Evol Ecol Res 9: 1199-1210 (2007) Full PDF if your library subscribes.
Selfish and spiteful behaviour through parasites and pathogens
Departamento de Biologia Vegetal, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C2, 1749-016 Lisboa and Instituto Gulbenkian de Ciencia, Apartado 14, 2781-901 Oeiras, Portugal
Questions: Can hosts use their parasites or pathogens to decrease the fitness of their conspecifics? Which conditions support the evolution of such harmful behaviour – expressed as spiteful or selfish behaviour?
Mathematical model: I calculate the selective pressure acting on a mutant expressing harmful behaviour. The direction of selection on this social trait is given by its effect on inclusive fitness. Individuals are haploid and form a population of constant size and structured in an infinite island model with migration. Individuals harm others through their parasites or pathogens.
Key assumptions: (1) An infected host may infect several other susceptible conspecifics simultaneously. (2) A variety of immunity mechanisms enables kin members to be immune to a given parasite or pathogen, a sort of kin recognition.
Conclusions: By using parasites to harm non-kin hosts, the harming host may partially align its interests with those of the parasites, even when there is a fitness cost for this act. The cost is compensated by the fact that the parasite may infect several non-kin hosts within a host generation. That is, by infecting several hosts, the ratio (cost to the actor)/(cost to the recipient) becomes very low, hence facilitating the spread of the harming allele. Immunity-mediated recognition of non-kin hosts or of migrant hosts in subdivided populations further helps this trait to spread.
Keywords: competition, epidemiology, manipulation of parasites, R0, sociobiology, spite.
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