Theory and examples of reciprocal influence between hosts and pathogens, from short-term to long term interactions: Coevolution, cospeciation and pathogen speciation following host shifts

A. Tellier, D. M. de Vienne, T. Giraud, M. E. Hood, G. Refrégier

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

7 Scopus citations


Hosts and their obligate pathogens exhibit intimate physiological interactions. How such interactions impact upon evolution of each partner varies depending on the timescale of interest. This chapter reviews theoretical advances and available data on host and pathogen evolution with regard to both short term (coevolution) and long term (cospeciation and speciation following host shifts) dynamics, and then discusses the possible links between processes acting at these two time scales.The genetic basis of the physiological interactions between host and pathogens has been identified in some systems, showing that as few as a single locus in each species can determine the success or failure of infection. Such simple interacting mechanism of infection and disease resistance has triggered theoretical developments on how allele frequencies in one species should evolve in response to the allele frequencies in the other species. This reciprocal influence in the short term is referred to as "coevolution" (in its narrow sense). The concept states that each species, host or pathogen, acts as a selective pressure on its partner in a frequency-dependent manner. Two simple outcomes for host and pathogen allele frequencies have been suggested. The "arms race" model describes frequency dynamics where advantageous new variants go to fixation. The "trench warfare" model depicts allele frequencies oscillating dynamically in time, several host and pathogen alleles being maintained over the long term. In this chapter, we detail the theoretical bases underlying arms race and trench warfare dynamics, and review empirical data supporting the different types of models. We also discuss recent theoretical advances that an attempt to analyze more complex coevolutionary scenarios and integrate environmental effects into these simple models. Another field of research on hostpathogen evolution is devoted to elucidating whether the partners in such associations speciate in parallel, i.e. diversify by cospeciation, or by other processes such as host shifts. We outline the approaches to compare the divergence between two species or loci and present insight gained on the long-term evolution of host-parasite associations, whether pathogenic or not. Speciation in parasites seems to regularly occur without tracking host speciation, for instance after host shifts. We finally examine the relationship between coevolution and pathogen diversification. We summarize theoretical and experimental works showing that coevolution can foster pathogen specialization, but that more frequently these events are associated with host shifts and subsequent speciation, than with cospeciation. As a conclusion, in contrast to previous assumptions, we now have substantial evidences that coevolutionary dynamics of hosts and pathogens do not favor long-term cospeciation patterns, and that the idea that cospeciation prevails among host-parasite associations is invalid.

Original languageEnglish
Title of host publicationHost-Pathogen Interactions
Subtitle of host publicationGenetics, Immunology and Physiology
PublisherNova Science Publishers, Inc.
Number of pages42
ISBN (Print)9781608762866
StatePublished - 2010
Externally publishedYes


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