We assessed genetic variation, using microsatellite markers, in 14 populations of northern pike (Esox lucius) in the North Central United States and in six populations from Quebec, Alaska, Siberia, and Finland. Eight of 13 loci examined were polymorphic in at least one population with an average heterozygosity at all loci and across all populations of 0.14. The R st and F st values indicated differentiation among populations (R st = 0.61, F st = 0.42). Although microsatellite variation found in northern pike was much lower than that found in sympatric and other fish species, the polymorphisms differentiated populations of greater geographical proximity than was possible in prior studies using allozymes and mitochondrial DNA. We generated UPGMA-clustering phenograms based on five genetic distance measures with 2000 bootstrap replicates per measure. All measures yielded highly repeatable population structure between continents (supporting values = 92.4-100%) and within Finland (42.3-98%). Four measures differentiated the Alaskan population and Young Lake (Great Lakes drainage) from other North American populations (56.6-87.7%). Relationships among other North Central United States populations were unclear, as indicated by low supporting values. Results support the hypotheses of one refugium in the North Central United States and more than one refugium in Europe during the last glaciation.Résumé : Nous avons évalué, au moyen de marqueurs microsatellites, la variation génétique dans 14 populations de grand brochet du centre-nord des États-Unis et dans six populations du Québec, de l'Alaska, de la Sibérie et de la Finlande. Huit des 13 loci examinés étaient polymorphes dans au moins une population, et l'hétérozygotie moyenne pour l'ensemble des loci de toutes les populations était de 0,14. Les valeurs de R st et F st indiquaient une différenciation parmi les populations (R st = 0,61, F st = 0,42). Alors que la variation des microsatellites observée chez le grand brochet était de beaucoup inférieure à celle observée chez des espèces sympatriques et chez d'autres espèces, notre examen des polymorphismes a permis de différencier des populations plus rapprochées géographiquement que celles différenciées dans des études antérieures utilisant des allozymes et l'ADN mitochondrial. Nous avons produit des phénogrammes par groupement UPGMA à partir de cinq mesures de la distance génétique, avec 2 000 réplicats bootstrap par mesure. Toutes les mesures ont donné une structure de population très constante entre continents (valeurs du bootstrap = 92,4-100%) et à l'intérieur de la Finlande (42,3-98%). Quatre mesures ont différencié les populations de l'Alaska et du lac Young (bassin des Grands Lacs) des autres populations nord-américaines (56,6-87,7%). Les relations entre les autres populations du centre-nord des États-Unis n'étaient pas claires, comme l'indiquent les basses valeurs du bootstrap. Nos résultats laissent croire qu'il y a eu un seul refuge dans le centre-nord des États-Unis et plus d'un refuge en Europe durant la derni...

We supplemented physical‐tagging data with genetic data to provide evidence for spawning‐site and natal‐site fidelity by two spawning populations of northern pike Esox lucius in Kabetogama Lake, Minnesota. A mark–recapture study supported previous reports that individual northern pike and other esocids tend to return to the spawning grounds that they used in previous years. Of 1,900 northern pike marked at two spawning sites in the first year of the study, 23% were recaptured on spawning grounds one to three times over the next 4 years. Of these recaptured fish, only 1.3% and 4.8%, respectively, of those marked at the two spawning sites were recaptured at the other site. Tag returns from anglers showed that the year‐round ranges for fish from the two sites overlapped, so that lack of dispersal could not completely explain the high fidelity to spawning sites. Significant allele frequency differences at five microsatellite DNA loci between the 1983 (P = 0.03) and 1985 (P = 0.002) spawning populations indicated low levels of gene flow between the populations. This reproductive isolation would only be expected if most individuals first spawn at the site of their own birth and subsequently return to that site. We therefore conclude that northern pike in Kabetogama Lake exhibit both natal‐site and spawning‐site fidelity. Management on the basis of discrete spawning populations within lakes may thus be appropriate for a larger number of species and locations than commonly practiced.

No abstract

No abstract