Animal migration is one of the great spectacles of nature that has long intrigued curious scientists. Migrants benefit from temporally changing relative benefits of alternative habitats. Individuals experience selection pressures for adaptation to at least two different environments often under intra- and interspecific competition. Current knowledge on adaptation to a migratory life history is limited to the migratory travel per se. However further research is needed to understand the interaction between migration and adaptation to alternative macrohabitats. Specifically, divergent local adaptation in natal habitats may very well determine niche divergence in a second habitat that is shared between multiple migratory populations. This may also cause non-neutral gene-flow between populations.
Migration of trout (Salmo trutta) between afferent streams and Lake Lucerne presents an ideal study system. Here individual migration can be accurately monitored with replication on an individual and population level. Stream-specific migration patterns are detected by PIT-tag antennas in the mouth of 12 tributaries to the lake. With its integrative approach, the study is significantly contributing to our understanding of the interplay between migration, local adaptation and ecological diversification. We are specifically monitoring out-migration of juvenile trout in spring and return migration of adult lake trout in autumn. Here, we see large within- and between stream variation in migration patterns, which we aim to explain through analyses of individual trait variables and external environmental variables.
We additionally study the interaction of trout with avian predators, by monitoring the abundance of piscivorous birds at the streams and detecting individual predation events through tracking of PIT-tags in the streams and underneath heron colonies. Lastly, we are studying migration patterns and fitness of hatchery-raised trout, which are stocked by cantonal authorities and fishing organizations to improve lake trout harvest in the lake.