Author contributions
JA wrote the first draft of the manuscript, did field work, the experiments, wet lab work and data analyses. PR contributed substantially to data analyses. HG performed RNA-seq library preparation with JA. DW did preliminary analyses of MiSeq transcriptome data that were used to decide on pooling for HiSeq. OSA oversaw the lab work at University of Iceland. SW conceived and designed the study, did field work, helped with the temperature shift experiment, and contributed to data analyses and manuscript writing.