Deme U maintained a population of 3125 until there was a shift 5322.178 generations ago that changed its numbers to 8245, a figure that has remained the same since.
time_units: generations
demes:
  - name: U
    start_time: .inf
    epochs:
      - start_size: 3125
        end_time: 5322.178
      - start_size: 8245
        end_time: 0