Lively and Dybdahl Studied Parasite Infection Rates in a Population

Lively and Dybdahl studied parasite infection rates in a population of asexual clonal snails. The graph below shows relative infection rates for the four most common clone genotypes and for several rare genotypes (all lumped together) . Based on these data, they hypothesized that parasites adapted to infecting the most common clone genotypes in the population, and thus these genotypes had lower fitness. This is consistent with ________ operating in the population. Further evidence would be provided if ________.

A) genetic drift; heterozygosity declined over time in the population
B) genetic drift; rare clones were lost from the population frequency-dependent selection
C) negative frequency-dependent selection; rare clones became common in the next generation but then declined in frequency in the following generation
D) negative frequency-dependent selection; rare clones became more common until they completely replaced the clones that were originally common