Mitochondrial DNA diversity in anadromous rainbow smelt, Osmerus mordax Mitchill: A genetic assessment of the member-vagrant hypothesis

We analyzed mitochondrial DNA genetic variance in anadromous smelt to test whether the ecological processes inferred by the member-vagrant hypothesis to explain spatial patterns of abundance may also have evolutionary consequences for the process of population divergence. Restriction enzyme analysis was performed on 568 adult smelt from 16 sites within the estuary and the Gulf of St. Lawrence (Canada). Hierarchical analysis of heterogeneity in the frequency of 140 mitochondrial DNA genotypes and clustering analysis revealed the existence of four distinct populations among which gene flow has been restricted. This population structure appeared to be organized by the number of suitable habitats for retention of early life-history stages and their probability of diffusion among populations. This suggests that ecological processes inferred by the member-vagrant hypothesis may be a primary factor controlling population genetic diversity in anadromous smelt. Biogeographic events may also have played a major role in shaping smelt population genetic diversity. Our results emphasize the importance of considering the interplay between the life-history characteristics of a species, its genetic diversity, and environmental constraints in a historical perspective to better understand its evolutionary ecology.