Forest stratification shapes allometry and flight morphology of tropical butterflies

Abstract

Studies of altitudinal and latitudinal gradients have identified links between the evolution of insect flight morphology, landscape structure and microclimate. Although lowland tropical rainforests offer steeper shifts in conditions between the canopy and the understorey, this vertical gradient has received far less attention. Butterflies, because of their great phenotypic plasticity, are excellent models to study selection pressures that mould flight morphology. We examined data collected over 5 years on 64 Nymphalidae butterflies in the Ecuadorian Chocó rainforest. We used phylogenetic methods to control for similarity resulting from common ancestry, and explore the relationships between species stratification and flight morphology. We hypothesized that species should show morphological adaptations related to differing micro-environments, associated with canopy and understorey. We found that butterfly species living in each stratum presented significantly different allometric slopes. Furthermore, a preference for the canopy was significantly associated with low wing area to thoracic volume ratios and high wing aspect ratios, but not with the relative distance to the wing centroid, consistent with extended use of fast flapping flight for canopy butterflies and slow gliding for the understorey. Our results suggest that microclimate differences in vertical gradients are a key factor in generating morphological diversity in flying insects.

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

“…Tropical butterflies provide a notable case study of vertical stratification, with several documented examples among butterfly communities (Burd, 1994; DeVries et al, 1997; DeVries & Walla, 2001; dos Santos et al, 2017; Fermon et al, 2003; Mena et al, 2020; Schulze et al, 2001). In this context, differences in flight height appear to be an important attribute in increasing diversity and facilitating speciation between closely related species.…”

“…Microhabitat partitioning is likely explained by habitat‐specific predation and variation in optimal properties of warning signals in different sensory conditions (Gompert et al, 2011; Willmott et al, 2017). However, flight height also plays a major role in this community structuring, but may be constrained by ecological factors besides mimicry and predation, including host‐plant use (Beccaloni, 1997), intraspecific signalling in different light environments (Dell'Aglio et al, 2019), aspects of sex‐specific behaviours (Joron, 2005), favourable nocturnal ‘roosting’ sites (Mallet & Gilbert, 1995) and wing morphology (Mena et al, 2020; Montejo‐Kovacevich et al, 2019).…”

A nondestructive method of calculating the wing area of insects

“…The wing morphology of insects strongly affects aerodynamic performance, and the diverse array of wing shapes reflects the insects’ adaptation to environmental differences (Aiello et al, 2021 ; Ellington, 1984 ). Wing loading (defined as body mass per unit wing area) has been demonstrated to reflect flight maneuverability of insects to a large extent (Byrne et al, 1988 ; Grabow & Rüppell, 1995 ; Mena et al, 2020 ), so calculation of wing area is of value in flight performance studies with insects. However, wing morphological diversity makes it difficult to develop a general geometric equation to describe wing outlines of insects.…”

Genomics of altitude‐associated wing shape in two tropical butterflies

“…Subtle variation in wing morphology can have big impacts on flight mode and performance (Berwaerts et al, 2002). For example, butterflies in tropical rain forests have been found to have rounder wings when they inhabit the understory, both within closely related taxa (Chazot et al, 2014) and across many species (Mena et al, 2020). Elongated wings reduce wing‐tip vortices, resulting in more efficient and faster flight, whereas short and wide wings are associated with higher manoeuvrability and lift (Le Roy et al, 2019a).…”