Understanding the drivers of current genetic patterns within species can provide important information about a species ability to adapt to future climate. Using balsam poplar (Populus balsamifera) as a study species, we assessed the relative importance of historic climate change, range expansion, and current range patterns in driving current genetic patterns. To quantify the effects of past climate change on balsam poplar, we used species distribution modeling to project balsam poplar’s distribution to 22 kya BP in 500 year increments. These predictions were used to calculate (i) climatic stability, a measure of the relative stability of balsam poplar’s suitable climate through time, and (ii) average bioclimatic speed, a measure of how fast balsam poplar’s suitable climate changed over space and time. We also quantified several measures related to balsam poplar’s current range, including distance from the range edge, distance from the geographic centroid, and distance from the environmental centroid. We developed a Random Forest model to determine the relative importance of these variables in driving patterns of balsam poplar genetic diversity, specifically observed heterozygosity and percent polymorphic loci.
Results/Conclusions
We found that climatic stability tended to be one of the most important variables in explaining current genetic patterns in balsam poplar, as quantified by a 15-20% increase in model error when values were permuted. The location of populations within the range was also found to be important in explaining current patterns of genetic diversity, in particular the population’s distance from the geographic range edge. Approximately 58% and 57% of the total variation in observed heterozygosity and percent polymorphic loci, respectively, could be explained by the three most important variables in each model. Bioclimatic speed was not found to be significantly related to either measure of genetic diversity, and had low importance in each model. Our study illustrates the role of both historic and current processes in shaping species current patterns. The importance of climatic stability, in particular, illustrates the importance of past climate change in shaping genetic patterns. Understanding the drivers of current genetic diversity can provide important information about where species may have the genetic resources to adapt to unique, future climates.