Biology subjects

Andraud, C.

Publications and source records attributed to Andraud, C..

10 recordsLinked to original sources

bioRxiv2025

Exploring the visual system of the black Grouse (Lyrurus tetrix): Combining experimental and molecular approaches to inform strategies for reducing collisions

Understanding the visual systems of birds can inform conservation efforts and mitigate the impact of collisions with man-made structures. Here we investigate the visual abilities of the black grouse Lyrurus tetrix (Galliformes: Phasianidae), a European mountain bird highly vulnerable to collisions with aerial infrastructures. Using behavioural assays, we show that black grouse have wide monocular lateral visual fields, extensive binocular overlap and a minimal blind area behind the head, altogether indicating the ability to detect aerial objects from different fields of view. The spatial resolution and contrast sensitivity of the black grouse are in the low avian range but align with the ecology of a prey species and allow to establish the limits of detection of an object size and contrast under variable environmental conditions. To characterize the range of wavelengths perceived, the four cone visual pigments (SWS1, SWS2, Rh2, and LW) were reconstituted and characterized functionally, showing detection of light across a spectral range spanning the visible spectrum up to 650 nm and with limited sensitivity below 400 nm. Combined with spectral and achromatic modelling analyses, our results inform on the limits of detection of aerial objects and the perception of existing visual markers, offering practical perspectives to continue mitigating black grouse collisions.

ecology↗

bioRxiv2024

Sending mixed signals: convergent iridescence and divergent chemical signals in sympatric sister-species of Amazonian butterflies

The evolution of traits in closely related species living in sympatry strongly depends on both shared selective pressures and reproductive interference. In closely-related Morpho butterfly species living in the understory of the neo-tropical rainforest, the blue iridescent coloration of the wings is likely involved in predation evasion, as well as in mate recognition and courtship. We used spectrophotometry, behavioral experiments, visual modeling and chemical analyses to characterize the evolution of visual and chemical traits in two closely-related species, Morpho helenor and Morpho achilles. We specifically compared trait variation between samples from allopatric and sympatric populations of M. helenor to test the effect of ecological interactions with M. achilles on trait evolution. We quantified the differences in wing iridescence and tested for variations in the sexual preference for this trait. We found a strong similarity in iridescence between M. helenor and M. achilles in sympatry while the iridescence of M. helenor diverged in allopatry, suggesting that predation favors local resemblance. Although intraspecific behavioral experiments showed that iridescent signals could be used as visual cues during intraspecific mate choice, the strong resemblance of the iridescent signals between species may impair these species visual recognition. In contrast, the divergent chemical bouquets detected between species suggest that the visual similarity of sympatric Morpho species may have favored the divergence of alternative traits involved in species recognition, such as chemical cues.

evolutionary biology↗

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

Convergence in light transmission properties of transparent wing areas in clearwing mimetic butterflies

Mullerian mimicry is a positive interspecific interaction, whereby co-occurring defended prey species share a common aposematic signal. In Lepidoptera, aposematic species typically harbour conspicuous opaque wing colour patterns with convergent optical properties among co-mimetic species. Surprisingly, some aposematic mimetic species have partially transparent wings, raising the questions of whether optical properties of transparent patches are also convergent, and of how transparency is achieved. Here we conducted a comparative study of wing optics, micro and nanostructures in neotropical mimetic clearwing Lepidoptera, using spectrophotometry and microscopy imaging. We show that transparency, as perceived by predators, is convergent among co-mimics. Underlying micro- and nanostructures are also convergent despite a large structural diversity. We reveal that while transparency is primarily produced by microstructure modifications, nanostructures largely influence light transmission, maybe enabling additional fine-tuning in transmission properties. This study shows that transparency might not only enable camouflage but can also be part of aposematic signals.

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↗

bioRxiv2019

Hummingbird iridescence: an unsuspected structural diversity influences colouration at multiple scales

AbstractIridescent colours are colours that change depending on the angle of illumination or observation. They are produced when light is reflected by multilayer structures or diffracted by gratings. While this phenomenon is well understood for simple optical systems, it remains unclear how complex biological structures interact with light to produce iridescence. There are very few comparative studies at interspecific level (often focusing on a single colour patch for each species), resulting in an underestimation of structure diversity. Using an interdisciplinary approach combining physics and biology, we here quantify the colour and structure of 36 hummingbirds species evenly distributed across the phylogeny. We explore at least 2 patches per species, which are assumed to be under different selective regimes. For each patch, we measure structural features (number of layers, layer width, irregularity, spacing, etc.) of the feathers at different scales using both optical and electronic microscopy and we measure colour using a novel approach we developed to encompass the full complexity of iridescence, including its angular dependency. We discover an unsuspected diversity of structures producing iridescence in hummingbirds. We also study the effect of several structural features on the colour of the resulting signal, using both an empirical and modelling approach. Our findings demonstrate the need to take into account multiple patches per species and suggest possible evolutionary pressures causing the evolutionary transitions from one melanosome type to another.

evolutionary biology↗

bioRxiv2019

Transparency, a better camouflage than crypsis in cryptically coloured moths

Predation is a ubiquitous and strong selective pressure on living organisms. Transparency is a predation defence widespread in water but rare on land. Some Lepidoptera display transparent patches combined with already cryptic opaque patches. While transparency has recently been shown to reduce detectability in conspicuous prey, we here test whether transparency decreases detectability in already cryptically-coloured terrestrial prey, by conducting field predation experiments with free avian predators and artificial moths. We monitored and compared survival of a fully opaque grey artificial form (cryptic), a form including transparent windows and a wingless artificial butterfly body. Survival of the transparent forms was similar to that of wingless bodies and higher than that of fully opaque forms, suggesting a reduction of detectability conferred by transparency. This is the first evidence that transparency decreases detectability in cryptic terrestrial prey. Future studies should explore the organisation of transparent and opaque patches on the animal body and their interplay on survival, as well as the costs and other potential benefits associated to transparency on land.

evolutionary biology↗

bioRxiv2019

Distribution of iridescent colours in hummingbird communities results from the interplay between selection for camouflage and communication

Identification errors between closely related, co-occurring, species may lead to misdirected social interactions such as costly interbreeding or misdirected aggression. This selects for divergence in traits involved in species identification among co-occurring species, resulting from character displacement. On the other hand, predation may select for crypsis, potentially leading co-occurring species that share the same environment and predators to have a similar appearance. However, few studies have explored how these antagonistic processes influence colour at the community level. Here, we assess colour clustering and overdispersion in 189 hummingbird communities, tallying 112 species, across Ecuador and suggest possible evolutionary mechanisms at stake by controlling for species phylogenetic relatedness. In hummingbirds, most colours are iridescent structural colours, defined as colours that change with the illumination or observation angle. Because small variations in the underlying structures can have dramatic effects on the resulting colours and because iridescent structures can produce virtually any hue and brightness, we expect iridescent colours to respond finely to selective pressures. Moreover, we predict that hue angular dependence - a specific aspect of iridescent colours - may be used as an additional channel for species recognition. In our hummingbird assemblages in Ecuador, we find support for colour overdispersion in ventral and facial patches at the community level even after controlling for the phylogeny, especially on iridescence-related traits, suggesting character displacement among co-occurring species. We also find colour clustering at the community level on dorsal patches, suspected to be involved in camouflage, suggesting that the same cryptic colours are selected among co-occurring species. This article has been peer-reviewed and recommended by Peer Community In Evolutionary Biology

ecology↗