Flight behaviour diverges more between seasonal forms than between species in Pieris butterflies.

In flying animals, wing morphology is typically assumed to influence flight behaviours. Whether seasonal polymorphism in butterfly morphology is linked to adaptive flight behaviour remains unresolved. Here, we compare the flight behaviours and wing morphologies of the spring and summer forms of two closely related butterfly species, Pieris napi and P. rapae. We first quantify three-dimensional flight behaviour by reconstructing individual flight trajectories using stereoscopic high-speed videography in an experimental outdoor cage. We then measure wing size and shape, which are characteristics assumed to influence flight behaviours in butterflies. We show that seasonal, but not interspecific, differences in flight behaviour might be associated with divergent forewing shapes. During spring, Pieris individuals are small and have elongated forewings, and generally fly at low speed and acceleration, while having a high flight curvature. On the contrary, summer individuals are larger and exhibit rounded forewings. They fly at high speed and acceleration, while having high turning acceleration and advance ratio. Our study provides one of the first quantitative pieces of evidence of different flight behaviours between seasonal forms of two Pieris butterfly species. We discuss the possibility that this co-divergence in flight behaviour and morphology is an adaptation to distinct seasonal environments. Properly identifying the mechanisms underpinning such divergence, nonetheless, requires further investigations to disentangle the interacting effects of microhabitats, predator community, parasitoid pressure and behavioural differences between sexes.

Region-specific remodeling of the enteric nervous system and enteroendocrine cells in the colon of spinal cord injury patients.

Patients with spinal cord injury (SCI) suffer from major bowel dysfunction, whose exact pathophysiology, particularly the involvement of the enteric nervous system or epithelial dysfunction is poorly understood. Herein, we aimed to characterize the mucosal biopsies of the right and left colon in SCI patients vs controls (CT): (1) remodeling of key enteric neurotransmitters, (2) remodeling of enteroendocrine cells, and (3) mucosal inflammation compared to those in controls. In SCI, mucosal ACh concentration was lower in the right colon as compared to CT, but no change was observed in the left colon, and AChE expression was lower in both the right and left colons than in CT. While the VIP concentration was similar in the right and left colons, VIP mRNA expression was increased in the right colon and decreased in the left colon, in SCI patients as compared to CT. Interestingly, 5-HT concentration was reduced in the left colon but not in the right colon in SCI patients. Moreover, in SCI patients, as compared to CT, SERT mRNA expression was selectively increased in the left colon while TPH1 mRNA expression was increased in the right and left colons. Although mucosal TNFα and IL-1ß mRNA expression did not significantly differ between SCI and CT groups, we identified a significant positive correlation between TNFα and IL-1ß mRNA expression and left colon transit time in the SCI group. In conclusion, region-specific changes occur in the enteric neurotransmitter, serotonergic, and inflammatory pathways in the colon of SCI patients. The significant correlations between these pathways and clinical parameters in the left colon further set a scientific basis for designing therapeutic targets to improve colonic motor dysfunction in patients.Biobank information: Spinal cord injury patients: PHRC ConstiCAPE-clinical trial NCT02566746. Controls: Anosain-clinical trial NCT03054415 and biobank of the "Institut des Maladies de l'Appareil Digestif (IMAD)" registered under number DC-2008-402.

Divergence of climbing escape flight performance in Morpho butterflies living in different microhabitats.

Habitat specialization can influence the evolution of animal movement in promoting divergent locomotor abilities adapted to contrasting environmental conditions, differences in vegetation clutter or predatory communities. While the effect of habitat on the evolution of locomotion and particularly escape performance has been well investigated in terrestrial animals, it remains understudied in flying animals. Here, we investigated whether specialization of Morpho butterfly species into different vertical strata of the Amazonian forest affects the performance of upward escape flight manoeuvres. Using stereoscopic high-speed videography, we compared the climbing flight kinematics of seven Morpho species living either in the forest canopy or in the understory. We show that butterflies from canopy species display strikingly higher climbing speed and steeper ascent angle compared with understory species. Although climbing speed increased with wing speed and angle of attack, the higher climb angle observed in canopy species was best explained by their higher body pitch angle, resulting in more upward-directed aerodynamic thrust forces. Climb angle also scales positively with weight-normalized wing area, and this weight-normalized wing area was higher in canopy species. This shows that a combined divergence in flight behaviour and morphology contributes to the evolution of increased climbing flight abilities in canopy species.

Convergent morphology and divergent phenology promote the coexistence of Morpho butterfly species.

The coexistence of closely-related species in sympatry is puzzling because ecological niche proximity imposes strong competition and reproductive interference. A striking example is the widespread wing pattern convergence of several blue-banded Morpho butterfly species with overlapping ranges of distribution. Here we perform a series of field experiments using flying Morpho dummies placed in a natural habitat. We show that similarity in wing colour pattern indeed leads to interspecific territoriality and courtship among sympatric species. In spite of such behavioural interference, demographic inference from genomic data shows that sympatric closely-related Morpho species are genetically isolated. Mark-recapture experiments in the two most closely-related species unravel a strong temporal segregation in patrolling activity of males. Such divergence in phenology reduces the costs of reproductive interference while simultaneously preserving the benefits of convergence in non-reproductive traits in response to common ecological pressures. Henceforth, the evolution of multiple traits may favour species diversification in sympatry by partitioning niche in different dimensions.

Adaptive evolution of flight in Morpho butterflies.

The diversity of flying animals suggests that countless combinations of flight morphologies and behaviors have evolved with specific lifestyles, thereby exploiting diverse aerodynamic mechanisms. How morphology, flight behavior, and aerodynamic properties together diversify with contrasting ecology remains to be elucidated. We studied the adaptive codivergence in wing shape, flight behavior, and aerodynamic efficiency among Morpho butterflies living in different forest strata by combining high-speed videography in the field with morphometric analyses and aerodynamic modeling. By comparing canopy and understory species, we show that adaptation to an open canopy environment resulted in increased glide efficiency. Moreover, this enhanced glide efficiency was achieved by different canopy species through distinct combinations of flight behavior, wing shape, and aerodynamic mechanisms, highlighting the multiple pathways of adaptive evolution.

Effects of natural wing damage on flight performance in Morpho butterflies: what can it tell us about wing shape evolution?

Flying insects frequently experience wing damage during their life. Such irreversible alterations of wing shape affect flight performance and ultimately fitness. Insects have been shown to compensate for wing damage through various behavioural adjustments, but the importance of damage location over the wings has scarcely been studied. Using natural variation in wing damage, we tested how the loss of different wing parts affects flight performance. We quantified flight performance in two species of large butterflies, Morpho helenor and Morpho achilles, caught in the wild and displaying large variation in the extent and location of wing damage. We artificially generated more severe wing damage in our sample to contrast natural versus higher magnitude wing loss. Wing shape alteration across our sample was quantified using geometric morphometrics to test the effect of different damage distributions on flight performance. Our results show that impaired flight performance clearly depends on damage location over the wings, pointing to a relative importance of different wing parts for flight. A deteriorated forewing leading edge most critically affected flight performance, specifically decreasing flight speed and the proportion of gliding flight. In contrast, the most frequent natural damage, deteriorated wing margin, had no detectable effect on flight behaviour. Damage located on the hindwings - although having a limited effect on flight - was associated with reduced flight height, suggesting that the forewings and hindwings play different roles in butterfly flight. By contrasting harmless and deleterious consequences of various types of wing damage, our study highlights different selective regimes acting on morphological variations of butterfly wings.

Adaptive evolution of butterfly wing shape: from morphology to behaviour.

Butterflies display extreme variation in wing shape associated with tremendous ecological diversity. Disentangling the role of neutral versus adaptive processes in wing shape diversification remains a challenge for evolutionary biologists. Ascertaining how natural selection influences wing shape evolution requires both functional studies linking morphology to flight performance, and ecological investigations linking performance in the wild with fitness. However, direct links between morphological variation and fitness have rarely been established. The functional morphology of butterfly flight has been investigated but selective forces acting on flight behaviour and associated wing shape have received less attention. Here, we attempt to estimate the ecological relevance of morpho-functional links established through biomechanical studies in order to understand the evolution of butterfly wing morphology. We survey the evidence for natural and sexual selection driving wing shape evolution in butterflies, and discuss how our functional knowledge may allow identification of the selective forces involved, at both the macro- and micro-evolutionary scales. Our review shows that although correlations between wing shape variation and ecological factors have been established at the macro-evolutionary level, the underlying selective pressures often remain unclear. We identify the need to investigate flight behaviour in relevant ecological contexts to detect variation in fitness-related traits. Identifying the selective regime then should guide experimental studies towards the relevant estimates of flight performance. Habitat, predators and sex-specific behaviours are likely to be major selective forces acting on wing shape evolution in butterflies. Some striking cases of morphological divergence driven by contrasting ecology involve both wing and body morphology, indicating that their interactions should be included in future studies investigating co-evolution between morphology and flight behaviour.