Researchers in Professor Naomi Pierce's lab teamed with researchers at the Kunming Institute, China, in a new study that used DNA samples extracted from the blood meals of leeches to map which animals live where in the Ailaoshan Nature Reserve in Yunnan, China. The study, published in Nature Communications, showed that the DNA samples can be used to find out which wild animals are present across large, protected areas such as national parks. The work helps establish leeches as a surveillance instrument for animal conservation.
Researchers used DNA extracted from more than 30,000 leeches to survey over 80 species of vertebrates, including amphibians, mammals, birds, and squamates. The leeches were collected over a three-month period by forest rangers throughout the 260 square mile nature reserve, which stretches for nearly 80 miles along a mountain ridge in Southern China.
“This study shows how leech-derived DNA can be used to estimate biodiversity on a scale that makes it useful as a real-world conservation tool,” said co-lead author Chris Baker, postdoctoral fellow in OEB. “We’re offering a way to measure the biodiversity of wild animals and, in particular, a way to measure biodiversity directly.”
Measuring animal biodiversity in detail over large spaces is a major challenge for researchers. Even with protected areas with the goal of conserving wild animal communities, are costly and time-consuming to monitor.
“You can set out automated cameras, you can set out acoustic recorders, or you could do it manually with people out into the field to survey things, but it’s difficult to do that on a really large scale,” Baker said. “We wanted to be able to use environmental DNA as a way to be able to address this problem…. instead of having to rely on proxies, like forest cover or the budget of forest rangers.”
Leeches are a perfect fit as they are abundant in tropical environments and they feed on a broad range of animals. Because their feeding strategy is sit-and-wait, it's highly likely that wherever they are collected the animal they fed on was in that area. Leeches also slowly digest their meals allowing researchers to gather animal blood from them four months after the last feed.
The researchers looked for DNA sequences present only in vertebrates to identify the animals the leeches fed on. Past studies have shown this was possible, but this is believed to be the first time that a DNA analysis has been done at such a large scale.
Researchers coordinated with 160 volunteer park rangers to collect the leeches. The team at Kunming Institute extracted DNA from the samples, arranged the sequencing, and investigated which animals the DNA belonged. The Pierce lab analyzed the locations of the animals using a technique known as multi-species occupancy modelling, which accounts for ecological patterns.
They identified 86 vertebrate species, some of which are listed as near-threatened or threatened by the International Union for Conservation of Nature. They also showed pressures from human activity such as farming, livestock management, and poaching. DNA from cows, sheep and goats was recovered from leeches collected within the reserve, especially close to the edges, suggesting that animals from surrounding farmland are grazing within the reserve and possibly competing for resources.
The study's results could be used as a baseline to help track changes in Ailaoshan's wild animal populations. More broadly, it could provide a method of tracking zoonotic reservoirs for diseases by screening leech blood meals for viruses in animals that could be transferred to humans.
“It’s a pretty effective way to sample a great diversity of wild animals, and if we think that [zoonotic disease reservoirs] are really something to worry about and monitor, this is a good way to do it,” said Pierce.
Images: Ailoshan National Park habitat; Leeches floating in ethanol in vial; Leech that has regurgitated part of its blood meal