Nonlethal parasites reduce how much their wild hosts eat, leading to
ecosystem effects
Date:
May 9, 2022
Source:
Washington University in St. Louis
Summary:
Pervasive parasitic infections reduce herbivory rates and can
therefore trigger trophic cascades that impact plant communities,
according to new research. This work helps fill a recognized
knowledge gap regarding the ecological consequences of parasitic
infections in natural ecosystems.
FULL STORY ========================================================================== Deer, caribou, bison and other similar animals are often infected by a
range of internal parasites, including worms called helminths. Although
many of these infections are not lethal, they can still impact health or
animal behavior. For example, infected animals can eat less grass or other vegetation than they normally would. In an interesting twist, this means
that a world with more sublethal parasitic infections is a greener world.
==========================================================================
A new study led by Washington University in St. Louis uses a mathematical
model and a global meta-analysis to highlight the cascading consequences
of common parasitic infections in wild animals on terrestrial ecosystems.
"Parasites are well known for their negative impacts on the physiology
and behavior of individual hosts and host populations, but these effects
are rarely considered within the context of the broader ecosystems
they inhabit," said Amanda Koltz, senior scientist in biology in Arts & Sciences at Washington University, first author of the study published
in the Proceedings of the National Academy of Sciences.
"In this study, we show that pervasive parasitic infections reduce
herbivory rates and can therefore trigger trophic cascades that impact
plant communities," Koltz said. "This work helps fill a recognized
knowledge gap regarding the ecological consequences of parasitic
infections in natural ecosystems." "In bringing together experts in
a transdisciplinary One Health approach, we bridged health, ecological
and theoretical scientists to expand on traditional studies addressing
impacts of parasites on individual hosts and host populations to better understand these impacts on the ecosystems where ruminant hosts and
their parasites live," said Sharon Deem, director of the Saint Louis
Zoo Institute for Conservation Medicine, a co-author of the new study.
The research effort was conducted by an interdisciplinary and
international working group funded by the Living Earth Collaborative,
a partnership among Washington University, the Missouri Botanical Garden
and the Saint Louis Zoo.
The team included biologists, wildlife veterinarians and epidemiologists, ecosystem ecologists, modelers and infectious disease specialists.
========================================================================== What's eating you? Deer, bison, giraffes, gazelles and antelopes are
hoofed animals known as ruminants: they're vegetarians whose eating
habits have measurable impacts on local ecosystems. Just picture how
much greenery one grazing deer could consume in an unfenced garden.
But each wild ruminant is a world unto itself for the multitude of
parasites that occupy its gut and tissues as it goes about its regular grass-munching business.
While other recent studies suggest that the kinds of parasites that
eventually kill their hosts can trigger cascading effects on ecosystems
in somewhat similar ways to predators, this study also considered the
impacts of nonlethal parasitic infections.
The researchers used a mathematical model and global meta-analysis to
test the potential for helminth parasites -- any of a group of common
parasitic worms - - to set off trophic cascades through both their lethal
and sublethal effects on ruminant hosts.
==========================================================================
"The potential for lethal infections that dramatically increase host
mortality to have ecosystem-level effects is somewhat intuitive,
especially when the hosts that are killed play a key role in the
ecosystem. For example, rinderpest, a virus that killed millions of
ruminants in sub-Saharan Africa prior to the 1960s, changed tree densities
in the Serengeti ecosystem through its effect on wildebeest mortality,"
said Vanessa Ezenwa, professor of ecology and evolutionary biology at
Yale University, a senior author of the study. "Our model suggests that sublethal infections, although more cryptic, can have equally important
effects on ecosystems; and our meta-analysis shows how pervasive the
sublethal effects of helminth parasites are in nature." Modeling led
by Dave Civitello at Emory University took advantage of well- documented examples of caribou and reindeer and their parasites. Caribou and their helminths are among the best-studied wild ruminant-parasite systems,
due to the ecological, economic and cultural importance of caribou in
tundra ecosystems and the ongoing disease threats to the system posed
by climate change.
"Our models allowed us to explore the consequences of different ways that parasites harm their hosts," said Rachel Penczykowski, assistant professor
of biology in Arts & Sciences at Washington University, a senior author
of the study. "We used the models to test effects of parasite infections
on population densities of caribou hosts and on their plant and lichen
food resources.
"We discovered that any of three types of harm caused by parasitic
infections - - that is, harm to host survival, feeding rates or
reproduction -- can cause a cascading effect," she said. "In short,
diseases of herbivores matter to plants." Next, the scientists turned to
data from more than 59 published, peer-reviewed studies to investigate
the links between helminth infections and those same key traits of
free-living ruminant hosts in nature.
Their analysis revealed that helminth infections significantly reduce
the feeding rates of hosts but are not, on average, associated with host survival or fecundity.
"Taken together, the broader relevance of these results is that there
are likely widespread -- yet overlooked -- ecological consequences of
sublethal parasitic infections," Koltz said.
"Given that helminth parasites are ubiquitous within free-living
populations of ruminants, our findings suggest that global herbivory rates
by ruminants are lower than they otherwise would be due to pervasive
helminth infections," she said. "By reducing ruminant herbivory, these
common infections may contribute to a greener world."
========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Talia
Ogliore. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Amanda M. Koltz, David J. Civitello, Daniel J. Becker, Sharon
L. Deem,
Aime'e T. Classen, Brandon Barton, Maris Brenn-White,
Zoe" E. Johnson, Susan Kutz, Matthew Malishev, Daniel
L. Preston, J. Trevor Vannatta, Rachel M. Penczykowski, Vanessa
O. Ezenwa. Sublethal effects of parasitism on ruminants can have
cascading consequences for ecosystems.
Proceedings of the National Academy of Sciences, 2022; 119 (20)
DOI: 10.1073/pnas.2117381119 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/05/220509162301.htm
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