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Alternative migratory tactics in brown trout (Salmo trutta) are underpinned by divergent regulation of metabolic but not neurological genes
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  • Robert Wynne,
  • Louise Archer,
  • Stephen Hutton,
  • Luke Harman,
  • Patrick Gargan,
  • Peter Moran,
  • Eileen Dillane,
  • Jamie Coughlan,
  • Tom Cross,
  • Philip McGinnity,
  • Thomas Colgan,
  • Tom Reed
Robert Wynne
University College Cork
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Louise Archer
University College Cork
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Stephen Hutton
University College Cork
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Luke Harman
University College Cork
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Patrick Gargan
Inland Fisheries Ireland
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Peter Moran
University College Cork
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Eileen Dillane
University College Cork
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Jamie Coughlan
University College Cork
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Tom Cross
University College Cork
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Philip McGinnity
University College Cork
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Thomas Colgan
University College Cork
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Tom Reed
University College Cork
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Abstract

The occurrence of alternative morphs within populations is common but the underlying molecular mechanisms remain poorly understood. Many animals, for example, exhibit facultative migration, where two or more alternative migratory tactics (AMTs) coexist within populations. In certain salmonid species, some individuals remain in natal rivers all their lives, whilst others (in particular, females) migrate to sea for a period of marine growth. Here we performed transcriptional profiling (“RNA-seq”) of the brain and liver of male and female brown trout to understand the genes and processes that differentiate migratory and residency morphs (AMT-associated genes) and how they may differ in expression between the sexes. We found tissue-specific differences with greater number of genes expressed differentially in the liver (n = 867 genes) compared to the brain (n = 10) between the morphs. Genes with increased expression in resident livers were enriched for Gene Ontology terms associated with metabolic processes, highlighting key molecular-genetic pathways underlying the energetic requirements associated with divergent migratory tactics. In contrast, smolt-biased genes were enriched for biological processes such as response to cytokines, suggestive of possible immune function differences between smolts and residents. Finally, we identified evidence of sex-biased gene expression for AMT-associated genes in the liver (n = 18) but not the brain. Collectively, our results provide insights into tissue-specific gene expression underlying the production of alternative life-histories within and between the sexes, and point towards a key role for metabolic processes in the liver in mediating divergent physiological trajectories of migrants versus residents.