The genomic consistency of the loss of anadromy in an Arctic fish (Salvelinus alpinus)

The potentially significant genetic consequences associated with the loss
of migratory capacity of diadromous fishes which have become landlocked in
freshwater are poorly understood. Consistent selective pressures
associated with freshwater residency may drive repeated differentiation
both between allopatric landlocked and anadromous populations and within
landlocked populations (resulting in sympatric morphs). Alternatively, the
strong genetic drift anticipated in isolated landlocked populations could
hinder consistent adaptation, limiting genetic parallelism. Understanding
the degree of genetic parallelism underlying differentiation has
implications for both the predictability of evolution and management
practices. We employed an 87k SNP array to examine the genetic
characteristics of landlocked and anadromous Arctic Charr (Salvelinus
alpinus) populations from five drainages within Labrador, Canada. One gene
was detected as an outlier between sympatric, size-differentiated morphs
in each of two landlocked lakes. While no single locus differentiated all
replicate pairs of landlocked and anadromous populations, several SNPs,
genes, and paralogs, were consistently detected as outliers in at least
70% of these pairwise comparisons. A significant C-score suggested the
amount of shared outlier SNPs across all paired landlocked and anadromous
populations was greater than expected by chance. Our results indicate that
despite their isolation, selection due to the loss of diadromy may drive
consistent genetic responses in landlocked populations.