Biology subjects

Barbut, J.

Publications and source records attributed to Barbut, J..

3 recordsLinked to original sources

bioRxiv2021

Hydrophobicity in clearwing butterflies and moths: impact of scale 2 micro and nanostructure, and trade-off with optical transparency

Living organisms are submitted to multiple developmental and selective constraints resulting in evolutionary compromises, one of the best examples being the integument (the outer protective layer of living organisms) which is fundamentally multifunctional. Integument anti-wetting or hydrophobicity - evolved in relation to complex and various structures - is a crucial property as it serves multiple functions like self-cleaning, locomotion, or defence against pathogens and may interfere with other functions like thermoregulation or communication. Elucidating the structure-property relationships and unravelling potential trade-offs is crucial to understand the evolution of the integument. In opaque Lepidoptera, wing scales actively contribute to anti-wetting. In clearwing Lepidoptera, wing scales are often reduced, raising the question of whether they can maintain similar hydrophobicity levels to those of opaque species and if not, whether wing microstructure (scale density, shape, insertion, and coloration) may mitigate the costs of a lower hydrophobicity. To answer these questions, we measure static contact angle (CA) of water droplets at different stages of evaporation in opaque and transparent patches of 23 Lepidoptera species that show a high diversity in wing microstructure. More specifically, we find that transparency is costly for hydrophobicity, and that such cost depends on wing microstructure. In general, transparent patches lose more hydrophobicity with water evaporation than opaque patches. Yet, this loss of hydrophobicity is attenuated for higher scale densities, erect scales compared to flat scales, coloured scales (for erect scales), multiple scale layers (for flat scales), or when combining two types of scales (piliform and lamellar) than having only one type of scale (piliform or lamellar). Nude membranes show the lowest hydrophobicity values. We find that wing hydrophobicity negatively relates to optical transparency, showing a trade-off between optics and hydrophobicity. Moreover, we find that tropical species have higher hydrophobicity in their transparent patches than temperate ones, suggesting transparent patches are under stronger selection for hydrophobicity in tropical than in temperate species. These novel findings, which are consistent with the physics of hydrophobicity, suggest that insect wings are evolutionary multifunctional compromises.

evolutionary biology↗

bioRxiv2020

Variation in transparency degree: response to light availability or part of mimicry syndrome?

Transparency reduces prey detectability by predators. While transparent aquatic species hold higher transparency levels as the light availability of their habitat increases, less is known about such variation in terrestrial species. Lepidoptera species exhibiting transparent wings display various levels of transparency. Using two complementary approaches, we explore how the evolution of different transparency degrees relates to habitat openness, activity rhythm and mimicry syndrome (bee/wasp versus dead-leaf mimic). First, by exposing artificial moth-like prey to wild avian predators in a range of habitat openness, we show that survival is lower in more open habitats. We also found that less transparent morphs are more attacked than more transparent ones, regardless of habitat openness degree. Second, by analysing the evolution of wing features and ecological traits in 107 clearwing species, we found that diurnal species transmit more light than nocturnal species under certain conditions (when considering only forewings, at smaller clearwing surfaces and at larger wing lengths) and that species flying in open habitats and exhibiting large percentages of clearwing surface transmit slightly more light than those flying in closed habitats, although this is reversed at smaller percentages of clearwing surfaces. Additionally, bee/wasp mimics are more often diurnal and have higher and less variable light transmittances than dead-leaf mimics, which are more often nocturnal. Flying during the day, in open habitats and mimicking insects with transparent wings seem to promote high light transmittance under certain circumstances. Activity rhythm, habitat openness and species interactions play a crucial role in determining transparency design on land.

evolutionary biology↗

bioRxiv2020

Transparency in butterflies and moths: structural diversity, optical properties and ecological relevance

In water, transparency seems an ideal concealment strategy, as testified by the variety of transparent aquatic organisms. By contrast, transparency is nearly absent on land, with the exception of insect wings, and knowledge is scarce about its functions and evolution, with fragmentary studies and no comparative perspective. Lepidoptera (butterflies and moths) represent an outstanding group to investigate transparency on land, as species typically harbour opaque wings covered with coloured scales, a key multifunctional innovation. Yet, many Lepidoptera species have evolved partially or fully transparent wings. At the interface between physics and biology, the present study investigates transparency in 123 Lepidopteran species (from 31 families) for its structural basis, optical properties and biological relevance in relation to thermoregulation and vision. Our results establish that transparency has likely evolved multiple times independently. Efficiency at transmitting light is largely determined by clearwing microstructure (scale shape, insertion, colouration, dimensions and density) and macrostructure (clearwing area, species size or wing area). Microstructural traits - density, dimensions - are tightly linked in their evolution, with different constraints according to scale shape, insertion, and colouration. Transparency appears highly relevant for vision, especially for camouflage, with size-dependent and activity-rhythm dependent variations. Links between transparency and latitude are consistent with an ecological relevance of transparency in thermoregulation, and not so for protection against UV radiation. Altogether, our results shed new light on the physical and ecological processes driving the evolution of transparency on land and underline that transparency is a more complex than previously thought colouration strategy.

evolutionary biology↗