Colour Morphs Research Articles

Color morphs of the fire salamander are discriminated at night by conspecifics and predators

AbstractThe coexistence of multiple discrete color phenotypes (i.e. color polymorphism) has been studied in many diurnal species where environmental light allows most visual systems to chromatically discriminate color morphs. However, there is a large gap in our understanding of the discrimination thresholds and the function color polymorphisms play at night. We collected spectral data from the throats of red‐ and yellow‐morph males in a polymorphic population of the nocturnal amphibian Salamandra salamandra gallaica. We estimated the discriminability between morphs and their conspicuousness at night by fitting visual models of conspecifics and predators. We also collected morphological, behavioral and physiological data and assessed the abundance and activity patterns of each morph to explore their potential function. Visual models indicated that both conspecifics and predators can visually discriminate salamander color morphs under night‐light conditions. Assuming the potential role of yellow and red color patches as visual signals, putatively related to social signaling, we could suspect that these colors represent different adaptive optima. Red‐morph individuals had shorter bodies and lower body condition, but both morphs showed similar space use. In addition, both color morphs exhibited similar metabolic physiology, suggesting that the observed similarity in these traits may be better explained by the shared environmental conditions, rather than color. Finally, differences in the conspicuousness of red and yellow morphs could result in differential predation pressure.

Phylogeographical patterns are governed by geography in endemic polymorphic snail Indrella ampulla (Gastropoda: Ariophantidae)

Abstract Genetic diversity within a species can be shaped by abiotic factors, such as climate and geography. We aimed to ascertain the relative importance of these two abiotic factors to Indrella ampulla, a monotypic snail species from the Western Ghats, India, that has three colour morphs with some overlapping distributions. We also wanted to investigate whether these colour morphs represent divergent lineages or incipient species. We sequenced one nuclear and two mitochondrial genes from 32 individuals of I. ampulla. We used phylogenetic, population genetic, and niche modelling tools to address these questions. The results suggested that the colour morphs were not reciprocally monophyletic and exhibited considerable niche overlap, suggesting that they cannot be considered as incipient species. Furthermore, the results showed that the impact of palaeoclimatic oscillations in shaping the genetic diversity of this species cannot be determined conclusively. The Palghat Gap seems to have shaped the genetic diversity in this group to a certain degree. The colour morph distributed south of the Palghat Gap did not show admixture and exhibited the least amount of niche overlap with the other morphs. The geography of the landscape seems to have played a prominent role in shaping genetic diversity in this species.

Experimental evidence of mate choice as the driving mechanism behind negative assortative mating for shell colour in a marine snail

Abstract How colour polymorphisms are maintained in natural populations constitutes a key subject of study for evolutionary ecologists. One of the mechanisms that has been put forward to explain this phenomenon is negative frequency-dependent selection, which can be caused by different mechanisms. Among these mechanisms is mate choice, or the selection as a potential mate of the rare or dissimilar colour morph by the choosy sex of a given species. In the context of colour polymorphism, mate choice predicts the occurrence of a negative assortative mating pattern, whereby different colour morphs mate more often than expected by chance alone. However, negative assortative mating can also result from other mechanisms, making it, at best, a fallible indicator of a mate choice-driven negative frequency-dependent selection. For this reason, experimental evidence explicitly connecting such a mating pattern to mate choice is necessary to claim that a particular colour polymorphism is being maintained by negative frequency-dependent selection. Here we present experimental evidence backing this relationship for the colour polymorphic marine gastropod Littorina saxatilis from the Ría de Vigo (NW Iberian Peninsula), although how specifically these organisms choose their mates remains unclear. This calls for further experimental efforts to clarify this issue and its relationship to the maintenance of colour polymorphism in L. saxatilis.

Artificial light at night alters predation on colour-polymorphic camouflaged prey

Artificial light at night (ALAN) disrupts biological processes across taxa and at all levels of organisation. Despite growing interest in this globally pervasive sensory pollutant, its impact on colour-guided processes remains largely unexplored. This is especially concerning given the rapid transition in recent years away from narrow-spectrum lighting and towards broad-spectrum options such as white LEDs, which are rich in the short wavelengths of light to which many taxa are particularly sensitive. Camouflage is particularly likely to be disrupted by broader spectra of ALAN due to changes in conspicuousness in background matching prey, which may alter prey recognition in visually guided predators. We simulated natural intensities of moonlight with and without ALAN, using both broad-spectrum (‘white’) ALAN and ALAN filtered to remove the characteristic short (blue) wavelength peak of broad-spectrum LEDs to test whether filtering might mitigate their effects. We tested how exposure to these light treatments impacted predator-prey interactions, using the intertidal crab Carcinus maenas and contrasting colour morphs of the colour-polymorphic snail Littorina obtusata as a model system. Exposure to broad-spectrum ALAN reduced overall predation and reversed the pattern of colour-based prey selection observed under control conditions. Snails were 55 % less likely to be attacked under broad-spectrum ALAN than in control conditions, with likelihood decreasing over 70 % for yellow snails. Yellow snails were over 26 % more likely to be attacked than brown ones under control conditions, but brown snails were over 40 % more likely to be attacked than yellow ones under broad-spectrum ALAN. Exposure to filtered ALAN removed any significant colour-based difference in prey recognition. Our results demonstrate that spectral composition is a crucial aspect of ALAN as a sensory pollutant, capable of instigating profound changes in predator-prey interactions that could drive changes in population demography and increase morphological homogeneity in species that depend on colour polymorphism for camouflage.

Survival of a polymorphic species in seasonally snow‐covered forests

Color polymorphism is an adaptive strategy in which a species exhibits multiple color phenotypes in a population. Often, phenotypes are variably suited to different environmental conditions which may buffer the population against variable conditions. Modern climate change is creating novel selective pressures for many species, especially in winter habitats. Few studies have quantified the benefits of polymorphism for allowing species to cope with climate‐induced environmental change, particularly for species with more cryptic differences between morphs. We investigated how color polymorphism mediates selective pressures in ruffed grouse Bonasa umbellus, a winter‐adapted bird species of North American forests. Ruffed grouse display phenotypic variation in plumage color, ranging from red to gray. Over five winters (2015–2022), we monitored weather conditions, habitat use, and weekly survival for 94 grouse to test whether individuals had lower survival when phenotypically mismatched with snow cover (e.g. a gray bird on a snowless landscape or a red bird in snow). Grouse phenotypically mismatched with snow cover had lower survival, but only when winter survival rates were lowest. During winters of lower overall survival, red grouse exhibited higher survival during snow‐free periods, whereas gray grouse had higher survival when snow was present. We also found that open habitat negatively impacted survival, regardless of color. While the effect of phenotypic mismatch was variable among years, it was a stronger predictor of survival than land cover, suggesting that snow is an important habitat feature mediating overwinter survival. Our work offers an advancement in understanding how environmental variability affects geographic variation in and maintenance of multiple color phenotypes in seasonally‐snow covered environments. Our finding that interactions between color morph and snow cover are important for conferring winter survival provides further evidence that color polymorphism may serve as a buffer against rapidly changing conditions and a pathway for persistence of polymorphic species.Keywords: Bonasa umbellus, color polymorphism, phenotypic mismatch, ruffed grouse, winter ecology, Wisconsin

Ontogeny of color development in two green-brown polymorphic grasshopper species.

Many insects, including several orthopterans, undergo dramatic changes in body coloration during ontogeny. This variation is particularly intriguing in gomphocerine grasshoppers, where the green and brown morphs appear to be genetically determined (Schielzeth & Dieker, 2020, BMC Evolutionary Biology, 20, 63; Winter etal., 2021, Heredity, 127, 66). A better understanding of how these color morphs develop during ontogeny can provide valuable insights into the evolution and ecology of such a widespread color polymorphism. Here, we focus on the color development of two green-brown polymorphic species, the club-legged grasshopper Gomphocerus sibiricus and the steppe grasshopper Chorthippus dorsatus. By following the color development of individuals from hatching to adulthood, we found that color morph differences begin to develop during the second nymphal stage, are clearly defined by the third nymphal stage, and remain stable throughout the life of an individual. Interestingly, we also observed that shed skins of late nymphal stages are identifiable by color morphs based on their yellowish coloration, rather than the green that marks green body parts. Furthermore, by assessing how these colors are perceived by different visual systems, we found that certain potential predators can chromatically discriminate between morphs, while others may not. These results suggest that the putative genes controlling color morph are active during the early stages of ontogeny, and that green color is likely composed of two components, one present in the cuticle and one not. In addition, the effectiveness of camouflage appears to vary depending on the specific predator involved.

Colour polymorphism associated with a gene duplication in male wood tiger moths.

Colour is often used as an aposematic warning signal, with predator learning expected to lead to a single colour pattern within a population. However, there are many puzzling cases where aposematic signals are also polymorphic. The wood tiger moth, Arctia plantaginis, displays bright hindwing colours associated with unpalatability, and males have discrete colour morphs which vary in frequency between localities. In Finland, both white and yellow morphs can be found, and these colour morphs also differ in behavioural and life-history traits. Here, we show that male colour is linked to an extra copy of a yellow family gene that is only present in the white morphs. This white-specific duplication, which we name valkea, is highly upregulated during wing development. CRISPR targeting valkea resulted in editing of both valkea and its paralog, yellow-e, and led to the production of yellow wings. We also characterise the pigments responsible for yellow, white, and black colouration, showing that yellow is partly produced by pheomelanins, while black is dopamine-derived eumelanin. Our results add to a growing number of studies on the genetic architecture of complex and seemingly paradoxical polymorphisms, and the role of gene duplications and structural variation in adaptive evolution.

Physiological phenotypes differ among color morphs in introduced common wall lizards (Podarcis muralis).

Many species exhibit color polymorphisms which have distinct physiological and behavioral characteristics. However, the consistency of morph trait covariation patterns across species, time, and ecological contexts remains unclear. This trait covariation is especially relevant in the context of invasion biology and urban adaptation. Specifically, physiological traits pertaining to energy maintenance are crucial to fitness, given their immediate ties to individual reproduction, growth, and population establishment. We investigated the physiological traits of Podarcis muralis, a versatile color polymorphic species that thrives in urban environments (including invasive populations in Ohio, USA). We measured five physiological traits (plasma corticosterone and triglycerides, hematocrit, body condition, and field body temperature), which compose an integrated multivariate phenotype. We then tested variation among co-occurring color morphs in the context of establishment in an urban environment. We found that the traits describing physiological status and strategy shifted across the active season in a morph-dependent manner-the white and yellow morphs exhibited clearly different multivariate physiological phenotypes, characterized primarily by differences in plasma corticosterone. This suggests that morphs have different strategies in physiological regulation, the flexibility of which is crucial to urban adaptation. The white-yellow morph exhibited an intermediate phenotype, suggesting an intermediary energy maintenance strategy. Orange morphs also exhibited distinct phenotypes, but the low prevalence of this morph in our study populations precludes clear interpretation. Our work provides insight into how differences among stable polymorphisms exist across axes of the phenotype and how this variation may aid in establishment within novel environments.

Rural selection drives the evolution of an urban-rural cline in coat color in gray squirrels.

Phenotypic differences between urban and rural populations are well-documented, but the evolutionary processes driving trait variation along urbanization gradients are often unclear. We combined spatial data on abundance, trait variation, and measurements of fitness to understand cline structure and test for natural selection on heritable coat color morphs (melanic, gray) of eastern gray squirrels (Sciurus carolinensis) along an urbanization gradient. Population surveys using remote cameras and visual counts at 76 sites along the urbanization gradient revealed a significant cline in melanism, decreasing from 48% in the city center to <5% in rural woodlands. Among 76 squirrels translocated to test for phenotypic selection, survival was lower for the melanic than gray morph in rural woodlands, whereas there was no difference in survival between color morphs in the city. These results suggest the urban-rural cline in melanism is explained by natural selection favoring the gray morph in rural woodlands combined with relaxed selection in the city. Our study illustrates how trait variation between urban and rural populations can emerge from selection primarily in rural populations rather than adaptation to novel features of the urban environment.

Colour-specific diet specialization is associated with differences in owlet weight in a polymorphic owl: influence of the trophic quality variation.

The niche divergence hypothesis proposes that the evolution and maintenance of colour polymorphism is based on a mechanism of disruptive selection. In a trophic context, the hypothesis predicts that individuals differing in colour vary in their trophic niche, either because they differ in foraging efficiency or feed in different habitats. A major evolutionary conundrum is how these expectations are affected by variation in trophic quality. Using an owl species with colour plumage polymorphism, the Eurasian scops owl Otus scops, we examined diet and habitat segregation during reproduction in relation to plumage colouration and trophic quality. Intensive sampling revealed that trophic quality for scops owls (i.e. abundance of grasshoppers and locusts) varied more among territories than between years, but scops owls did not segregate among territories of different quality by their colouration. However, we found that sex, plumage colouration and territory differences in trophic quality explained differences in the degree of dietary specialization. Brownish males delivered a higher diversity of prey to the nest than greyish ones in high trophic quality territories. We also found that the more diverse the diet provided by males, the heavier the owlets at fledging. Our study provides evidence for a different sensitivity to trophic quality of the colour morphs with potential fitness consequences in scops owls. We highlight the importance of studying the mechanisms leading to the persistence of colour polymorphism in patchy environments, since segregation may pass otherwise unnoticed if only habitats or years with similar conditions are considered.

Testing the function of a colour pattern polymorphism in a lizard

Abstract Trait polymorphisms can vary across different contexts of selection and be maintained through trade-offs between these contexts. For example, colour polymorphic variants may represent alternative strategies optimizing crypsis or thermoregulation in different populations. Here we use visual modelling to test the conspicuousness of different colour pattern morphs in males and females of an Australian lizard, Lampropholis delicata, to predators and conspecifics. We further assess differences in reflectance, microhabitat selection, and mate preference to determine the functional role of the polymorphism and explain its variable distribution across latitude and the sexes. Plain morphs are more conspicuous than striped morphs in both bird and lizard visual models, suggesting predation selection, and habitat structure varies among sex-morph types, but we find no difference in microhabitat selection or mate preference based on colour. We suggest that a combination of spatially varying selection, habitat preference, and context-specific behaviour may be necessary to explain spatial patterns of colour morph frequencies.

Body color plasticity of Diaphorina citri reflects a response to environmental stress.

Body color polyphenism is common in Diaphorina citri. Previous studies compared physiological characteristics in D.citri, but the ecological and biological significance of its body color polyphenism remains poorly understood. We studied the ecological and molecular effects of stressors related to body color in D.citri. Crowding or low temperature induced a high proportion of gray morphs, which had smaller bodies, lower body weight, and greater susceptibility to the insecticide dinotefuran. We performed transcriptomic and metabolomics analysiis of 2 color morphs in D.citri. Gene expression dynamics revealed that the differentially expressed genes were predominantly involved in energy metabolism, including fatty acid metabolism, amino acid metabolism, and carbohydrate metabolism. Among these genes, plexin, glycosidase, phospholipase, take out, trypsin, and triacylglycerol lipase were differentially expressed in 2 color morphs, and 6 hsps (3 hsp70, hsp83, hsp90, hsp68) were upregulated in gray morphs. The metabolome data showed that blue morphs exhibited a higher abundance of fatty acid and amino acid, whereas the content of carbohydrates was elevated in gray morphs. This study partly explains the body color polyphenism of D.citri and provides insights into the molecular changes of stress response of D.citri.

Clarifying a male color morph of Sphaerodactylus macrolepis Gnther, 1859 and resolving the taxonomic confusion on Saint Croix.

Many species of sphaerodactyl gecko exhibit sexual dichromatism. In particular, dichromatism plays an important role in intersexual signaling for Sphaerodactylus. Furthermore, some species exhibit polymorphism in male color and pattern. Here, we describe a regional male color morph of Sphaerodactylus macrolepis from St. Croix. After generating both mitochondrial and nuclear phylogenies, we found that individuals with the St. Croix-specific yellow/orange head morph are part of the S. macrolepis clade. This distinct color morph likely contributed to the turbulent taxonomic history of the S. macrolepis species group. Given the documented diversity of the color patterns in this group and that sexual signals evolve rapidly, we suggest S. macrolepis is an excellent group to study the ecological and evolutionary consequences of dichromatism and polymorphism.

Review of the genus Sparasion Latreille, 1802 (Hymenoptera: Platygastroidea: Sparasionidae) of the Oriental region with descriptions of new species from India

BackgroundThe genus Sparasion, endoparasitoids of Tettigoniidae, occur in the Nearctic, Palearctic, Afrotropical and Oriental regions. It is absent in the Neotropics and Australasia. Of the thirteen species found in the Oriental region only a single species is from India.ResultsTwo new species groups - Sparasion bilahari species group and Sparasion manavati species group - are proposed for species from the Oriental region. Thirty-six species are described and illustrated of which twenty-four are new: Sparasion albopilosellus Cameron, 1906 (Pakistan); S. bhairavi Veenakumari, sp. n. (India); S. bhupali Veenakumari, sp. n. (India); S. bihagi Veenakumari, sp. n. (India); S. bilahari Veenakumari, sp. n. (India); S. cellularis Strand, 1913 (Taiwan); S. coconcus Kozlov and Lê, 2000 (Vietnam); S. coeruleus Kieffer, 1905 (Sumatra); S. cullaris Kozlov and Lê, 2000 (Vietnam); S. darbari Veenakumari, sp. n. (India); S. deepaki Veenakumari, sp. n. (India); S. domes Kozlov and Lê, 2000 (Vietnam); S. elbakyanae Veenakumari, sp. n. (India); S. formosus Kieffer, 1910 (Taiwan); S. hindoli Veenakumari, sp. n. (India); S. kalyani Veenakumari, sp. n. (India); S. kanakangi Veenakumari, sp. n. (India); S. karivadana Veenakumari, sp. n. (India); S. lividus Johnson, Masner & Musetti, 2008 (Philippines); S. manavati Veenakumari, sp. n. (India); S. meghmalhari Veenakumari, sp. n. (India); S. micromerus Kozlov and Lê, 2000 (Vietnam); S. pahadi Veenakumari, sp. n. (India); S. philippinensis Kieffer, 1913 (Philippines); S. ratnangi Veenakumari, sp. n. (India); S. rupavati Veenakumari, sp. n. (India); S. salagami Veenakumari, sp. n. (India); S. shulini Veenakumari, sp. n. (India); S. sinensis Walker, 1852 (China); S. sivaranjini Veenakumari, sp. n. (India); S. syamalangi Veenakumari, sp. n. (India); S. todi Veenakumari, sp. n. (India); S. travancoricus Mani and Sharma, 1981 (India); S. vanaspati Veenakumari, sp. n. (India); S. visvambari Veenakumari, sp. n. (India) and S. zeelafi Veenakumari, sp. n. (India). Keys to Oriental species of Sparasion are furnished. Intrasexual colour morphs among females of Sparasion is reported. Lectotype is designated for Sparasion cellularis Strand.ConclusionsTwenty-four new species are added to the Indian fauna of Sparasion. Previously described species of Oriental Sparasion are redescribed and illustrated. Keys are furnished for all Oriental species.

Are there differences in behaviour between the two colour morphs of the mountain stone wētā, Hemideina maori?

ABSTRACT A robust understanding of an organism’s behavioural and ecological characteristics is an integral part of conservation; unfortunately, many of New Zealand’s native insect fauna still show a degree of data deficiency in these areas. Predator avoidance behaviours are one such area, and where there are colour morphs in New Zealand native and threatened insects, potential differences in the behaviour of these morphs can often be under investigated. The mountain stone wētā (Hemideina maori) possesses two distinct colour morphs, melanic and yellow, though the reason for this distinction is unclear. This study uses laboratory based assays to compare the behaviour of the morphs, including activity, refuge seeking, cohabitation, emergence and defensive behaviour. We observed emergence and cohabitation regularly, used video recordings to assay activity and refuge seeking behaviours, and measured defensive behaviours by probing individuals until a defensive response was displayed. Differences in all tested behaviours between colour morphs were non-significant; however, there were significant differences in defensive behaviour between sexes. We also discuss how defensive behaviours of H. maori compare with another tree wētā. Overall, the colour morphs in H. maori are similar in their predator responses and there may be a driving factor for melanism other than predation pressure. urn:lsid:zoobank.org:pub:D54E864D-844F-4619-84E6-44BBAC1DE4E5

Restoring declining species through translocations: A test case using flightless grasshoppers in an urban setting

Abstract Population translocations are used increasingly as a conservation strategy for vertebrates. However, relatively few attempts have been made to translocate invertebrates despite their potential benefits for food webs, and despite the practicality of undertaking such translocations in small areas including urban environments where space is limited. We conducted 36 translocations of 1851 individuals of the generalist flightless grasshopper Vandiemenella viatica across urban Melbourne, where 93% of its original habitat has been lost. We aimed to understand characteristics essential for grasshopper persistence and to investigate detection, occupancy, dispersal and habitat suitability throughout its active period to improve insect translocation success in urban settings using revegetated sites and small remnant habitats. We also measured movement and detection probability after one week in short‐term trials. The one‐week trial indicated that grasshopper sex and colour morph did not influence the probability of detection, and there was no evidence of directional movement by females and males. One year after translocation, V. viatica were found in 28 out of 36 translocation sites. These surveys showed that detection probability changed across survey seasons and was influenced by soil temperature. Also, soil temperature positively affected detection in the winter surveys. Occupancy probability was influenced by graminoid cover, plant species richness and weed cover. We found no evidence of directional movement by females and males in the F1 generation. Abundance and presence/absence data were best explained by graminoid cover and plant species richness. Our findings suggest that wingless grasshopper translocations are feasible in small urban patches of suitable habitat, helping to restore invertebrate biodiversity and ecological services.

Morphological changes in female reproductive organs in the African monarch butterfly, host to a male-killing Spiroplasma.

Sexual selection and conflicts within and between sexes promote morphological diversity of reproductive traits within species. Variation in the morphology of diagnostic reproductive characters within species offer an excellent opportunity to study these evolutionary processes as drivers of species diversification. The African monarch, Danaus chrysippus (Linnaeus, 1758), is widespread across Africa. The species is polytypic, with the respective geographical ranges of the four colour morphs only overlapping in East Africa. Furthermore, some of the populations host an endosymbiotic bacterium, Spiroplasma, which induces son-killing and distorts the local host population sex-ratio, creating sexual conflicts between the females seeking to optimize their fecundity and the limited mating capacity of the rare males. We dissected females from Kenya, Rwanda and South Africa, where Spiroplasma vary in presence and prevalence (high, variable and absent, respectively), and conducted microscopy imaging of their reproductive organs. We then characterized the effect of population, female body size, and female mating status, on the size and shape of different genitalia characters of the D. chrysippus female butterflies. We showed that although the general morphology of the organs is conserved in D. chrysippus, female genitalia vary in size and shape between and within populations. The virgin females have smaller organs, while the same organs were expanded in mated females. Females from highly female-biased populations, where the male-killing Spiroplasma is prevalent, also have a larger area of their corpus bursae covered with signa structures. However, this pattern occurs because a larger proportion of the females remains virgin in the female-biased populations rather than because of male depletion due to the symbiont, as males from sex-ratio distorted populations did not produce significantly smaller nutritious spermatophores.

Dots in the dark: dorsal polychromatism in the endemic Xingu Freshwater Stingray

AbstractPolychromatism refers to the presence of two or more color patterns within a species. Several species exhibit polychromatic patterns, including some elasmobranchs such as the Xingu Freshwater Stingray (Potamotrygon leopoldi), a threatened, endemic freshwater stingray species that is exploited in the international aquarium trade. Analysis of polychromatic patterns can provide insight into evolutionary mechanisms and be a useful tool for monitoring international trade. In this context, the present study analyzed intraspecific color variation in P. leopoldi. A total of 241 individuals collected in two areas along the Xingu River in Brazil were used for the study. Four dorsal color patterns of P. leopoldi were described. Size differences between color classes were statistically significant, suggesting that these color variations are associated with ontogenetic color changes. In addition, two color morphs specific to each locality were identified and described. Moreover, the occurrence of polychromatic forms in a Potamotrygoninae species may contribute to the understanding of diversification in this group, since some mechanisms of speciation are associated with polychromatism. Analysis of color variation in P. leopoldi is expected to help improve trade monitoring, especially given the existence of look‐alike species.

Exceptional population genomic homogeneity in the black brittle star Ophiocomina nigra (Ophiuroidea, Echinodermata) along the Atlantic-Mediterranean coast

The Atlantic-Mediterranean marine transition is characterised by strong oceanographic barriers and steep environmental gradients that generally result in connectivity breaks between populations from both basins and may lead to local adaptation. Here, we performed a population genomic study of the black brittle star, Ophiocomina nigra, covering most of its distribution range along the Atlantic-Mediterranean region. Interestingly, O. nigra is extremely variable in its coloration, with individuals ranging from black to yellow-orange, and different colour morphs inhabiting different depths and habitats. In this work, we used a fragment of the mitochondrial COI gene and 2,374 genome-wide ddRADseq-derived SNPs to explore: (a) whether the different colour morphs of O. nigra represent different evolutionary units; (b) the disruptive effects of major oceanographic fronts on its population structure; and (c) genomic signals of local adaptation to divergent environments. Our results revealed exceptional population homogeneity, barely affected by oceanographic fronts, with no signals of local adaptation nor genetic differentiation between colour morphs. This remarkable panmixia likely results from a long pelagic larval duration, a large effective population size and recent demographic expansions. Our study unveils an extraordinary phenotypic plasticity in O. nigra, opening further research questions on the ecological and molecular mechanisms underpinning coloration in Ophiuroidea.

Single-Cell Transcriptome and Pigment Biochemistry Analysis Reveals the Potential for the High Nutritional and Medicinal Value of Purple Sea Cucumbers.

The sea cucumber Apostichopus japonicus has important nutritional and medicinal value. Unfortunately, we know little of the source of active chemicals in this animal, but the plentiful pigments of these animals are thought to function in intriguing ways for translation into clinical and food chemistry usage. Here, we found key cell groups with the gene activity predicted for the color morphology of sea cucumber body using single-cell RNA-seq. We refer to these cell populations as melanocytes and quinocytes, which are responsible for the synthesis of melanin and quinone pigments, respectively. We integrated analysis of pigment biochemistry with the transcript profiles to illuminate the molecular mechanisms regulating distinct pigment formation in echinoderms. In concert with the correlated pigment analysis from each color morph, this study expands our understanding of medically important pigment production, as well as the genetic mechanisms for color morphs, and provides deep datasets for exploring advancements in the fields of bioactives and nutraceuticals.