They don’t just eat whatever comes their way when digging: gophers “cultivate” and harvest roots that sprout in their underground tunnels, a study shows. According to the researchers’ calculations, the regrowing feed covers 20 to 60 percent of the ground squirrels’ daily calorie requirements. They argue that this is the first example of a system in a non-human mammal that can be termed agriculture. However, the definition of the term is important, the scientists concede.
Normally, animals eat what they find or capture – even our ancestors once lived in this way as hunters and gatherers. But then man began to provide himself with food, which he gained through the targeted care of plants and animals. There are also examples of this peasant way of life in the animal kingdom: some species of ants and termites grow mushrooms to feed themselves. Apart from us, no similar behavior for food production was known from the group of mammals. But now biologists Francis Putz and Veronica Selden of the University of Florida at Gainesville conclude: “The southeastern gophers are the first known non-human mammalian farmers.”
Tunnel systems in sight
These rodents, which are widespread in North America, are usually hardly seen – they are usually only noticeable by small mounds of earth on the earth’s surface. It is the excavation of their underground work: gophers dig a vast labyrinth of tortuous tunnels underground. The study started with the question of how the animals can come across enough food when digging to achieve a net energetic gain – because burrowing is very strenuous. So the suspicion arose that the animals might not have to dig that much. One indication was the well-known problem that roots tend to grow into the sewage system, which is fertilized with excrement, and must be removed regularly. “If roots sprout into these man-made tunnels, we thought that maybe they also grow into these rodent tunnels that are fertilized with feces,” says Selden.
So Putz and Selden decided to pursue their suspicion in a targeted manner: For their study, they used a gopher gopher tunnel system outdoors to record how much root mass grew into the underground cavities. As they report, this involved a lot of excavation work and one of the major challenges was keeping the rodents out of the examined tunnel area so that they could not harvest there during the investigation period of a few months. The researchers finally managed to do this with a few tricks. This enabled them to determine the root growth rate and estimate the energy content of the material that a typical tunnel system can provide. The scientists were then able to relate these results to estimates of the rodents’ energy requirements.
A root farm is emerging
The calculations and comparisons showed that digging a tunnel would cost much more energy than the fodder found could provide. However, by harvesting the roots that grow into the tunnels they have already dug, the gophers can gain enough energy to continue digging tunnels in search of more food: the daily harvest covers 20 to 60 percent of the rodents’ energy needs, came the estimates. “In the tunnels it is actually dark and damp like in a sewage pipe and the roots grow in there like stalactites and stalagmites,” says Putz. Selden continues: “The animals there ensure a perfect environment for the roots to grow in and they fertilize them with their waste”. According to the researchers, this importance of the extensive tunnel system explains why the gophers maintain and defend them.
By encouraging root growth in their tunnels and then harvesting them, it’s a form of food production that can be called agriculture, the scientists argue. “This depends on the definition,” says Putz. “If farming means planting crops, then gophers don’t count. However, for someone with a more horticultural perspective, where plants are carefully tended like fruit trees are in a forest, this seems far too narrow a definition. Many cultures around the world have developed a form of agriculture based on perennial crops, many of which are not planted, only tended. I think the issue of definition is interesting because it hasn’t really been clarified,” said Putz.
“Regardless of whether gophers are considered animal farmers or not, their behavior should be further studied,” the researchers write. This could make it clearer to what extent the animals create optimal conditions for root growth and whether they might also be harvesting fungi in their tunnels. “Purchassies may appear inconspicuous at first, but that is deceptive. They deserve our attention,” concludes Selden.
Source: Cell Press, University of Florida, Specialist article: Current Biology, doi: 10.1016/j.cub.2022.06.003