Speaker

Prof. Mercedes Pascual

Abstract

A central question in Ecology concerns the coexistence of a large number of species in ecosystems. Theory on the subject ranges from explanations where differences between species do not matter and stochastic demography prevails, to those where specific ecological interactions are key in determining the emergence of niches. The same question can be asked at a different level of biological organization for the diversity of coexisting strains within a pathogen population. The ecological interaction of interest is here that of strain competition for hosts through cross-protection from specific immune memory. Because specific immunity confers an advantage to rare types and a disadvantage to common ones, it can lead to selection of strains as a function of their frequency. I ask whether such frequency-dependent competition/selection matters to the strain structure and diversity of the hyper-diverse malaria parasite Plasmodium falciparum in high-transmission regions. I also ask whether the resulting strain diversity matters to the resilience of the epidemiological system to transmission-reducing interventions. I end with brief mention of other microbial populations of large diversity, and of other ecological systems to which similar ideas may apply