Uganda: Wild animals leave DNA on plants, making them easier to track – here’s what scientists found in Uganda’s rainforests

The world is losing animals at an alarming rate due to habitat degradation, climate change and illegal human activities in protected wildlife areas. In fact, it is estimated that by 2100, more than half of Africa’s bird and mammal species may be lost.

Efforts to conserve biodiversity depend on information about where animals are located. Wildlife tracking is useful. Current tracking methods include camera trapping and transects, which are defined areas and designed paths in a row, which can be revisited from time to time to monitor habitat conditions and species changes. These methods can be expensive, labor-intensive, time-consuming, and difficult to use, and may not detect all species present in an area. Dense rainforests present a particular problem in tracking, since the vegetation is often very dense and does not let in much light.

Recent research has shown that vertebrates leave their DNA in the environment, either as airborne particles or on vegetation. This provides a useful new way to monitor species.

Our international research team, working in the rainforests of Kibale National Park in Uganda, wondered whether environmental DNA methods would be useful to us. We reasoned that if animal DNA was present in the air, it would likely have settled and stuck to tree leaves. The waxy, sticky, or toothed surfaces of leaves may be ideal traps for DNA. Would simply scanning leaves collect enough DNA to monitor species and map biodiversity?

Our study showed that many birds and mammals can be detected using this simple, low-tech method. It is a promising tool for large-scale biomonitoring efforts.

Kibale National Park

Kibale National Park in Uganda is known for its rich biodiversity and has earned its status as the ‘major capital’ of the world. It is home to 13 species of non-human primates including the endangered red colobus monkey and chimpanzee.

To test our idea, the research team went into the park’s dense tropical forest armed with 24 cotton swabs. Our task was to clear as many leaves as possible with each bud in three minutes.

To find out which animals gave rise to DNA in the swabs, the team sequenced a short piece of DNA, called a barcode. Barcodes are different for each animal, so the barcode on the swabs can be compared to a barcode library containing all animals sampled to date.

The team did not expect great results, because in rainforest conditions – hot by day, cold by night, humid and humid – DNA degrades quickly.

So we were surprised when the results came back from the DNA sequencer. We captured more than 50 species of mammals, birds and frogs, with swabs collected in just over an hour, from just 24 cotton swabs.

We detected approximately eight species of animals in each of the cotton buds. These species include a great diversity, from the very large and endangered African elephant, to the very small species of sunbirds.

Animals discovered included the hammerhead fruit bat, which has a wingspan of up to one metre, monkeys such as the elusive L’Hoest’s monkey and the endangered gray red colobus, as well as rodents such as the giant forest squirrel. A wide variety of birds were also discovered, including the great blue turaco and the endangered gray parrot.

The great diversity of animals, coupled with the astonishing rate of animal detection per smear, suggests that we can now collect a lot of animal DNA simply from leaves. The ease of sampling, a task we could quickly ask anyone on our team to do when in the forest, suggests that we can use this method to track animal diversity in the park, especially in areas that are changing rapidly.

One of the team members, Emmanuel Obito, is studying these exact areas in the park for his doctoral project. He is trying to understand how the invasive Lantana camara and the woody weed Acanthus pubescens prevent forest regeneration. Using this leaf scanning method, it will be easier to explore how removing invasive species and allowing the forest to regenerate will help restore animal biodiversity.