Coevolutionary changes in antagonistic interacting populations can constantly change the mode, strength and direction of selection through the link between the ecological and evolutionary dynamics (eco-evolutionary dynamics). To explore the role of eco-evolutionary dynamics and their effects on selection over time, we conducted a series of experimental evolution studies using an algal host (Chlorella) and its dsDNA virus. We followed population and evolutionary dynamics of host and virus for ~100 host generations and found continuous reciprocal adaptations of host resistance and virus infectivity, resulting in rapid antagonistic coevolution. The coevolutionary dynamics were initially driven by arms race dynamics with consecutive selective sweeps, but shifted towards trade- off driven dynamics as a result of an evolutionary constraint in the virus and the evolution of a trade- off between host resistance range and growth rate. We further examined evolutionary changes at the genome level, and our results show that the eco-evolutionary feedback dynamics drove genetic divergence when looking at variants due to demographic effects and selective sweeps. All populations evolved, however, duplication in a large genomic region, reflecting the parallelism found at the phenotypic level (resistance). Overall, the entanglement of ecology and evolution has important consequences and might substantially lower the predictability of the mode and tempo of adaptive change.