• Nonlethal parasites reduce how much thei

    From ScienceDaily@1:317/3 to All on Monday, May 09, 2022 22:30:44
    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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