Feather reflectance in visible (VIS) and near-infrared (NIR) wavelengths influences avian heat balance by modulating the absorption of solar energy, yet the evolutionary and ecological patterns of NIR reflectance remain poorly understood. We developed a cross-taxonomic predictive framework linking NIR to VIS reflectance using a full-spectrum dataset of 531 bird species from 23 orders and 106 families, integrating 439 newly measured spectra with published data. Across species, VIS and NIR reflectance were strongly correlated (R² = 0.667), but regression slopes differed significantly among orders, indicating lineage-specific spectral scaling. When controlling for visible coloration, NIR reflectance still varied markedly across orders, revealing taxon-specific thermal properties beyond colour. Morphological and ecological traits further predicted these patterns, with hand-wing-index, migratory status, habitat types, habitat temperature and precipitation all exerting significant effects on NIR reflectance. Residual analysis revealed that Gruiformes, Pelecaniformes and Charadriiformes (i.e. waders, gulls, terns and allies) showed low and variable NIR reflectance, possibly reflecting structural adaptations to heterogeneous thermal environments. Collectively, our results provide the first large-scale, phylogenetically informed framework for predicting NIR reflectance from VIS data, advancing mechanistic understanding of avian thermal adaptations.

The presence of multiple color variants within a single population, known as color polymorphism, is a striking example of intraspecific phenotypic variation and a model for studying evolutionary processes. These processes depend on the underlying mechanisms such as the genes and pigments involved; but we currently lack such information for non-model groups such as arachnids. We examined the genes associated with color polymorphism in the Australian Christmas spider, Austracantha minax, a widespread species with two female-restricted color morphs: one that is completely black and the other presenting a black-and-white pattern on its dorsum. We sequenced the mRNA of individuals of both morphs at different developmental stages and assessed differences in gene expression between color morphs based on a de novo transcriptome assembly for the species, and integrated this with high resolution electron microscopy observations. We found that gene expression patterns are primarily influenced by the stage of development, and within each stage we found differentially expressed genes between the black and black-and-white morphs, especially in the adult stage. Contrary to expectations, these genes were not associated with melanin or guanine crystal deposition (detected in the microscopy), but were associated with chitin and cuticle metabolic processes. By exploring arachnid coloration at the transcriptomic level, our work reveals for the first time genetic mechanisms underpinning the evolution of color polymorphism in spiders.

ABSTRACT Aim Environmental drivers frequently predict global patterns of colour diversity, but whether such patterns depend on the underlying colour mechanisms—pigments or microscopic structures—has scarcely been considered. Structural colour may have different functional properties that result in different associations with environmental variables. Here we test whether the presence of structural colour is linked with environmental variables that reflect potential thermoregulatory and water‐repellent properties. Location Global. Major Taxa Studied Bees (Hymenoptera: Anthophila). Methods We scored the presence of structural colour and extracted climate data for 1784 bee species. We used phylogenetic generalised linear mixed models to control for phylogenetic relatedness and tested whether environmental variables related to temperature and humidity explain the presence of structural colour. Results A higher proportion of tropical species had structural colour, despite the higher species richness of bees at higher latitudes. Structural colouration was more likely to occur in cool, sunny environments, in which it is expected to provide the greatest thermal benefit. Structural colour was also more prevalent in environments with higher annual precipitation. These ecogeographic patterns were independent of body size. Main Conclusions Our study reveals global ecogeographic patterns of structural colouration in bees, consistent with thermoregulatory and potentially water‐repellence functions. In addition, our findings highlight that structural colours probably have multiple coexisting functions including both visual and non‐visual functions that need to be disentangled to understand global patterns of colour diversity.

Vivid colours in nature often arise from photonic nanostructures that have inspired diverse technologies. Yet most known examples fall within a limited set of structural themes. Here, we describe a biologically and optically novel structure in the bright green, violin-shaped stripes of the fiddler beetle Eupoecila australasiae. The green colour is produced by a composite, hierarchical structure comprising dense arrays of microscopic, fin-like elements located beneath the cuticle. Each vertical fin, patterned with complementary lattices of nanospheres and indentations, can be approximated by two photonic crystal slabs mounted on a solid central core. Optical modelling shows that the fins are strongly iridescent, reflecting light with longer wavelengths near the normal and light with shorter wavelengths at oblique angles. However, disorder in fin orientation and filtering by the overlying cuticle converts the opaline cyan appearance of the fins into the bright diffuse green seen externally. Our work expands the known diversity of biological photonic nanostructures and offers new inspiration for biomimetic designs.

Abstract Colour polymorphism, the presence of multiple colour variants within a population, is a common example of intraspecific phenotypic variation and has served as a model for studying drivers of diversity. Climatic factors can influence the distribution of colour variants, but effects may vary depending on the lineage‐specific functions of colour. Colour polymorphism is widespread in arachnids, in which colour functions in intra‐ and interspecific interactions such as prey‐luring; yet, the drivers of colour diversity in this lineage remain largely unexplored. Here, we investigated climatic factors influencing colour polymorphism in a widely distributed colour polymorphic spider ( Austracantha minax ) using a combination of controlled experiments, field measurements and tests for macroecological associations. We showed that although different colour morphs occupy distinct climatic niches across Australia, in the laboratory and field, dark colouration is unlikely to provide biologically relevant thermal benefits. Instead, precipitation, rather than temperature, appears to be the strongest driver of colour morph frequencies: there were higher frequencies of dark individuals in regions with higher precipitation while orange individuals were more common in drier areas. We discuss potential mechanisms related to background matching and pathogen protection in humid environments. Our findings highlight the role of climatic factors in shaping colour variation and demonstrate the value of combining macroecological, field and laboratory approaches. Read the free Plain Language Summary for this article on the Journal blog.

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.

Theory posits that warning signals should converge phenotypically to reinforce predator memory, yet many aposematic species show substantial variation in warning signals within and between populations. This could be explained by alternative selective pressures on phenotype beyond predation such as thermoregulation, but empirical tests are scarce and do not consider the full spectrum of sunlight. To examine whether trade-offs with thermoregulation could explain variation in warning colouration, we examined thermal properties of colour variants of the aposematic cotton harlequin bug (Tectocoris diophthalmus). This species shows striking variation in warning signals: it is sexually dichromatic, varies within sexes, and shows clinal variation in colour frequencies, with iridescent blue-green colouration prevalent in cooler climates and non-iridescent red–orange colouration prevalent in warmer climates. We quantified reflectivity between colour variants over the full solar spectrum and investigated the contribution of ultraviolet and visible (UV–visible, 300–700 nm) and near infrared (NIR, 700–1700 nm) light on heating. Differences in reflectivity of iridescent and non-iridescent colour patches were greater in NIR than UV–visible wavelengths but did not result in significant differences in heating. However, we found a tight link between body size and reflectivity, with smaller males having lower reflectivity and heating faster. Due to the strong correlation between body size and colouration, thermal constraints related to body size may help to explain the observed clinal variation in colour frequencies.

Escape is a life critical defensive behaviour. One potential escape strategy is using ultrafast movements to relocate quickly. These movements do not rely solely on muscle activation and are beneficial for ectotherms at low temperatures when muscle performance is constrained. However, the functional significance of ultrafast motions is often assumed. Here, we show with high-speed videos that Astraeus jewel beetles (Buprestidae) rapidly open their elytra to flick themselves into the air and the movement is of comparable speed to other known ultrafast movements. Our calculations indicate that it is likely a power-amplified mechanism. Behavioural trials and thermal imaging demonstrate that Astraeus beetles can flick at >15°C lower body temperatures than walking or flying, suggesting that the behaviour could provide a significant survival advantage at low ambient temperatures. Taken together, we reveal a novel ultrafast movement and show its potential functional value in escape. Astraeus jewel beetles flick themselves upward by opening their elytra extremely fast which is comparable with top ultrafast movements in biological systems, allowing them to escape predators when the ambient temperatures are too low to fly away.

Many animals, including humans, nonhuman primates, birds and honey bees, show associations between space and quantity. This association can manifest as a left-to-right mental number line (MNL), which is the preference to spatially order smaller quantities on the left and larger quantities on the right. However, the nature and mechanisms underlying this association between space and quantity are inconsistent among species, and they remain poorly understood, particularly in invertebrates. In this study, the link between magnitude and space in honey bees, Apis mellifera, was investigated to improve our understanding of the evolution of space and quantity associations in diverse taxa. First, we tested whether free-flying honey bees have an innate left-to-right or right-to-left bias for associations between quantity and space similar to the MNL and whether bees showed any evidence of a vertical preference. Along the horizontal orientation, bees only showed a preference for larger quantities on the right, indicating a leftto-right magnitude bias interacting with a weak right spatial bias. No evidence of a vertical magnitude preference was observed as bees had an overall ventral preference. Whether honey bees could be conditioned to order quantities along the left-to-right or right-to-left dimensions of quantity and space was also determined. Although honey bees could learn either a left-to-right or right-to-left quantity and space association during conditioning trials, in subsequent unconditioned tests, they only demonstrated a significant preference for arranging larger quantities on the right when trained to a left-to-right quantity association. Results indicate that bees have an innate left-to-right quantity bias interacting with a right spatial bias. The results of this study improve our understanding of the evolution of quantity processing and the complexities that exist in spatial-magnitude associations. (c) 2024 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

Aim: Environmental drivers frequently predict global patterns of colour diversity, but whether such patterns depend on the underlying colour mechanisms – pigments or microscopic structures – has scarcely been considered. Structural colour may have different functional properties that result in different associations with environmental variables. Here we test whether the presence of structural colour is linked with environmental variables that reflect potential thermoregulatory and water repellent properties. Location: Global. Major taxa studied: Bees (Hymenoptera: Anthophila). Methods: We scored the presence of structural colour and extracted climate data for 1,784 bee species. We used phylogenetic generalised linear mixed models to control for phylogenetic relatedness and tested whether environmental variables, related to temperature and humidity, explain the presence of structural colour. Results: A higher proportion of tropical species had structural colour, despite the higher species richness of bees at higher latitudes. Structural colouration was more likely to occur in cool, sunny environments, in which it is expected to provide the greatest thermal benefit. Structural colour was also more prevalent in environments with higher annual precipitation. These ecogeographic patterns were independent of body size. Main conclusions: Our study reveals global ecogeographic patterns of structural colouration in bees, consistent with thermoregulatory and potentially water repellence functions. In addition, our findings highlight that structural colours probably have multiple coexisting functions, including both visual and non-visual functions, that need to be disentangled to understand global patterns of colour diversity.

When moving, animals are vulnerable to predation because movement can rapidly attract the attention of a predator. To reduce the risk of predation while moving, animals can use a variety of different strategies (eg erratic movement, coloration). These strategies often work in combination or may be influenced by other prey characteristics (eg size), but few studies have explored these interactions. Here, we investigate how movement trajectory (linear or erratic), prey size (small or large) and prey coloration (glossy or matte) interact to impact the attack behavior of giant rainforest mantids (Hierodula majuscula). We presented mantids with animations of moving targets and filmed their response with a high-speed camera. As expected, mantids were more likely to track large than small targets and targets moving linearly than erratically. Counterintuitively, however, mantids were quicker to strike at erratically moving targets, perhaps because they more closely resembled preferred prey. When mantids attacked the target, their accuracy was influenced by the interaction of target trajectory and glossiness. As predicted, mantids had larger attack errors (ie lower accuracy) toward erratically moving glossy targets compared with linearly moving glossy targets or erratically moving matte targets. However, contrary to our prediction that linearly moving matte targets would be easiest to capture, these targets also elicited large attack errors, similar to those recorded for erratically moving glossy targets. Together, our results demonstrate that anti-predator tactics for prey in motion may interact in complex ways, and simple experimental scenarios may overlook context-dependent effects that emerge when multiple factors interact.

The increasing availability of large molecular phylogenies has provided new opportunities to study the evolution of species traits, their origins and diversification, and biogeography; yet there are limited attempts to synthesise existing phylogenetic information for major insect groups. Bees (Hymenoptera: Anthophila) are a large group of insect pollinators that have a worldwide distribution, and a wide variation in ecology, morphology, and life-history traits, including sociality. For these reasons, as well as their major economic importance as pollinators, numerous molecular phylogenetic studies of family and genus-level relationships have been published, providing an opportunity to assemble a bee 'tree-of-life'. We used publicly available genetic sequence data, including phylogenomic data, reconciled to a taxonomic database, to produce a concatenated supermatrix phylogeny for the Anthophila comprising 4,586 bee species, representing 23% of species and 82% of genera. At family, subfamily, and tribe levels, support for expected relationships was robust, but between and within some genera relationships remain uncertain. Within families, sampling of genera ranged from 67 to 100% but species coverage was lower (17-41%). Our phylogeny mostly reproduces the relationships found in recent phylogenomic studies with a few exceptions. We provide a summary of these differences and the current state of molecular data available and its gaps. We discuss the advantages and limitations of this bee supermatrix phylogeny (available online at beetreeoflife.org), which may enable new insights into long standing questions about evolutionary drivers in bees, and potentially insects more generally.

1. Symbiotic relationships shape ecological communities and often involve more than two species. Yet few experimental studies examine the impact of symbioses involving three species, particularly any mediating role of third parties, and none involving symbioses of predators. 2. We investigated experimentally the synergistic and antagonistic fitness effects of three symbiotic spider predators across a broad latitudinal range and involving different species combinations. 3. The three-dimensional web complex of Cyrtophora spiders is a habitat patch to different associates-species of Argyrodes and web-building Leucauge spider guests. Our field experiments, which manipulated the presence of each guest species and determined the subsequent host weight change, revealed a remarkable consistency in fitness outcomes across the three populations, with the consequences of the interactions between two species depending upon the services provided by a third. 4. Cyrtophora hosts intercepted more prey when web-building Leucauge guests were present and thus gained more weight. In contrast, Argyrodes guests exerted a fitness cost on their Cyrtophora host, but only when Leucauge guests were absent. A comparison of the prey consumed by Cyrtophora hosts and Argyrodes guests revealed that their diets (reflected in the size of prey) overlapped less in the presence of Leucauge web-building guests. 5. Our novel experimental study highlights the importance of exploring synergistic effects in multi-species symbioses. Read the free Plain Language Summary for this article on the Journal blog.

One of the most evident sources of phenotypic diversity within a population is colouration, as exemplified by colour polymorphism. This is relevant to a greater extent in animals with visually biased sensory systems. There is substantial evidence suggesting that different colour morphs can access a broader range of habitats or niches, leading to larger geographic range sizes. However, this hypothesis has been tested in few lineages, comprising species where colour is likely to be involved in sexual selection. Furthermore, some available evidence considers geographical variation as polymorphism, thus limiting our comprehension of how sympatric colour polymorphism can influence a species' geographic range. Through an extensive systematic literature review and a comparative analysis, we examined the relationship between colour polymorphism and range size or niche breadth in web-building spiders. We identified 140 colour polymorphic spider species, belonging mainly to the families Araneidae and Theridiidae. We found no evidence that colour polymorphic species differ significantly from non-polymorphic species in terms of range size and niche breadth, after accounting for phylogenetic relationships and other covariates. However, we did observe that colour polymorphic species were more likely to be found on islands compared to non-polymorphic species. Overall, our results indicate that the association between colour polymorphism and geographic range size may not exist among web-building spiders, or be as pronounced as in other lineages. This suggests that the strength of the association between colour polymorphism and ecological success might depend on the ecological role that colouration plays in each clade.

Beetles exhibit an extraordinary diversity of brilliant and colourful appearances and optical effects invisible to humans. Their underlying mechanisms have received some attention, but we know little about the ecological variables driving their evolution. Here we investigated environmental correlates of reflectivity and circular polarization in a group of optically diverse beetles (Scarabaeidae-Rutelinae). We quantified the optical properties of 261 specimens representing 46 species using spectrophotometry and calibrated photographs. Then, we examined associations between these properties and environmental variables such as temperature, humidity and vegetation cover, controlling for body size and phylogenetic relatedness. Our results showed larger beetles have higher visible reflectivity in drier environments. Unexpectedly, near-infrared (NIR) reflectivity was not correlated with ecological variables. However, we found a correlation between humidity and polarization (chiral nanostructures). We identified trade-offs between optical properties: beetles without polarization-associated nanostructures had higher NIR reflectivity. By contrast, visible reflectivity was negatively correlated with the accumulation of pigments such as melanin. Our study highlights the value of a macroecological approach for testing alternative hypotheses to explain the diversity of optical effects in beetles and to understand the link between structure and function.

Predator-prey interactions have been suggested as drivers of diversity in different lineages, and the presence of anti-predator defences in some clades is linked to higher rates of diversification. Warning signals are some of the most widespread defences in the animal world, and there is evidence of higher diversification rates in aposematic lineages. The mechanisms behind such species richness, however, are still unclear. Here, we test whether lineages that use aposematism as anti-predator defence exhibit higher levels of genetic differentiation between populations, leading to increased opportunities for divergence. We collated from the literature more than 3000 pairwise genetic differentiation values across more than 700 populations from over 60 amphibian species. We find evidence that over short geographical distances, populations of species of aposematic lineages exhibit greater genetic divergence relative to species that are not aposematic. Our results support a scenario where the use of warning signals could restrict gene flow, and suggest that anti-predator defences could impact divergence between populations and potentially have effects at a macro-evolutionary scale.

Colour polymorphism, the presence of multiple colour variants within a population, is a common example of intraspecific phenotypic variation and has served as a model for studying drivers of diversity. Climatic factors can influence the distribution and abundance of colour variants, yet research often focuses on lineages where sexual selection covaries with the climate-colouration associations. Research has also focussed disproportionately on vertebrates and a few insects, neglecting other taxa where polymorphism is widespread, like arachnids. Here, we investigated climatic factors influencing colour variation in a widely distributed colour polymorphic spider using a combination of controlled experiments, field measurements and tests for macroecological associations. We showed in the lab and field that dark colouration is unlikely to provide biologically relevant thermal benefits; yet different colour morphs occupy distinct climatic niches across Australia. Precipitation, rather than temperature, appears to be the strongest driver of colour morph frequencies: there were higher frequencies of dark individuals in regions with higher precipitation while orange individuals were more common in drier areas. We discuss potential mechanisms related to background matching or pathogen protection in humid environments. Our findings highlight the role of climatic factors in shaping colour variation, and demonstrate the value of combining macroecological, field, and laboratory approaches.

Abstract Red sensitivity is the exception rather than the norm in most animal groups. Among species with red sensitivity, there is substantial variation in the peak wavelength sensitivity (λmax) of the long wavelength sensitive (LWS) photoreceptor. It is unclear whether this variation can be explained by visual tuning to the light environment or to visual tasks such as signalling or foraging. Here, we examine long wavelength sensitivity across a broad range of taxa showing diversity in LWS photoreceptor λmax: insects, crustaceans, arachnids, amphibians, reptiles, fish, sharks and rays. We collated a list of 161 species with physiological evidence for a photoreceptor sensitive to red wavelengths (i.e. λmax ≥ 550 nm) and for each species documented abiotic and biotic factors that may be associated with peak sensitivity of the LWS photoreceptor. We found evidence supporting visual tuning to the light environment: terrestrial species had longer λmax than aquatic species, and of these, species from turbid shallow waters had longer λmax than those from clear or deep waters. Of the terrestrial species, diurnal species had longer λmax than nocturnal species, but we did not detect any differences across terrestrial habitats (closed, intermediate or open). We found no association with proxies for visual tasks such as having red morphological features or utilising flowers or coral reefs. These results support the emerging consensus that, in general, visual systems are broadly adapted to the lighting environment and diverse visual tasks. Links between visual systems and specific visual tasks are commonly reported, but these likely vary among species and do not lead to general patterns across species.