SNP Discovery and Marker Development as a First Step to look for Local Adaptation in Two Closely Related White Pine Species

Under rapid global warming, it is of crucial importance for us to better understand the capacity of forest trees to adapt to a changing climate, especially for species that are more at risk such as five-needle pines. Eastern white pine (Pinus strobus) and western white pine (Pinus monticola) have fragmented ranges and have suffered declines due to harvesting, fire suppression and introduced insects and diseases. In the present study, we aim to identify and compare genetic variations involved in adaptation to climate in natural populations of these two closely related species. A set of 267 orthologous genes, including candidates for growth, bud phenology and resistance to biotic and abiotic stress, was used to develop ~200 single nucleotide polymorphism (SNP) markers for each P. strobus and P. monticola. Each set of SNPs was genotyped on range-wide samples of 840 Pinus strobus and 380 Pinus monticola individuals. The genotyping success was similar for both species (88% for P. strobus and 83% for P. monticola). It resulted in 177 and 103 SNPs representing 79 orthologous and 89 non-orthologous genes, respectively. This will make it possible to compare the patterns of adaptation at the intra- and inter-specific level revealed by F_st outliers and environmental association analysis. We expect that some genes or gene families under strong selection in both species will show similar patterns of genetic variation along climatic gradients. However, different genes may have contributed to local adaption in these two geographically distant species.