This talk is divided into two distinct parts, both concerned with ancestral processes in multitype populations, but addressing different questions and using different modeling approaches.

The first part considers critical multitype branching processes conditioned on non-extinction. We study their long-term behaviour both forward in time and along ancestral lineages. We obtain a functional limit theorem for the forward process and investigate the type distribution of distant ancestors and the type process along ancestral lines.

The main part of the talk considers a structured population with d colonies, where individuals migrate between colonies at a rate proportional to a pa- rameter K, and ancestral lineages within the same colony can coalescence pairwisely. We study the ancestral process of a sample of N_K individuals as K → ∞. The state of the process is encoded by a d-dimensional vector of empirical measures, recording both the current colony of each ancestral lineage and the initial locations of its sampled descendants. We distinguish a critical-sampling regime, N_K ∼ K, from a large-sample regime, N_K ≫ K. After suitable rescaling, the empirical-measure-valued process converges to a d-dimensional coagulation equation. In the critical regime, the limiting equa- tion admits a representation in terms of a multitype branching process, while in the large-sample regime it is described by the entrance law of a multitype Feller diffusion.