The genomic and physiological basis of the timing of life history transition in Atlantic salmon

The migration of young Atlantic salmon from the river to the sea involves complex behavioural and physiological changes that are precisely timed in the spring. An interesting aspect is how the adult fish is able to smell its way back to the river. In this project we want to look into the underlying molecular events in the neuroendocrinal and olfactory system, driving the seasonal changes.

In migratory Atlantic salmon, the process whereby young fish born in freshwater streams (parr) become migratory "smolts" and go to sea represents a crucial life-history transition, involving complex behavioural and physiological changes. Most mysterious amongst these is the acquisition of an olfactory "imprint" of the natal stream, prior to smolt migration, upon which return as adults later depends. Similarly the neural and neuroendocrine events governing the precise spring timing of the parr-smolt transition (PST) are also very poorly understood. Hence practical definition of the smolt phenotype is largely based on behaviour or unreliable gross traits such as "silverness", manifest long after the process has been initiated. Molecular, physiological and genetic understanding of these processes is potentially of major value for management of wild and farmed Atlantic populations.

We are taking a multi-pronged approach to address this problem, capitalising on a unique combination of expertises and resources. Using parr reared in semi-natural conditions and in dedicated photoperiod / temperature controlled aquaculture facilities, we are (a) assessing the expression patterns of key elements of the neuroendocrine system recently shown to play a key role in driving seasonal changes in physiology in other vertebrate groups, but so far unexplored in fish and (b) using ultra-high throughput sequencing methods to generate transcriptome-wide profiles of gene expression in the hypothalamus/pituitary and the olfactory bulbs during the PST.

Together these approaches will yield a candidate gene list for upstream regulators of key neural aspects of PST, and begin to address the question of extent to which changes in the neuroendocrine system drive or parallel changes in the olfactory bulbs. In further experiments, taking advantage of access to a range of Norwegian and Scottish river systems, the expression of these genes will be assessed during PST in wild caught fish from high- and low-land streams, allowing us to both to define the molecular events (in both the neuroendocrine and olfactory systems) through which differential timing of migratory behaviour and physiology develops. Finally, using genomic DNA samples taken from these same wild fish, we are developing a high resolution genetic map within which we will seek single nucleotide polymorphisms associated with differentially expressed candidate genes in high versus lowland fish. Collectively these studies will greatly advance understanding of the neurobiology of PST.

Contacts: Prof. David Hazlerigg (project leader), Prof. Even Jørgensen, both UiT/BFE/AMB, Dr Sam Martin, Aberdeen, Scotland, Dr Lars Ebbesson, Bergen.

Funding: Biotechnology and Biological Sciences Research Council, UK.