Kin selection and the evolution of virulence

Abstract

Social interactions between conspecific parasites are partly dependent on the relatedness of interacting parasites (kin selection), which, in turn, is predicted to affect the extent of damage they cause their hosts (virulence). High relatedness is generally assumed to favour less competitive interactions, but the relationship between relatedness and virulence is crucially dependent on the social behaviour in question. Here, we discuss the rather limited body of experimental work that addresses how kin-selected social behaviours affect virulence. First, if prudent use of host resources (a form of cooperation) maximizes the transmission success of the parasite population, decreased relatedness is predicted to result in increased host exploitation and virulence. Experimental support for this well-established theoretical result is surprisingly limited. Second, if parasite within-host growth rate is a positive function of cooperation (that is, when individuals need to donate public goods, such as extracellular enzymes), virulence is predicted to increase with increasing relatedness. The limited studies testing this hypothesis are broadly consistent with this prediction. Finally, there is some empirical evidence supporting theory that suggests that spiteful behaviours are maximized at intermediate degrees of relatedness, which, in turn, leads to minimal virulence because of the reduced growth rate of the infecting population. We highlight the need for further thorough experimentation on the role of kin selection in the evolution of virulence and identify additional biological complexities to these simple frameworks.

Intensive aquaculture selects for increased virulence and interference competition in bacteria

“…Although the strains isolated from the inlet water were able to inhibit each other and the outlet water strains, significant difference in inhibition was observed only when the outlet water isolates acted as inhibitors. The strains isolated from outlet water seemed to be able to inhibit the growth of the inlet water strains but tolerated well the toxins produced by other outlet water strains, probably due to more homogeneous population structure resulting in less competitive interactions [61]. While these results are in accordance with the general expectations of the evolution of interference competition in mixed populations [54,57], whether these interactions are relevant during disease outbreaks is unknown, and type I error in the interpretation of the results is possible.…”

Fitness costs restrict niche expansion by generalist niche-constructing pathogens

“…It appears that the concomitant induction of the two opine niches affected one another. The mechanism by which this occurs remains unknown, but different parasite genotypes infecting the same host may interact in a diversity of ways, including interference or cooperation (Buckling and Brockhurst, 2008). Nopaline and octopine both require arginine as precursor for their synthesis (Figure 1b), so the two strains compete for this common substrate whose concentration in plants is tightly regulated (Winter et al, 2015).…”

Within-host competitive interactions as a mechanism for the maintenance of parasite diversity

“…As outlined above (figure 1), different mechanisms of within-host competition select for different parasite traits, some of which may increase or decrease within-host growth. Accordingly, a high prevalence of multiple infections is predicted to have varied effects on host health [22,83]. The earliest theoretical treatment of the effect of multiple infections on the evolution of virulence assumed that pathogens compete within the host rstb.royalsocietypublishing.org Phil.…”