Exploring the "Worm Wide Web" of wildlife

Exploring the “Worm Wide Web” of wildlife

Water pits bring together both wildlife and livestock, enabling parasites to move between hosts. Credit: Georgia Titcombe et al

Many of us try to suppress our thoughts, while others accept them. Whatever your opinion of parasites, they can tell scientists a lot about ecology, health, and the environment.


For example, consider which animals share parasites. It’s a simple question that has many implications for food webs, rare species, and even environmental change. It is also critical to understand disease transmission in a world of increasing interdependence between human and animal hosts. However, answering this question is difficult, especially when research relates to endangered and endangered species.

An international study led by a researcher from the University of California, Santa Barbara, offers a promising solution. Using DNA from the dung of large herbivores, scientists have discovered an entire network of gastrointestinal parasites shared between 17 species of land and domestic herbivores. The paper published in Proceedings of the Royal Society B, sheds light on the patterns of parasite diversity at the wildlife-livestock interface. In particular, the authors found that gastrointestinal parasites tend to infect hosts with similar gut types and evolutionary history, and that domestic animals play a key role in this network.

The lead author, Georgia Titcombe, was a graduate student at the University of California, Santa Barbara, when she started getting her hands dirty with a giant breast tube. While working on her thesis, she wanted to understand how large, wild, and domestic animals might share parasites in the water sources where they congregate. But she is becoming increasingly frustrated with the typical methods of manually identifying and counting parasite eggs. “I was looking at the microscope and seeing the eggs were exactly the same,” she said. “There was no way of knowing if the microscopic, amorphous oval that I found in cow poop could infect an antelope.”

In search of a better way, Titcomb reached out to co-author Rob Pringle at Princeton University, who used DNA in the dung of herbivores to learn about their diets. “I was inspired by their research paper,” recalls Titcombe, who joins the faculty at Colorado State University. “I wondered: What if we could adapt this method to detect the enormous diversity of parasites in these herbivores?” Perhaps they could reveal predictable patterns of parasite diversity and involvement.

“We wanted to understand the factors that influence the composition and similarity of parasite communities in different host species, as well as to identify who might share parasites with whom,” Pringle said.

The team used DNA metabolism — a technique that amplifies a short strand of DNA in a sample and matches it to sequences in a genetic database — to discover the presence and diversity of parasites in 17 species of large herbivores housed in the Mbala Research Center in central Kenya. . “Having such a rich diversity of herbivores all overlapping in one study site allowed us to investigate a wide range of factors that may explain parasite infection,” Titcomb said.

The authors tested several variables — such as the host’s body size, diet, and social group size — and found some key patterns. “The most important factor is the evolutionary history of the host,” Titcomb explained. “The more closely related hosts had more closely related parasites.” In addition, the structure of the host’s gut – the parasite’s habitat – can determine the community of parasites present there.

Mammal herbivores are divided into two main groups: those that digest plant matter in their foregut, and those that digest plant matter in the hindgut. Foregut fermenters – such as cows, antelopes, buffaloes, and giraffes – are very effective at extracting nutrients from plants because they have complex stomachs. The authors suspected that this multi-chamber stomach might provide a lot of habitat complexity for gut parasites. As a result, these animals may have a different set of parasites than their hindgut fermenters—such as zebras, donkeys, elephants, and pigs—which have a long colon where they absorb most nutrients.

Why are there different parasites in different areas of the intestine? “One reason may be that the digestion process involves such amazing variability in acidity as well as the microbes,” Titcomb said. Parasites have to adapt to live in these conditions, so they are likely to specialize in different areas of the digestive system.

Animals with similar gut types also tend to have similar evolutionary histories – and thus may share many other factors that influence parasites, such as immunity – so it is very difficult to separate the role of gut type from the host relationship. However, the authors found genetically similar parasites in very different groups of animals — such as pigs, zebras and elephants — so they suspect gut type is responsible for much of the difference.

One conclusion the authors had not anticipated turned out to be rather significant. “We found that many livestock species were integral to this parasite-sharing network,” Titcomb said. “Camels, cows, and donkeys all share parasites with many species of wildlife. Although deworming at weaning, cows still share parasites with at least eight other species.”

Accounting for the important role livestock play in these networks is crucial to planning for the future. “All over the world, large mammal populations are declining and livestock displacement is increasing,” Pringle said. “The parasites of these animals have important impacts on their health and fitness, which presents a potential problem for their conservation and human livelihoods insofar as wildlife can transmit diseases to livestock.”

The authors believe that their findings will be important for livestock management. Pringle added that a proper understanding of the factors that influence parasite networks is critical to designing effective protection plans and anticipating and managing disease outbreaks.

For example, it is important to understand the extent to which camels and cattle share parasites with wild herbivores. The team found that 90% of camels were infected with at least one type of parasitic nematode. Camels are increasingly replacing livestock in the study area due to their drought tolerance, and were among the most important species in the parasite participation network.

Titcomb also noted that these are still early stages, and there is a lot of work to be done. “We only looked at one aspect of the world of parasites, albeit an important aspect of herbivores,” she said. “But there are many other groups of parasites to look at as well.”

The authors also point out that the method of metabolism is not ideal. “There are many aspects to consider when using these technologies, and they are constantly evolving,” Titcomb said. “In addition, we are not yet able to reliably determine the severity of infection, which is important for animal health and to detect potential spread of infection.”

In the future, Titcomb anticipates that parasite DNA metabolism will be an important tool for parasitologists and pathologists as they study contagion across a changing landscape. “I think the most amazing thing is that we can now take this very small piece of DNA, completely non-invasively, and be able to expose an entire world of parasites cheaply and effectively to hundreds of samples,” she said. This provides unprecedented power to link animals to common parasites, to study them over time and consider how these dynamics change in different contexts.


Exploring parasite populations in savanna watering pits


more information:
Georgia C. Titcomb et al, Large herbivorous nemabiomes: patterns of parasite diversity and sharing, Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098 / rspb.2021.2702

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the quote: Exploring the ‘Worm Web’ for Wildlife (2022, June 6) Retrieved June 6, 2022 from https://phys.org/news/2022-06-exploring-wildlife-worm-wide-web.html

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2022-06-06 17:08:28

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