Lack of Resilience? Evolutionary Hypotheses for an Apparently Maladaptive Life History in a Depleted Lineage of Atlantic Salmon

There is mounting evidence that genetic variability in reaction norms (e.g. discontinuous, bivariate) underlies much of the life history diversity within salmonids (e.g. alternative phenotypes related to migration, age-at-maturity). Given this, to fully understand ‘resilience’ at the population level, one must consider the potential for evolutionary constraints on life history plasticity, and the costs of such plasticity, to affect individual fitness and ultimately population persistence. To stimulate further discussion on these topics, I combine a review of plasticity theory and empirical research conducted on a depleted lineage of Atlantic salmon from eastern Canada to formulate several hypotheses for why this lineage continues to express an apparently maladaptive life history in the face of environmental change. This lineage is particularly intriguing to consider from the standpoint of understanding resilience or the lack thereof, because either it, or geographically-proximate lineages with which it may exchange gene flow, have life history attributes that arguably should favour resilience (e.g. high degree of iteroparity, multiple ages-at-maturity, both long- and short-distance migration ecotypes).