Endogenous control of fuelling in a migratory songbird

Transcriptome signatures of the lipid metabolism in the liver and partial characterisation of the plasma phospholipidome of a long-distance migratory bird, the Northern Wheatear (Oenanthe oenanthe)

The Northern Wheatear (Oenanthe oenanthe) is a long-distance migratory bird that has become a model species for the study of the phenomenology and molecular aspects of avian migration. Here, we analysed transcriptomic data related to the lipid metabolism in the liver of wheatears during the development and termination of the migratory fattening. In parallel, we partially characterised their plasma phospholipidome. Based on transcriptomic data, we found evidence of a fine-scale regulation of the lipogenesis/lipolysis rate and over the fatty acid composition during the migratory season. Furthermore, our results suggest a regulated production of oxylipins, signaling lipids derivatives of polyunsaturated fatty acids (PUFAs). Regarding the plasma phospholipid profiling, different lipid species showed a significant differential abundance among migratory stages: lysophosphatidylcholine (LPC 18:0), sphingomyelin (SM 34:1;O2) and phosphatidylinositols (PI 36:4 and PI 38:4). The liver transcriptomic and plasma lipidomic data agree well, showing the relevance of the liver in controlling the lipid metabolism in relation to migration. We hope that the results discussed in this publication would open the door for future functional genetic and metabolic studies regarding avian migration.

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.

De novo annotation of the transcriptome of the Northern Wheatear (Oenanthe oenanthe)

We have sequenced a partial transcriptome of the Northern Wheatear (Oenanthe oenanthe), a species with one of the longest migrations on Earth. The transcriptome was constructed de novo using RNA-Seq sequence data from the pooled mRNA of six different tissues: brain, muscle, intestine, liver, adipose tissue and skin. The samples came from nine captive-bred wheatears collected at three different stages of the endogenous autumn migratory period: (1) lean birds prior the onset of migration, (2) during the fattening stage and (3) individuals at their migratory body mass plateau, when they have almost doubled their lean body mass. The sample structure used to build up the transcriptome of the Northern Wheatears concerning tissue composition and time guarantees the future survey of the regulatory genes involved in the development of the migratory phenotype. Through the pre-migratory period, birds accomplish outstanding physical and behavioural changes that involve all organ systems. Nevertheless, the molecular mechanisms through which birds synchronize and control hyperphagia, fattening, restlessness increase, immunity boosting and tuning the muscles for such endurance flight are still largely unknown. The use of RNA-Seq has emerged as a powerful tool to analyse complex traits on a broad scale, and we believe it can help to characterize the migratory phenotype of wheatears at an unprecedented level. The primary challenge to conduct quantitative transcriptomic studies in non-model species is the availability of a reference transcriptome, which we have constructed and described in this paper. The cDNA was sequenced by pyrosequencing using the Genome Sequencer Roche GS FLX System; with single paired-end reads of about 400 bp. We estimate the total number of genes at 15,640, of which  67% could be annotated using Turkey and Zebra Finch genomes, or protein sequence information from SwissProt and NCBI databases. With our study, we have made a first step towards understanding the migratory phenotype regarding gene expression of a species that has become a model to study birds long-distance migrations.