Divergence inHeliconiusflight behaviour is associated with local adaptation to different forest structures

Abstract

Microhabitat choice plays a major role in shaping local patterns of biodiversity. In butterflies, stratification in flight height has an important role in maintaining community diversity. Despite its presumed importance, the role of behavioural shifts in early stages of speciation in response to differences in habitat structure is yet to be established. Here, we investigated variation in flight height behaviour in two closely related Heliconius species, H. erato cyrbia and H. himera, which produce viable hybrids but are isolated across an environmental gradient, spanning lowland wet forest to high‐altitude scrub forest. Speciation in this pair is associated with strong assortative mating, but ecological isolation and local adaptation are also considered essential for complete reproductive isolation. We quantified differences in flight height and forest structure across the environmental gradient and tested the importance of resource distribution in explaining flight behaviour. We then used common garden experiments to test whether differences in flight height reflect individual responses to resource distribution or genetically determined shifts in foraging behaviour. We found that the two species fly at different heights in the wild, and demonstrated that this can be explained by differences in the vertical distribution of plant resources. In both the wild and captivity, H. himera choose to fly lower and feed at lower positions, closely mirroring differences in resource availability in the wild. Given expectations that foraging efficiency contributes to survival and reproductive success, we suggest that foraging behaviour may reflect local adaptation to divergent forest structures. Our results highlight the potential role of habitat‐dependent divergence in behaviour during the early stages of speciation.

Adult neurogenesis does not explain the extensive post-eclosion growth of Heliconius mushroom bodies

“…The role of adult neurogenesis in the optic lobes is currently unknown, however Heliconius erato have been shown to have age-dependent volumetric plasticity in the optic lobes [ 33 ]. As Heliconiini butterflies use visual cues to navigate between resources [ 39 , 68 ] and discriminate hostplants [ 69 ], floral cues [ 70 – 72 ] and mating cues [ 73 – 77 ], we suggest the continued development of the optic lobes into adulthood may have important behavioural effects. Of potential relevance is the observation that Heliconius are not behaviourally mature until approximately 8 days post eclosion [ 78 ].…”

Sex-limited diversification of the eye in Heliconius butterflies

“…3) showed that H.c. alithea had the most divergent organization, even compared to the outgroup H. melpomene . Additionally, H.c. alithea lives in Ecuador, in contrast to all other butterflies in this study which were from Costa Rica, so the observed variability may reflect differences in habitat structure or ambient light levels in these two locations, such as differences in elevation due to the Andes (Dell’Aglio et al, 2022; Sondhi et al, 2021).…”

Scale‐dependent environmental effects on phenotypic distributions inHeliconiusbutterflies

“…McMillan et al ( 1997 ), for example, suggested that adaptation to wet and dry forests along with strong mate preference and FDS by predators was important in speciation between H. erato and H. himera . More recent work on this pair of incipient species demonstrated genetic differences in flight height and foraging behaviors associated with adaptation to different habitat characteristics (Dell'Aglio et al, 2022 ). Similarly, Muñoz et al ( 2010 ) showed combination of pre‐ and post‐mating isolation mechanisms are important in the early stages of speciation in H. erato subspecies, H. e. chestertonii and H. e. venus .…”