A new study has used camera-trap footage and scent analysis to confirm the unusual relationship between an African melon and the aardvark, an elusive ant-eating mammal found in sub-Saharan Africa.
Cucumbers and similar melon-like plants generally display their fruits aboveground, but an African melon (Cucumis humifructus) buries its fruit about 20 centimeters (8 inches) underground, a rare approach to seed dispersal.
Previous evidence suggests aardvarks help disperse the melon’s seeds: Researchers have found the seeds in aardvark intestines and poop and observed the plant emerging from aardvark droppings. Indigenous people and local communities also speak of the duo’s close association; in Afrikaans, C. humifructus is known as erdvarkkomkommer, or “aardvark cucumber.”
To verify the aardvark’s role, the new study deployed camera traps on a farm in Namibia at three kinds of sites: those where C. humifructus plants were fruiting at natural depths, those where the researchers placed the melon’s fruits at shallow depths, and those with the fruits kept aboveground.
The cameras recorded 11 mammal species around the fruits, but aardvarks and porcupines were the most frequent visitors.
The aardvarks were the only ones who dug deeply enough to remove the naturally buried fruits, while the porcupines ate only the shallow-buried fruits or those aboveground. Moreover, aardvark poop contained intact melon seeds, while porcupine droppings tended to have damaged ones. The authors posit that C. humifructus evolved to bury its fruits deep to avoid the seeds being destroyed by animals like porcupines.
As to how aardvarks detect the deeply buried fruits, the researchers analyzed the scents of C. humifructus fruits and found that their chemical signature is quite different from the fruits of related melons in the same region. It’s likely that the C. humifructus’s smell is “an important advertising signal,” the authors write.
Aardvarks are known to have powerful a sense of smell to sniff out ants and termites, and the researchers’ videos showed them vigorously sniffing, with their nose pressed to the ground where the C. humifructus fruits were buried.
“This is a really neat attempt to clarify what is actually a reasonably well-documented mutualism,” Graham Kerley, professor of zoology at Nelson Mandela University in South Africa, who wasn’t involved in the study, told Mongabay. “Good science is often about the clear quantification of what we think we know, so super well-done to the authors.”
However, the study may have missed other species that may be interested in the melons and act like dispersers, Kerley added.
The study doesn’t address why aardvarks seek out the melons, when they mostly eat ants and termites, but some researchers have suggested the melons may be a source of water in arid areas.
The authors write they hope the study will draw attention to the value of aardvarks for the seed dispersal of C. humifructus, which has greatly declined in countries like South Africa.
Banner image of an aardvark by Theo Kruse via Wikimedia Commons (CC BY-SA 4.0).
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