Biology subjects

Lienard, M. A.

Publications and source records attributed to Lienard, M. A..

7 recordsLinked to original sources

bioRxiv2026

Seeing danger? Visual constraints and collision risk in the Bearded Vulture Gypaetus barbatus

The Bearded Vulture, Gypaetus barbatus is highly vulnerable to collisions with human-made aerial infrastructures. Yet, its visual sensory system remains poorly understood, limiting the development of species-specific collision mitigation measures. To address this gap, we characterized its visual ecology across four complementary dimensions: visual fields, spatial resolution, contrast sensitivity and spectral sensitivity of cone visual rhodopsins. Bearded vultures have no blind area in the direction of travel during foraging flight, indicating that frontal visual-field limitations are unlikely to contribute to their risk of collisions. Their axial length predicts high spatial visual resolution, suggesting that insufficient spatial resolution is unlikely to be a primary cause of collisions. By contrast, Bearded Vultures display very low peak contrast sensitivity compared to other birds, which may limit their ability to detect objects when contrast with the background, or within the objects themselves, is low. Functional characterization of the four cone visual pigments indicated sensitivity spanning approximately 350-640 nm, with a potential chromatic-discrimination range from 400 to 602 nm. Together, these results identify that contrast sensitivity, rather than visual-field configuration or spatial resolution, is a key perceptual constraint to consider in collision mitigation of the Bearded Vulture. Visual markers should therefore maximize both internal contrast and brightness contrast against the surrounding environment. More broadly, our multidisciplinary approach highlights how birds differ substantially in how they perceive anthropogenic structures and illustrates the importance of incorporating species-specific sensory ecology into conservation efforts, especially in the design of collision-mitigation strategies.

ecology↗

bioRxiv2026

Under pressure: Evolutionary trade-offs shape the single visual opsin of deep-sea octopods

Octopods possess remarkable camera-type eyes and specialised image-forming vision that support orientation, prey detection, predator avoidance and visual communication. Unlike vertebrates and arthropods, however, octopod vision is thought to rely mainly on a single rhodopsin (r-opsin1), raising the question of how such a constrained system adapts across contrasting light environments from shallow coastal waters to deep-sea habitats. Using transcriptional profiling of the retina and optic lobe from seven native octopod species of the Gulf of Naples, we show that r-opsin1 is the predominant visual gene across all species and investigate how contrasting photic habitats have shaped its molecular and functional evolution. Although positive selection analyses revealed no general association between habitat depth and r-opsin1 evolution, twelve codons in the deep-mesopelagic Pteroctopus tetracirrhus r-opsin1 showed evidence of positive selection, including two residues located on opposing helices of the retinal-binding pocket. In vitro experiments demonstrated that substituting either I87V and F201N produced a marked bathochromatic shift from the wild-type blue-green spectrum towards red wavelengths, whereas their combination restored the wild-type spectral profile. Other deep-sea octopod r-opsin1 naturally bearing one of these substitutions retained blue-green sensitivity. Reconstructed ancestral proteins similarly maintained blue-green absorption, supporting conservation of this spectral phenotype throughout octopod r-opsin1 evolution. We further show that F201N reduces adiabatic compressibility within the retinal-binding pocket, by co-evolving compensatory sites offering a structural trade-off, favouring pressure adaptation while restraining spectral tuning. Together, our findings support that octopod visual rhodopsin evolution has been shaped by the multiple ecological pressures of contrasting marine environments, illustrated with lineage-specific and habitat-dependent trajectories on a single locus while preserving a conserved visual phenotype.

evolutionary biology↗

bioRxiv2025

Spectral tuning and signaling of diverse and most red sensitive visual rhodopsins that drive high colour discrimination in Mantis Shrimp eyes

Stomatopod crustaceans (mantis shrimps) possess extraordinary eyes with unmatched visual opsin diversity, but their potential for broad colour detection remains unclear. Here, we report that seventeen opsins, mostly from the midband eye region, are involved in colour sensing and signaling via Gq/Gi-coupling and describe the underlying mechanisms of spectral tuning. Two mid-wavelength opsins preferentially absorb blue light and a majority of long-wavelength opsins absorb in the green range, but three absorb light beyond 600 nm, representing exquisite far-red-sensitive animal opsins. Several blue and red opsins exhibit photoreversibility with opposite spectral shifts explained by retinal binding interactions, revealing unrecognised photochemical flexibility in stomatopod photoreception. Row-specific spectral sensitivity results from combining carotenoid filters with multiple individually-tuned rhodopsins, altogether extending broad vision to the far-red spectrum.

biophysics↗

bioRxiv2024

Discovery and isolation of novel capsaicinoids and their TRPV1-related activity

Chilis contain capsaicin and other structurally related molecules known as capsaicinoids. Capsaicins target protein, the transient receptor potential cation channel subfamily V member 1 (TRPV1), has been linked to many post-activation effects, including changes in metabolism and pain sensation. Capsaicinoids also bind to TRPV1, but current studies often disregard non-capsaicin interactions. To fill in these gaps, we screened 40 different chili varieties derived from four Capsicum species by means of untargeted metabolomics and a rat TRPV1 (rTRPV1) calcium influx activation assay. The resulting capsaicinoid profiles were specific to each variety but only partially corresponded with species delimitations. Based on rTRPV1 activation elicited by crude chili extracts, capsaicinoids act in an additive manner and a capsaicinoid profile can serve as a gauge of this activation. In addition, we isolated eighteen capsaicinoids, including five previously unreported ones, and confirmed their structure by NMR and MS/MS. We then tested rTRPV1 activation by 23 capsaicinoids and three related compounds. This testing revealed that even slight deviations from the structure of capsaicin reduce the ability to activate the target, with a mere single hydroxylation on the acyl tail reducing potency towards rTRPV1 by more than 100-fold. In addition, we tested how rTRPV1 activity changes in the presence of capsaicin together with non-activating capsaicin analogs and weakly activating capsaicinoids and found both classes of molecules to positively modulate the effects of capsaicin. This demonstrates that even such compounds have measurable pharmacological effects, making a case for the use and study of natural chili extracts. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=76 SRC="FIGDIR/small/620944v2_ufig1.gif" ALT="Figure 1"> View larger version (17K): org.highwire.dtl.DTLVardef@1d56d02org.highwire.dtl.DTLVardef@e7a66dorg.highwire.dtl.DTLVardef@5f409forg.highwire.dtl.DTLVardef@18b88f7_HPS_FORMAT_FIGEXP M_FIG C_FIG Created in BioRender. Smith, J. (2025) https://BioRender.com/a61h668 HighlightsO_LI5 novel capsaicinoids (vanilloids) and 13 other capsaicinoids were isolated from chilis. C_LIO_LIThe slightest deviation in the capsaicin structure results in decreased TRPV1 activity. C_LIO_LIA single hydroxylation can reduce potency to TRPV1 100-fold. C_LIO_LINon-pungent vanilloids modulate capsaicin-TRPV1 activity. C_LI

pharmacology and toxicology↗

bioRxiv2023

Opsin gene expression plasticity and spectral sensitivity as mechanisms for search image formation in mate-searching male damselflies

The visual systems of Odonata are characterized by many opsin genes, which form the primary light-sensitive photopigments of the eye. Female-limited colour polymorphisms are also common in Odonata, with one morph typically exhibiting male-like (androchrome) colouration and one or two morphs exhibiting female-specific colouration (gynochromes). These colour polymorphisms are thought to be maintained by frequency-dependent sexual conflict, in which males form search images for certain morphs, causing disproportionate mating harassment. Here, we investigate opsin sensitivity and gene expression plasticity in mate-searching males of the damselfly Ischnura elegans during adult maturation and across populations with different female morph frequencies. We find evidence for opsin-specific plasticity in relative and proportional opsin mRNA expression, suggesting changes in opsin regulation and visual sensitivity during sexual maturation. In particular, expression of the long-wavelength sensitive opsin LWF2 changed over development and varied between populations with different female morph frequencies. UV-Vis analyses indicate that short- and long-wavelength opsins absorb wavelength of light between 350 and 650 nm. Assuming opponency between photoreceptors with distinct short- and long-wavelength sensitivities, these sensitivities suggest male spectral visual discrimination ability of andromorph and gynomorph females. Overall, our results suggest that opsin sensitivity and expression changes contribute to visual tuning that could impact conspecific discrimination.

evolutionary biology↗

bioRxiv2023

Convergent evolution of noxious heat sensing by TRPA5, a novel class of heat sensor in Rhodnius prolixus

As ectotherms, insects need a multifaceted repertoire of heat-sensitive receptors to monitor environmental temperatures and finely control behavioral thermoregulation. Here, we show that TRPA5 genes, a class of ankyrin transient receptor potential channels lost in genomes of model fruit flies or mosquitoes, are widespread across insect orders, and encode a previously uncharacterized type of heat receptors. We demonstrate that RpTRPA5B, a TRPA5 channel of the triatomine bug Rhodnius prolixus (Insect: Hemiptera), primary vector of Chagas disease, forms a homo-tetrameric channel displaying a uniquely high thermosensitivity. The channel biophysical determinants include a large channel activation enthalpy change (72 kcal/mol), a high temperature coefficient (Q10 = 25), and temperature-induced currents from 53 {degrees}C to 68 {degrees}C (T0.5= 58.6 {degrees}C) in vitro, similar to mammalian noxious TRPV heat receptors. Monomeric and tetrameric predictions of the ion channel architecture show reliable and conserved structural parallels with fruit fly dTRPA1, albeit depicting structural uniqueness from dTRPA, Painless and Pyrexia in the ankyrin repeat domain and the channel selectivity filter, potential modulator regions of functional characteristics of TRPs. The channel activation response, structural features and ubiquitous sensory tissue expression delineate a potential thermosensitive physiological niche close to that of Pyrexia genes, lost during the evolution of true bugs. Overall, the finding of TRPA5 genes as a class of temperature-activated receptor illustrates the dynamic evolution of a large family of insect molecular heat detectors, with TRPs as promising multimodal sensory targets for triatomine vector control.

evolutionary biology↗

bioRxiv2020

The evolution of red colour vision is linked to coordinated rhodopsin tuning in lycaenid butterflies

Colour vision is largely mediated by changes in number, expression, and spectral properties of rhodopsins, but the genetic mechanisms underlying adaptive shifts in spectral sensitivity remain largely unexplored. Using in vivo photochemistry, optophysiology, and in vitro functional assays, we link variation in eye spectral sensitivity at long wavelengths to species-specific absorbance spectra for LW opsins in lycaenid butterflies. In addition to loci specifying an ancestral green-absorbing rhodopsin with maximum spectral sensitivity ({lambda}max) at 520-530 nm in Callophrys sheridanii and Celastrina ladon, we find a novel form of red-shifted LW rhodopsin at {lambda}max = 565-570 nm in Arhopala japonica and Eumaeus atala. Furthermore, we show that Ca. sheridanii and Ce. ladon exhibit a smaller bathochromic shift at BRh2 (480-489 nm), and with the ancestral LW rhodopsin, cannot perceive visible red light beyond 600 nm. In contrast, molecular variation at the LW opsin in A. japonica and E. atala is coordinated with tuning of the blue opsin that also shifts sensitivity to longer wavelengths enabling colour discrimination up to 617 nm. We then use E. atala as a model to examine the interplay between red and blue spectral sensitivity. Owing to blue duplicate expression, the spatial distribution of opsin mRNAs within an ommatidium defines an expanded retinal stochastic mosaic of at least six opsin-based photoreceptor classes. Our mutagenesis in vitro assays with BRh1 ({lambda}max = 435 nm) chimeric blue rhodopsins reveal four main residues contributing to the 65 nm bathochromic shift towards BRh2 ({lambda}max = 500 nm). Adaptations in this four-opsin visual system are relevant for discrimination of conspecific reflectance spectra in E. atala. Together, these findings illustrate how functional changes at multiple rhodopsins contribute to the evolution of a broader spectral sensitivity and adaptation in visual performance. Significance StatementRhodopsins are photosensitive protein molecules that absorb specific wavelengths of incoming light and convey colour information in the visual system. We show that molecular evolution in a green insect opsin gene resulted in a shift in its maximal absorbance peak, enabling some lycaenid butterflies to use spectral energy of longer wavelengths (LW) to discriminate colours in the red spectrum better than relatives bearing ancestral green LW rhodopsins. Lycaenids also evolved a duplicate blue opsin gene, and we illustrate an example where species equipped with red LW rhodopsins shifted their blue sensitivity peak to longer wavelengths due to changes in several blue-tuning residues that have evolved repeatedly in different insect lineages. We demonstrate how changes at multiple vision genes in the insect eye effectively create a coordinated mechanism expanding spectral sensitivity for visually guided behaviours such as selecting host plants and mates.

evolutionary biology↗