Immune defence, parasite evasion strategies and their relevance for ‘macroscopic phenomena’ such as virulence

The discussion of host–parasite interactions, and of parasite virulence more specifically, has so far, with a few exceptions, not focused much attention on the accumulating evidence that immune evasion by parasites is not only almost universal but also often linked to pathogenesis, i.e. the appearance of virulence. Now, the immune evasion hypothesis offers a deeper insight into the evolution of virulence than previous hypotheses. Sensitivity analysis for parasite fitness and life-history theory shows promise to generate a more general evolutionary theory of virulence by including a major element, immune evasion to prevent parasite clearance from the host. Also, the study of dose–response relationships and multiple infections should be particularly illuminating to understand the evolution of virulence. Taking into account immune evasion brings immunological processes to the core of understanding the evolution of parasite virulence and for a range of related issues such as dose, host specificity or immunopathology. The aim of this review is to highlight the mechanism underlying immune evasion and to discuss possible consequences for the evolutionary ecology analysis of host–parasite interactions

The ecology and evolution of microbes that manipulate host reproduction

Inherited microorganisms that manipulate the reproduction of their host are a common feature in arthropod biology. Although research initially concentrated on why these manipulations were observed, more recent study has emphasized the profound effects they may have on the ecology and evolution of their host. We review the natural history and evolutionary ecology of inherited reproductive parasites, before examining their impact on host ecology and evolution. We posit that sex-ratio distorting microorganisms sometimes dominate their host's microevolution and reproductive ecology, driving extremely rapid natural selection, altering the molecular evolution landscape, and potentially causing evolution in conserved systems such as sex determination. The evolutionary importance of symbionts inducing cytoplasmic incompatibility lies more in the barriers to gene flow they can produce, which may then contribute to reproductive isolation and speciation. Throughout, we link theory with empirical data, point to areas of ignorance, and identify promising avenues of future research