The evolution of broad seascape utility and ontogenetic life history variation in lutjanids.

While ontogenetic habitat shifts are a widely appreciated phenomenon across fishes, the macroevolutionary implications of habitat shifts and subsequent ecological opportunity have mainly focused on adult organisms, largely overlooking juvenile life history diversification. The snappers and fusiliers (Lutjanidae) represent a successful tropical teleost radiation exhibiting complex ontogenetic shifts and use of diverse nursery and adult habitats across the marine-freshwater interface. Lutjanids collectively occupy a broad range of environments within the seascape mosaic, including freshwater rivers, estuaries, reefs, and deep offshore slopes. Using an extensive phylogenomic dataset of ~ 110 species, we test models of juvenile and adult habitat evolution across seascape gradients. Evolutionary model fitting and ancestral state reconstructions, conducted independently for juvenile nurseries and adult habitats, both support an ordered, stepwise pattern of habitat transitions, with low-salinity associations evolving only via intermediate coastal habitats. This 'stepping stone' model of marine-freshwater macroevolution saw adoption of low salinity habitats preceded by adaptation to intermediate brackish habitats, rather than random jumps between widely separated seascape components. While our results highlight that ontogenetic shifts have been central to lutjanid diversification, more consistent and transferable research frameworks are required to clarify the ecological and evolutionary implications of lutjanid life history diversity.