Research

Infectious disease is a ubiquitous force on the evolution and ecology of species. Understanding evolutionary processes in natural populations is of practical importance for conservation biology, management of genetically modified crops, invasion biology, and for understanding the origins and dynamics of infectious disease in humans. 

The evolution of transmission mode

 

This research investigates how the presence of multiple routes of pathogen transmission impact disease dynamics both in theory and in a real world-natural system, and how different transmission modes evolve. Our study emphasizes that the evolution of transmission mode is a co-evolutionary process involving both host and pathogen traits. We are investigating how transmission evolves when it is determined by the differential susceptibility of the host to pathogen entry into different tissues and at different ages, focusing on the contrast between aerial and vector transmission. Our empirical model system is anther-smut  (caused by the fungal pathogen Microbotryum) in Dianthus pavonius (an alpine carnation). Anther-smut is vector transmitted (by pollinators) and aerially transmitted (by spores falling on vegetative plants), with both transmission routes resulting in more than a third of the plants becoming diseased and sterile.

Healthy and diseased flowers of alpine carnation

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We study how alternate transmission modes are favored at different densities, and how changes in plant density feed back to affect the evolutionary process. 

     This research is in conjunction with Drs. Emme Bruns, soon moving to University of Maryland, Mike Boots at University of California, Berkeley, Michael Hood at Amherst College, Massachusetts, and with scientists at the Parco Marguareis in Italy (Bruno Gallino and Valentina Carasso). This research is funded by the Ecology and Evolution of Infectious Disease Program of the NSF and NIH.

Metapopulation dynamics of disease

 

Theory has shown that conclusions regarding ecological and evolutionary dynamics derived from single populations can be radically different when considered in a spatial context of multiple populations interconnected by movement (metapopulations). Nevertheless there is a lack of field data on spatially distributed populations over extended periods of time to guide and focus this theory. We have been studying the metapopulation biology of the plant Silene latifolia and its associated pathogen, Microbotyrum violaceum for over 30 years in the area around Mountain Lake Biological Station, Virginia. Our annual census data has provided long-term demographic, sex ratio and disease incidence data for more than 800 populations of Silene latifolia, which in turn has generated key insights into how extinction and colonization affects the larger scale population dynamics of the host and pathogen. We are using our knowledge of the age structure of populations to test hypotheses about the forces determining genetic structure (using neutral markers) and selection (as instantiated by evolution of disease resistance to Microbotryum). Using a high throughput marker approach and likelihood methods, we are assessing the source of colonists and migrants and the degree to which source populations and founding events affect the genetic composition of popuations and over what time scale. The census is continuing as is the banking of seeds, collection of DNA and of pathogen cultures. This will provide a multi-year longitudinal data set on evolution in spatially structured populations.

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Map of section of the metapopulation

     This research is with Dr. Doug Taylor at the University of Virginia, and is funded by the Long Term Ecological Research program at NSF.

Community Coalescence and Microbial Biospherics

Organisms live in complex communities, and understanding such complexity is a major challenge in biology, relevant to conservation, ecosystem productivity and human health. We are taking two approaches to this problem, focusing very much on microbial systems. We are studying the consequences of merger and separation of whole communities (community coalescence) as this is a common occurrence in the microbial world, and how this process affects species diversity and evolution. We are also working in the opposite direction and asking how simple communities can  be self-sustaining in closed systems (biospheres), with only light as an energy source. Understanding the long-term persistence of simple communities, is directly relevant for understanding the stability of ecosystem processes, and for life support systems in space travel.

     This research is in conjunction with Prof. Matthias Rillig and his lab at the Free University, Berlin, Germany and has been funded by the Humboldt Foundation and the European Research Council.

Schematic  of a microbial biosphere 

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Historical Studies

Linnaeus and the germ theory of disease

We are examining Linnaeus' interest in infectious disease, and the factors that led him to be the first to name disease-causing microorganisms. We are exploring why Linnaeus' realization that living organisms could cause disease, one hundred years before Pasteur. failed to convince others of the germ-theory of disease.

Linnaeus' annotations to the 12th edition of 'Systema Naturae' (at Linnean Society)

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Lydia Becker, Darwin, and disease

Lydia Becker (1827-1890) was a pioneer in the Women's suffragette movement, and an enthusiastic botanist. We are researching the interactions between Lydia Becker and Charles Darwin from two major perspectives. First, we are tracing the scientific thread of Becker's work, and focusing on some of the difficulties her ideas had in being accepted by the predominantly male scientific community, including Darwin himself. Second, we use the correspondence between Darwin and Becker as a mirror against which to gauge why Darwin (perhaps because of his medical school experiences or for some other other reasons) was disinterested in disease and did not elaborate on how evolutionary ideas might impinge on our understanding of epidemics. We suggest that Darwin's disinterest in disease contributed to the present schism between evolutionary biology and medical research.

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Lydia Becker (detail from Manchester

Art Gallery)

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Wilhelm Ludwig: the life of a biologist in wartime Germany

Wilhelm Ludwig (1901-1958) was a German evolutionary biologist who did extensive research on gene frequency change, sex ratio bias, and methods of paternity analysis. He also developed a cogent theory of sympatric speciation. We are studying why his work has been largely ignored, and researching the circumstances of his life before, during and after the second world war as an example of an academic that survived but did not embrace the Nazi regime.

Wilhelm Ludwig

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Support for our historical research has come from an NSF grant on Public Understanding of Science, from the Wissenshcaftskolleg in Berlin, and from the Humboldt Foundation.