Genetic variation, climate models and the ecological genetics of Larix occidentalis

Abstract

Provenance tests of 143 populations of Larix occidentalis revealed genetic differentiation for eight variables describing growth, phenology, tolerance to spring frosts, effects of Meria laricis needle cast, and survival. Geographic variables accounted for as much as 34% of the variance among Rocky Mountain populations. Patterns of genetic variation were dominated by the effects of latitude and elevation, with populations from the north and from high elevations having the lowest growth potential, the least tolerance to the needle cast, and the lowest survival. However, the slope of the geographic clines was relatively flat. Populations in the same geographic area, for instance, need to be separated by about 500 m in elevation before genetic differentiation can be expected.Regression models using geographic predictors were developed to describe variation in ten climatic variables from 192 weather stations that best represented the Rocky Mountain distribution of L. occidentalis. Values of R2 ranged from 0.42 to 0.92 and were higher for temperature than for precipitation variables.Using climatic effects predicted for each provenance to describe genetic variation produced values of R2 between 0.15 and 0.27 which accounted for nearly as much (68–100%) of the genetic variance as had geographic variables. The analyses suggested that genetic differentiation was controlled primarily by the relative mildness of the climate. Secondary effects of precipitation were implicated for variables measuring the impact of Meria needle cast and survival.