Genetic variation inPinus strobiformisgrowth and drought tolerance from southwestern US populations

Abstract

The persistence of some tree species is threatened by combinations of novel abiotic and biotic stressors. To examine the hypothesis that Pinus strobiformis Engelm., a tree threatened by an invasive forest pathogen and a changing climate, exhibits intraspecific genetic variation in adaptive traits, we conducted a common garden study of seedlings at one location with two watering regimes using 24 populations. Four key findings emerged: (i) growth and physiological traits were low to moderately differentiated among populations but differentiation was high for some traits in water-stressed populations; (ii) seedlings from warmer climates grew larger, had higher stomatal density and were more water-use efficient (as measured by the carbon isotope ratio) than populations from colder climates; (iii) seedlings from the northern edge of the species' distribution had lower water-use efficiency, higher stomatal conductance, slower growth and longer survival in a lethal drought experiment compared with seedlings from more southern populations; and (iv) based on non-metric multidimensional scaling analyses, populations clustered into southern and northern groups, which did not correspond to current seed transfer zones. Our discovery of a clinal geographic pattern of genetic variation in adaptive traits of P. strobiformis seedlings will be useful in developing strategies to maintain the species during ongoing climate change and in the face of an invasive pathogen.

The role of hybridization during ecological divergence of southwestern white pine (Pinus strobiformis) and limber pine (P. flexilis)

“…Limited variation in β is associated with a diffuse genomic architecture of isolation (Gompert et al 2012b), whereas the high genomic heterogeneity in α , under the estimated demographic scenario, could imply divergent natural selection operating within the hybrid zone (Gompert & Buerkle 2011). This agrees with the higher values of multilocus F ST within the putative hybrid zone ( F ST -periphery ) and previous evidence of local adaptation in this region (Goodrich et al 2016). A similar genomic mosaic of introgression has been noted across several studies (Lexer et al 2010; Parchman et al 2013; Gompert et al 2014; Lindtke et al 2014; de Lafontaine et al 2015) and is likely a result of complex interactions between divergence history, selection, and genomic features.…”

“…Such novel allelic combinations have often contributed to the ability of populations to colonize new niches that are intermediate to the climatic conditions experienced by the parental species (De Carvalho et al 2010; Hamilton et al 2013; De La Torre et al 2014b; Geraldes et al 2014). Presence of a locally adapted and historical hybrid zone is supported by the absence of β outliers in our genomic cline results (Kamdem et al 2016) and a recent study uncovering high Q ST values associated with physiological traits primarily linked to drought tolerance within the group Periphery (Goodrich et al 2016). The geographic cline in h , asymmetry in excess ancestry loci towards P. flexilis , and elevated estimates of F ST –periphery , however, indicate the potential for geographically driven neutral introgression to generate biased signals of local adaptation within the peripheral populations (Geraldes et al 2014).…”

“…Our focal species inhabit a wide latitudinal range in the western part of North America, with a putative area of sympatry located in the southern Rocky Mountains and Colorado Plateau in which morphological evidence points towards the occurrence of hybridization (Steinhoff & Andresen 1971; Tomback & Achuff 2010). These species also display limited differences in morphological and reproductive traits (Benkman et al 1984; Tomback et al 2011; Bisbee 2014) and show evidence of local adaptation to the heterogeneous climatic conditions across their geographical range and also within the area of putative hybridization (Steinhoff & Andresen 1971; Moreno-Letelier et al 2013; Borgman et al 2015; Moreno-Letelier & Barraclough 2015; Goodrich et al 2016). To examine the processes influencing species boundaries between these two conifer species, we asked three questions: (1) Is there niche divergence among P. strobiformis , P. flexilis and the putative hybrid zone?…”

The role of hybridization during ecological divergence of southwestern white pine (Pinus strobiformis) and limber pine (P. flexilis)

“…Such novel allelic combinations have often contributed to the ability of populations to colonize new niches that are intermediate but beyond the climatic conditions experienced by the parental species (De Carvalho et al., ; De La Torre, Wang, Jaquish, & Aitken, ; Geraldes et al., ; Hamilton et al., ). Presence of a locally adapted and historical hybrid zone is supported by the absence of β outliers in our genomic cline results (Fouet, Kamdem, Gamez, & White, ), as well as by a recent study identifying high Q ST values associated with physiological traits primarily linked to drought tolerance within Periphery (Goodrich, Waring, & Kolb, ). The geographic cline in h , asymmetry in excess ancestry loci towards P. flexilis and elevated estimates of F ST–periphery , however, indicate the potential for geographically driven neutral introgression to generate biased signals of local adaptation within the peripheral populations (Geraldes et al., ).…”

Natural selection and neutral evolutionary processes contribute to genetic divergence in leaf traits across a precipitation gradient in the tropical oak Quercus oleoides

“…The fact that Q ST was invariant indicated that r 2 B and r 2 w compensate each other and suggests that either populations or families responded similarly to the environment (i.e., no genotype 9 environment interaction). Only Goodrich, Waring, and Kolb (2016) showed strong environmental dependency of both variance components and patterns of population divergence in Pinus strobiformis. Generally, these authors observed that Q ST values were lower in a dry treatment than in an ambient treatment.…”