Benefits of host genetic diversity for resistance to infection depend on parasite diversity

Abstract

Abstract. Host populations with high genetic diversity are predicted to have lower levels of infection prevalence. This theory assumes that host genetic diversity results in variation in susceptibility and that parasites exhibit variation in infectivity. Empirical studies on the effects of host heterogeneity typically neglect the role of parasite diversity. We conducted three laboratory experiments designed to test if genetic variation in Daphnia magna populations and genetic variation in its parasites together influence the course of parasite spread after introduction. We found that a natural D. magna population exhibited variation in susceptibility to infection by three parasite species and had strong host clone-parasite species interactions. There was no effect of host heterogeneity in experimental host populations (polycultures and monocultures) separately exposed to single strains of three parasite species. When we manipulated the genetic diversity of a single parasite species and exposed them to host monocultures and polycultures, we found that parasite prevalence increased with the number of parasite strains. Host monocultures exposed to several parasite strains had higher mean parasite prevalence and higher variance than polycultures. These results indicate that effect of host genetic diversity on the spread of infection depends on the level of genetic diversity in the parasite population.

Effects of genotypic and phenotypic variation on establishment are important for conservation, invasion, and infection biology

“…The key challenges and mechanisms of importance in invasion biology are similar in many respects to those of interest for researchers and practitioners concerned with ecology and evolution of host-parasite interactions, infectious diseases, and epidemiology. Support for the notion that diversity promotes population fitness comes also from experimental demonstrations that genetic diversity makes populations more resistant to infectious diseases (22,(59)(60)(61). Conversely, evidence is mounting that genetically diverse viruses, bacteria, and parasites are better able to infect their vectors and hosts.…”

Effects of Host Variability on the Spread of Invasive Forest Diseases

“…The same authors showed that in Pinus radiata different mechanisms of resistance against Fusarium circinatum are active in seedlings and adult trees. Still, benefits deriving from a genetically diverse host population may also depend on the genetic diversity of the pathogen population [99].…”

Host resistance influences patterns of experimental viral adaptation and virulence evolution

“…Variability in levels of resistance among hosts is thought to be an important force of selection influencing these phenomena. [1][2][3][4][5][6] Additionally, theoretical considerations regarding the evolution of virulence (here defined as infectioninduced host morbidity/mortality) are dominated by the assumption that virulence is an emergent property of pathogen fitness tradeoffs between within-host growth rate and transmissibility. 7 This further implicates variability in resistance among hosts as a crucial factor influencing infectious disease dynamics in nature as it represents a direct force of selection capable of acting on both of these pathogen phenotypes.…”

“…7 This further implicates variability in resistance among hosts as a crucial factor influencing infectious disease dynamics in nature as it represents a direct force of selection capable of acting on both of these pathogen phenotypes. Finally, the multiple studies demonstrating that genetic variation within host populations can limit the burden of infectious disease 4,[8][9][10][11][12][13][14][15] imply that polymorphisms among individuals (e.g., at resistance loci) are important determinants of the epidemiological and evolutionary outcomes of host-pathogen interactions. However, despite our substantial understanding of how the immune system operates to control Infectious diseases are major threats to all living systems, so understanding the forces of selection that limit the evolution of more virulent pathogens is of fundamental importance; this includes the practical application of identifying possible mitigation strategies for at-risk host populations.…”