Final answer:
The rabbit myxoma virus in Australia became less virulent over time due to opportunities for pathogen transmission decreasing, infected rabbits living longer, and more virulent strains replicating less within the host.
Step-by-step explanation:
The rabbit myxoma virus in Australia became less virulent over time due to all of the above - opportunities for pathogen transmission decreased, infected rabbits lived longer, and more virulent strains replicated less within the host.
The initial introduction of the myxoma virus caused devastating mortality in rabbits, but over time, the virus and the rabbits evolved. The virus became more benign, while rabbits evolved to be more resistant to the virus, resulting in decreased mortality in each successive epidemic.