Epidemiological and evolutionary consequences of life-history trade-offs in pathogens

Trade-offs in life-history traits are a central tenet in evolutionary biology, yet their ubiquity and relevance to realized fitness of populations remains questioned. Trade-offs in pathogens are of particular interest because they may constrain the evolution and epidemiology of diseases. Here, studies that have measured life-history trade-offs in pathogens (fungi, oomycetes and viruses) of agricultural crops, as well as pathogens attacking wild host plants, are reviewed. The majority of studies report a penalty associated with high virulence as is evidenced by lower performance during subsequent life-history stages. However, costs are not pervasive, and the strength and even shape of life-history correlations can vary according to host genotype, and abiotic environment. Importantly, life-history trade-offs are shown to have profound epidemiological implications ranging from lower disease prevalence of strains harbouring unnecessary virulence, to increased extinction risk at the metapopulation level. From an evolutionary perspective, costs of virulence are shown to constrain the range of R genes, and hence host genotypes, a given strain can adapt to. Moreover, costs of virulence play an important role in limiting the host range of pathogens. Hence, analysis of pathogen life history plays a key role in identifying means of battling disease, from breeding durable resistance to epidemiological intervention strategies.