I'm not sure about S. Fimicola but I do know the answer to the first bit.
During Meiosis some parts of chromosomes are swapped so that by the end of the final stage, 4 new completely different cells are formed. Those small swapped chromosome pieces are what make siblings look similar but different and therefore populations different. We all have noses eyes and ears but those meiosis changes give the diffrence in a population of blue or brown or green eyes.
Hope I was helpful!
