SRA

We used populations of alewife (Alosa pseudoharengus) to explore the transcriptional mechanisms that underlie adaptation to fresh water. Ancestrally anadromous alewives have recently formed multiple landlocked populations, which exhibit reduced tolerance of seawater and enhanced tolerance of freshwater. Using RNAseq, we compared transcriptional responses of an anadromous alewife population to two landlocked populations after a two-week challenge in freshwater and seawater. Our results suggest that responses of the gill transcriptome to different salinities have evolved in primarily discordant ways between independent landlocked and anadromous populations. In contrast to the generally discordant pattern, evolved shifts in the transcription of a small suite of well-characterized osmoregulatory genes exhibited a strong degree of parallelism. Our results suggest that changes to the gill’s transcriptional response to salinity facilitates freshwater adaptation.