Diversification along environmental gradients


Variable selection pressures can promote divergence among populations that are distributed along environmental gradients. To place our mechanistic studies into a broader context, we are using a series of replicate transects in the Peruvian Andes and the Rocky Mountains to examine the role of elevational gradients in promoting genetic and morphological differentiation among bird and mammal populations at different elevations. Using a combination of population genetic analyses and morphological measurements of museum specimens, we have found that elevational gradients are important factors driving the morphological and genetic evolution of these species, and that differentiation among populations appears to have occurred in the face of considerable amounts of gene flow. More broadly, these results suggest that elevational gradients may warrant special conservation concern as areas that promote biological diversification. Although elevational gradients have long been known to harbor high levels of species richness, our work is adding to a growing body of evidence demonstrating that these gradients also contain substantial amounts of intraspecific diversity. More recently, we have also begun to examine the role of variation in biotic interactions among species along elevational gradients with members of the Carling Lab at the University of Wyoming. Much of this work has focused on adaptation to spatial variation in the abundance of avian malaria in the Andes . Because anemia is a primary symptom of malarial infections, examining the interactions between disease dynamics and hypoxia along elevational gradients offers exciting opportunities to study the interplay between biotic and abiotic selective pressures in the process of local adaptation. Lab PhD student Phred Benham has recently expanded this line of research to salinity gradients and osmoregulatory adaptations in Savannah Sparrows that repeatedly colonized saltmarsh habitats in Baja California.