War and peace: social interactions in infections

Abstract

One of the most striking facts about parasites and microbial pathogens that has emerged in the fields of social evolution and disease ecology in the past few decades is that these simple organisms have complex social lives, indulging in a variety of cooperative, communicative and coordinated behaviours. These organisms have provided elegant experimental tests of the importance of relatedness, kin discrimination, cooperation and competition, in driving the evolution of social strategies. Here, we briefly review the social behaviours of parasites and microbial pathogens, including their contributions to virulence, and outline how inclusive fitness theory has helped to explain their evolution. We then take a mechanistically inspired ‘bottom-up’ approach, discussing how key aspects of the ways in which parasites and pathogens exploit hosts, namely public goods, mobile elements, phenotypic plasticity, spatial structure and multi-species interactions, contribute to the emergent properties of virulence and transmission. We argue that unravelling the complexities of within-host ecology is interesting in its own right, and also needs to be better incorporated into theoretical evolution studies if social behaviours are to be understood and used to control the spread and severity of infectious diseases.

Challenges in microbial ecology: building predictive understanding of community function and dynamics

“…For example, secretion of ‘public goods' such as toxins, enzymes, metabolic co-factors or signalling molecules can lead to intricate evolutionary dynamics (Leggett et al , 2014). Game theory provides a way to model complex social behaviours in mixed MCs.…”

Variable effects on growth and defense traits for plant ecotypic differentiation and phenotypic plasticity along elevation gradients

“…Based on the theoretical framework shown in Figure (Leggett, Brown, & Reece, ; Schlichting & Pigliucci, ), we expected five alternative scenarios: (a) no ecotypic variation or plasticity: traits remain constant across ecotypes and environments (Figure a). (b) ecotypic differentiation (ecotype effect only) with no plasticity: trait variation remains constant across elevations but different across ecotypes (Figure b).…”

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

“…Nevertheless, it is clear that the complex competitive environment within the host can favour different strategies in different host individuals: the competitive strategy that is successful in one host may depend on the presence of a specific competitor, and may be costly in the next host due to absence of that competitor. One result of this complex selective landscape is that parasites can evolve adaptive plastic responses to deal with the varied competitive environments encountered within hosts [23,24]. Host populations can, however, support many parasite species, and considerable genetic diversity within a given parasite species.…”