As many other salmonids, brown trout (Salmo trutta) displays diverse life history types related to the migratory behavior. Typically, after two to three years in a natal river, brown trout adopts one of two main life-history strategies. It either stays in the river for its entire life and therefore becomes a so-called resident trout or undergoes a physiological and morphological transformation called smoltification and migrates to a larger river or a lake (potamodromous), or to the sea (anadromous). Until now, it has not been conclusively resolved if the migration decision has any genetic underpinning.
Intraspecific genetic variation associated with different life history strategies in brown trout has not been extensively studied using high throughput sequencing. To investigate the genetic causes and consequences of the life-history dichotomy in brown trout, we used ddRAD-sequencing. We compared specific pairs of resident and migratory populations of brown trout to identify potential candidate genes associated with migratory behavior using a combination of genome scans. Understanding the mechanisms behind migratory behavior could be of great help in terms of management and conservation but could also shed light into the general evolution of the migration patterns in salmonids.
Results/Conclusions
Two sets of ca. 5000 SNPs were obtained through sequencing and after subsequent filtering. Multiple genome scan approaches detected seven outlier SNPs in the first data set and one in the second one. Using the published Atlantic salmon genome, we identified putative functions for these SNPs. We found two genes involved in osmoregulation processes, suggesting biological relevance when migrating to the sea (as all brown trout assumedly descent from anadromous brown trout). Three other genes from cadherin, glutamate and zinc-finger -families were identified. These three gene families are also involved in migratory behavior of other salmonids such as rainbow trout (Onchorynchus mykiss) and sockeye salmon (Onchorynchus nerka). Two other outliers were linked to thermal adaptation processes, while the last one, identified in the second watershed, was associated with muscle growth.
For the first time, we revealed candidate genes linked to the life-history dichotomy in brown trout. The identification of gene families that were shared with other migratory salmonids suggests that migrations in salmonids may have a shared evolutionary origin.