Genetic and Non-Genetic Effects in the Early Divergence of Salmonids

Salmonid exhibit complex life histories ranging from populations displaying multiple saltwater migrations to populations that are freshwater resident or landlocked. Such diversity has been of interest for evolutionary biologists in understanding the maintenance of diversity but in turn it has been a constant challenge for management of populations. Focusing on Arctic charr (Salvelinus alpinus) and Steelhead trout (Oncorhynchus mykiss) we studied the genetic and non-genetic effects of egg size on early life history traits. We assessed short-term effects of egg size on early development, survival, growth and behavior of alevins and juveniles. Additionally, we investigated whether egg size affected growth of yearling fish, their physiology at the time of smolting and their saltwater preference.

We found both short and long-term effects of egg size on life history traits with potential significant effects on early divergence. The same trends were observed in both species but the variation in egg size and in turn the magnitude of the effects differed. We also report a rapid decrease in egg size consecutive to domestication. Egg size may be an important mechanism facilitating the early divergence of salmonids though resource polymorphism. We discuss both the evolutionary and management implications of maternal effects through egg size.