LAUSR

Genetic diversity and divergence patterns of smallmouth bass Micropterus dolomieu spawning groups are analysed across its northern native range with mtDNA cytochrome b gene sequences and eight unlinked nuclear DNA microsatellite loci. Results reveal high levels of genetic variability and significant differences in allelic representation among populations (mtDNA: mean ± s.e., HD = 0·50 ± 0·06, mean ± s.e., θST = 0·41 ± 0·02 and microsatellites: mean ± s.e. HO = 0·46 ± 0·03, mean ± s.e. θST = 0·25 ± 0·01). The distributions of 28 variant mtDNA haplotypes, which differ by an average of 3·94 nucleotides (range = 1-8), denote divergent representation among geographic areas. Microsatellite data support nine primary population groups, whose high self-assignment probabilities likewise display marked divergence. Genetic patterns demonstrate: (1) high genetic diversity in both genomes, (2) significant divergence among populations, probably resulting from natal site homing and low lifetime migration, (3) support for three post-glacial refugia that variously contributed to the current northern populations, which remain evident today despite waterway connectivity and (4) a weak yet significant genetic isolation by geographic distance pattern, indicating that other processes affect the differences among populations, such as territoriality and site fidelity.