Altered within- and between-host transmission under coinfection underpin parasite co-occurrence patterns in the wild

Interspecific interactions among parasites in multiple infections

Individual hosts and populations frequently harbour multiple parasite species simultaneously. Despite their commonness, the consequences of interspecific interactions among parasites for determining infection outcomes are still poorly understood. We review and propose several expectations for multiple infections involving different species. We highlight that interspecific interactions affect the outcome of competition within hosts and that heterospecific parasites engage in cotransmission, gene exchange, and reproductive interference. Studies specifically comparing intra- and inter-specific coinfections and knowledge from community ecology may be instrumental to fully understand the consequences of interspecific multiple infections for parasite life history, ecology, and evolution.

Revisiting implementation of multiple natural enemies in pest management

A major goal of biological control is the reduction and/or eradication of pests using various natural enemies, in particular, via deliberate infection of the target species by parasites. To enhance the biological control, a promising strategy seems to implement a multi-enemy assemblage rather than a single control agent. Although a large body of theoretical studies exists on co-infections in epidemiology and ecology, there is still a big gap in modelling outcomes of multi-enemy biological control. Here we theoretically investigate how the efficiency of biological control of a pest depends on the number of natural enemies used. We implement a combination of eco-epidemiological modelling and the Adaptive Dynamics game theory framework. We found that a progressive addition of parasite species increases the evolutionarily stable virulence of each parasite, and thus enhances the mortality of the target pest. However, using multiple enemies may have only a marginal effect on the success of biological control, or can even be counter-productive when the number of enemies is excessive. We found the possibility of evolutionary suicide, where one or several parasite species go extinct over the course of evolution. Finally, we demonstrate an interesting scenario of coexistence of multiple parasites at the edge of extinction.