Nested analysis of genetic diversity in northwestern North American char, Dolly Varden (Salvelinus malma) and bull trout (Salvelinus confluentus)

Abstract

Partitioning within-species genetic diversity is fundamental to conservation of the bioheritage, current viability, and evolutionary potential of individual taxa. We conducted a hierarchical analysis of genetic diversity in Dolly Varden (Salvelinus malma) and bull trout (Salvelinus confluentus) involving analysis of hybrid zones between Dolly Varden and bull trout, analysis of phylogenetic structure within species across their native ranges using mitochondrial DNA, and a microsatellite DNA survey of population subdivision of bull trout within single watersheds. Our analyses documented hybridization and some introgression between Dolly Varden and bull trout across a geographically widespread zone of secondary contact between the two species. Both species were subdivided into two major mtDNA lineages, and one lineage in Dolly Varden may have arisen through introgression with bull trout. Bull trout have low levels of microsatellite diversity within populations, but there was substantial interpopulation variation in allele frequencies. Allele frequency distributions suggested that recent, severe bottlenecks occur frequently in some bull trout populations. Our results illustrate partitioning of genetic variation at distinct levels of biological organization (species, phylogeographic lineages, local populations), and we address how such nested variation is fundamental to conservation of biodiversity.Résumé : La compartimentation de la diversité génétique intraspécifique est une opération essentielle pour la conservation de l'héritage biologique, de la viabilité actuelle et du potentiel évolutif de taxons particuliers. Nous avons procédé à une analyse hiérarchique de la diversité génétique de la Dolly Varden (Salvelinus malma) et de l'Omble à tête plate (Salvelinus confluentus) qui comprend une étude des zones d'hybrides entre les deux espèces, une analyse basée sur l'ADN mitochondrial de la structure phylogénétique des espèces sur toute leur répartition géographique d'origine et un inventaire des microsatellites de l'ADN dans les subdivisions de populations de l'Omble à tête plate à l'intérieur de bassins hydrographiques particuliers. Nos analyses révèlent l'existence d'hybridation et d'introgression dans une large zone géographique de contact secondaire entre les deux espèces. Chacune des espèces se divise en deux lignées principales d'après son ADNmt; l'une des lignées de la Dolly Varden est peut-être apparue par introgression avec l'Omble à tête plate. L'Omble à tête plate possède une faible diversité des microsatellites à l'intérieur des populations, mais il y a une importante variation des fréquences d'allèles entre les populations. Les distributions de fréquence des allèles laissent croire que d'importants goulots d'étranglement récents se sont produits à plusieurs reprises dans quelques populations d'Omble à tête plate. Notre étude est un exemple de la compartimentation de la variation génétique à plusieurs niveaux distincts de l'organisation biologique (espèce, lignées phylogénétiques, populations locales); nou...

Effects of coancestry on accuracy of individual assignments to population of origin: examples using Great Lakes lake trout (Salvelinus namaycush)

“…One hundred nanograms of DNA was used for each PCR. We used six microsatellite loci that were originally developed for other salmonid species including brook trout (Salvelinus fontinalis) (Sfo1, Sfo12 and Sfo18; Angers & Bernatchez, 1996), pink salmon (Onchorynchus gorbuscha) (Ogo1a; Olsen, Bentzen & Seeb, 1998), bull trout (Salvelinus confluentus) (Scol19; Taylor et al, 2001), and Atlantic salmon (Salmo salar) (Ssa85; O'Reilly et al, 1996). PCRs were performed in 25 ll volumes using conditions provided by the respective authors.…”

Microsatellite data resolve phylogeographic patterns in European grayling, Thymallus thymallus, Salmonidae

“…Dramatic population size reductions, such as those mediated by the Pleistocene glaciations, may potentially cause decreased variation in populations inhabiting formerly glaciated regions. For instance, glaciations have been argued to contribute to the low intrapopulation diversity observed in another freshwater salmonid, bull trout, Salvelinus confluentus (Taylor et al, 2001). An important consequence of this theory is, that because many northern regions were formerly completely 399 covered with ice (including the whole of northern Europe; Svendsen et al, 1999), the contemporary northern populations should display lower levels of molecular variation than southern populations (reviewed in Bernatchez and Wilson, 1998).…”

Movement patterns, timing of migration and genetic population structure of bull trout (Salvelinus confluentus) in the Morice River Watershed, British Columbia.

“…Hardy-Weinberg equilibrium in other populations of bull trout (see Spruell et al 1999;Neraas and Spmell 2001;Taylor et al 2001), those populations may have been unaffected by the presence of the null allele, even though it may be prevalent in the M orice River population of bull trout. As a result, S col9 was eliminated from the analysis.…”

“…Many studies throughout the geographical range of bull trout indicate low levels of genetic variation within populations and higher levels of variation among populations (Leary et al 1993;Kanda et al 1997;Taylor et al 1999;Kanda and Allendorf 2001;Taylor et al 2001). However, Spruell et al (1999) was able to identify five genetically distinct populations within the Lightning Creek drainage area, a small watershed, but found little correlation between geographic distance and genetic differentiation.…”