OOS 10-2
Genomic responses to variable environments across physiological and evolutionary timescales in killifish
Physiological plasticity enables organisms to persist and thrive in variable environments, and this flexibility may facilitate rapid and opportunistic invasion of new or suddenly available niches. Environmental salinity strongly limits distributions of aquatic organisms, and regulation of water and osmolytes is carefully defended in most species. Euryhalinity is a type of physiological plasticity that enables success in osmotically-dynamic environments, and is likely important for enabling diversification across osmotic boundaries. Estuarine killifish (Fundulus species) exhibit extreme euryhalinity that is exceptional among fishes. Diversification across osmotic boundaries is particularly labile within Fundulus: populations and species have repeatedly diversified across osmotic boundaries, enabled by both expansion and loss (assimilation) of physiological plasticity at the freshwater (FW) and saline ends of the osmotic continuum. We present the Fundulus comparative system for studying the functional genomic mechanisms that enable extreme physiological plasticity, with particular focus on identifying the mechanisms that evolve to enable or limit adaptation and diversification across different osmotic niches.
Results/Conclusions
We find that the mechanisms that underlie rapid acclimation to salinity extremes include tight junction regulation and oxidative energy metabolism. The mechanisms that underlie divergence in osmotic plasticity include cell volume regulation, osmolyte synthesis, and cell stabilization pathways, and the genes that facilitate these evolved responses are canalized in their expression and display reduced trans-regulatory complexity. We find that the genomic and physiological mechanisms that are associated with adaptive fine-tuning within species also contribute to macroevolutionary divergence as species diversify across osmotic niches.