Parallel shifts in flight-height associated with altitude across incipientHeliconiusspecies

Abstract

AbstractVertical 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 early population divergence. We analysed flight-height variation across speciation events inHeliconiusbutterflies representing parallel instances of divergence between low and high-altitude populations. We measured flight-height in wildH. erato venus andH. chestertonii, lowland and mountain specialists respectively, and found thatH. chestertoniiconsistently flies at a lower height. We compared these data with previously published results forH. e. cyrbiaandH. himera, the latter of which flies lower and, likeH. chestertonii, recently colonised high-altitude, dry forests. We show that these repeated trends largely result from shared patterns of selection across equivalent environments, producing parallel trait-shifts inH. himeraandH. chestertonii. Although our results imply a signature of local adaptation, we did not find an association between resource distribution and flight-height inH. e. venusandH. chestertonii. We discuss how this pattern may be explained by variation in forest structure and microclimate. Overall, our findings underscore the importance of behavioural adjustments during early divergence mediated by altitude-shifts.