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.
Life histories and ecotype conservation in an adaptive vertebrate: Genetic constitution of piscivorous brown trout covaries with habitat stability
