Fluctuations in cell lineages and population trees

We study universal properties of biological systems described by branching trees. Based on two different samplings of the lineages within a tree, we derive a set a results constraining the growth of the tree, the mean number of divisions along lineages, and the strength of selection. This allows us to quantify the bias between the statistics obtained at the level of the single lineage and the population statistics. These results are interpreted in the frameworks of stochastic thermodynamics and linear response theory, and are universal in that they only depend on the branching structure of the tree but not on the precise dynamics generating it. Although our research is mainly framed in the context of bacterial colonies, it applies to any branching process such as the species/gene trees encountered in evolution.