| Phenotypic and genetic approaches were combined to examine factors contributing to divergence among sympatric populations of migratory brook charr (Salvelinus fontinalis) inhabiting post-glacial Mistassini Lake (Quebec, Canada). A negative association was observed between the extent of interpopulation differences in migration and the amount of gene flow among populations. Migration timing, spatial habitat use associated with feeding areas, migratory distance, and body morphology related to migratory distance, especially differed between outflow and inflow breeding populations, and these populations exchanged less gene flow than among inflows. Behavioural attributes of populations (sex-biased dispersal, non-random schooling) were also consistent with local adaptations among divergent populations, and that such behaviours modulate interpopulation gene flow. Comparisons of genetic relationships with surrounding drainages indicated that outflow and inflow populations did not originate from a common ancestor. Interactions between the nature of colonization of ancestral populations may have affected the mode of evolution among populations in sympatry. These results illustrate how population phenotypic and genetic differentiation may arise through interactions between historical events and selection. |
