Marked Animals Research Articles

Hidden in red: evidence for and against red camouflage in a jumping spider (Saitis barbipes)

Investigating the conspicuousness of animal color patterns to different observers is crucial for understanding their function. This study examines the peculiar case of a jumping spider (Saitis barbipes) whose males display red and black ornaments during courtship despite an apparent inability to distinguish these colors. We propose that, through predator eyes, red may actually be a better match than black to the spiders’ leaf litter background, and that the black fringe of hairs surrounding red ornaments may blur with red at natural predator acuities and viewing distances to produce a background-matching desaturated red. In a field experiment, we test whether red ornaments reduce predation relative to red ornaments painted black, and find that, unexpectedly, spiders with red ornaments are more heavily predated upon. Having established birds as the spiders’ primary predators, we image the spiders in their natural habitat using an avian-vision camera. We find their red coloration to have similar color contrast, but lower achromatic contrast, with the background than black coloration. We also find that red and black elements blur together at typical avian acuities and viewing distances to produce lower chromatic and achromatic contrasts with the background than would be seen by animals with higher acuities and/or closer viewing distances. Interestingly, red ornaments appear orange or yellow when viewed obliquely, which reduces their achromatic, but not chromatic, contrast with the background. Our imaging results provide support for our hypothesis that red is camouflaging, whereas the results of our predation experiment do not. Any functional significance of the spiders’ red coloration therefore remains unresolved.

Pterin-Based Red Coloration Predicts the Outcome of Male-Male Competition in Guinan Toad-Headed Lizard.

Animal coloration offers a unique opportunity to explore the evolutionary mechanisms underlying phenotypic diversity. Conspicuous coloration caused by pigments plays a crucial role in social signaling across multiple species by conveying information about individual quality, social ranks, or reproductive condition. Nevertheless, most previous studies have focused predominantly on colors produced by the exogenous pigments-carotenoids. Pterins are another prevalent group of conspicuous pigments, which can be produced endogenously and have received comparatively little attention. Whether pterin-based colors represent reliable signals remains elusive. The remarkable red ventrolateral coloration exhibited by males of the Guinan toad-headed lizard (Phrynocephalus guinanensis) in the Mugetan Desert presents an ideal model for investigating pterin-based coloration. Through electron microscopy and metabolomic identification, we discovered three types of pterin pigments within xanthophores. Integrating a series of morphological measurements and behavioral experiments, we found that this red coloration was not correlated with body size, bite force, and testosterone level, nor did females show a preference bias toward it. However, the red intensity predicted male-male competition outcomes, with deeper red males being more likely to emerge as winners. Our results indicated that the pterin-based coloration could convey information about male quality, suggesting its potential role in honest signaling, given the vital importance of pterin metabolism in physiological processes. This study provides a novel case into the understanding of pterin-based colors in animals.

Drivers of continuous colour variation in the Madeiran wall lizard (Teira dugesii)

Abstract Animal coloration is often shaped by a myriad of factors that lead to differences in colour through changes in the chromatophores. Depending on how this variation is partitioned, coloration is often categorized as continuous or polymorphic. However, the boundaries between these two categories are not always clear. Here, we investigated whether the ventral coloration of the Madeiran wall lizard (Teira dugesii) varies continuously or corresponds to discrete colour morphs, via by-eye colour classification and visual modelling. By combining these two approaches, we show that T. dugesii coloration varies continuously and that colour classifications based on anthropomorphic approaches alone are ill suited to describe animal coloration. We also tested the influence of size, body condition, and sex as possible factors that might explain differences in T. dugesii coloration. We found that body condition, and especially size and sex, explain a great proportion of the variability observed in this species. These differences point to an effect of ontogeny, which might play a major role in colour development owing to the longevity of this species. Moreover, the sexual dichromatism that this species shows is indicative of an effect of sexual selection on coloration, perhaps explained by differences in circulating hormones.

A call to integrate non‐visual functions of pigments and their interactions with visual functions to understand global change impacts on visual systems

Abstract Animal coloration serves a variety of visually related functions in nature (e.g. mate choice, aposematism and camouflage) but the pigments in integumentary tissues such as skin, scales and feathers may also serve functions unrelated to the visual environment (e.g. temperature regulation, detoxification and pollutant protection). Our understanding of the significance of the non‐visual functions of animal integumentary pigments, as well as how they interact with the visually related functions to shape animal visual systems, remains limited. Furthermore, due to their important roles in shaping species interactions and mediating interactions in the environment, animal colour traits are likely to be impacted by global change (e.g. increased temperatures, altered habitat quality and quantity, increased environmental stochasticity, pollutants and novel species assemblages). Considering the effects of global change on both visual and non‐visual functions is important for understanding whether the selection is acting directly on the pigment or on coloration. Since changing the trait distributions can then lead to changes in visual systems, we advocate for studies to consider all potential functions of integumentary pigments, both visual and non‐visual functions and their interaction. Towards this goal, we first highlight common functions of pigments with a focus on non‐visual functions across animal systems. Then we synthesize our current understanding of how global change can impact pigmentation and discuss factors that can modify the interactions between climate change and pigment function. Lastly, we discuss how changes in colour traits can impact visual systems and provide an example using amphibians and their responses to climate change as a model. Read the free Plain Language Summary for this article on the Journal blog.

How life became colourful: colour vision, aposematism, sexual selection, flowers, and fruits.

Plants and animals are often adorned with potentially conspicuous colours (e.g. red, yellow, orange, blue, purple). These include the dazzling colours of fruits and flowers, the brilliant warning colours of frogs, snakes, and invertebrates, and the spectacular sexually selected colours of insects, fish, birds, and lizards. Such signals are often thought to utilize pre-existing sensitivities in the receiver's visual systems. This raises the question: what was the initial function of conspicuous colouration and colour vision? Here, we review the origins of colour vision, fruit, flowers, and aposematic and sexually selected colouration. We find that aposematic colouration is widely distributed across animals but relatively young, evolving only in the last ~150 million years (Myr). Sexually selected colouration in animals appears confined to arthropods and chordates, and is also relatively young (generally <100 Myr). Colourful flowers likely evolved ~200 million years ago (Mya), whereas colourful fruits/seeds likely evolved ~300 Mya. Colour vision (sensu lato) appears to be substantially older, and likely originated ~400-500 Mya in both arthropods and chordates. Thus, colour vision may have evolved long before extant lineages with fruit, flowers, aposematism, and sexual colour signals. We also find that there appears to have been an explosion of colour within the last ~100 Myr, including >200 origins of aposematic colouration across nine animal phyla and >100 origins of sexually selected colouration among arthropods and chordates.

PMEL is involved in snake colour pattern transition from blotches to stripes

Corn snakes are emerging models for animal colouration studies. Here, we focus on the Terrazzo morph, whose skin pattern is characterized by stripes rather than blotches. Using genome mapping, we discover a disruptive mutation in the coding region of the Premelanosome protein (PMEL) gene. Our transcriptomic analyses reveal that PMEL expression is significantly downregulated in Terrazzo embryonic tissues. We produce corn snake PMEL knockouts, which present a comparable colouration phenotype to Terrazzo and the subcellular structure of their melanosomes and xanthosomes is also similarly impacted. Our single-cell expression analyses of wild-type embryonic dorsal skin demonstrate that all chromatophore progenitors express PMEL at varying levels. Finally, we show that in wild-type embryos PMEL-expressing cells are initially uniformly spread before forming aggregates and eventually blotches, as seen in the adults. In Terrazzo embryos, the aggregates fail to form. Our results provide insights into the mechanisms governing colouration patterning in reptiles.

Retraction Note: Design of 3D animation color rendering system supported by cloud computing based on genetic algorithm

Retraction Note: Design of 3D animation color rendering system supported by cloud computing based on genetic algorithm

Correlated evolution of conspicuous colouration and burrowing in crayfish.

Conspicuous colours have fascinated biologists for centuries, leading to research on the evolution and functional significance of colour traits. In many cases, research suggests that conspicuous colours are adaptive and serve a function in sexual or aposematic signalling. In other cases, a lack of evidence for the adaptive value of conspicuous colours garners interest from biologists, such as when organisms that live underground and are rarely exposed to the surface are nevertheless colourful. Here, we use phylogenetic comparative methods to investigate colour evolution throughout freshwater crayfishes that vary in burrowing ability. Within the taxa we analysed, conspicuous colours have evolved independently over 50 times, and these colours are more common in semi-terrestrial crayfishes that construct extensive burrows. The intuitive but not evolutionarily justified assumption when presented with these results is to assume that these colours are adaptive. But contrary to this intuition, we discuss the hypothesis that colouration in crayfish is neutral. Supporting these ideas, the small population sizes and reduced gene flow within semi-terrestrial burrowing crayfishes may lead to the fixation of colour-phenotype mutations. Overall, our work brings into question the traditional view of animal colouration as a perfectly adapted phenotype.

Barred, blotched or intermediate? A photographic-based survey on the spatial distribution of &lt;em&gt;Vipera aspis&lt;/em&gt; phenotypes from central-southern Italy

Variation in animal colouration, which holds ecological and evolutionary significance, is evident in snakes, including the polytypic and highly polymorphic asp viper Vipera aspis. This species, currently acknowledged with four subspecies, features three of them (V. a. aspis, V. a. francisciredi and V. a. hugyi) within the Italian territory, each displaying distinct dorsal patterns. Analysing 143 georeferenced photos from personal surveys and citizen science, the present study explores transition areas between V. a. francisciredi and V. a. hugyi, revealing the coexistence of three dorsal pattern phenotypes (i.e. francisciredi, hugyi, and intermediate) across central-southern Italy. The outcome of the work reveals occurrences of francisciredi phenotypes considerably beyond the southern limit indicated in recent literature. Remarkably, intermediate phenotypes cover a significant portion of southern Italy, including Apulia (three records), Basilicata (six records) and Campania (three records) regions, and overlapping with both hugyi and francisciredi ranges. These findings suggest asymmetrical gene flow from northern to southern populations, resembling patterns observed in other reptiles. The intricate distribution of colour phenotypes underscores the necessity for molecular investigations to comprehend the genetic context and evolutionary history of V. aspis populations from central-southern Italy.

Seasonal Alternation of Putative Camouflage Wing Morphs of the American Snout Butterfly (Libytheana carinenta).

AbstractIntraspecific variation in camouflage is common in animals. Sexual dimorphism in camouflage is less common and, where observed, attributed to trade-offs between natural selection for predator avoidance and sexual selection for conspicuous mating signals. Here we report on variation in putatively cryptic ventral hindwing patterns in the American snout butterfly, Libytheana carinenta. We use field surveys and crowdsourced data to characterize three morphs. One is found in both sexes, one is male specific, and one is female specific. The sex-specific morphs constitute a sexually dimorphic set whose frequencies change together in time. Field surveys indicate that butterflies in southern Arizona transition from midsummer dominance of the sexually monomorphic pattern to early-fall dominance of the sexually dimorphic set. Crowdsourced data indicate that the sexually dimorphic set dominates in early spring, transitioning later into a mixture of morphs dominated by the monomorphic pattern, with the dimorphic set rising in frequency again in late fall. We discuss this unique pattern of camouflage variation with respect to contemporary theory on animal coloration.

Role of body size and shape in animal camouflage.

Animal camouflage serves a dual purpose in that it enhances both predation efficiency and anti-predation strategies, such as background matching, disruptive coloration, countershading, and masquerade, for predators and prey, respectively. Although body size and shape determine the appearance of animals, potentially affecting their camouflage effectiveness, research over the past two centuries has primarily focused on animal coloration. Over the past two decades, attention has gradually shifted to the impact of body size and shape on camouflage. In this review, we discuss the impact of animal body size and shape on camouflage and identify research issues and challenges. A negative correlation between background matching effectiveness and an animal's body size has been reported, whereas flatter body shapes enhance background matching. The effectiveness of disruptive coloration is also negatively correlated with body size, whereas irregular body shapes physically disrupt the body outline, reducing the visibility of true edges and making it challenging for predators to identify prey. Countershading is most likely in larger mammals with smaller individuals, whereas body size is unrelated to countershading in small-bodied taxa. Body shape influences a body reflectance, affecting the form of countershading coloration exhibited by animals. Animals employing masquerade achieve camouflage by resembling inanimate objects in their habitats in terms of body size and shape. Empirical and theoretical research has found that body size affects camouflage strategies by determining key aspects of an animal's appearance and predation risk and that body shape plays a role in the form and effectiveness of camouflage coloration. However, the mechanisms underlying these adaptations remain elusive, and a relative dearth of research on other camouflage strategies. We underscore the necessity for additional research to investigate the interplay between animal morphology and camouflage strategies and their coevolutionary development, and we recommend directions for future research.

Urbanization alters the geographic patterns of passerine plumage color in China

Urbanization has altered natural landscapes and serves as an environmental filter that selects species with specific traits. Coloration is an important trait associated with biotic interactions and thermoregulation, enabling species’ survival and reproductive success. However, few studies have focused on how species coloration changes in response to urbanization. Here, we used 547 passerine bird species from 42 cities and their corresponding non-urban communities in China to test whether urban species are darker and if they have duller plumage colors than their non-urban counterparts. Furthermore, we examined whether and how urbanization influences avian plumage color homogenization and the extent to which urbanization has altered the strength of the color–latitude geographic pattern in passerine birds across China. We found a 3.2% loss in the coloration space of birds after urbanization, although there were no significant differences in the individual dimensions of colorfulness and lightness between urban and non-urban birds. Avian communities in cities exhibited more plumage color homogenization than those in non-urban communities. There were significant latitudinal gradients in plumage colorfulness and lightness in non-urban communities, but these correlations were weaker in urban communities. Non-urban communities that were more colorful and lighter tended to be duller and darker in urban environments, and vice versa. Our results provide national-scale evidence that urbanization has led to reduced color diversity, increased color-based community similarity, and altered geographic patterns of avian plumage color gradients in China. These findings provide new insights into how rapid human-induced environmental changes have affected animal coloration during the Anthropocene.

Network and Experimental Pharmacology on Mechanism of Yixintai Regulates the TMAO/PKC/NF-κB Signaling Pathway in Treating Heart Failure.

This study aims to explore the mechanism of action of Yixintai in treating chronic ischemic heart failure by combining bioinformatics and experimental validation. Five potential drugs for treating heart failure were obtained from Yixintai (YXT) through early mass spectrometry detection. The targets of YXT for treating heart failure were obtained by a search of online databases. Gene ontology (GO) functional enrichment analysis and Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analyses were conducted on the common targets using the DAVID database. A rat heart failure model was established by ligating the anterior descending branch of the left coronary artery. A small animal color Doppler ultrasound imaging system detected cardiac function indicators. Hematoxylin-eosin (HE), Masson's, and electron microscopy were used to observe the pathological morphology of the myocardium in rats with heart failure. The network pharmacology analysis results were validated by ELISA, qPCR, and Western blotting. A total of 107 effective targets were obtained by combining compound targets and eliminating duplicate values. PPI analysis showed that inflammation-related proteins (TNF and IL1B) were key targets for treating heart failure, and KEGG enrichment suggested that NF-κB signaling pathway was a key pathway for YXT treatment of heart failure. Animal model validation results indicated the following: YXT can significantly reduce the content of intestinal microbiota metabolites such as trimethylamine oxide (TMAO) and improve heart failure by improving the EF and FS values of heart ultrasound in rats and reducing the levels of serum NT-proBNP, ANP, and BNP to improve heart failure. Together, YXT can inhibit cardiac muscle hypertrophy and fibrosis in rats and improve myocardial ultrastructure and serum IL-1β, IL-6, and TNF-α levels. These effects are achieved by inhibiting the expressions of NF-κB and PKC. YXT regulates the TMAO/PKC/NF-κB signaling pathway in heart failure.

Estimating migration timing and abundance in partial migratory systems by integrating continuous antenna detections with physical captures.

Many populations migrate between two different habitats (e.g. wintering/foraging to breeding area, mainstem-tributary, river-lake, river-ocean, river-side channel) as part of their life history. Detection technologies, such as passive integrated transponder (PIT) antennas or sonic receivers, can be placed at boundaries between habitats (e.g. near the confluence of rivers) to detect migratory movements of marked animals. Often, these detection systems have high detection probabilities and detect many individuals but are limited in their ability to make inferences about abundance because only marked individuals can be detected. Here, we introduce a mark-recapture modelling approach that uses detections from a double-array PIT antenna system to imply movement directionality from arrays and estimate migration timing. Additionally, when combined with physical captures, the model can be used to estimate abundances for both migratory and non-migratory groups and help quantify partial migration. We first test our approach using simulation, and results indicate our approach displayed negligible bias for total abundance (less than ±1%) and slight biases for state-specific abundance estimates (±1%-6%). We fit our model to array detections and physical captures of three native fishes (humpback chub [Gila cypha], flannelmouth sucker [Catostomus latipinnis] and bluehead sucker [Catostomus discobolus]) in the Little Colorado River (LCR) in Grand Canyon, AZ, a system that exhibits partial migration (i.e. includes residents and migrants). Abundance estimates from our model confirm that, for all three species, migratory individuals are much more numerous than residents. There was little difference in movement timing between 2021 (a year without preceding winter/spring floods) and 2022 (a year with a small flood occurring in early April). In both years, flannelmouth sucker arrived in mid-March whereas humpback chub and bluehead sucker arrivals occurred early- to mid-April. With humpback chub and flannelmouth sucker, movement timing was influenced by body size so that large individuals were more likely to arrive early compared to smaller individuals. With more years of data, this model framework could be used to evaluate ecological questions pertaining to flow cues and movement timing or intensity, relative trends in migrants versus residents and ecological drivers of skipped spawning.

What If I Told You Camouflage is a Myth? Animal Coloration is Mainly A-biotic and not Biotic (Camouflage)

In the present article, the author posits that the perception that animals apparently display a strategy of avoiding detection by means of camouflage—i.e., by disguising themselves in the natural colours of their environment—is not the actual case in nature but, rather, merely anecdotal. Animal coloration is mainly a-biotic (eco-physiological) and not biotic (camouflage). The contention regarding the absence of the phenomenon of camouflage among animals as a common evolutionary response is based on three arguments: 1) that reflecting the natural colours of the environment is linked to ecophysiology; 2) that predator and prey constitute “an evolutionary pair” and, accordingly, they know how to identify one another (in order to survive they employ different strategies, of which camouflage is not one of them); and 3) that the approach of relating animal camouflage to reflecting the colours of the environment is an anthropocentric one. Rather than the accepted biotic-ethological approach (colour camouflage), the present article suggests the recognition of a-biotic and eco-physiological conditions as a distinct research field, whose title “Reflection of environmental colours by animals”, along with this article, calls for eco-physiologists to demonstrate that this approach indeed offers a special contribution to the understanding of colouration in animals.

Bright Colors: Eat Me at Your Own Risk

Some poisonous animals use bright coloration to protect themselves from other animals that want to eat them. These bright colors are also called warning colors. Frogs, snakes, butterflies, skunks, and more all use warning coloration. But how do the animals get their bright colors and toxic poisons? Warning colors can be passed down to certain animals from their parents, and other animals get them from the foods they eat. Just because some animals have bright colors does not always mean they are toxic. Some animals, also known as mimics, copy the colors of toxic animals so they can protect themselves from being eaten. We will explore how poisonous animals show their true colors, and how non-poisonous animals that display the same signals can also be protected from predators. You may notice similar connections between color and warning signals all around you!

Genetic Basis and Evolutionary Forces of Sexually Dimorphic Color Variation in a Toad-Headed Agamid Lizard.

In the animal kingdom, sexually dimorphic color variation is a widespread phenomenon that significantly influences survival and reproductive success. However, the genetic underpinnings of this variation remain inadequately understood. Our investigation into sexually dimorphic color variation in the desert-dwelling Guinan population of the toad-headed agamid lizard (Phrynocephalus putjatai) utilized a multidisciplinary approach, encompassing phenotypic, ultrastructural, biochemical, genomic analyses, and behavioral experiments. Our findings unveil the association between distinct skin colorations and varying levels of carotenoid and pteridine pigments. The red coloration in males is determined by a genomic region on chromosome 14, housing four pigmentation genes: BCO2 and three 6-pyruvoyltetrahydropterin synthases. A Guinan population-specific nonsynonymous single nucleotide polymorphism in BCO2 is predicted to alter the electrostatic potential within the binding domain of the BCO2-β-carotene complex, influencing their interaction. Additionally, the gene MAP7 on chromosome 2 emerges as a potential contributor to the blue coloration in subadults and adult females. Sex-specific expression patterns point to steroid hormone-associated genes (SULT2B1 and SRD5A2) as potential upstream regulators influencing sexually dimorphic coloration. Visual modeling and field experiments support the potential selective advantages of vibrant coloration in desert environments. This implies that natural selection, potentially coupled with assortative mating, might have played a role in fixing color alleles, contributing to prevalence in the local desert habitat. This study provides novel insights into the genetic basis of carotenoid and pteridine-based color variation, shedding light on the evolution of sexually dimorphic coloration in animals. Moreover, it advances our understanding of the driving forces behind such intricate coloration patterns.

The Source of Melanocytes in Ortho- and Heterotopic Tail Regenerates of Axolotls and the Dependence of the Regenerative Response on the Presence of Neural Tissue

We studied the regeneration of orthotopic and heterotopic tails in larval axolotls. First, we analyzed tail regeneration following reciprocal exchange of cuffs of tail integument between dark-colored (wild-type) and yellow-colored (hybrid) larval animals. Second, we studied tail regeneration in larval axolotls following transplantation of cuffs of tail integument from metamorphosed dark-colored conspecifics and from an adult fire salamander. In all cases, the amputation planes involved the transplanted integumental cuffs. In the first experiment, the regenerated tails showed the color of the host animals, not that of the transplanted cuffs. This suggests that the melanocytes of the regenerated tails were derived from the host hypodermis. Following transplantation of metamorphosed skin from axolotls and a fire salamander onto larval axolotls, the metamorphosed epidermis reverted to a larval condition. This indicates that the state of differentiation of the metamorphosed epidermis was not permanent. Rather, in order to maintain the metamorphosed epidermal structure, a continuous exposure of the animals to sufficient levels of thyroid hormones was required. Transplantation of tail buds from yellow-colored onto dark-colored axolotl embryos caused the formation of yellow-colored tails both in the head and the anterior limb region of the hosts. Incomplete resection of these heterotopic tails was followed by tail regeneration, while no tail regeneration occurred following complete resection of the heterotopic tails. Successful tail regeneration depended on the presence of neural tissue along the resection plane.

A demographic survey of the Davis Strait polar bear subpopulation using physical and genetic capture‐recapture‐recovery sampling

AbstractConducting assessments to understand the effects of changing environmental conditions on polar bear (Ursus maritimus) demography has become increasingly important to inform management and conservation. Here, we combined physical (2005–2007) and genetic (2017–2018) mark‐recapture with harvest recovery data (2005–2018) to estimate demographic rates of the Davis Strait polar bear subpopulation and examine the possible effects of climate, dynamic ice habitat, and prey resources on survival. Large sample sizes (e.g., 2,513 marked animals) allowed us to estimate temporal variation in annual survival rates using multistate mark‐recapture‐recovery models. We did not detect statistically significant effects of climate, ice habitat, and prey during the 13‐year study. Estimated total abundance in 2006 was 2,190, credible interval (CRI) [1,954, 2,454] and 1,944, CRI [1,593, 2,366] in 2018. Geometric mean population growth rate (0.99, 95% CRI [0.97, 1.01]) indicated the subpopulation may have declined slightly between 2006 and 2018. However, we did not detect a declining trend in survival or substantial change in reproductive metrics over this period. Given forecasts of major environmental change we emphasize the need to review monitoring programs for this subpopulation.

On the role of TFEC in reptilian coloration.

Reptilian species, particularly snakes and lizards, are emerging models of animal coloration. Here, I focus on the role of the TFEC transcription factor in snake and lizard coloration based on a study on wild-type and piebald ball pythons. Genomic mapping previously identified a TFEC mutation linked to the piebald ball python phenotype. The association of TFEC with skin coloration was further supported by gene-editing experiments in the brown anole lizard. However, novel histological analyses presented here reveal discrepancies between the ball python and the anole TFEC mutants phenotype, cautioning against broad generalizations. Indeed, both wild-type and piebald ball pythons completely lack iridophores, whereas the TFEC anole lizard mutants lose their iridophores compared to the wild-type anole. Based on these findings, I discuss the potential role of the MiT/TFE family in skin pigmentation across vertebrate lineages and advocate the need for developmental analyses and additional gene-editing experiments to explore the reptilian coloration diversity.