History rather than hybridization determines population structure and adaptation in Populus balsamifera

Area of Science:

• Population Genetics
• Evolutionary Biology
• Plant Genomics

Background:

• Hybridization impacts species' genetic diversity and evolution.
• Within-species genetic clusters can limit gene flow and affect natural selection.
• Few studies examine both inter- and intra-specific gene flow influences simultaneously.

Purpose of the Study:

• Investigate hybridization effects between Populus balsamifera and Populus trichocarpa.
• Analyze population structure and adaptation in Populus balsamifera.
• Understand the interplay of among-species and within-species gene flow.

Main Methods:

• Sampled 1517 individuals of Populus balsamifera and Populus trichocarpa.
• Genotyped using 93 nuclear and 17 cpDNA SNPs.
• Conducted outlier analysis to identify loci associated with population structure and climate.

Main Results:

• Hybridization is largely confined to the species' contact zone.
• Populus balsamifera exhibits multi-level population structure with distinct Eastern, Central, and Western clusters.
• A sharp border between Eastern and Central clusters shows association with climate-related loci, while the Central-Western border is diffuse due to gene flow.

Conclusions:

• Large-scale genetic structure of Populus balsamifera is primarily shaped by historical factors, likely Pleistocene refugia.
• Endogenous genomic barriers may contribute to the sharp border in the Eastern cluster.
• Interspecific hybridization has a limited impact on the overall population structure and adaptation of Populus balsamifera.