explore the long-term question of social foraging ecology.
The team combined the analysis of carbon-stable isotopes from the hair of elephants and 20-year-old feces with dietary DNA metabarcoding, GPS-tracking, and remote-sensing data.
This approach allowed them to assess the dietary variations among individual elephants in two groups. By matching the unique DNA sequences in the samples to a collection of reference plants, they could compare the diets of individual elephants over time.
Their findings revealed significant dietary differences among individuals, often more substantial than previously assumed. This was true even for family members that foraged together on a given day.
This study tackles a long-standing puzzle in wildlife ecology, as explained by Kartzinel: "How do social bonds hold family groups together in a world of limited resources?"
Put simply, even though elephants primarily consume the same plants, it remains to be seen why they don't compete for food and end up foraging separately – until now.
The reason is that elephants adjust their diets not only based on what food is accessible but also according to their preferences and physiological needs, said Kartzinel. For instance, a pregnant elephant may experience different cravings and dietary requirements at different stages of her pregnancy.
The complete study was published in Royal Society Open Science.
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