Blood-sucking leeches can help scientists map biodiversity

Scientists looking to measure the biodiversity of wild animals have added a surprising tool to their arsenal.

In a new study led by a team of Harvard researchers, DNA samples from the blood meals of leeches were used to map which animals live in the Ailaoshan Nature Reserve in China. According to the findings from the study, the samples can be used to find out which wild animals are present in large protected areas, such as national parks, and help establish the use of leeches as a surveillance instrument for animal protection.

Chris Baker, a graduate student in Naomi Pierce's lab at Harvard and one of the study's authors, said that the 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.

Over 80 species of animals, including mammals, birds, and squamates, are being surveyed by the research using DNA from more than 30,000 leeches. Over a three-month period, forest rangers collected the leeches from the 260 square mile nature reserve, which spans nearly 80 miles along a mountain ridge in Southern China.

The work addresses a major practical challenge in measuring animal biodiversity by providing a way to do so in detail over large spaces. It is costly and time consuming to monitor protected areas that are set aside to conserve wild animal communities.

It is difficult to set out automated cameras, set out acoustic recorders, or do it manually with people out in the field. We wanted to be able to use environmental DNA as a way to address this problem instead of relying on proxies.

Leeches were perfect for the job.

They are abundant in tropical environments. Large bears to small mice are some of the animals they feed on. It is highly likely that the animal they fed on was in that area, making it easy to map. They digest their meals slowly from one meal to the next. Four months after the last feed, the Harvard researchers collaborated with scientists from China's Kunming Institute of Zoology, who could still get animal blood from the leeches.

The researchers looked for the same genes in the same places as the animals they fed on. This is believed to be the first time that a large scale DNA analysis has been done.

The researchers and park rangers collected the leeches. The team in China took the samples, arranged the sequencing, and looked at which animals the DNA belonged to. The team at Harvard analyzed the locations of the animals using a technique that accounts for ecological patterns.

The team was able to identify 86 species. Some of those species are listed as threatened or near threatened by the International Union for Conservation of Nature. The animals included were the black bear, the deer, the macaque, and the serow.

The study showed that there were encroaching pressures on the reserve from human activity. Animals' DNA was recovered from leeches collected close to the edges of the reserve. It suggests that animals from surrounding farmland are being grazed within the reserve where they could start competing for resources or otherwise degrading the habitat.

The researchers are optimistic that the results from their study can be used as a baseline to help track changes in Ailaoshan's wild animal populations going forward, and that the method could grow as strategy for the improved monitoring of wild animals in tropical and subtropical areas.

They see broader applicability in terms of tracking zoonotic reservoirs for diseases, since blood meals can be screened for the viruses they contain. The COVID-19 Pandemic was believed to be harbored by animals before being transferred to humans.

The Hessel Professor of Biology in OEB and Curator of the Museum of Comparative Zoology said that you can use the leeches to look for viruses.

More information: Yinqiu Ji et al, Measuring protected-area effectiveness using vertebrate distributions from leech iDNA, Nature Communications (2022). DOI: 10.1038/s41467-022-28778-8 Journal information: Nature Communications Citation: Blood-sucking leeches can help scientists map biodiversity (2022, April 5) retrieved 5 April 2022 from https://phys.org/news/2022-04-blood-sucking-leeches-scientists-biodiversity.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.