Endosymbiotic ratchet accelerates divergence after organelle origin

We hypothesize that as one of the most consequential events in evolution, primary endosymbiosis accelerates lineage divergence, a process we refer to as the endosymbiotic ratchet. Our proposal is supported by recent work on the photosynthetic amoeba, Paulinella, that underwent primary plastid endosymbiosis about 124 Mya. This amoeba model allows us to explore the early impacts of photosynthetic organelle (plastid) origin on the host lineage. The current data point to a central role for effective population size (Ne) in accelerating divergence post‐endosymbiosis due to limits to dispersal and reproductive isolation that reduce Ne, leading to local adaptation. We posit that isolated populations exploit different strategies and behaviors and assort themselves in non‐overlapping niches to minimize competition during the early, rapid evolutionary phase of organelle integration. The endosymbiotic ratchet provides a general framework for interpreting post‐endosymbiosis lineage evolution that is driven by disruptive selection and demographic and population shifts. Also see the video here: https://youtu.be/gYXrFM6Zz6Q Primary endosymbiosis gave rise to mitochondria and plastids. The proximate impacts of organelle origin on lineage evolution have not been addressed at the population level. Using data from the photosynthetic amoeba Paulinella, we hypothesize that primary endosymbiosis accelerates lineage divergence, a process we refer to as the endosymbiotic ratchet.