Abstract
miRNAs play important role in the various physiological and evolutionary processes, however, there is no data allowing comparison of evolutionary differences between various ecotypes adapted to different environmental conditions and specimen demonstrating immediate physiological response to the environmental changes. We compared miRNA expression profiles between marine and freshwater stickleback populations of the three-spined stickleback to identify the evolutionary differences. To study the immediate physiological response to foreign environment, we explored the changes induced by transfer of marine sticklebacks into freshwater environment and vice versa. Comparative analysis of changes in miRNA expression suggested that they are driven by three independent factors: (1) non-specific changes in miRNA expression under different environmental conditions; (2) specific response to freshwater conditions in the marine stickleback ecotype; (3) specific response to extreme osmotic conditions for both marine and freshwater ecotypes during the contact with non-native environment. Gene Ontology enrichment analysis of differential expressed miRNA targets supports our current hypothesis.