Wednesday, August 8, 2007: 8:40 AM
Willow Glen I, San Jose Marriott
To better understand the epidemiology of disease, we evaluated the spatial and temporal dynamics of infection of the woodland annual jewelweed (Impatiens capensis, Balsaminaceae) by the rust Puccinia recondita (Uredinales). Jewelweed has a plastic reproductive system, producing dimorphic flowers, including obligately self-pollinated cleistogamous (CL) flowers and, when growing with adequate resources, open-pollinated, chasmogamous (CH) flowers. Rust infection may not only increase mortality and lower growth rates, but may reduce resources for CH flowering, lowering outcrossed fitness in infected relative to uninfected plants. We studied the prevalence of infection in three populations of jewelweed, the effect of infection on host mating system, spatial patterns of infection, and the biotic and abiotic correlates of infection. Infection prevalence did not vary among sites in 2005, but at one site there was more disease in 2004 than in 2005. Infection was seasonal, occurring early in the growing season and ending by mid-July. Infected plants had reduced fitness and increased reproductive allocation to CH flowering relative to uninfected plants. A greater allocation to outcrossing by infected plants may increase the chances of producing resistant offspring, or may be an indication of a cost of resistance. Rust infection also showed negative host density dependence, which is unusual for most pathogens, but not unexpected for heterocyclic rusts. We found no clustering of infection as the scale of tens of meters, but spatial patterning may occur at larger scales. These results indicate that disease can affect host fitness and mating system and that these effects vary in time.
