Patterns of gene flow across elevation in Andean scarabs

Janzen's seasonality hypothesis predicts that organisms inhabiting environments with limited climatic variability will evolve a reduced thermal tolerance breadth compared with organisms experiencing greater climatic variability. In turn, narrow tolerance breadth may select against dispersal across strong temperature gradients, such as those found across elevation. This can result in narrow elevational ranges and generate a pattern of isolation-by-environment, or neutral genetic differentiation correlated with environmental variables that is independent of geographic distance. We generated genome-wide SNP data from 5 species of dung beetle from the two elevational transects and two horizontal control transects in the Ecuadorean Andes to test this prediction.