Evol Ecol Res 9: 1199-1210 (2007)     Full PDF if your library subscribes.

Selfish and spiteful behaviour through parasites and pathogens

Francisco Dionisio*

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

e-mail: dionisio@fc.ul.pt


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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