Variation in the genetic architecture of ecologically relevant traits along elevational gradients

Species are confined within spatial boundaries, which may be determined by various factors. An understudied one is the genetic non-independence of traits, which can reduce the adaptive potential. We tested this hypothesis on elevational gradients, where environmental change occurs over short geographic distances. We collected seeds of three montane and three alpine Brassicaceae species, each from its core and both the lower and upper range edges, and reared offspring plants of matrilines in the greenhouse under two thermal treatments: warm and control. We measured key growth and leaf traits that diverge across elevation in Brassicaceae and estimated the genetic covariance (G-)matrix for each population and growth treatment. Genetic variances were reduced in lower-edge populations of montane species, while those of alpine species did not differ over the elevational gradients but were consistently low. Genetic integration-the reduction in evolvability due to genetic covariances-differed little over the elevational gradients and was generally strong. Similarly, the evolutionary potential ("evolvability") varied little and was low across populations. Finally, populations had substantial genetic variation in the direction of divergence along elevational gradients. Overall, our findings suggest that substantial genetic integration restricts population divergence along certain trait axes and reduces the evolutionary potential, which may hinder the evolution of species' ranges.