Supplemental data for: Parallel shifts in flight-height associated with altitude across incipient Heliconius species

Vertical gradients in microclimate, resource availability and interspecific interactions are thought to underly stratification patterns in tropical insect communities. However, only a few studies have explored the adaptive significance of vertical space use during the early stages of reproductive isolation. We analysed flight-height variation across speciation events in Heliconius butterflies representing parallel colonisations of high-altitude forest. We measured flight-height in wild H. erato venus and H. chestertonii, parapatric lowland and mountain specialists respectively, and found that H. chestertonii consistently flies at a lower height. By comparing our data to previously published results for the ecologically equivalent H. e. cyrbia (lowland) and H. himera (high-altitude), we found that the species flying closest to the ground are those that recently colonised high-altitude forests. We show that these repeated trends largely result from shared patterns of ecological selection ...