Biology subjects

Pinna, C.

Publications and source records attributed to Pinna, C..

4 recordsLinked to original sources

bioRxiv2023

Clearwing butterflies challenge the thermal melanism hypothesis

In contrast to most butterflies harboring opaque wing colorations, some species display large transparent patches on their wings. Wing transparency, which entails a dramatic reduction of pigmentation, raises the question of potential costs for vital functions, such as thermoregulation, especially along climatic gradients. The thermal melanism hypothesis posits that darker colorations should be favored in colder environments, which enables them to absorb more radiation and maintain a body temperature compatible with activity. This prediction extends to the near infrared (NIR) range, which represents a large proportion of solar radiation. Here we assess the implications of wing transparency for light absorption and thermal properties in 42 butterfly species from the neotropical tribe Ithomiini that range the extent of transparency, from fully opaque to highly transparent, and we test whether those species conform to the prediction of the thermal melanism hypothesis. We find that transparent wings are less efficient than opaque wings to absorb light across UV, Visible and NIR wavelength ranges, and are also less efficient to collect heat. Moreover, dark coloration occupies a lower proportion of wing area as altitude increases, and ithomiine species harbor more transparency at higher altitudes, where climatic conditions are colder, going strongly against the prediction of the thermal melanism hypothesis. We discuss these surprising results in light of recent studies suggesting that factors other than adaptation to cold, such as predation pressure, physiology or behavior, may have driven the evolution of wing patterns in Ithomiini. Significance StatementThe thermal melanism hypothesis predicts that organisms should be darker and absorb solar radiation more efficiently in colder environments. The Neotropical butterflies Ithomiini are unusual in that many species harbor large transparent patches on their wings, raising questions related to their efficacy of solar radiation absorption and heating capacities. We investigate optical and thermal properties of several ithomiine species along a climatic gradient. We find that transparent wings are less efficient at absorbing radiation and collecting heat. Unexpectedly, the proportion of transparent species increases with altitude, challenging the thermal melanism hypothesis and suggesting that factors other than adaptation to cold, such as predation pressure, may have driven the evolution of wing patterns in Ithomiini.

evolutionary biology↗

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

Developmental, cellular, and biochemical basis of transparency in the glasswing butterfly Greta oto

Numerous species of Lepidoptera have transparent wings, which often possess scales of altered morphology and reduced size, and the presence of membrane surface nanostructures that dramatically reduce reflection. Optical properties and anti-reflective nanostructures have been characterized for several clearwing Lepidoptera, but the developmental basis of wing transparency is unknown. We apply confocal and electron microscopy to create a developmental time-series in the glasswing butterfly, Greta oto, comparing transparent and non-transparent wing regions. We find that scale precursor cell density is reduced in transparent regions, and cytoskeletal organization differs between flat scales in opaque regions, and thin, bristle-like scales in transparent regions. We also reveal that sub-wavelength nanopillars on the wing membrane are wax-based, derive from wing epithelial cells and their associated microvillar projections, and demonstrate their role in enhancing-anti-reflective properties. These findings provide insight into morphogenesis of naturally organized micro- and nanostructures and may provide bioinspiration for new anti-reflective materials.

developmental 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↗