{"55592":{"#nid":"55592","#data":{"type":"news","title":"Epidemic This Year? Check the Lake\u0027s Shape","body":[{"value":"\u003Cp\u003EOf all the things that might control the onset of disease epidemics in Michigan lakes, the shape of the lakes\u0027 bottoms might seem unlikely. But that is precisely the case, and a new BioScience report by scientists from the Georgia Institute of Technology, Indiana University Bloomington and three other institutions explains why.\u003C\/p\u003E\u003Cp\u003E\u0022In the paper, we go through several explanations for what is going on,\u0022 said IU Bloomington biologist Spencer Hall, the report\u0027s lead author. \u0022We are looking at the zooplankton that is infected, the fish and other creatures, the ecology, the limnology and even the physics. Of all those explanations, the shape of the lake basins was the most powerful factor.\u0022\u003C\/p\u003E\u003Cp\u003EAlso contributing to the report were scientists from the University of Illinois at Urbana-Champaign, the National Science Foundation and the University of California at Santa Barbara.\u003C\/p\u003E\u003Cp\u003E\u0022This paper is a synthesis of research on a model system for the study of disease ecology,\u0022 said Alan Tessier, coauthor and program director in the NSF\u0027s Division of Environmental Biology. \u0022It combines limnological, epidemiological, ecological and evolutionary perspectives to address a general question about the occurrence of epidemics in nature. It illustrates the value of interdisciplinary approaches to understanding the emergence of patterns in systems of complex biotic and abiotic interactions.\u0022\u003C\/p\u003E\u003Cp\u003EThe disease in question is caused by a fungus that infects Daphnia dentifera, the water flea that plays a critical \u0022grazer\u0022 role in many freshwater lakes of the American Midwest. Recent research by Illinois biologist Carla C\u00e1ceres, Hall and others shows the epidemics usually start in late summer or early fall.\u003C\/p\u003E\u003Cp\u003EThe fungus slowly consumes the tiny crustacean\u0027s blood (hemolymph) and produces spores that fill all that remains. For the fungal spores to make it to the next potential host, the Daphnia host\u0027s exoskeleton must be opened -- and it must be opened in an area where the spores are exposed to living, uninfected Daphnia dentifera. Whether that happens effectively each year can be predicted by ascertaining whether the lake bottom is v-shaped, with gently sloping sides, or u-shaped, with walls that descend rapidly away from shore.\u003C\/p\u003E\u003Cp\u003EThe topography of lake bottoms has profound consequences for the lakes\u0027 ecology and movement of water that is driven by surface and subsurface temperatures.\u003C\/p\u003E\u003Cp\u003EU-shaped lakes have less near-shore nursery areas, and likely as a result, bluegill fish populations tend to be lower. Bluegill are a major Daphnia dentifera predator.\u003C\/p\u003E\u003Cp\u003EWith fewer bluegill in u-shaped lakes, Daphnia tend to be larger, and larger Daphnia have a higher chance of eating spores and becoming infected. Fewer bluegill also means more Chaoborus, an invertebrate that is also eaten by bluegill -- and that also eats Daphnia dentifera.\u003C\/p\u003E\u003Cp\u003EUnlike bluegill, which tends to eat Daphnia dentifera cleanly and excrete a heavy spoor that quickly sinks to the lake bottom (and probably out of the ecological picture), Chaoborus are \u0022messy\u0022 eaters that chew up Daphnia and spit quite a bit of the exoskeleton -- and spores contained in it -- back out. This invertebrate predator, then, spreads spores of the parasite and catalyzes epidemics.\u003C\/p\u003E\u003Cp\u003EWith the scene set, all that\u0027s needed, Hall said, is a beginning.\u003C\/p\u003E\u003Cp\u003E\u0022Physics gets the epidemic going,\u0022 Hall said. \u0022Chaoborus keeps it going.\u0022\u003C\/p\u003E\u003Cp\u003EAs evening air and\/or late summer storms cools the near-shore waters of u-shaped lake basins, the water sinks until it reaches water of similar temperature, at which point the waters move away from shore. This creates a water flow, bringing nutrients (and latent spores) from shore out to the middle of the lake, where more Daphnia dentifera and Chaoborus live.\u003C\/p\u003E\u003Cp\u003EDaphnia dentifera filter feed, ingesting some spores. Chaoborus eats the water fleas, breaking some husks and spewing spores into near-surface waters. Some of the spores may sink to the lake bottom and out of the picture, but during the day, the warmth of summer and fall air keeps the near-surface waters turbulent and that creates a churning effect. Some spores are pulled upward and remain available for Daphnia dentifera to eat. Spore-containing waste produced by Chaoborus and bluegill near shore can re-feed the system in subsequent evening, as cool air drives shore waters back to the lakes\u0027 centers.\u003C\/p\u003E\u003Cp\u003E\u0022We hypothesize that spores are pulled out to the water column by these flows, called \u0027gravity currents,\u0027\u0022 Hall said. \u0022Several physical factors inhibit gravity currents in v-shaped lakes.\u0022\u003C\/p\u003E\u003Cp\u003EHall and his coauthors argue that fungal disease epidemics infrequently occur in v-shaped lakes because dense bluegill populations prey intensely on both infected Daphnia dentifera and Chaoborus. High predation intensity inhibits production and spread of infectious spores, thereby damping spread of epidemics.\u003C\/p\u003E\u003Cp\u003E\u0022The system is really interesting, but this research also gets at a bigger issue -- how do the basic features of habitats drive major biological phenomena?\u0022 Hall said. \u0022Understanding the relationship between the spatial aspects of a habitat and what happens within it will be a major focus of future study.\u0022\u003C\/p\u003E\u003Cp\u003EThe scientists also considered six other basic mechanisms behind fungal disease. These included links between phosphorus and host density, nutrition of algal resources for hosts, and genotype differences between the hosts of u- and v-shaped lakes. All of these were rejected based on the evidence. Selective predation by bluegill, sloppy predation by Chaoborus, Daphnia body size and gravity currents were supported, and all four of these mechanisms were influenced -- or controlled -- by lake basin shape. The scientists also found a possible relationship between epidemic likelihood and the density of another Daphnia species, D. pulicaria, but confirmation requires more study.\u003C\/p\u003E\u003Cp\u003EAlso contributing to the BioScience report were Carla C\u00e1ceres and Christine Knight (UIUC), Robyn Smyth and Sally MacIntyre (UC Santa Barbara), Claes Becker (formerly of IU Bloomington, now at Sweco Environment, Stockholm), Meghan Duffy (Georgia Tech) and Alan Tessier (National Science Foundation). The study was funded by the NSF.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWritten by David Bricker, Indiana University\u003C\/strong\u003E\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EOf all the things that might control the onset of disease epidemics in Michigan lakes, the shape of the lakes\u0027 bottoms might seem unlikely. But that is precisely the case, and a new report explains why.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Shape of lake bottoms may control onset of disease epidemics."}],"uid":"27310","created_gmt":"2010-05-06 11:02:37","changed_gmt":"2016-10-08 03:05:33","author":"David Terraso","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2010-05-05T00:00:00-04:00","iso_date":"2010-05-05T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"55591":{"id":"55591","type":"image","title":"Baker Lake","body":null,"created":"1449175342","gmt_created":"2015-12-03 20:42:22","changed":"1475894442","gmt_changed":"2016-10-08 02:40:42","alt":"Baker Lake","file":{"fid":"190328","name":"9134_h.jpg","image_path":"\/sites\/default\/files\/images\/9134_h_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/9134_h_0.jpg","mime":"image\/jpeg","size":314976,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/9134_h_0.jpg?itok=mrHpvONO"}},"55593":{"id":"55593","type":"image","title":"Infected Daphnia","body":null,"created":"1449175556","gmt_created":"2015-12-03 20:45:56","changed":"1475894491","gmt_changed":"2016-10-08 02:41:31","alt":"Infected Daphnia","file":{"fid":"190329","name":"9135_h.jpg","image_path":"\/sites\/default\/files\/images\/9135_h_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/9135_h_0.jpg","mime":"image\/jpeg","size":88858,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/9135_h_0.jpg?itok=ibJ6Ibe0"}},"55594":{"id":"55594","type":"image","title":"Lake dye","body":null,"created":"1449175556","gmt_created":"2015-12-03 20:45:56","changed":"1475894491","gmt_changed":"2016-10-08 02:41:31","alt":"Lake dye","file":{"fid":"190330","name":"9137_h.jpg","image_path":"\/sites\/default\/files\/images\/9137_h_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/9137_h_0.jpg","mime":"image\/jpeg","size":136245,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/9137_h_0.jpg?itok=9DUUeE_-"}}},"media_ids":["55591","55593","55594"],"groups":[{"id":"1183","name":"Home"}],"categories":[{"id":"154","name":"Environment"},{"id":"146","name":"Life Sciences and Biology"}],"keywords":[{"id":"8356","name":"epidemic"},{"id":"9262","name":"lake"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003E\u003Cstrong\u003EGeorgia Tech Media Relations\u003C\/strong\u003E\u003Cbr \/\u003ELaura Diamond\u003Cbr \/\u003E\u003Ca href=\u0022mailto:laura.diamond@comm.gatech.edu\u0022\u003Elaura.diamond@comm.gatech.edu\u003C\/a\u003E\u003Cbr \/\u003E404-894-6016\u003Cbr \/\u003EJason Maderer\u003Cbr \/\u003E\u003Ca href=\u0022mailto:maderer@gatech.edu\u0022\u003Emaderer@gatech.edu\u003C\/a\u003E\u003Cbr \/\u003E404-660-2926\u003C\/p\u003E","format":"limited_html"}],"email":["david.terraso@comm.gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}