A REVIEW OF LOCAL ADAPTATION IN SALMONIDAE, WITH PARTICULAR REFERENCE TO PACIFIC AND ATLANTIC SALMON

Rapid development of aquacultural operations for various salmonids has raised concern that interbreeding between wild salmon and hatchery strays or fish that have escaped from salmon farms may alter "locally adapted" traits of wild populations. Local adaptation is defined as a process whereby natural selection increases the frequency of traits within a population that enhance the survival or reproductive success of individuals expressing them. The study of local adaptation in salmonid populations is important because of: (i) its relevance to evolutionary theory; (ii) its role in promoting genetic divergence between populations and the identification of genetic resources of fish; (iii) its potential role in ecological-genetic population "matching" for population rehabilitation programs or in the identification of unique traits of aquacultural significance; and (iv) its role in understanding the diversity of populations and for establishing baseline data for studies designed to investigate ecological-genetic interaction between wild and cultured salmon. A survey of studies is presented which favours the idea that local adaptation is responsible for much of the genetic variation observed among populations in morphological and meristic, behavioural, developmental, physiological and biochemical. and life history traits. Local adaptation is evident both on a broad geographic scale (between populations separated by hundreds of kilometers) and microgeographically (between populations separated by a few kilometers or less) and even between "seasonal races" inhabiting the same habitats. Manipulative experiments could provide valuable information on the potential for, and consequences of, changes to adaptive character complexes of wild fish from interbreeding with cultured salmon.