The ability to identify candidate biological processes associated
with a behavioural trait may also allow researchers to assess adaptive
trade-offs associated with different phenotypes. For instance,
males of the Atlantic salmon, Salmo salar, exist in two morphs that
differ in life-history strategy. One morph matures at an early age and
small size and adopts a sneaking strategy. The other morph matures
later and at a larger size. These two alternative strategies represent a
classic life-history trade-off of reproduction for growth. Aubin-
Horth et al. (2005) showed that these adaptive trade-offs are reflected
at the level of brain gene expression. These authors
compared brain gene expression signatures of immature males
(which would have presumably continued to grow and reproduce
later in life had they not been sacrificed for the analysis) to sneaker
males, which matured and began to reproduce at a smaller size.
Immature males showed upregulation of genes involved in growth
and energy storage relative to sneakers, while the sneakers showed
upregulation of genes related to reproduction and mate acquisition,
including hormone production and neural plasticity.