community ecology of disease: barley yellow dwarf viruses in west coast grasslands eric seabloom
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Community ecology of disease: Barley Yellow Dwarf viruses in west coast
grasslands
Eric SeabloomElizabeth BorerParviez Hosseini
Dept. of ZoologyOregon State University
Host-pathogen interactions are often studied in isolation
HostPathogen
Vector
However, pathogens act within a community context
Resource
Host
Host
Pathogen
Pathogen
Vector
Vector
Community context of host-pathogen interactions
Resource supply: Abiotic resources can alter host, vector, and community dynamics.
Host Community: Most emerging human and plant diseases are host generalists
Vector Community: Many emerging animal and plant diseases are vector transmitted
Pathogen Community: Most host species are co-infected by multiple pathogens and co-infection can alter transmission and host mortality rates
Community context of host-pathogen interactions: B/CYDV in California
grasslands
1. Host Community: How do changes in the host community affect host-pathogen dynamics?
2. Resource supply: How does nitrogen alter the host community and pathogen prevalence?
System Overview:
Invasion of California Grasslands
• 9.2 million ha of California grasslands invaded by exotic annual grasses for at least 150 years
• Persistence and abundance of annuals generally interpreted as evidence of competitive superiority
• However, recent work shows native perennial grasses are better competitors and can invade stands of exotic annual grasses1
1Seabloom et al. 2003. PNAS,
The conundrum: How did competitively inferior species invade and dominate in this system?
Recent experiments show that exotic annual grasses can increase prevalence of Barley Yellow Dwarf Virus in native grasses1,2
Can disease allow persistence of competitively-inferior exotic annual grasses?1Malmstrom et al. 2005. Oecologia,
2Malmstrom et al. 2005. New Phytologist.
Barley and Cereal Yellow Dwarf Viruses• One of the most economically
important diseases of grasses worldwide
• One of the most prevalent of all viral diseases
• Over 150 hosts including cereal crops, exotic grasses, and native grasses
• RNA luteoviruses that infect sieve tubes of grasses
• Causes stunting, yellowing, increased mortality, and decreased fecundity
• Obligate vectors are aphids
Irwin and Thresh. 1990. Annual Review of Phytopathology. D'Arcy and Burnett 1995.
B/CYDV Strain and Vector Communities
http://www.ento.csiro.au/http://www.biokids.umich.edu/http://www.viarural.com.ar/
Sitobion avenae
I. SGV
I. MAV
I. PAV
II. RPV
II. RMV
Rhopalosiphum padi
Schizaphis graminum
Rhopalosiphum maidis
Community context of host-pathogen interactions: BYDV in California
grasslands
1. Host Community: How do changes in the host community affect host-pathogen dynamics?
2. Resource supply: How does nitrogen alter the host community and pathogen prevalence?
3. Vector and Pathogen Community: How do vector and pathogen interactions affect pathogen prevalence and coexistence?
1. How do changes in the host community affect host pathogen dynamics?
Resource
Host
Host
Pathogen
Pathogen
Vector
Vector
Disease Effects on CompetitionConceptual Model
Discrete Time– Survival between seasons– Reset of system Loss of Disease
Continuous Time– Growing (Winter Rainy) Season – Ongoing infection processes (SI model)– Competition (Lotka-Volterra)
Integro-Difference EquationsParameterized with data from field experiments
The Ugly Math: Between seasons
t
t
IPSPtS dtFFbp 1,
t
t
SStS dtGFP 1,
t
t
IaSAtS dtHHba 1,
01, tIp
t
t
IItI dtGFP 1,
01, tIa
The Ugly Math: Growing season
SpppS
S pVdt
dptF )( spspp
II pVp
dt
dptF )(
SpS
S PVdt
dPtG )( Sp
II PV
dt
dPtG )(
SaaaS
S aVdt
datH )( Sasaa
II aVa
dt
datH )(
IsaPIsapIsaaa PPppaa 1
IspPIspaIsppp PPaapp 1
III PpaV
Dominance mediated by Disease
• Without Disease– Perennials invade
– And replace annuals
Healthy Annuals
Healthy Perennials
Diseased Annuals
Diseased Perennials
• With Disease– Annuals invade
– Dominate system
– High disease prevalence
Borer et al. 2007. PNAS
2. How does nitrogen alter host community and pathogen prevalence?
Resource
Host
Host
Pathogen
Pathogen
Vector
Vector
Host community•Annual dominated•Perennial dominated
Nitrogen addition•Control•4 g N m-2 yr-1
Treatments started in 2000
BYDV prevalence•exotic annual B. hordeaceus monitored from 2002-2003•native perennial E. glaucus monitored from 2002-2005
Experimental manipulation of host community composition and nitrogen
Nitrogen increased annual grass abundance and BYDV prevalence in the native perennial, Elymus glaucus
Community context of host-pathogen interactions: BYDV in California
grasslands
1. Host Community: BYDV presence was a necessary precondition to allow invasion by exotic annual grasses in California
2. Resource supply: Nitrogen increases both exotic annual invasion and BYDV prevalence in native grasses
Community context of host-pathogen interactions: general implications
1. Host Community: there can be strong feedbacks between changes in the host community and pathogen dynamics.
2. Resource supply: changing supply of abiotic resources can indirectly affect pathogens via effects on host communities
All this is well and good, but we are still lacking a large-scale experimental test of the model predictions
Hopland
McLaughlin
Finley
Basket Slough
Sierra Foothills
Experimental Test of Resource Supply and Host Community effects on Disease
•Replicated at five Sites with two replicates per site•N and P added in factorial combination•Monitor Disease incidence in 3 congeneric pairs of annual and perennial grasses
We have good estimates for end of season status for discrete time portion of model
A key challenge is to track within season growth rates used in disease model as sites are widely scattered.
Hopland
McLaughlin
Finley
Basket Slough
Sierra Foothills
Experimental Test of Resource Supply effects on Disease
•Remote meteorological stations will allow us to track changes in light interception, a surrogate for plant biomass.
•These continuous data will allow us to estimate the effects of resource supply (rainfall, nitrogen, phosphorous) on the phenology of annual and perennial grasslands.
Sensor setup for one reserve (site)
NP plot
Neon Wireless Platform: light, soil moisture, rainfall, temperature senors and compactrio, wireless, and power (solar & battery),…
Radio Relay: may be necessary to compete connection to internet point of contact
Internet point of contact: Cheap CPU with wireless antenna. This point will have power available.
Ground-level light and soil moisture sensors in and out of N&P fertilization plot with ambient light, rain, and temp sensors at platform
Example workflow for BYDV models
1. Collection of raw sensor data from met stations2. Data processing in R3. Model fitting and parameter estimation of
growth models in R4. Run disease model simulations in R5. Produce graphics from model output in R
General features for REAP to consider from BYDV case study
1. Need for continuous data from remote locations2. Well-documented workflows between raw data, data
processing, parameter fitting with statistical models, and analytical/simulation models
3. Ability to use a wide range of sensor configurations.
Considerations not well-represented in current case study
1. Mobile sensor/data loggers as in the case with GPS radio collars
2. High density networks of sensor spatial sensor grids3. Need for adaptive real-time reconfiguration of sensor
networks
Funding•NSF/NIH EID 05-25666 (Borer, Dobson, Mitchell, Power, and Seabloom)
•Murdock Foundation (Borer and Engler)
•USDA NRICGP 2003-35316-13767 (Briggs and Borer)
•NSF DEB 02-35624 (Reichman, Seabloom, and Schimel)
•NSF DEB 04-44639 (Power and Mitchell)
People•Field work: T. Yoshida, A. Borcher, J. Quinn, T. Mizerek, G. Creager, A. Brandt, B. Martin
•ELISAs: Kai Blaisdell and Craig Kahlke
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