Abstract
The ability of a parasite strain to establish and grow on its host may be drastically altered by simultaneous infection by other parasite strains. However, we still lack an understanding of how life‐history allocations may change under coinfection, although life‐history correlations are a critical mechanism restricting the evolutionary potential and epidemiological dynamics of pathogens. Here, we study how life‐history stages and their correlations change in the obligate fungal pathogen Podosphaera plantaginis under single infection and coinfection scenarios. We find increased pathogen loads under coinfection, but this is not explained by an enhanced performance at any of the life‐history stages that constitute infections. Instead, we show that under coinfection the correlation between timing of sporulation and final pathogen load becomes positive. The changes in pathogen life‐history allocations leading to more severe infections under coinfection can have far‐reaching epidemiological consequences, as well as implication for our understanding of the evolution of virulence.
Highlights
Throughout the growing season, as epidemics proceed, the same host individual may be challenged by more than one pathogen strain of the same species or different pathogen species
HOST–PATHOGEN INTERACTION We focused our study on the obligate fungal pathogen P. plantaginis
When measuring pathogen load of GC strains, we found a significant interaction between the original strain genotype and genotype of the challenging strain (P < 0.0001; Table S1)
Summary
Throughout the growing season, as epidemics proceed, the same host individual may be challenged by more than one pathogen strain of the same species or different pathogen species. The outcome may range from rapid competitive exclusions, resulting in single strain infection (i.e., superinfection; Nowak and May 1994) to multiple infections with several pathogen genotypes coinfecting the same host individual. Given the often inconspicuous nature of the parasitic lifestyle and lack of morphological differentiation among strains, empirical studies of disease dynamics under coinfection have lagged behind theoretical predictions. Theory predicts that under diverse parasitic infections competition for limited host resources results in a “tragedy of the commons” situation where higher levels of host exploitation may emerge (Hamilton 1972).
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