Color Pattern Analyses Research Articles

Citizen science and color pattern analysis indicate unreported Batesian mimicry between Neotropical snakes

AbstractBatesian mimics decrease their chance of predation by their resemblance to different, dangerous or unpalatable species but this relationship is often inferred without quantitative approaches. Snakes are notorious Batesian mimics, especially the Neotropical genus Xenodon, which comprises species that are putative mimics of venomous snakes such as coral snakes (genus Micrurus) and lanceheads (or “fer‐de‐lance,” genus Bothrops). Herein, we propose that Xenodon severus is a batesian mimic of the sympatric and highly venomous Amazonian bushmaster (Lachesis muta), the longest viper in the world, and not of lanceheads (Bothrops spp.). We compiled all available photographs of X. severus from citizen science platforms and published literature to test this mimicry through a quantitative dorsal color pattern analysis between this species and both L. muta and a lancehead Bothrops brazili. We classified georeferenced photographs as potential “mimic” or “non‐mimic” and tested whether “mimics” were found on average closer to L. muta's range centroid than “non‐mimics.” The color pattern analysis showed that X. severus is more similar to L. muta than to B. brazili. Furthermore, “mimics” were significantly closer to the centroid of L. muta. Our results suggest that X. severus is likely a mimic of L. muta and that this relationship may vary across their distribution. Our findings highlight the significant role of citizen science platforms in assessing ecological relationships and the importance of using quantitative methods such as dorsal color pattern analysis to test mimicry.Abstract in Portuguese is available with online material.

Chemical defences indicate bold colour patterns with reduced variability in aposematic nudibranchs.

The selective factors that shape phenotypic diversity in prey communities with aposematic animals are diverse and coincide with similar diversity in the strength of underlying secondary defences. However, quantitative assessments of colour pattern variation and the strength of chemical defences in assemblages of aposematic species are lacking. We quantified colour pattern diversity using quantitative colour pattern analysis (QCPA) in 13 dorid nudibranch species (Infraorder: Doridoidei) that varied in the strength of their chemical defences. We accounted for the physiological properties of a potential predator's visual system (a triggerfish, Rhinecanthus aculeatus) and modelled the appearance of nudibranchs from multiple viewing distances (2 and 10 cm). We identified distinct colour pattern properties associated with the presence and strength of chemical defences. Specifically, increases in chemical defences indicated increases in colour pattern boldness (i.e. visual contrast elicited via either or potentially coinciding chromatic, achromatic and/or spatial contrast). Colour patterns were also less variable among species with chemical defences when compared to undefended species. Our results indicate correlations between secondary defences and diverse, bold colouration while showing that chemical defences coincide with decreased colour pattern variability among species. Our study suggests that complex spatiochromatic properties of colour patterns perceived by potential predators can be used to make inferences on the presence and strength of chemical defences.

Highly defended nudibranchs "escape" to visually distinct background habitats.

The "escape and radiate" hypothesis predicts that once species have evolved aposematism, defended species can utilize more visually diverse visual backgrounds as they "escape" the need to be well camouflaged. This enables species to explore new ecological niches, resulting in increased diversification rates. To test this hypothesis "escape" component, we examined whether the background habitats of 12 nudibranch mollusk species differed among species depending on the presence and strength of chemical defenses. We obtained a rich array of color pattern statistics using quantitative color pattern analysis to analyze backgrounds viewed through the eyes of a potential predator (triggerfish, Rhinecanthus aculeatus). Color pattern analysis was done at viewing distances simulating an escalating predation sequence. We identified 4 latent factors comprising 17 noncorrelated color pattern parameters, which captured the among-species variability associated with differences in chemical defenses. We found that chemically defended species, indeed, were found on visually distinct backgrounds with increased color and luminance contrast, independent of viewing distance. However, we found no evidence for increased among-species background diversity coinciding with the presence and strength of chemical defenses. Our results agree with the "escape and radiate" hypothesis, suggesting that potent chemical defenses in Dorid nudibranchs coincide with spatiochromatic differences of visual background habitats perceived by potential predators.

P060 An analysis of eye colour and iris pattern as a risk factor for skin cancer in immunosuppressed renal transplant recipients

P060 An analysis of eye colour and iris pattern as a risk factor for skin cancer in immunosuppressed renal transplant recipients

Automated workflows using Quantitative Colour Pattern Analysis (QCPA): a guide to batch processing and downstream data analysis

Animal and plant colouration presents a striking dimension of phenotypic variation, the study of which has driven general advances in ecology, evolution, and animal behaviour. Quantitative Colour Pattern Analysis (QCPA) is a dynamic framework for analysing colour patterns through the eyes of non-human observers. However, its extensive array of user-defined image processing and analysis tools means image analysis is often time-consuming. This hinders the full use of analytical power provided by QCPA and its application to large datasets. Here, we offer a robust and comprehensive batch script, allowing users to automate many QCPA workflows. We also provide a complimentary set of useful R scripts for downstream data extraction and analysis. The presented batch processing extension will empower users to further utilise the analytical power of QCPA and facilitate the development of customised semi-automated workflows. Such quantitatively scaled workflows are crucial for exploring colour pattern spaces and developing ever-richer frameworks for analysing organismal colouration accounting for visual perception in animals other than humans. These advances will, in turn, facilitate testing hypotheses on the function and evolution of vision and signals at quantitative and qualitative scales, which are otherwise computationally unfeasible.

Signal detectability and boldness are not the same: the function of defensive coloration in nudibranchs is distance-dependent.

Aposematic signals visually advertise underlying anti-predatory defences in many species. They should be detectable (e.g. contrasting against the background) and bold (e.g. using internal pattern contrast) to enhance predator recognition, learning and memorization. However, the signalling function of aposematic colour patterns may be distance-dependent: signals may be undetectable from a distance to reduce increased attacks from naïve predators but bold when viewed up close. Using quantitative colour pattern analysis, we quantified the chromatic and achromatic detectability and boldness of colour patterns in 13 nudibranch species with variable strength of chemical defences in terms of unpalatability and toxicity, approximating the visual perception of a triggerfish (Rhinecanthus aculeatus) across a predation sequence (detection to subjugation). When viewed from an ecologically relevant distance of 30 cm, there were no differences in detectability and boldness between well-defended and undefended species. However, when viewed at closer distances (less than 30 cm), well-defended species were more detectable and bolder than undefended species. As distance increased, detectability decreased more significantly than boldness for defended species. For undefended species, boldness and detectability remained comparatively consistent, regardless of viewing distance. We provide evidence for distance-dependent signalling in aposematic nudibranchs and highlight the importance of distinguishing signal detectability from boldness in studies of aposematism.

Sashimi: A toolkit for facilitating high‐throughput organismal image segmentation using deep learning

Abstract Digitized specimens are an indispensable resource for rapidly acquiring big datasets and typically must be pre‐processed prior to conducting analyses. One crucial image pre‐processing step in any image analysis workflow is image segmentation, or the ability to clearly contrast the foreground target from the background noise in an image. This procedure is typically done manually, creating a potential bottleneck for efforts to quantify biodiversity from image databases. Image segmentation meta‐algorithms using deep learning provide an opportunity to relax this bottleneck. However, the most accessible pre‐trained convolutional neural networks (CNNs) have been trained on a small fraction of biodiversity, thus limiting their utility. We trained a deep learning model to automatically segment target fish from images with both standardized and complex, noisy backgrounds. We then assessed the performance of our deep learning model using qualitative visual inspection and quantitative image segmentation metrics of pixel overlap between reference segmentation masks generated manually by experts and those automatically predicted by our model. Visual inspection revealed that our model segmented fishes with high precision and relatively few artifacts. These results suggest that the meta‐algorithm (Mask R‐CNN), in which our current fish segmentation model relies on, is well suited for generating high‐fidelity segmented specimen images across a variety of background contexts at rapid pace. We present Sashimi, a user‐friendly command line toolkit to facilitate rapid, automated high‐throughput image segmentation of digitized organisms. Sashimi is accessible to non‐programmers and does not require experience with deep learning to use. The flexibility of Mask R‐CNN allows users to generate a segmentation model for use on diverse animal and plant images using transfer learning with training datasets as small as a few hundred images. To help grow the taxonomic scope of images that can be recognized, Sashimi also includes a central database for sharing and distributing custom‐trained segmentation models of other unrepresented organisms. Lastly, Sashimi includes both auxiliary image pre‐processing functions useful for some popular downstream color pattern analysis workflows, as well as a simple script to aid users in qualitatively and quantitatively assessing segmentation model performance for complementary sets of automatically and manually segmented images.

Sexual selection on jumping spider color pattern: investigation with a new quantitative approach

Abstract How animals assess information encoded in individual color patches have been extensively studied, yet the role of both individual color patches and gross color pattern (i.e., the combination of color patches) remains understudied. We tested the functioning of both individual color patches and gross color pattern in sexual selection using the jumping spider Siler semiglaucus as a study system. We first quantified sexual dimorphism in S. semiglaucus in both individual patches and gross color pattern using the newly developed quantitative color pattern analysis (QCPA) framework. After detecting sexual differences in color coverage and pattern contrast, we manipulated the abdomen color pattern of males and had them engage in both female mate choice and male contest trials. Females spent more time watching males with lower pattern contrast and greater red coverage during mate assessment, suggesting that they evaluate information from both individual patches and gross color pattern of males. However, male color pattern had no significant effect on the outcomes of male contests. Thus, we suggest that the observed sexual color pattern dimorphism evolved primarily through female mate choice in S. semiglaucus. This is the first study to use QCPA framework to quantify sexual dimorphism in within-pattern conspicuousness from an intraspecific perspective in invertebrates. Our study also highlights the importance of both individual color patches and gross color pattern in sexual selection.

Taxonomic revision of the genus Xenopholis Peters, 1869 (Serpentes: Dipsadidae): Integrating morphology with ecological niche.

A reliable identification and delimitation of species is an essential pre-requisite for many fields of science and conservation. The Neotropical herpetofauna is the world’s most diverse, including many taxa of uncertain or debated taxonomy. Here we tackle one such species complex, by evaluating the taxonomic status of species currently allocated in the snake genus Xenopholis (X. scalaris, X. undulatus, and X. werdingorum). We base our conclusions on concordance between quantitative (meristic and morphometric) and qualitative (color pattern, hemipenes and skull features) analyses of morphological characters, in combination with ecological niche modeling. We recognize all three taxa as valid species and improve their respective diagnosis, including new data on color in life, pholidosis, bony morphology, and male genitalia. We find low overlap among the niches of each species, corroborating the independent source of phenotypic evidence. Even though all three species occur in the leaf litter of distinct forested habitats, Xenopholis undulatus is found in the elevated areas of the Brazilian Shield (Caatinga, Cerrado and Chaco), whereas X. scalaris occurs in the Amazon and Atlantic rainforests, and X. werdingorum in the Chiquitanos forest and Pantanal wetlands. We discuss the disjunct distribution between Amazonian and Atlantic Forest snake species in the light of available natural history and ecological aspects. This study shows the advantages of combining multiple data sources for reliable identification and circumscription of ecologically similar species.

Quantitative Colour Pattern Analysis (QCPA): A comprehensive framework for the analysis of colour patterns in nature

Abstract To understand the function of colour signals in nature, we require robust quantitative analytical frameworks to enable us to estimate how animal and plant colour patterns appear against their natural background as viewed by ecologically relevant species. Due to the quantitative limitations of existing methods, colour and pattern are rarely analysed in conjunction with one another, despite a large body of literature and decades of research on the importance of spatio‐chromatic colour pattern analyses. Furthermore, key physiological limitations of animal visual systems such as spatial acuity, spectral sensitivities, photoreceptor abundances and receptor noise levels are rarely considered together in colour pattern analyses. Here, we present a novel analytical framework, called the Quantitative Colour Pattern Analysis (QCPA). We have overcome many quantitative and qualitative limitations of existing colour pattern analyses by combining calibrated digital photography and visual modelling. We have integrated and updated existing spatio‐chromatic colour pattern analyses, including adjacency, visual contrast and boundary strength analysis, to be implemented using calibrated digital photography through the Multispectral Image Analysis and Calibration (MICA) Toolbox. This combination of calibrated photography and spatio‐chromatic colour pattern analyses is enabled by the inclusion of psychophysical colour and luminance discrimination thresholds for image segmentation, which we call ‘Receptor Noise Limited Clustering’, used here for the first time. Furthermore, QCPA provides a novel psycho‐physiological approach to the modelling of spatial acuity using convolution in the spatial or frequency domains, followed by ‘Receptor Noise Limited Ranked Filtering’ to eliminate intermediate edge artefacts and recover sharp boundaries following smoothing. We also present a new type of colour pattern analysis, the ‘local edge intensity analysis’ as well as a range of novel psycho‐physiological approaches to the visualization of spatio‐chromatic data. QCPA combines novel and existing pattern analysis frameworks into what we hope is a unified, free and open source toolbox and introduces a range of novel analytical and data‐visualization approaches. These analyses and tools have been seamlessly integrated into the MICA toolbox providing a dynamic and user‐friendly workflow.

An Integrated Approach to Delimit Species in the Puzzling Atractus emmeli Complex (Serpentes: Dipsadidae)

We evaluated the taxonomic status of snakes from the Atractus emmeli species complex (composed by A. boettgeri, A. emmeli, A. paravertebralis, and A. taeniatus) on the basis of concordance between quantitative (meristics and morphometrics) and qualitative (pholidosis, color pattern, and hemipenis) analyses of morphological characters, in combination with ecological niche modeling and niche overlapping. We synonymize A. boettgeri, A. paravertebralis, and A. taeniatus with A. emmeli based on the congruent analytical results. We also describe a new species to accommodate the Brazilian populations from the state of Mato Grosso mainly based upon some unique states of morphological characters, including hemipenial morphology, color pattern, and meristics. We found that the new species has a distinct ecological niche compared with A. emmeli and some level of niche overlapping with A. albuquerquei. We found great differences in ecological niches of species occurring in the Cerrado versus those occurring in the Western Amazon–Andean foothills, suggesting a putative niche evolution in this group.

An Integrated Approach to Delimit Species in the Puzzling Atractus emmeli Complex (Serpentes: Dipsadidae)

We evaluated the taxonomic status of snakes from the Atractus emmeli species complex (composed by A. boettgeri, A. emmeli, A. paravertebralis, and A. taeniatus) on the basis of concordance between quantitative (meristics and morphometrics) and qualitative (pholidosis, color pattern, and hemipenis) analyses of morphological characters, in combination with ecological niche modeling and niche overlapping. We synonymize A. boettgeri, A. paravertebralis, and A. taeniatus with A. emmeli based on the congruent analytical results. We also describe a new species to accommodate the Brazilian populations from the state of Mato Grosso mainly based upon some unique states of morphological characters, including hemipenial morphology, color pattern, and meristics. We found that the new species has a distinct ecological niche compared with A. emmeli and some level of niche overlapping with A. albuquerquei. We found great differences in ecological niches of species occurring in the Cerrado versus those occurring in the Western Amazon–Andean foothills, suggesting a putative niche evolution in this group.

Development of Integrated Device of Trace Bloodstains Imaging and Age Analysis.

Objective To develop a device of trace bloodstains imaging and age analysis, so as to provide a non-destructive, simple and objective method for age estimation of bloodstains at the crime scene. Methods Based on the principle of digital imaging and color pattern analysis, the mobile terminal of the device was used to collect images of bloodstains of different ages. The time-dependent pattern of 6 parameters （R, G, B, C, Y, M） reflecting the changes of color of images of different ages was obtained by computer image analysis. A multiparameter comprehensive inference equation of bloodstains age was established and embedded into the device software to realize the intelligent inference of the bloodstains age. Then the capability and reliability of the device was verified. Results This integrated device of bloodstains imaging and age analysis could quickly collect bloodstains at the crime scene and automatically analyze and infer the age of bloodstains combined with related intelligence software. In the blind test, the detection accuracy of this device was 95% in both natural light airtight group and dark airtight group, and 80% in the natural light ventilation group. Conclusion The integrated device of trace bloodstains imaging and age analysis can be used in a simple manner, which provides a new objective method for bloodstains age estimation.

A phylogenetic taxonomy of the Cyrtodactylus peguensis group (Reptilia: Squamata: Gekkonidae) with descriptions of two new species from Myanmar.

A phylogenetic taxonomy of species in the Cyrtodactylus peguensis group from the Ayeyarwady Basin of Myanmar is constructed based on color pattern, morphology, and molecular systematic analyses using the mitochondrial gene NADH dehydrogenase subunit 2. Newly collected samples from the type locality of C. peguensis and other localities indicate that this clade is endemic to central Myanmar and contains at least seven species, four of which are undescribed. Three species, including C. peguensis occur in the low hills of the Bago Yoma Range within the central portion of the Ayeyarwady Basin. Two of these, C. myintkyawthurai sp. nov. from the northern and central Bago Yoma and C. meersi sp. nov. which is syntopic with C. peguensis in the southern Bago Yoma are described herein. As more lowland hilly areas bordering, and within the Ayeyarwady Basin are surveyed, more new species of this group are likely to be discovered. These discoveries continue the recent surge of descriptions of new species of Cyrtodactylus that are being discovered in Myanmar.

Text extraction in images using simplify color and edges pattern analysis

Text extraction in images using simplify color and edges pattern analysis

The phylogenetic relationships of a new Stream Toad of the genus Ansonia Stoliczka, 1870 (Anura: Bufonidae) from a montane region in Peninsular Malaysia

Twelve species of Ansonia occur on the Thai-Malay peninsula, of which, five from Peninsular Malaysia, form a monophyletic group. One of these, A. jeetsukumarani, is endemic to the Titiwangsa Mountain Range, in which, we discovered a new population of Ansonia that is not A. jeetsukumarani or even its closest relative. Based on morphology, color pattern, and molecular phylogenetic analyses using the mitochondrial genes 12s and 16s rRNA, we have determined that this new species, A. smeagol sp. nov., forms the sister lineage to an upland, monophyletic group composed of A. jeetsukumarani, A. lumut, A. malayana, and A. penangensis. We have noted similar biogeographic patterns in other taxa from the Titiwangsa Mountain Range in a number of upland lineages in Peninsular Malaysia. We hypothesize that the phylogeographic structure of these upland populations is a result of stochastic processes stemming from interaction of climate-driven forest dynamics and life histories.

Morphological and molecular evidence supports recognition of Danaus petilia (Stoll, 1790) (Lepidoptera: Nymphalidae) as a species distinct from D. chrysippus (Linnaeus, 1758)

The danaine butterfly Danaus chrysippus (Linnaeus, 1758) occurs widely in the Afrotropical, Oriental and Australian regions and comprises a taxonomic complex, with recent authors recognizing between one and three species. Danaus petilia (Stoll, 1790) has previously been considered to be a subspecies of D. chrysippus, but we present evidence from wing colour pattern, morphological characters and molecular data that support a recent proposal to treat D. petilia as a separate, parapatric species. The subspecies D. chrysippus cratippus (C. Felder 1860) has a limited range in Indonesia, and was until recently known in Australia from only two specimens. However, on Cobourg Peninsula in the Northern Territory of Australia, D. chrysippus cratippus and D. petilia were observed flying together in Melaleuca swampland. Comparative analysis of wing colour pattern and quantitative morphological characters of material of both taxa sampled from this geographical region of sympatry indicates at least six diagnostic features that distinguish D. petilia from D. chrysippus cratippus. Moreover, a well-sampled molecular phylogeny of the D. chrysippus complex based on sequence data from mitochondrial (cytochrome oxidase subunit 1, cytochrome b) and nuclear (wingless, elongation factor 1 alpha) genes, demonstrates that D. petilia and D. chrysippus are reciprocally monophyletic, suggesting that the two species maintain their distinctiveness even when given the spatiotemporal opportunity for interbreeding. Phylogenetic reconstruction based on molecular data and extensive sampling of the D. chrysippus complex confirms that: (1) samples of D. chrysippus cratippus from Indonesia and Australia and D. chrysippus bataviana (Moore, 1883) from Indonesia are indeed D. chrysippus; (2) specimens from India (incorrect type locality of D. petilia) are D. chrysippus; and (3) the taxon D. chrysippus dorippus (Klug, 1845) (type locality Dongala, Sudan) is not a distinct species as has recently been proposed, and is best treated either as a subspecies of D. chrysippus restricted to Africa or a genetic colour morph of D. chrysippus that extends more widely into Asia. A lectotype designation is made for Danais cratippus C. Felder, 1860, and the status of the type material and application of the name Papilio petilia is discussed. Attention is drawn to the likely clinal variation (an east–west morphocline) of the D. chrysippus complex in Southeast Asia and Australia, and the dubious utility of attempting to discriminate subspecies within D. chrysippus.

Genetic structure and different color morphotypes suggest the occurrence and bathymetric segregation of two incipient species of Sebastes off Argentina

Rockfishes of the genus Sebastes are extensively distributed in the Pacific and Atlantic oceans. Although the occurrence of two morphologically similar species in the Southern Hemisphere, Sebastes oculatus and Sebastes capensis, is now clearly established, the taxonomic status and phylogeographic patterns for the genus in the region have not yet been completely resolved. In this study, we provide new insights into the taxonomy and evolutionary relationships of rockfishes inhabiting the Southwestern Atlantic Ocean, off the coast of mainland Argentina, by combining mitochondrial DNA (mtDNA) control region sequences, microsatellite data, and color pattern analyses. Differences in coloration ("dark" and "light" fish) together with bathymetric segregation between color morphotypes were evident from fish collection and literature review. In addition, the mtDNA phylogenetic analysis and Bayesian clustering analysis using microsatellite data separated the fish into two distinct groups (F ST = 0.041), most likely representing incipient species. Our results suggest that speciation-by-depth in the absence of physical barriers could be a widespread mechanism of speciation in Sebastes from both the Northern and Southern Hemispheres. Nevertheless, the degree of genetic differentiation found, added to the large number of individuals displaying high levels of admixture, points to the occurrence of incomplete reproductive barriers between color morphotypes. Beyond the taxonomic and phylogeographic implications of our findings, the occurrence of distinct groups of Sebastes off the coast of Argentina being targeted by different fisheries (angling and trawling) has consequences for the design and implementation of appropriate fishery regulations to avoid overharvest of either group.

Phylogeography, geographic variation, and taxonomy of the Bent-toed Gecko Cyrtodactylus quadrivirgatus Taylor, 1962 from Peninsular Malaysia with the description of a new swamp dwelling species

A review of the taxonomic status of the Bent-toed Gecko Cyrtodactylus quadrivirgatus Taylor, 1962 based on a molecularphylogeny, scalation, and color pattern analyses indicate that it is composed of a single, recently expanding, widespreadpopulation with weakly supported phylogeographic substructuring with no discrete morphological differentiation betweenpopulations. However, based on sampling, significant mean differences in selected scale counts occur between some pop-ulations. The molecular phylogeny and morphological analysis strongly indicate lineage independence between a subsetof individuals from the Bukit Panchor, Penang population and their closest relative C. pantiensis Grismer, Chan, Grismer,Wood & Belabut, 2008 from southern Peninsular Malaysia. Furthermore, the analyses indicate that the individuals of thissubset are conspecific and not part of C. quadrivirgatus as previously suggested. Additionally, this subset is morphologi-cally distinct from all other Sundaland species of Cyrtodactylus, and as such is described herein as Cyrtodactylus payacola sp. nov.

Structural analysis of eyespots: dynamics of morphogenic signals that govern elemental positions in butterfly wings.

BackgroundTo explain eyespot colour-pattern determination in butterfly wings, the induction model has been discussed based on colour-pattern analyses of various butterfly eyespots. However, a detailed structural analysis of eyespots that can serve as a foundation for future studies is still lacking. In this study, fundamental structural rules related to butterfly eyespots are proposed, and the induction model is elaborated in terms of the possible dynamics of morphogenic signals involved in the development of eyespots and parafocal elements (PFEs) based on colour-pattern analysis of the nymphalid butterfly Junonia almana.ResultsIn a well-developed eyespot, the inner black core ring is much wider than the outer black ring; this is termed the inside-wide rule. It appears that signals are wider near the focus of the eyespot and become narrower as they expand. Although fundamental signal dynamics are likely to be based on a reaction-diffusion mechanism, they were described well mathematically as a type of simple uniformly decelerated motion in which signals associated with the outer and inner black rings of eyespots and PFEs are released at different time points, durations, intervals, and initial velocities into a two-dimensional field of fundamentally uniform or graded resistance; this produces eyespots and PFEs that are diverse in size and structure. The inside-wide rule, eyespot distortion, structural differences between small and large eyespots, and structural changes in eyespots and PFEs in response to physiological treatments were explained well using mathematical simulations. Natural colour patterns and previous experimental findings that are not easily explained by the conventional gradient model were also explained reasonably well by the formal mathematical simulations performed in this study.ConclusionsIn a mode free from speculative molecular interactions, the present study clarifies fundamental structural rules related to butterfly eyespots, delineates a theoretical basis for the induction model, and proposes a mathematically simple mode of long-range signalling that may reflect developmental mechanisms associated with butterfly eyespots.