During a late-winter field survey in Baihuashan National Nature Reserve, Beijing, several noctuid moths were observed flying during the daytime at low temperatures and being actively preyed upon by Marsh tits, which removed the heads and wings of captured individuals. These observations indicate that adults of this noctuid lineage are active in late winter, providing a critical nutritional resource for insectivorous birds during the ecologically constrained, food-limited winter period. Here, we formally describe this lineage as a new genus, Shoudus gen. nov., based on a new species, S. baihuashanus sp. nov., collected from Baihuashan reserve, including three specimens retrieved during active interception of tit predation, along with detached wings and heads recovered from the snow. The new genus is placed in the tribe Orthosiini Guenée, 1837, primarily based on adult external morphology, including large compound eyes with long interfacetal hairs and bipectinate male antennae, as well as forewing patterning similar to certain orthosiine genera such as Perigrapha and Clavipalpula. Notably, the dark reddish-brown forewings with sharply contrasting pale markings, as seen in the new genus and these related genera, appear well adapted for camouflage against bark, leaf litter, and exposed soil in their habitats-potentially functioning as both background matching and disruptive coloration. To further assess its phylogenetic placement, we conducted a molecular analysis based on mitochondrial COI sequences (13 newly generated and 6 retrieved from BOLD/NCBI). The resulting maximum likelihood and Bayesian trees consistently support the monophyly of the new genus and reveal a close phylogenetic relationship with Orthosia, the type genus of Orthosiini. This integrative evidence strongly supports the recognition of Shoudus as a distinct lineage within Orthosiini.

To assess the efficacy of trabecular micro-bypass stents (IS) versus ab interno trabeculotomy (LOT) performed alongside cataract surgery; and to ensure patient comparability across both surgical groups concerning age, intraocular pressure (IOP), medication score, and disease type. Retrospective cohort METHODS: Overall, 194 eyes were assessed from 107 Japanese patients with open-angle glaucoma or exfoliation glaucoma who received IS plus cataract surgery at Saitama Red Cross Hospital between July 2017 and January 2022. Another 88 eyes were assessed from 58 patients who underwent combined LOT and cataract surgery at the same hospital between January 2018 and December 2019. Both cohorts were followed-up for ≥6 months. Propensity scoring facilitated between-group patient background matching. Overall, 62 eyes per group matched for preoperative characteristics were analyzed. Six-month postoperative IOP was 14.50 ± 2.26 and 14.08 ± 2.50 mmHg for IS and LOT, respectively, with medication scores of 1.50 ± 1.17 (IS) and 1.71 ± 1.60 (LOT), indicating no significant differences. The IOP reduction rate was 19.03 ± 13.34% (IS) and 18.94 ± 23.26% (LOT), showing no significant difference. Both groups exhibited similar medication score reductions (-1.11 ± 1.04 [IS], and -0.92 ± 1.47 [LOT]). Preoperative IOP significantly correlated with IOP reduction rate in both procedures. LOT patients experienced more hyphema postoperatively, versus IS patients. In eyes with relatively well-controlled preoperative IOP-where either IS or LOT could be reasonably selected-either procedure offers similar surgical outcomes, with comparable postoperative performance and complication rates, except for postoperative hyphema.

ABSTRACTFor species found in multiple habitats, the problem of camouflage against visually different backgrounds can be challenging. This is particularly so for bird eggs in open nests, as the scope for movement or alternative defensive strategies is limited. We studied egg camouflage in a small shorebird, the Kentish plover Anarhynchus alexandrinus, in two different coastal habitats in Cádiz province, Spain: sandy beaches and saltmarshes. Using calibrated photographs taken in situ and neurophysiologically plausible models of colour and pattern vision, we assessed the predicted discriminability of egg colour and patterning from those of backgrounds for likely nest predators (avian and mammalian carnivore) and, for comparison, humans. The findings suggest that at close range A. alexandrinus eggs are more susceptible to detection by visual predators based on their patterns (aka visual texture) rather than their colours, but at distances beyond which individual pattern elements can be resolved, they are highly cryptic. Although the colours and patterns of the saltmarsh and beach nest sites differ, the colours and surface patterning of eggs do not, suggesting that there is no local adaptation. However, the colours of eggs are similar to the types of background colours that overlap between the beach and saltmarsh. This suggests that, although the gross visual appearances of beach and salt marsh are quite different, egg camouflage in Kentish plovers relies on behavioural nest‐site selection and a good colour match to the average location type. The maculation on the eggs does not appear to represent background matching in terms of pattern, so its function remains speculative.

Many predators aim to approach prey without being detected or identified. Ambush predators often achieve this through camouflage, such as background matching. This strategy is thought to be ineffective for actively moving predators, as motion typically breaks camouflage. However, if animals could select and remain close to similarly coloured moving objects, then camouflage could be achieved on the move. Using detailed natural observations, we demonstrate that colour polymorphic trumpetfish (Aulostomus maculatus) selectively choose to 'shadow'-swim closely alongside-other fishes of similar colour to themselves. Specifically, yellow trumpetfish individuals most frequently shadow yellow Spanish hogfish (Bodianus rufus), while blue morph individuals most frequently shadow the blue terminal phase of queen parrotfish (Scarus vetula). When we experimentally presented three-dimensional models of these shadowing combinations to bicolour damselfish (Stegastes partitus) colonies in situ, these prey exhibited reduced anti-predator responses towards trumpetfish that were paired with a similarly coloured species versus trumpetfish that were dissimilar in colour to the fish they were shadowing, particularly for the yellow trumpetfish morph. Selecting a similarly coloured moving object (here a fish) represents a novel form of moving camouflage and illustrates how some predators can use strategic decision-making to improve their hunting success on the move.

Fur coloration serves several functions, including crypsis or background matching, an important feature to reduce predation. A dimorphic population, with rare light-colored guinea pigs is reported here at Colonia Pellegrini, Corrientes, Argentina. In May 2025, two Brazilian guinea pigs separated by a distance of 900-1000 m were observed grazing alongside normal-colored individuals. Multiple observations of this light morph have been consistently recorded since 2008 by a local resident. Although the frequency of the light morph in this population remains low, its persistent and widespread presence suggests that it has not experienced extremely high selection pressure.

Abstract Predation is pervasive in the natural world, where predators and prey have evolved spectacular mechanisms to avoid detection and recognition. An example is camouflage through background matching, which allows animals to resemble their background. Animals can move strategically towards backgrounds that match their morphology (background choice) to enhance camouflage. We studied the relevance of background choice in lionfish (Pterois miles), conspicuous stalking predators that could take advantage of background matching by resembling corals and other invertebrates in their surroundings. We offered different background combinations to hunting lionfish and we found that they indeed account for their background while hunting, although the response did not support the hypothesis that the preference is determined by background matching. Lionfish deviated towards a rocky background, which closely resembled the substrate where lionfish were caught (rocky reefs in the Mediterranean Sea). We suggest that lionfish showed a preference for a rocky background because in the Mediterranean they live on rocky reefs. While we cannot rule out that background matching played a role in background choice, we suggest that remaining close to a rocky reef while hunting offers lionfish the best combination of easy access to hiding spots and high availability of prey.

Sexual dimorphism is classically attributed to sexual selection, yet natural selection via sex-specific ecological pressures is equally important. We investigated this interplay by testing how camouflage and thermoregulation shape sexual color dimorphism across four Diploderma lizards with a comparative framework capturing diverse ecologies. Using spectrometry and image analysis, we documented pronounced sexual color dimorphism in dorsal patterns. Females prioritized background matching, while males favored high-contrast surface disruption, except in Diploderma slowinskii where monomorphic strategies suggested habitat-specific adaptations. Male stripes critical for disruption significantly reduced solar heat gain, imposing a physiological cost absent in females. This sex-specific optimization, males sacrificing thermoregulation for camouflage efficacy and females favoring crypsis, demonstrates how divergent natural selection pressures drive sexual color dimorphism evolution. Our findings enhance the understanding of animal coloration beyond the sexual selection paradigm, positioning ecological trade-off as a fundamental mechanism shaping sexual color dimorphism.

The role of background matching and disruptive coloration in impeding detection and recognition

Background matching is a common form of crypsis in animals, resulting from selective pressures imposed by visual systems of predators and/or prey. Therefore, it could be expected that novel backgrounds would pose a barrier to the establishment of invasive species, due to a lack of crypsis. Behavioural flexibility in crypsis—through facultative crypsis and/or choice of matching backgrounds—has been suggested as a trait that may facilitate invasiveness. We assessed background-matching and facultative brightness-change in an Australian population of the invasive Asian House Gecko (Hemidactylus frenatus). This species is currently expanding from urban environments into surrounding tropical woodland, and demonstrates great variability in colour and pattern among individuals. We quantified wild background-matching in terms of both colour and brightness. We then experimentally tested whether geckos facultatively change brightness in the direction expected for a given background. Hemidactylus frenatus consistently brightness-matched across the backgrounds on which they were found, more than would be expected by chance. Experiments showed that H. frenatus rapidly changed in their dorsal brightness, in the direction expected given their background, suggesting that brightness-matching observed in wild geckos is due to facultative brightness-change. Successful invasion may benefit from facultative crypsis; however, it remains to be demonstrated how facultative brightness-change in H. frenatus is linked to predation and invasion success. We outline how recognition of facultative colour-pattern change in invasive species may be important for early detection and management actions.

Abstract Background and Aims Automatic intracardiac pattern matching (aICPM) can be used to monitor the stability of atrial tachycardia (AT) during activation mapping or to perform an atrial pace mapping (APM) for localizing the origin of non-sustained atrial tachycardia (nsAT), or atrial fibrillation (AF) triggers. When aICPM is performed, IC pattern similarity score can fluctuate despite a stable pacing site and the score is usually less than 100%, even when paced from the site of origin (SOO). We assessed the underlying cause of the fluctuation and aimed to define an optimal cutoff, which ensures to accurately detect the SOO by aICPM. Methods aICPM was performed with six biatrial unipolar signals to create two sets of score maps: one for the stable rhythm from the same SOO and one for paced IC patterns outside the SOO. The dispersion of the IC pattern similarity score was assessed in 17 consecutive patients during stable focal (n=5) and reentry (n=12) AT. For the same SOO score map, an IC pattern of the first atrial beat was acquired and automatically matched to the subsequent IC morphologies without catheter manipulation to exclude the mechanically induced beats. For the score map with the beats outside the SOO, the IC pattern of the SOO was automatically matched to the paced morphologies from different locations outside the SOO. Results The median number of points per score map was 848 (IQR 460; 1016). The median IC pattern similarity for the same SOO was 86% (IQR 75%; 94%). The KDE curve of the IC pattern similarity distribution showed a non-gaussian form with multiple local maximums corresponding to the overlay of the p-wave with the different segments of the QRST, resulting in fluctuation of the IC pattern similarity score. (Figure 1). There is a moderate positive correlation between the median score and cycle length (r = 0.49, p=0.045), as well as a strong negative correlation between the cycle length and score standard deviation (r = -0.88, p<0.0001). That indicates a lower median IC pattern similarity score and higher variability in the rhythms with shorter cycle lengths. The ROC-curve analysis showed an optimal IC similarity threshold for the rhythm of the same SOO of 63% with a sensitivity of 95% and specificity of 98%. The inflexion point analysis using the peak detection in the KDE first derivative curve revealed an optimal IC pattern similarity cutoff of 69% for the rhythm of the same SOO with a sensitivity of 90.4% and specificity of 99%. Conclusion Fluctuations in IC pattern morphology can occur due to an intermittent overlay of the paced unipolar morphology with farfield electrograms of different QRST segments. The IC pattern similarity score is cycle length dependent with higher scores and less dispersion in slower tachycardias. The newly defined IC similarity cutoff allows a better applicability of aICPM in electrophysiological procedures.

Abstract Visual camouflage via background matching involves a variety of adaptative traits to maintain crypsis, including intraspecific color variation, behavioral choice of substrates, and color change. These non-mutually exclusive solutions frequently act together to conceal and deceive prey and enemies. Here, we combine field observations, image analysis, and laboratory experiments to investigate which processes drive camouflage in the garden cross spider (Araneus diadematus), a species with body coloration that varies in shades of brown. We demonstrate that A. diadematus does not change color significantly, at least within the same instar, when retained on substrates of different coloration. However, there is strong behavioral selection through active substrate choice across spiders for color-matching substrates (dead brown leaves over green leaves) when offered a choice under laboratory conditions. Similar background selection also apparently occurs in nature, where spiders were often observed on brown leaves, even though they are less common than green ones. In general, vision modeling shows that there is a high overlap in the diversity of brown shades (from pale to dark) between spider bodies and dead leaves available in the environment. Image analyses also revealed that spiders fine-tune their camouflage on an individual level by matching the tones (from pale to dark) of their host leaves. Therefore, we demonstrate how behavior coupled with variation in color phenotypes facilitates camouflage at different scales.

Camouflage is a critical survival strategy that helps to evade predation and increase hunting success. Background matching and disruptive colouration are different camouflage strategies that are subject to different selective pressures and can drive divergence in their associated traits such as colour pattern and behaviour. This study tested whether two closely related reef fish species (Hypoplectrus spp.) with distinct colour patterns exhibit different predator escape responses and differential gene expression in the brain indicative of divergent camouflage strategies. Combining field and laboratory experiments, we show that barred hamlets, characterised by disruptive colouration, are dynamic in their escape responses, while black hamlets, with their darker colouration, had a preference for hiding. The behavioural differences between these species seem to be limited to divergent predator escape responses since other behaviours such as activity or sociability did not differ. Importantly, the observed behavioural differences were accompanied by transcriptomic differences in their brains, particularly in regions associated with the perception of looming threats and less so in the region involved in conditioning. Differential expression in the diencephalon suggests enhanced neuronal plasticity in barred hamlets, which might allow for rapid adjustments in their escape response, while black hamlets exhibited upregulation in genes linked to immune response and oxygen transport in the optic tectum. Overall, our findings suggest that the two species utilise different camouflage strategies, which might contribute to the maintenance of colour pattern differences and thereby influence the speciation and diversification of these closely related sympatric reef fishes.

Many cryptic green animals match leaves in invisible near-infrared (NIR) wavelengths. This observation is an enduring puzzle because animals do not see NIR light, so NIR background matching is unlikely to contribute to visual camouflage. Two alternative explanations have been proposed-infrared camouflage (i.e. matching the temperature of the background) and thermoregulation-but neither hypothesis has been experimentally tested. To test these hypotheses, we developed bilayer coatings that mimicked the reflectivity of green leaf-sitting frogs with high NIR (HNIR) or low NIR (LNIR) reflectance. Under a solar simulator in the laboratory, agar model frogs with LNIR reflectance heated up more quickly and reached higher temperatures than those with HNIR reflectance. However, when placed in a tropical rainforest (natural habitat of leaf-sitting frogs), HNIR and LNIR models did not significantly differ in the similarity of surface temperature to the adjacent leaves or in core temperature, thus failing to support the infrared camouflage and thermoregulation hypotheses, respectively. The lack of difference between treatments is probably due to the limited exposure of frogs to direct solar radiation in their natural habitats. We propose an explanation for NIR background matching based on specific mechanisms underlying green coloration and translucence in frogs and caution against assuming adaptive convergence.

A key selection pressure in most habitats is predation, and a common strategy adopted by prey is crypsis through background matching. Many marine blenny fishes are in the process of a dramatic transition across one of the world's most extreme ecotones: the invasion of land across the intertidal zone. We investigated the impact of this transition on body crypsis versus the conspicuousness of visual signals across 56 blenny taxa relative to 59 biologically relevant backgrounds, and as viewed by conspecifics and four representative fish and avian predators. We computed 33 colour and 23 pattern indices from standardised digital photographs of six individuals for each taxa (median sample). Six of these indices were selected for detailed analysis following phylogenetic Principal Component Analysis. While phylogenetic regressions revealed some aspects of body crypsis appeared to have changed adaptively with the progressive transition to land (specifically a reduction in body colour saturation), colonisation was primarily facilitated by a generalist form of crypsis. That is, the colours and patterns of aquatic blennies were already well matched to the range of terrestrial backgrounds where amphibious and terrestrial species were observed out of water. Predation appears to have been an important selection pressure constraining the colour and pattern of the dorsal fins used in social communication, which also matched visual backgrounds. Our data implies anti-predator strategies that translate well across habitats and different predator regimes will facilitate colonisation by either reducing predation risk or allowing species to persist long enough to respond adaptively to environmental change.

Camouflage through colour change can involve reversible or permanent changes in response to cyclic predator or herbivore pressures. The evolution of background matching in camouflaged phenotypes partly depends on the genetics of the camouflage trait, but this has received little attention in plants. Here we clarify the genetic pathway underlying the grey-leaved morph of fumewort, Corydalis hemidicentra, of the Qinghai-Tibet Plateau that by being camouflaged escapes herbivory from caterpillars of host-specialized Parnassius butterflies. Field experiments show that camouflaged grey leaves matching the surrounding scree habitat experience reduced oviposition by female butterflies and herbivory by caterpillars, resulting in higher fruit set than that achieved by green-leaved plants. The defence is entirely visual. Multi-omics data and functional validation reveal that a 254-bp-inserted transposon causes anthocyanin accumulation in leaves, giving them a rock-like grey colour. Demographic analyses of plant and butterfly effective population sizes over the past 500 years indicate that plant populations have been more stable at sites with camouflage than at sites with only green-leaved plants. In the recent past, populations of Parnassius butterflies have declined at sites with camouflaged plants. These findings provide insights into the genetics of a plant camouflage trait and its potential role in the rapidly changing dynamics of plant-herbivore interactions.

Abstract Animals use colour for a wide range of adaptive functions, ranging from cryptic colours that blend into their environments to bright, conspicuous signals that convey information, either to attract mates or to ward off predators and rivals. However, perhaps one of the most intriguing adaptations is how animals can make use of the absence of colour through transparency. Animal transparency has long been understood as a form of camouflage, allowing predators to see straight through their prey as if it were not there. However, transparency can take many different forms, both in terms of the degree of transparency, ranging from opaque through translucent to transparent and in the extent of coverage, with different combinations of transparent and opaque regions. Despite this variation, transparency has often either been regarded as a unique form of concealment or synonymised with background‐matching camouflage. Yet, empirical evidence is increasingly demonstrating how different forms of transparency may facilitate different defensive and communicative strategies. Here, we contextualise the potential functions of transparency into the wider framework of visual ecology, review the evidence for different strategies and highlight areas in need of continued research. We find that, despite its seemingly intuitive role in camouflage, transparency can fulfil many different functions, including facilitating several conceptually distinct forms of camouflage (e.g. background matching, disruption, masquerade and edge diffusion), mimicry (both Batesian and Müllerian) and enhancing communicative signals (such as aposematism, mate choice and territory defence). Yet, many ecological and behavioural questions remain to be addressed, and caution is needed when assessing or interpreting the function of transparency. Read the free Plain Language Summary for this article on the Journal blog.

Background matching and disruptive coloration are defense mechanisms of animals against visual predators. Disruptive coloration tends to evolve in microhabitats that are visually heterogeneous, while background matching is favored in microhabitats that are chromatically homogeneous. Controlling for the phylogeny, we explored the evolution of the coloration and the marking patterns in the sexual dichromatic and widely distributed neotropical grasshoppers of the genus Sphenarium. These grasshoppers represent an excellent model to investigate the evolution of cryptic coloration on insects due to the heterogeneity of the environments where they have evolved. We found a correlation between the grasshoppers' coloration and disruptive markings with the chromatic properties of their environments that was inferred by the levels of precipitation during the rainy season. The results suggest that colors and marking patterns could evolve due to predation pressures. Color in both sexes could offer camouflage that is not perfectly background matched to a single habitat but instead offers a degree of resemblance to multiple backgrounds. Moreover, we found that males and females chromatic properties differ between them and precipitation levels where the species are found. This suggests that the sexes have diverged in their response to the environments, favoring the evolution of sexual dichromatism in these grasshoppers.

Many animals are capable of rapid dynamic colour change, which is particularly well represented in fishes. The proximate mechanisms of dynamic colour change in fishes are well understood; however, less attention has been given to understanding its ecological relevance. In this study, we investigate dynamic colour change in zebrafish (Danio rerio) across multiple contexts, using a protocol to image the colouration of live fish without anaesthesia under standardized conditions. We show that zebrafish respond to different visual environments by darkening their overall colouration in a dark environment and lightening in a light environment. This is consistent with crypsis through background matching as a function of dynamic colour change. Additionally, we find that zebrafish use dynamic colour change to increase the internal contrast of their striped patterning in the presence of conspecifics. We speculate that this may function in social signalling and/or dazzle colouration. We find no effect of a predator stimulus on dynamic colour change. Finally, we discuss the potential for zebrafish to use multiple colouration strategies simultaneously as distance-dependent effects, considering the typical viewing distances of zebrafish and their predators.

Background matching, an important form of camouflage, can be challenging for animals that range across heterogeneously colored habitats. To remain cryptic in such habitats, animals may employ color change, background choice, or generalist coloration, and the efficacy of these strategies may be influenced by an animal's mobility. We examined camouflage strategies in the praying mantis Stagmomantis limbata. We reared mantids in green or brown containers to test whether mantids change color over development to match their background. Additionally, we tested whether adult mantids (i) employ behavioral background choice, (ii) exhibit sexual color dimorphism, and (iii) differ in mobility in the field. Mantids changed color during development in response to their background, but the effect was small and variable. Adult mantids did not show background choice. In the field, adult males moved greater distances than females. Adults exhibited sexual color dimorphism: Males were heterogeneous in coloration (green body with brown pronotum), while females were more homogeneous in color, ranging continuously from green to brown. We suggest a hypothesis that differences in mobility between the sexes have led to the sexual color dimorphism observed and that this dimorphism reflects different camouflage strategies, with highly mobile males showing a generalist coloration and more sedentary females showing a specialist coloration.

Camouflage is often considered a daytime phenomenon based on light and shade. Nocturnal camouflage can also occur, but its mechanistic basis remains unclear. Here, we analyze the conditions for background matching (BM) of avian predators against the night sky. Such concealment is achieved when the contrast between the predator and the sky is smaller than the contrast detection threshold of prey. This condition cannot be fulfilled under isotropic skies, as in fully overcast or moonless nights. However, on clear moonlit nights, the isotropy of the sky radiance is broken due to the presence of the Moon, and the conditions for BM can be met for a wide range of sky directions. This effect is mainly dependent on the altitude of the Moon above the horizon, rather than on Moon phase. We have modeled the feasibility of concealment through BM of a typically white barn owl (Tyto alba) when hunting rodents, based on its contrast against the moonlit sky. We considered the radiometric quantities of the sky, the ground, and the bird's undersides. Our results show that a barn owl with highly reflecting underparts may approach a rodent from broad regions of the moonlit sky while keeping itself below the contrast detection threshold of the mouse M-cones and rods. S-cones, in turn, remain below their excitation threshold for most of the lunar cycle. Our results demonstrate that the white color of barn owls serves as camouflage tailored to the moonlit sky background, providing a mechanistic basis for understanding nocturnal camouflage.