Hybridization and introgression are pervasive evolutionary phenomena that provide insight to the selective forces that maintain species boundaries, permit gene flow and control the direction of evolutionary change. Poplar trees (Populus L.) are well known for their ability to form viable hybrids and maintain their distinct species boundaries despite this interspecific gene flow. We sought to quantify the hybridization dynamics and postzygotic fitness within a hybrid stand of balsam poplar (Populus balsamifera L.), eastern cottonwood (P. deltoides Marsh.) and their natural hybrids to gain insight to the barriers maintaining this stable hybrid zone. We observed asymmetrical hybrid formation with P. deltoides acting as the seed parent, but with subsequent introgression biased towards P. balsamifera. Native hybrids expressed fitness traits intermediate to the parental species and were not universally unfit. That said, native hybrid seedlings were absent from the seedling population, which may indicate additional selective pressures controlling their recruitment. It is imperative that we understand the selective forces maintaining this native hybrid zone in order to quantify the impact of exotic poplar hybrids on this native system.
Usage Notes:
R code for analysis of fitness data
All R code associated with the manuscript are included. The file has been extensively commented as well.
All analysesNativePoplar_submit.R
Tree stand characteristics
This file contains the tree height, diameter at breast height, age classification, and genotype.
Stand_TreeData.csv
Biomass and yield fitness traits
This file contains the following biomass fitness traits: total catkin biomass, total seed biomass, 100 seed biomass, capsule biomass, stem biomass, and cotton biomass. It also contains the following yield measurements: capsules per catkin, seeds per capsule, and seeds per catkin.
Biomass.csv
Germination
This file contains two measures of germination success, as well as tree genotype class: germination success and number of abnormal germinants.
Disease Susceptibility
This file contains the results of the controlled inoculation of trees with three fungal diseases: Melampsora larici-populina, M. medusae f.sp. deltoidae, and M. occidentalis. Susceptibility was measured by number of uredia by unit area.
Inoculations.csv
Structure file for genotype assignment
This file contains the recoded SNP data for input into Structure to estimate admixture in each individual.
BPSF_NativeOnly_CompleteRef.xls
New Hybrid data file
The file contains the recoded genotype data for each tree for analysis in New Hybrids.
BPSF_NativeOnly_NH.txt