In this study, Dr. Greischar examined the growth-reproduction tradeoff faced by malaria parasites, which must allocate resources to within-host proliferation as well as the production of specialized life stages for onward transmission. The way parasites balance this tradeoff influences exploitation of host resources---and hence virulence---and the rate of disease spread through host populations. She built a within-host model to examine the conflicting selection pressures and identify the optimal allocation to transmission. She developed novel computational methods to consider a wide range of potential strategies, using splines to describe plastic allocation with few parameters. The model suggested that parasites benefit from delaying transmission stage production, just as macroorganisms can benefit from delayed reproductive effort. Innate immunity and coinfecting parasites imposed strong selection favoring parasites that invest disproportionately in proliferation rather than transmission ("reproductive restraint"), resulting in more rapid and extreme exploitation of host resources. Selection on transmission investment therefore represents one mechanism by which enhanced virulence could be adaptive for parasites. More generally, the approach can accommodate highly complex strategies within richly detailed ecological models, providing a much-needed alternative to analytical methods that could be adapted to diverse organisms.

Learn more about the R. A. Fisher Prize here [1].