SYDNEY: Nigerian baboons appear to be self-medicating with a wild plum that has a contraceptive effect. This is the first known example of an animal deliberately ingesting a contraceptive plant.
Biologists have found that fruit and leaves of the Vitex donian plant, otherwise known as the African black plum, are affecting female baboon hormones and preventing pregnancy in a similar way to the human contraceptive pill.
“The hypothesis that [this fruit] can regulate sexual behaviour… is very exciting and, if supported, could have a major impact on the study of primate reproduction”, commented primatologist Wendy Saltzman, at the University of California in Riverside, USA.
After detecting unusual progesterone levels in olive baboons (Papio anubis) in Nigeria’s Gashaka-Gumti National Park, British researchers set out to probe the effect of the plum on the primate’s reproductive biology. They tracked two troops of baboons and recorded their consumption of the plum as a proportion of their total diet.
“The plant directly affects sexual signalling,” which is controlled by hormones, said James Higham, study biologist at Roehampton University in London, England and lead author of a study due to be published in the journal Hormones and Behavior.
Sexual swelling in females – where the rump and genital area becomes red and swollen – is activated by hormone levels, and in turn causes males to be more attracted to females and encourages sexual advances. However, the researchers found that consuming the plums increased progesterone levels and decreased the length of the period of sexual swelling during the normally receptive part of the female cycle.
The experts observed the wild baboons and estimated their hormone levels from faeces for a five-year period from 2001. They learnt that the increase in progesterone levels correlated with an exclusive period when the baboons consumed the black plum during the annual rainy season.
Further analysis revealed that every year there was a six-week period where no births were recorded from either troop, which correlated with a hiatus of mating activity.
Higham’s team don’t believe that the contraceptive effect is intentional. The baboons may be self-medicating for another purposes and the contraceptive effect is likely a side effect, said Higham; “There is evidence of medicinal plant use in primates, but this tends to be associated with apes, especially chimpanzees.”
Plants of the same genus as the black plum have been used in traditional African medicine and are renowned for their anti-microbial and insecticidal properties. Current medical trials are testing compounds in the plants for use in commercial drugs.
Higham argues that the baboons may be using the plant to self-medicate, as the medicinal properties would make the plant invaluable during the rainy season when female and infant mortality rates peak. Infection rates and discomfort also increase when female baboons experience sexual swelling, so there’s a chance they could be medicating to avoid this too. However, further research is required to confirm these behaviours, he said.
It’s hard to say if the baboons could be deliberately using a contraceptive, commented Lesley Rogers, professor of neuroscience and animal behaviour at the University of New England in Armidale, Australia. “Actions that affect consequences not minutes or days but months later would be very hard, if not impossible to conclude… in terms of consciousness,” she said. If that were the case – “that’s a big deal.”