Transcriptome signatures in the brain of a migratory songbird.

Most of the birds's adaptations for migration have a neuroendocrine origin, triggered by changes in photoperiod and the patterns of Earth's magnetic field. Migration phenomenology has been well described in the past decades, yet the genetic structure behind it remains terra incognita. We used RNA-Seq data to investigate which biological functions are linked with the seasonal brain adaptations of a long-distance trans-continental migratory passerine, the Northern Wheatear (Oenanthe oenanthe). We sequenced the wheatear's transcriptomes at three different stages: lean birds, a characteristic phenotype before the onset of migration, during fattening, and at their maximal migratory body mass. We identified a total of 15,357 genes in the brain of wheatears, of which 84 were differentially expressed. These were mostly related to nervous tissue development, angiogenesis, ATP production, innate immune response, and antioxidant protection, as well as GABA and dopamine signalling. The expression pattern of differentially expressed genes is correlated with typical phenotypic changes before migration, such as hyperphagia, migratory restlessness, and a potential increment in the visual and spatial memory capacities. Our work points out, for future studies, biological functions found to be involved in the development of the migratory phenotype -a unique model to study the core of neural, energetic and muscular adaptations for endurance exercise. Comparison of wheatears' transcriptomic data with two other studies with similar goals shows no correlation among the trends in the gene expression. It highlights the complexity and diversity of adaptations for long-distance migration in birds.