MSGID: 1:317/3 6279eadf   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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   
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   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.   
      
      
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   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.   
      
      
      
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   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.   
      
      
      
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   "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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