The transcriptomic signature of cyclical parthenogenesis.

Cyclical parthenogenesis, where females can engage in sexual or asexual reproduction depending on environmental conditions, represents a novel reproductive phenotype that emerged during eukaryotic evolution. The fact that environmental conditions can trigger cyclical parthenogens to engage in distinct reproductive modes strongly suggests that gene expression plays a key role in the origin of cyclical parthenogenesis. However, the genetic basis underlying cyclical parthenogenesis remains understudied. In this study we characterize the female transcriptomic signature of sexual vs. asexual reproduction in the cyclically parthenogenetic microcrustacean Daphnia pulex and D. pulicaria. Our analyses of differentially expressed genes, pathway enrichment, and GO term enrichment clearly show that compared to sexual reproduction the asexual reproductive stage is characterized by both the under-regulation of meiosis and cell-cycle genes and the up-regulation of metabolic genes. The consensus set of differentially expressed genes that this study identifies within the meiotic, cell-cycle, and metabolic pathways serve as candidate genes for future studies investigating how the two reproductive cycles in cyclical parthenogenesis are mediated at a molecular level. Furthermore, our analyses identify some cases of divergent expression among gene family members (e.g., doublesex, NOTCH2) associated with asexual or sexual reproductive stage, suggesting potential functional divergence among gene family members.