Parasite load unrelated to host body size

Number of parasites an animal can host depends on amount of energy host can provide to parasites.

January 8, 2020

2 Min Read
Parasite load unrelated to host body size

A breakthrough by ecologists at the Scripps Institution of Oceanography has implications for multiple fields of biology, according to the National Science Foundation (NSF), which funded the research.

Ecologist Ryan Hechinger and colleagues tested a new way to predict the parasite load carried by California shorebirds, but the researchers suggested that their results could apply to any organism that could host parasites, including livestock and poultry as well as people and wildlife.

Hechinger described parasites as the "dark matter" of ecosystems, explaining that they are ubiquitous and a key component of energy flow through those systems, but their ecological function is often overlooked.

The study appears in the journal Proceedings of the Royal Society B. The team described how the amount of space inside or on a host, whether it's an ostrich, hummingbird, elephant or mouse, has less to do with the total parasite load it can carry at any given time and more to do with how much energy it can supply to those parasites, NSF said.

In work funded by a NSF Ecology & Evolution of Infectious Diseases grant, Hechinger's team collected California shorebirds from estuaries from near San Francisco to San Diego, Cal. They found that every bird collected carried parasites — in this case, lice and mites — on the exterior of its body. The sizes of the parasites tended to be in keeping with the body sizes of the hosts, such that smaller birds had more tiny mites and larger birds had relatively more large lice.

"This is a macroecological pattern that no one has ever seen before," Hechinger said.

While the total number of individual parasites might have varied from bird to bird, the maximum load of those parasites remained in proportion to the energy the bird supplied to them, regardless of species. Hechinger said the finding shows the promise of the theory to understand the role of parasites in complex ecosystems.

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