Differences in transcription regulation of diurnal metabolic support to physiologically contrasting seasonal life-history states in migratory songbirds

We hypothesized that there were diurnal differences in metabolism, with major transcriptional changes occurring early during the day and/or night between migratory and non-migratory states of avian migrants. Present study investigated this in captive Black-headed Buntings (Emberiza melanocephala) exhibiting long-day stimulated vernal migratory and post-breeding non-migratory states, by using RNA-Seq and qPCR assays of liver samples collected at 1 h into day (hour 1) and 1 h into night (hour 17) of the 16-h photoperiod (16L:8D). There were differentially expressed genes (DEGs) both within (day vs. night) and between (vernal migratory vs. non-migratory) states. Within the state, 358 and 52 DEGs were identified in migratory and non-migratory states, respectively. In the migratory state, genes associated with oxidative phosphorylation (sdh) had higher expression, and genes associated with fat metabolism (acaca and elovl6) and ABC transporters (abcg5, abcg8) had lower expression at night, compared to the daytime. In the non-migratory state, among genes associated with fat metabolism and gluconeogenesis, ppara and hmgcl had higher while aacs had lower expression at night. Between states, 35 and 180 DEGs were identified in day and night, respectively, with highly expressed genes associated with fat metabolism (acsbg2, cetp) found in migratory, and those associated with cell death (casp7), gluconeogenesis (stat3) and circadian rhythm pathway (cry1) in the non-migratory state. These results demonstrate differentially activated hepatic molecular pathways during photostimulated vernal migratory and post-breeding non-migratory states of buntings and provide molecular insights into differential metabolic support to physiologically contrasting seasonal life-history states in migratory songbirds.