Ecotypic mode of regional differentiation caused by restricted gene migration: a case in black cottonwood (Populus trichocarpa) along the Pacific Northwest coast

Abstract

Genetic differentiation of black cottonwood ( Populus balsamifera subsp. trichocarpa (Torr. & A. Gray ex Hook) Brayshaw) across a “no-cottonwood” belt on the coast of central British Columbia (BC), Canada, was examined using data on 3 year height, severity of infection by Valsa sordida Nitschke and Melampsora occidentalis H. Jacks., and abnormality of leaf flushing. The data were collected in a common-garden test consisting of 180 provenances of 36 drainages ranging from northern BC to Oregon, USA. The results demonstrated an ecotypic mode, north–south regional differentiation. Valsa sordida and M. occidentalis infected 41% and 89%, respectively, of the trees from the northern region, while 66% showed flushing abnormality. In contrast, only 1% and 27% of their southern counterparts were infected by the same diseases, and 1% had abnormal flushing. Trees from the northern region averaged 87% shorter than those from the south. Regional differentiation accounted for the highest amount of variation observed in all traits, with 60% in 3 year height, 34% in V. sordida, 76% in M. occidentalis, and 50% in abnormal leaf flushing. Regression analysis revealed geographic patterns that essentially reflected regional differentiation along the no-cottonwood belt. The species’ distribution biography, ecological characteristics, and life history suggest that restricted gene migration was the main factor responsible for the observed geographic patterns of genetic differentiation.

Genomic and functional approaches reveal a case of adaptive introgression fromPopulus balsamifera(balsam poplar) inP. trichocarpa(black cottonwood)

“…Gene expression data were obtained from a population‐wide RNAseq data set based on a subset of the P. trichocarpa accessions from trees outplanted in the common garden at the University of British Columbia as described above (Xie et al . ; McKown et al . ).…”

Scale and direction of adaptive introgression between black cottonwood (Populus trichocarpa) and balsam poplar (P. balsamifera)

“…Populus trichocarpa accessions used in this study were collected by the British Columbia Ministry of Forests, Lands and Natural Resource Operations (MFLNRO) (Xie, Ying, Yanchuk, & Holowachuk, ), and planted in a common garden at the University of British Columbia (McKown et al., ). These individuals were from 28 “drainages” (i.e., topographic units separated by watershed barriers) spanning 14° in latitude (45.6°–59.6°) from throughout the species range.…”

Comparative resource-use efficiencies and growth ofPopulus trichocarpaandPopulus balsamiferaunder glasshouse conditions

“…This study uses only a small proportion of available native collections of P. trichocarpa and P. balsamifera (e.g., Soolanayakanahally et al 2009 andXie et al 2009). More extensive work with a greater number of provenances might allow for the detection of more subtle differences between the species.…”

“…The study used 20 native P. trichocarpa genotypes from the British Columbia Ministry of Forests collection (Xie et al 2009) and 20 P. balsamifera genotypes from the Agriculture and Agri-Food Canada AgCanBaP collection (Soolanayakanahally et al 2009). For balsam poplar, the provenances were Gillam (GIL), Manitoba, and Carnduff (CAR), Saskatchewan (Table 1).…”