Phenotypic, Ecological and Genomic Divergence of the Planktivorous and Piscivorous Lake Trout (Salvelinus namaycush) Ecotypes in Quebec, Canada

Planktivorous and piscivorous Lake Trout (Salvelinus namaycush) ecotypes could be associated with divergent selection on morphological traits and underlying genomic regions. Here, we aim to quantifying phenotypic, ecological and genomic divergence between both ecotypes. For 378 lake trout sampled in 13 geographically distinct lakes in Quebec (6 harbouring piscivorous fish, 4 planktivorous, and 3 with both ecotypes), we assessed trophic level using stable isotopes analyses (¹³C & ¹⁵N), growth patterns from otolith structure, body shape, gill raker number, and genomic characteristics using genotyping-by-sequencing. Planktivorous fish had a lower trophic position and a slower growth rate than piscivorous fish, confirming the individuals’ classification in both ecotypes. Planktivorous fish had a more streamlined body shape and significantly more gill rakers, suggesting a phenotypic divergence associated with the capture of distinct types of preys. Individuals were genotyped at more than 5000 single-nucleotide-polymorphisms. Genetic differentiation between populations (F_ST) ranged from 0.05 to 0.22 and each population had up to 70% of the markers fixed, both results illustrating high genetic drift in these isolated populations. Nevertheless, several allelic variants associated to ecotypes have been detected and could reflect a parallel adaptation to foraging tactic.