Acute exposure to oil induces age and species-specific transcriptional responses in embryo-larval estuarine fish

Because oil spills frequently occur in coastal regions that serve as spawning habitat, characterizing the effects of oil in estuarine fish carries both economic and environmental importance. There is a breadth of research investigating the effects of crude oil on fish, however few studies have addressed how transcriptional responses to oil change throughout development or how these responses might be conserved across taxa. To investigate these effects, we performed RNA-seq and pathway analysis following oil exposure 1) in a single estuarine species (Cyprinodon variegatus) at three developmental time points (embryos, yolk-sack larvae, free-feeding larvae), and 2) in two ecologically similar species (C. variegatus and Fundulus grandis), immediately post-hatch (yolk-sack stage). Our results indicate that C. variegatus embryos mount a diminished transcriptional response to oil compared to later stages, and that few transcriptional responses are conserved throughout development. Pathway analysis of larval C. variegatus revealed dysregulation of similar biological processes at later larval stages, including alteration of cholesterol biosynthesis pathways, cardiac development processes, and immune functions. Our cross-species comparison showed that F. grandis exhibited a reduced transcriptional response compared to C. variegatus. Pathway analysis revealed that the two species shared similar immune and cardiac responses, however pathways related to cholesterol biosynthesis exhibited a divergent response as they were activated in C. variegatus but inhibited in F. grandis. Our results suggest that examination of larval stages may provide a more sensitive estimate of oil-impacts than examination of embryos, and challenge assumptions that ecologically comparable species respond to oil similarly.