Divergent melanism strategies in Andean butterfly communities structure diversity patterns and climate responses

Abstract

Aim: Geographic distributions are driven by a combination of species sensitivity and exposure to climate. We quantified colour lightness, a trait that mediates the interaction between sensitivity and exposure, of diverse butterfly communities to test whether colour lightness is associated with community assembly across climate‐elevation gradients.

Location: Ecuadorian Andes.

Methods: We used a long‐term dataset of museum specimens for two of the most species‐rich genera of Pieridae butterflies in Ecuador, Catasticta and Leptophobia. Within a phylogenetic framework, we examined how communities assemble based on four traits across elevation: colour lightness, species‐specific heating rate, maximum temperature (under experimental solar exposure), and elevation breadth.

Results: We found that colour lightness in both genera was related to elevation, but the two genera exhibited opposite patterns; Catasticta are darker and Leptophobia are lighter with increasing elevation. The two genera have opposite configurations of body and body + wings colour lightness but achieve comparable thermoregulation, assessed via their rates of heating under experimental solar exposure. Additionally, we found that the phylogenetic signal for colour lightness was strong, and that patterns between traits and elevation held after correction for phylogeny in Catasticta but not in Leptophobia.

Main conclusions: The two genera exhibit divergent relationships between elevational and colour lightness patterns, with evidence that these relationships evolved multiple times in Catasticta. Communities from these two genera have likely been shaped by selection on different traits, with Catasticta colour lightness more responsive to temperature than Leptophobia. The observed geographic patterns of colour lightness in both body + wings (Catasticta) and body (Leptophobia) correspond strikingly with the distribution of montane cloud forests. Habitat fragmentation and cloud lifting from climate change documented across the Andes may therefore significantly impact communities through increased exposure to solar radiation, highlighting the complexity of conserving these diverse montane communities.