Genomics of rafting crustaceans reveals adaptation to climate change in tropical oceans.

Rafting dispersal has been proposed as a way for coastal species to track climate-driven niche shifts. However, little information exists on how rafting species disperse and adapt to shifting environmental conditions, particularly ocean currents and salinity. Here, we integrate dispersal simulations, ecological genomics, and salinity stress experiments to investigate rafting dynamics and adaptive shifts in widely distributed crustaceans across the Indo-Australian Archipelago. We develop a quantified model to examine asymmetric gene flow between populations driven by recent seasonal oceanographic shifts. Our climatic and dispersal models suggest that rafting populations must cope with increasing salinity fluctuation caused by rapidly-shifting oceanic connectivity patterns. Our genomic data provide evidence for recent selective sweeps at osmoregulatory loci, and key duplications at glycoside hydrolase gene families. Our experimental data reveal plastic expression of osmoregulatory genes required for survival during long-distance rafting voyages. These synergies between rafting dispersal and genomic change highlight the potential for rafting species to adapt to rapidly shifting oceanographic conditions.