Final answer:
Ellen Decaestecker predicts that present-day hosts are less susceptible to past or future parasites due to the Red Queen effect, which describes how hosts and parasites constantly co-evolve, leading hosts to be best adapted to their contemporary parasites.
Step-by-step explanation:
Ellen Decaestecker tested the Red Queen effect to explore the evolutionary arms race between hosts and their parasites. The Red Queen hypothesis, named after a concept from Lewis Carroll's 'Through the Looking-Glass', suggests that organisms must constantly adapt and evolve not just to gain an advantage, but to maintain their current fitness in relation to others in a constantly changing environment.
The prediction that present-day hosts would be less susceptible to parasites from the past or future than to contemporary parasite strains is based on the idea that host and parasite populations are engaged in a co-evolutionary race. Genetic variations emerging through sexual reproduction provide survival advantages against parasites. Since each population continuously adapts to the other, a host will most likely be best adapted to its current, co-evolving parasites, thus present-day hosts might struggle more when facing parasites from different times, which have a different set of adaptations or have yet to develop certain traits.
The lack of strong support for the hypothesis that parasites demonstrate genetic bottlenecks or lower genetic diversity ratios compared to their hosts, as Ellen Decaestecker's research indicates, leads to the conclusion that more comprehensive studies are needed to fully understand the co-evolutionary dynamics of host-parasite relationships and the Red Queen effect.