Receding ice drove parallel expansions in Southern Ocean penguins

Significance We analyze population genomic datasets across 3 penguin genera to test for demographic shifts driven by historical climate events. Numerous species inhabiting coastlines affected by heavy sea ice during the Last Glacial Maximum show genomic signatures of near-simultaneous population expansions associated with postglacial warming, contrasting with stable or declining demographic histories inferred for species occupying consistently ice free habitats. Shallow population genomic structure detected within species distributed across the vast Southern Ocean likely provides further evidence for recent demographic shifts and recent genetic exchange among populations. Our results demonstrate dramatic, ecosystem-wide responses to climate change and highlight the potential for future biological shifts in the Southern Ocean as global warming continues.