Predicting disease risk from community context and host phenotype: a trait-based approach.

Research Objectives

Our objectives are to test five hypotheses:

• Ecophysiological traits covary along a quick to slow return continuum.
• Ecophysiological traits (i.e., host phenotype) determine epidemiological traits.
• Nitrogen addition to intact grassland decreases host species richness, alters phenotypic composition, and increases vector density and community virus prevalence.
• The effects of host community species composition, species richness, and nitrogen supply on vector density and community virus prevalence are modulated by their impacts on the phenotypic composition of the community.
• An individual’s disease risk is determined jointly by its community context and its own phenotype.

Study Species

• Aegilops triuncialis L. (barbed goatgrass)
• Aira caryophyllea L. (silver hairgrass)
• Arrhenatherum elatius (L.) P. Beauv. ex J. Presl & C. Presl (tall oatgrass)
• Avena barbata Pott ex Link (slender oat)
• Avena fatua L. (wild oat)
• Briza maxima L. (big quakinggrass)
• Bromus carinatus Hook. & Arn. (California brome)
• Bromus diandrus Roth (ripgut brome)
• Bromus hordeaceus L. (soft brome)
• Cynosurus echinatus L. (bristly dogstail grass, or hedgehog dogtail)
• Elymus glaucus Buckley (blue wildrye)
• Elymus multisetus M.E. Jones (big squirreltail)
• Gastrdium phleoides (Nees & Meyen) C.E. Hubbard (nit grass)
• Koeleria macrantha (Ledeb.) Schult. (Junegrass)
• Lolium multiflorum Lam. (Italian ryegrass)
• Melica californica Scribn. (California melicgrass)
• Nassella lepida (Hitchc.) Barkworth (foothill needlegrass)
• Nassella pulchra (Hitchc.) Barkworth (purple needlegrass)
• Poa bulbosa L. (bulbous bluegrass)
• Poa secunda J. Presl (Sandberg bluegrass)
• Schedonorus phoenix (Scop.) Holub (tall fescue)
• Taeniatherum caput-medusae (L.) Nevski (medusahead)
• Vulpia microstachys (Nutt.) Munro (small fescue)
• Vulpia myuros (L.) C.C. Gmel. (rat-tail fescue)

Project leaders

• James P. Cronin, Postdoctoral Research Associate
• Miranda E. Welsh , Ph.D. Candidate

Collaborators

• Marm Kilpatrick, University of California - Santa Cruz

This project will test whether an individual’s risk of acquiring an infectious disease (disease risk) is determined by a handful of easily measured ecological traits of the host individual (host phenotype), and of other host species that are potential sources of infection (“community context”). Experiments will be conducted using a model system for multi-host vector-borne pathogens: cereal and barley yellow dwarf viruses (BYDVs), aphid (insect) vectors that transmit them, and 20 wild grass host species. First, greenhouse experiments (conducted at the University of North Carolina, Chapel Hill) will quantify these grass species’ host phenotypes, at low and high nitrogen (nutrient) availability. Phenotypes will be quantified based on a suite of physiological traits including rate of photosynthesis, concentration of nutrients in leaves, leaf growth rate, and leaf lifespan. Hosts with high nutrient concentrations are expected to also have high metabolic rates (comprising “quick-return” or QR phenotypes) while hosts with low nutrient concentrations will have low metabolic rates (“slow-return” or SR phenotypes). Greenhouse experiments will also test whether QR phenotypes are more heavily fed upon by vectors, more susceptible to infection by feeding vectors, and better able to withstand (tolerate) the negative impacts of infection than are SR phenotypes. Field experiments will test whether QR phenotypes experience greater risk than SR phenotypes of disease transmission from other host species, and whether that risk depends on community context. The field experiments will test whether increased nutrient availability, a major result of human activities, alters disease risk. This work is based at the University of California’s Hopland Research and Extension Center. It was funded by NSF through 2013.