Proteomic and gene expression differences between post-diapause and subitaneous offspring phenotypes in the cyclic parthenogen Daphnia pulex

In temperate waters, post-diapause and subitaneous offspring in Daphnia vary in life history traits and metabolic rates, and presumably are adapted to the seasonal environments in which they dwell. These offspring types result from different developmental programs of the same genetic background, representing the phenomenon of phenotypic plasticity. We aimed to explore the molecular mechanism of this phenotypic plasticity in Daphnia pulex from an intermittent population by applying a high-throughput proteomic analysis and expression analysis of several genes. The study revealed 176 proteins that were differentially expressed among offspring phenotypes. Post-diapause and subitaneous females clearly differed in their upregulated protein profiles and gene expression levels. There were more upregulated proteins with oxidoreductase and binding activity in post-diapause offspring, whereas more upregulated proteins with transporter and transferase activity were seen in subitaneous offspring. In contrast to subitaneous phenotype, over 1.5-fold more of the proteins that were upregulated in post-diapause phenotype are involved in metabolism and biosynthesis. Expression levels of several selected genes linked to cellular metabolism were also higher in post-diapause females. The greatest difference, 5-fold upregulation in post-diapause compared to subitaneous offspring, was recorded for the target of rapamycin-like (TOR) protein. Expression of ribosomal proteins in this offspring phenotype was also increased. These upregulations suggest that the TOR signaling pathway is involved and may be responsible for the regulation of the developmental program underlying post-diapause and subitaneous offspring phenotypes in Daphnia. Gene regulatory patterns observed in post-diapause and subitaneous offspring were in agreement with the expectations based on previously observed organismal traits of these Daphnia offspring types.