The structure of genetic diversity in Engelmann spruce and a comparison with blue spruce

Abstract

Genetic diversity and genetic structure in Engelmann spruce (Picea engelmannii Parry ex Engelm.) were interpreted with respect to the effects of glacial and interglacial displacement and compared with patterns in blue spruce (Picea pungens Engelm.), which occupies a range well south of the last glacial front. On average, Engelmann spruce populations were polymorphic at 80% of 24 isozyme loci, with 2.4 alleles per locus and expected heterozygosity of 0.255. The respective means for four populations of blue spruce were 42.7%, 1.6 alleles, and 0.138. Of total diversity, 14.7% was among populations in Engelmann spruce and 8.6% in blue spruce. In Engelmann spruce, numbers of alleles increased from south to north. Recent bottlenecks were indicated in the three southernmost populations of Engelmann spruce and in the northernmost population of blue spruce. Cluster analysis divided Engelmann spruce into a northern group and a Southwestern group; however, populations from Utah were distributed among both clusters. Genetic distance was correlated with geographic distance between northern populations but not between Southwestern populations, where drift predominated over gene flow. In two Engelmann spruce populations from Utah, multilocus outcrossing rates were 0.951 (±0.016) and 0.940 (±0.071). At Flys Peak, Arizona, the southernmost location of Engelmann spruce, outcrossing was also high, 0.899 (±0.017). Thus, inbreeding coefficients observed for parental (-0.104 to 0.047) and filial (0.011 to 0.026) generations were low. Although Engelmann spruce seemed genetically robust, the evidence of bottlenecks in the southern extreme of its range suggested future problems in an era of global warming.Résumé : Les auteurs ont interprété la diversité génétique et la structure génétique de l'épinette d'Engelmann (Picea engelmannii Parry ex Engelm.) en relation avec les effets des déplacements glaciaires et interglaciaires, et les ont comparées avec les patrons de l'épinette bleue (Picea pungens Engelm.), qui occupe une région bien au sud du dernier front glaciaire. En moyenne, les populations de l'épinette d'Engelmann sont polymorphes chez 80 % de 24 loci isozymiques, avec 2.4 allèles par locus et une hétérozygocité attendue de 0,255. Ces moyennes respectives, chez quatre populations d'épinette bleue, sont de 42,7 %, 1,6 allèles, et 0,138. De la diversité totale, 14,7 % se retrouve parmi les populations de l'épinette d'Engelmann, et 8,6 % parmi celles de l'épinette bleue. Chez l'épinette d'Engelmann, les nombres d'allèles augmentent du sud au nord. On observe des goulots d'étranglements récents dans les trois populations les plus méridionales de l'épi-nette d'Engelmann et dans la population la plus nordique de l'épinette bleue. L'analyse par regroupement divise l'épinette d'Engelmann en un groupe nordique et un groupe du sud-ouest; cependant les populations de l'Utah sont présentes dans les deux regroupements. La distance génétique est corrélée avec les distances géographiques entre les populations du nord, mais non entre les populatio...

Multilocus genetic analyses and spatial modeling reveal complex population structure and history in a widespread resident North American passerine (Perisoreus canadensis)

“…Birds in this area are isolated from adjacent populations by the Columbia Basin/Okanogan Highlands to the west (Pacific populations), Columbia Mountains and Rocky Mountain Trench to the north and Columbia Mountains to the east (Boreal‐east), and the Snake River Basin to the south (Colorado and Utah). A similar genetic break occurs in mtDNA patterns in Engelmann spruce (Ledig et al., ) and Douglas fir (Gugger, Sugita, & Cavender‐Bares, ); both species of trees that gray jays are closely associated with in the Intermountain West area (Strickland & Ouellet, ).…”

“…The divergence between Colorado and neighboring populations in Utah, but not between Colorado and neighboring populations in New Mexico, has been observed in other taxa (Albach, Schonswetter, & Tribsch, ; Runck & Cook, ). Most notably, congruent patterns of isolation are found in Engelmann and blue spruce (Ledig et al., ), which were restricted to higher elevations and isolated on mountains as aridification occurred in the Great and Wyoming Basins. In addition, both the UT and CO populations are currently ~390–700 km, respectively, to the nearest population within the contiguous portion of the gray jay range.…”

“…Gray jays are dependent on forested habitat and, in particular, several species of spruce trees ( Picea spp.). CO‐NM, UT, and IMW groups are all closely associated with Engelmann and blue spruce, which are highly fragmented in the southern portion of their range (i.e., UT and CO; Ledig, Hodgskiss, & Johnson, ). Populations of Engelmann and blue spruce in the IMW and NE UT are genetically distinct (cpDNA) and physically isolated from each other by the Snake River Basin (Ledig et al., ), corresponding to the mitochondrial DNA patterns found here.…”

Genome‐wide admixture and ecological niche modelling reveal the maintenance of species boundaries despite long history of interspecific gene flow

“…Their extensive hybrid zone is mainly composed of hybrids with a clinal intergradation of morphological and genetic characteristics along elevational gradients between parental species' habitats (Ledig et al . ).…”

Genetic evidence for species cohesion, substructure and hybrids in spruce

“…Given the general gaps in our knowledge of the distribution of genetic variation near the species level, and the potential for differences among spruces, we investigated two levels of genetic diversity in the spruce of western North America. We built on earlier research (e.g., Daubenmire, ; de la Torre Cuba, ; Haselhorst & Buerkle, ; Ledig, Hodgskiss, & Johnson, ; Ledig et al, ; Rajora & Dancik, ; Rehfeldt, ; Rehfeldt, ) and analysed DNA polymorphisms across thousands of genomic sites, derived from a reduced representation of the genomes using genotyping‐by‐sequencing (GBS), from 2,219 individuals and 135 localities across the ranges of the six western North American spruce species that occur north of Mexico (blue, Brewer, Sitka, white, black and Engelmann spruce). We used these DNA polymorphisms to test for species cohesion and the extent of hybridization among taxa.…”