Adaptations to marine environments and the evolution of slow-paced life histories in endotherms

All organisms face a certain risk of dying before reproducing, putting strong pressure on individuals to reproduce as early as possible. Despite this, some organisms delay maturity, defer reproduction, and age slowly. The evolution of such slow-paced life is classically attributed to allometric effects and reduced extrinsic mortality, but might also result from the invasion of challenging environments requiring adaptations that boost adult survival yet impose substantial energetic and developmental costs. Here, we reveal that the invasion of marine environments by endotherms may have triggered adaptive shifts towards slow life histories, particularly in pelagic lineages. Such life history convergences may have been facilitated by the slow-paced nature of their non-marine ancestors, and were associated with adaptations for enhanced energy acquisition and storage, enabling a long reproductive lifespan at the expense of extended development. Ancestral traits and lifestyle changes might thus have been important in shaping the evolution of slow life histories.