title: Gene expression in the brain of a migratory songbird during breeding and migration.
abstract: BACKGROUND
  We still have limited knowledge about the underlying genetic mechanisms that enable migrating species of birds to navigate the globe. Here we make an attempt to get insight into the genetic architecture controlling this complex innate behaviour. We contrast the gene expression profiles of two closely related songbird subspecies with divergent migratory phenotypes. In addition to comparing differences in migratory strategy we include a temporal component and contrast patterns between breeding adults and autumn migrating juvenile birds of both subspecies. The two willow warbler subspecies, Phylloscopus trochilus trochilus and P. t. acredula, are remarkably similar both in phenotype and genotype and have a narrow contact zone in central Scandinavia. Here we used a microarray gene chip representing 23,136 expressed sequence tags (ESTs) from the zebra finch Taeniopygia guttata to identify mRNA level differences in willow warbler brain tissue in relation to subspecies and season.
  
  
  RESULTS
  Out of the 22,109 EST probe sets that remained after filtering poorly binding probes, we found 11,898 (51.8 %) probe sets that could be reliably and uniquely matched to a total of 6,758 orthologous zebra finch genes. The two subspecies showed very similar levels of gene expression with less than 0.1 % of the probe sets being significantly differentially expressed. In contrast, 3,045 (13.8 %) probe sets were found to be differently regulated between samples collected from breeding adults and autumn migrating juvenile birds. The genes found to be differentially expressed between seasons appeared to be enriched for functional roles in neuronal firing and neuronal synapse formation.
  
  
  CONCLUSIONS
  Our results show that only few genes are differentially expressed between the subspecies. This suggests that the different migration strategies of the subspecies might be governed by few genes, or that the expression patterns of those genes are time-structured or tissue-specific in ways, which our approach fails to uncover. Our findings will be useful in the planning of new experiments designed to unravel the genes involved in the migratory program of birds.
authors.affiliation: Karolinska Institute, Department of Laboratory Medicine, Clinical Research Center, Karolinska University Hospital, SE-14186 Huddinge, Sweden ; School of Natural Sciences, Technology and Environmental Studies, Södertörn University, SE-141 89 Huddinge, Sweden.
authors.forename: John
authors.initials: J
authors.lastname: Boss
authors.affiliation: Department of Biology, Molecular Ecology and Evolution Laboratory, Lund University, Ecology Building, SE-22362 Lund, Sweden ; Max Planck Institute for Evolutionary Biology, AG Behavioural Genomics, August-Thienemann-Straße 2, 24306 Plön, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Liedvogel
authors.affiliation: Department of Biology, Molecular Ecology and Evolution Laboratory, Lund University, Ecology Building, SE-22362 Lund, Sweden.
authors.forename: Max
authors.initials: M
authors.lastname: Lundberg
authors.affiliation: Centre of Environmental and Climate Research, Lund University, Ecology Building, SE-223 62 Lund, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Olsson
authors.affiliation: Department of Biology, Molecular Ecology and Evolution Laboratory, Lund University, Ecology Building, SE-22362 Lund, Sweden.
authors.forename: Nils
authors.initials: N
authors.lastname: Reischke
authors.affiliation: Department of Biology, Molecular Ecology and Evolution Laboratory, Lund University, Ecology Building, SE-22362 Lund, Sweden.
authors.forename: Sara
authors.initials: S
authors.lastname: Naurin
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, SE-22362 Lund, Sweden.
authors.forename: Susanne
authors.initials: S
authors.lastname: Åkesson
authors.affiliation: Department of Biology, Molecular Ecology and Evolution Laboratory, Lund University, Ecology Building, SE-22362 Lund, Sweden.
authors.forename: Dennis
authors.initials: D
authors.lastname: Hasselquist
authors.affiliation: Karolinska Institute, Department of Laboratory Medicine, Clinical Research Center, Karolinska University Hospital, SE-14186 Huddinge, Sweden.
authors.forename: Anthony
authors.initials: A
authors.lastname: Wright
authors.affiliation: Karolinska Institute, Department of Laboratory Medicine, Clinical Research Center, Karolinska University Hospital, SE-14186 Huddinge, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Grahn
authors.affiliation: Department of Biology, Molecular Ecology and Evolution Laboratory, Lund University, Ecology Building, SE-22362 Lund, Sweden.
authors.forename: Staffan
authors.initials: S
authors.lastname: Bensch
keywords: Behavior; Birds; Calcium transport; Gene expression; Microarray; Migration; Phylloscopus trochilus; Synapse