Alternative life histories in Brown Trout
Brown trout can show dramatic variation in life-history tactics, with some individuals undertaking impressive migrations to larger rivers, lakes, or the sea, before returning to spawn in freshwater, while others remain in freshwater for their entire life-cycle, typically maturing at smaller sizes than ther migratory counterparts. Despite the cultural, economic, and ecological importance of these facultative migratory tactics, the mechanisms that generate this phenotypic variation in brown trout are unresolved.
As part of my PhD research, I aimed to explore the evolutionary and environmetal drivers of alternative migratory tactics in brown trout through a long-term tank-rearing experiment. Offspring from several wild populations that varied in migration tendency (some sea-migratory, termed "anadromous"), some freshwater resident (termed "resident") were reared under different environmental treatments (high or low food, warm or cool temperatures) for ~ two years, at which point we measured migratory phenotypes. This common garden experiment allowed us to explore the interplay between population-background (i.e., ultimate factors) and environmental conditions (i.e., proximate factors) in determing facultative migration. We found that environmental warming tended to reduce anadromy (sea-migration), but reduced food availability increased the frequency of migratory tactics, even in a freshwater resident population that had no recent history of sea-migration.
Read more about this research in the published papers, available here and here.