Color Pattern Variation Research Articles

Anthropogenic Influence on Moth Populations: A Comparative Study in Southern Sweden.

As moths are vital components of ecosystems and serve as important bioindicators, understanding the dynamics of their communities and the factors influencing these dynamics, such as anthropogenic impacts, is crucial to understand the ecological processes. Our study focuses on two provinces in southern Sweden, Västergötland and Småland, where we used province records from 1974 to 2019 in combination with light traps (in 2020) to record the presence and abundance of moth species, subsequently assessing species traits to determine potential associations with their presence in anthropogenically modified landscapes. This study design provides a unique opportunity to assess temporal changes in moth communities and their responses to shifts in environmental conditions, including anthropogenic impacts. Across the Västergötland and Småland provinces in Sweden, we recorded 776 moth taxa belonging to fourteen different taxonomic families of mainly Macroheterocera. We captured 44% and 28% of the total moth species known from these provinces in our traps in Borås (Västergötland) and Kalmar (Småland), respectively. In 2020, the species richness and abundance were higher in Borås than in Kalmar, while the Shannon and Simpson diversity indices revealed a higher species diversity in Kalmar. Between 1974 and 2019, the colonisation rates of the provinces increased faster in Småland. Ninety-three species were found to have colonised these provinces since 1974, showing that species richness increased over the study period. We reveal significant associations between the probability of a species being present in the traps and distinct traits compared to a provincial species pool. Traits over-represented in the traps included species with a high variation in colour patterns, generalist habitat preferences, extended flight periods, lower host plant specificity, and overwintering primarily as eggs. Our findings underscore the ongoing ecological filtering that favours certain species-specific traits. This study sheds light on the roles of climate change and anthropogenic impacts in shaping moth biodiversity, offers key insights into the ecological processes involved, and can guide future conservation efforts.

Sexual signal evolution and patterns of assortative mating across an intraspecific contact zone.

Contact zones provide important insights into the evolutionary processes that underlie lineage divergence and speciation. Here, we use a contact zone to ascertain speciation potential in the red-eyed treefrog (Agalychnis callidryas), a brightly coloured and polymorphic frog that exhibits unusually high levels of intraspecific variation. Populations of A. callidryas differ in a number of traits, several of which are known sexual signals that mediate premating reproductive isolation in allopatric populations. Along the Caribbean coast of Costa Rica, a ~100 km contact zone, situated between two phenotypically and genetically divergent parent populations, contains multiple colour pattern phenotypes and late-generation hybrids. This contact zone provides the opportunity to examine processes that are important in the earliest stages of lineage divergence. We performed analyses of colour pattern variation in five contact zone sites and six parental sites and found complex, continuous colour variation along the contact zone. We found discordance between the geographic distribution of colour pattern and previously described genomic population structure. We then used a parental site and contact zone site to measure assortative mating and directional selection from naturally-occurring amplectant mating pairs. We found assortative mating in a parental population, but no assortative mating in the contact zone. Furthermore, we uncovered evidence of directional preference towards the adjacent parental phenotype in the contact zone population, but no directional preference in the parent population. Combined, these data provide insights into potential dynamics at the contact zone borders and indicate that incipient speciation between parent populations will be slowed.

Molecular species delimitation reveals hidden endemism in Faxonius placidus (Hagen 1870) (Decapoda: Astacidea: Cambaridae) in southeastern USA

Abstract Molecular surveys are critical for understanding species boundaries and evolutionary relationships of North American crayfishes, as traditional morphological characters used for taxonomy frequently misrepresent crayfish diversity. The bigclaw crayfish, Faxonius placidus (Hagen, 1870), is currently described as a widely distributed crayfish that is common throughout the Cumberland, Tennessee, and Lower Ohio river drainages. The geographic distribution of F. placidus is based on identifications using traditional morphological characters including the first-form male gonopod, chelae, and rostrum. Within F. placidus, color pattern variation is specific to populations separated by hydrogeographic barriers. We used DNA barcoding data (mtDNA-COI) and genome-wide molecular markers (nuclear SNPs) to examine geographic patterns of genetic variation in F. placidus within the Cumberland and Tennessee river drainages. The federally endangered Nashville crayfish, F. shoupi (Hobbs, 1948), was included in our analyses, as previous phylogenetic reconstructions suggest F. placidus is paraphyletic with respect to F. shoupi. Phylogenetic reconstructions and molecular species delimitation identified four genetically distinct lineages within F. placidus that are paraphyletic with respect to F. shoupi. Our results add to numerous studies demonstrating the utility of robust molecular analyses for understanding the biodiversity of North American crayfishes.

Environment drives color pattern polymorphism in sand lizards beyond the Gloger's rule

AbstractSpecies color and color pattern vary geographically contributing to environmental tolerance of the species to the fluctuating climate. In a constantly changing environment, the population remains polymorphic, when individuals that are not acclimated to the current environment can survive adverse time periods. Factors influencing color morph frequencies in populations affect spatial variation through local adaptation, which is in turn linked to large‐scale environmental gradients. The influence of environmental factors has not been adequately studied in many polymorphic organisms where the influence of sexual selection on the persistence of polymorphisms is widely recognized. We hypothesized that different color morphs of sand lizard are distributed throughout the Palearctic depending on different environmental conditions. The goal of this study was to examine if the range of morph composition in a color polymorphic lizard can be explained by geographic and climatic variation in the Palearctic. We used publicly available data on sand lizard occurrence from the Global Biodiversity Information Facility and environmental variables from WorldClim and SEDAC databases. We categorized sand lizards' photos to 10 discrete color morphs based on color and color pattern variation. We predicted the color morph distribution using maximum entropy models. We found that variations in morph distributions were mostly related to temperature seasonality, precipitation, elevation, and anthropogenic activities. Our findings support the relationship between environmental conditions and color morph distribution, implying that environmental selection acts differently on color morphs, most likely in conjunction with sexual selection.

Phenotypic and genomic dissection of colour pattern variation in a reef fish radiation.

Coral reefs rank among the most diverse species assemblages on Earth. A particularly striking aspect of coral reef communities is the variety of colour patterns displayed by reef fishes. Colour pattern is known to play a central role in the ecology and evolution of reef fishes through, for example, signalling or camouflage. Nevertheless, colour pattern is a complex trait in reef fishes-actually a collection of traits-that is difficult to analyse in a quantitative and standardized way. This is the challenge that we address in this study using the hamlets (Hypoplectrus spp., Serranidae) as a model system. Our approach involves a custom underwater camera system to take orientation- and size-standardized photographs in situ, colour correction, alignment of the fish images with a combination of landmarks and Bézier curves, and principal component analysis on the colour value of each pixel of each aligned fish. This approach identifies the major colour pattern elements that contribute to phenotypic variation in the group. Furthermore, we complement the image analysis with whole-genome sequencing to run a multivariate genome-wide association study for colour pattern variation. This second layer of analysis reveals sharp association peaks along the hamlet genome for each colour pattern element and allows to characterize the phenotypic effect of the single nucleotide polymorphisms that are most strongly associated with colour pattern variation at each association peak. Our results suggest that the diversity of colour patterns displayed by the hamlets is generated by a modular genomic and phenotypic architecture.

Morphological and molecular characteristics of Donax incarnatus (Bivalvia: Donacidae) from Badur Beach, Madura Island, Indonesia based on the COX1 gene

Abstract. Wijaya CB, Ambarwati R, Rahayu DA. 2023. Morphological and molecular characteristics of Donax incarnatus (Bivalvia: Donacidae) from Badur Beach, Madura Island, Indonesia based on the COX1 gene. Biodiversitas 24: 2805-2813. Donacidae, a family of marine bivalve mollusks, has a high diversity of morphological traits, including shape and color pattern variations. However, these variations often led to errors in morphological identification, necessitating the use of molecular identification methods for accurate species identification and support. This study aims to analyze the morphological and molecular characteristics of Donax incarnatus Gmelin, 1791 collected from Badur Beach of Madura Island, Sumenep District, East Java Province, Indonesia, using the COX1 gene as a molecular marker. Morphological characterization was conducted through qualitative and quantitative observations, while sequencing results were analyzed using bioinformatics software. The results showed that the exterior color of D. incarnatus has three morphological variations, namely purple-black (OQ692130.1), yellowish orange (OQ692131.1), and white (OQ692132.1). Molecular characterization indicated that the similarity value of D. incarnatus with these variations ranged from 96.06% to 99.61%. At the same time, the alignment results of all samples with reference species and outgroups obtained five variations of nucleotide bases. The average genetic distance between D. incarnatus and the in group was 0.01. The phylogenetic tree results obtained using Neighbor-Joining (NJ) and Maximum Likelihood (ML)methods were categorized into two subclusters: D. incarnatus species from Thailand and the study sample from Badur Beach, Madura Island, Indonesia, were placed in the same cluster.

Unexpected colour pattern variation in mimetic frogs: implication for the diversification of warning signals in the genus Ranitomeya.

Predation is expected to promote uniformity in the warning coloration of defended prey, but also mimicry convergence between aposematic species. Despite selection constraining both colour-pattern and population divergence, many aposematic animals display numerous geographically structured populations with distinct warning signal. Here, we explore the extent of phenotypic variation of sympatric species of Ranitomeya poison frogs and test for theoretical expectations on variation and convergence in mimetic signals. We demonstrate that both warning signal and mimetic convergence are highly variable and are negatively correlated: some localities display high variability and no mimicry while in others the phenotype is fixed and mimicry is perfect. Moreover, variation in warning signals is always present within localities, and in many cases this variation overlaps between populations, such that variation is continuous. Finally, we show that coloration is consistently the least variable element and is likely of greater importance for predator avoidance compared to patterning. We discuss the implications of our results in the context of warning signal diversification and suggest that, like many other locally adapted traits, a combination of standing genetic variation and founding effect might be sufficient to enable divergence in colour pattern.

Leukocyte Tyrosine Kinase (Ltk) Is the Mendelian Determinant of the Axolotl Melanoid Color Variant.

The great diversity of color patterns observed among amphibians is largely explained by the differentiation of relatively few pigment cell types during development. Mexican axolotls present a variety of color phenotypes that span the continuum from leucistic to highly melanistic. The melanoid axolotl is a Mendelian variant characterized by large numbers of melanophores, proportionally fewer xanthophores, and no iridophores. Early studies of melanoid were influential in developing the single-origin hypothesis of pigment cell development, wherein it has been proposed that all three pigment cell types derive from a common progenitor cell, with pigment metabolites playing potential roles in directing the development of organelles that define different pigment cell types. Specifically, these studies identified xanthine dehydrogenase (XDH) activity as a mechanism for the permissive differentiation of melanophores at the expense of xanthophores and iridophores. We used bulked segregant RNA-Seq to screen the axolotl genome for melanoid candidate genes and identify the associated locus. Dissimilar frequencies of single-nucleotide polymorphisms were identified between pooled RNA samples of wild-type and melanoid siblings for a region on chromosome 14q. This region contains gephyrin (Gphn), an enzyme that catalyzes the synthesis of the molybdenum cofactor that is required for XDH activity, and leukocyte tyrosine kinase (Ltk), a cell surface signaling receptor that is required for iridophore differentiation in zebrafish. Wild-type Ltk crispants present similar pigment phenotypes to melanoid, strongly implicating Ltk as the melanoid locus. In concert with recent findings in zebrafish, our results support the idea of direct fate specification of pigment cells and, more generally, the single-origin hypothesis of pigment cell development.

Geographical variation in abdominal colour pattern in Criorhina pachymera (Egger, 1858) (Diptera: Syrphidae)

The bee-mimicking hoverfly species Criorhina pachymera shows pronounced geographical variation in abdominal colour pattern. Based on 218 records from 22 European countries, we describe six abdomen forms divided over two main groups. Group A in western, northern and central parts of Europe contains abdomen forms A1–A3 with slender pollinose bands on the third and fourth tergite. Group B in south-eastern Europe contains forms B1–B3 with broad pollinose bands. These groups are separated by the Alps and the Carpathians, such as the separation of the original distributions of the two main postglacial recolonization lineages of honey bees in Europe. As these honey bee groups differ by the width of the pollinose bands on the third to fifth tergite, Batesian mimicry can explain the group distribution of C. pachymera with slender or broad pollinose bands. The different forms of C. pachymera in both groups are categorised by the extent of orange colouration on the second and third tergite. The darkest form A1, has a widespread distribution in Europe. Intermediate bright forms A2 and A3 occur predominantly in a belt along the southern margin of the group A distribution and in Sweden. Dark form B1 and intermediate bright form B2 occur on the Balkan peninsula and in neighbouring regions. The brightest form B3, is found in Italy, Switzerland (Ticino) and Greece. There is an average increase in the extent of orange colouration on the second and third tergite with decreasing geographical latitude, making temperature a likely additional cause for the described abdominal colour variation.

Geographical variation in abdominal colour pattern in Criorhina pachymera (Egger, 1858) (Diptera: Syrphidae)

The bee-mimicking hoverfly species Criorhina pachymera shows pronounced geographical variation in abdominal colour pattern. Based on 218 records from 22 European countries, we describe six abdomen forms divided over two main groups. Group A in western, northern and central parts of Europe contains abdomen forms A1–A3 with slender pollinose bands on the third and fourth tergite. Group B in south-eastern Europe contains forms B1–B3 with broad pollinose bands. These groups are separated by the Alps and the Carpathians, such as the separation of the original distributions of the two main postglacial recolonization lineages of honey bees in Europe. As these honey bee groups differ by the width of the pollinose bands on the third to fifth tergite, Batesian mimicry can explain the group distribution of C. pachymera with slender or broad pollinose bands. The different forms of C. pachymera in both groups are categorised by the extent of orange colouration on the second and third tergite. The darkest form A1, has a widespread distribution in Europe. Intermediate bright forms A2 and A3 occur predominantly in a belt along the southern margin of the group A distribution and in Sweden. Dark form B1 and intermediate bright form B2 occur on the Balkan peninsula and in neighbouring regions. The brightest form B3, is found in Italy, Switzerland (Ticino) and Greece. There is an average increase in the extent of orange colouration on the second and third tergite with decreasing geographical latitude, making temperature a likely additional cause for the described abdominal colour variation.

Color pattern complexity in dwarf minke whales (Balaenoptera acutorostrata) of the northern Great Barrier Reef of Australia

AbstractComplex color patterning is a characteristic feature of dwarf minke whales (DMWs; Balaenoptera acutorostrata) which has been used to photographically identify (photo‐ID) individuals and to research an aggregation on Australia's Great Barrier Reef (GBR). DMW color patterns have been described and applied in various studies, but a detailed and systematic analysis of their complexity is yet to be performed. Here, we applied a novel categorization tool to assess the variation, asymmetry, and association of several DMW color pattern elements, subelements, and their character states. Proportions, hierarchical clustering, and multiple correspondence analysis revealed a high level of asymmetric color pattern variation, with white markings dominant and associated on the right of the body. Our results will improve the citizen science driven photo‐ID of this little‐known cetacean as labor‐intensive manual methods transition to more efficient automated approaches. Such advancement will be challenging, yet beneficial for broader research into the poorly understood areas of DMW life history, evolution, genetics, social structure, and feeding. This could also potentially allow investigation into the functional significance of their color patterns.

New Color-Patterned Species of Microtendipes Kieffer, 1913 (Diptera: Chironomidae) and a Deep Intraspecific Divergence of Species by DNA Barcodes.

The genus Microtendipes Kieffer (Diptera: Chironomidae) has a nearly worldwide distribution, comprising more than 60 species, which are further divided into two species groups based on larval stage. However, species delimitation and identification among the adults of this genus are controversial and uncertain. For instance, previous studies have provided many synonymies based on conspecific color pattern variations in Microtendipes species. Here, we used DNA barcode data to address Microtendipes species delimitation as well as to test whether color pattern variations can be diagnostic characters for interspecific identification. The 151 DNA barcodes used, 51 of which were contributed by our laboratory, represent 21 morphospecies. Species with specific color patterns could be accurately separated based on DNA barcodes. Consequently, the color patterns of adult males could be important diagnostic characters. The average intraspecific and interspecific sequence divergences were 2.8% and 12.5%, respectively, and several species exhibited deep intraspecific divergences higher than 5%. Molecular operational taxonomic units (OTUs) ranged from 21 to 73, based on methods including phylogenetic trees, the assemble species by automatic partitioning method, the Poisson tree process (PTP), and the general mixed Yule-coalescent (GMYC) method. As a result of these analyses, five new species were recognized (M. baishanzuensis sp. nov., M. bimaculatus sp. nov., M. nigrithorax sp. nov., M. robustus sp. nov., and M. wuyiensis sp. nov.).

Positive shifts in species richness and abundance of moths over five decades coincide with community-wide phenotypic trait homogenisation

While some species rapidly decline, compromising vital ecosystem services, others are stable or even increasing in abundance. We studied shifts in species richness and abundance of moths over five decades in Central Sweden and examined whether and how changes were associated with phenotypic traits. We combined information from captures in a light trap in historical time (the 1970s) and contemporarily (2019) with provincial colonisation records. Both community species richness and the abundance of moths increased between the time periods. A large fraction (38%) of the 410 species were not present in both periods, 101 species had colonised the area (an estimated influx of about 2.5 new species per year), and 51 species had disappeared (an estimated local extinction rate of about 1.16 species per year). Abundance increased with an increasing number of host plants and with increasing colour pattern variation. The composition of the community shifted towards species characterised by smaller wingspan and larger ranges. The functional trait variability of the moth community was homogenised from the historical to the contemporary period, in line with reports from other species communities in modern landscapes. However, our finding of a concomitant increase in species richness and total abundance differs from the results of many recent studies of insect communities in other geographic regions.Implication for insect conservationWe conclude that the entire boreal moth fauna is undergoing a substantial biogeographical shift, changing to the moth species historically occurring at more southern latitudes. The alterations in species composition, overall abundance, and community-wide trait distribution described here may cascade up and down in the ecosystem because moths are important pollinators, herbivores, and prey.

Tadpoles of four sympatric megophryinid frogs (Anura, Megophryidae, Megophryinae) from Mangshan in southern China.

Sympatric distribution and potentially long larval development time make the assignment of tadpoles confusing in Asian-horned frogs of the subfamily Megophryinae. In this study, we used molecular data to identify four syntopic megophryinid tadpoles from Mangshan on the border between Hunan and Guangdong provinces in southern China: Brachytarsophryspopei, Boulenophrysshimentaina, Bo.cf.ombrophila, and Bo.nanlingensis. A detailed re-description of the Br.popei tadpoles is provided as well as the first descriptions of three Boulenophrys tadpoles based on external morphology and coloration. An effort is attempted to distinguish these tadpoles by coloration patterns: the dorsal pattern, ventral pattern, and pattern on tail are useful for field identification of these tadpoles. However, the variation of color pattern could sometimes make species delineation difficult. Researchers are encouraged to document coloration in life with photographs and the collection of tadpoles of different development stages and sizes advocated in order to better understand how color may change during larval development.

Selection and Admixture in a Polytypic Aposematic Frog.

AbstractPhenotypic differentiation within polytypic species is often attributed to selection, particularly when selection might be acting on a trait that serves as a signal for predator avoidance and mate choice. We evaluated this hypothesis by examining phenotypic and genotypic clines between populations of the strawberry poison frog Oophaga pumilio, a polytypic species that exhibits aposematic color pattern variation that is thought to be subject to both natural and sexual selection. Our aim was to assess the extent of admixture and to estimate the strength of selection acting on coloration across a region of Panama where monomorphic populations of distinctly colored frogs are separated by polymorphic populations containing both color variants alongside intermediately colored individuals. We detected sharp clinal transitions across the study region, which is an expected outcome of strong selection, but we also detected evidence of widespread admixture, even at sites far from the phenotypic transition zone. Additionally, genotypic and phenotypic clines were neither concordant nor coincident, and with one exception, selection coefficients estimated from cline attributes were small. These results suggest that strong selection is not required for the maintenance of phenotypic divergence within polytypic species, challenging the long-standing notion that strong selection is implicit in the evolution of warning signals.

Dominance mechanisms in supergene alleles controlling butterfly wing pattern variation: insights from gene expression in Heliconius numata.

Loci under balancing selection, where multiple alleles are maintained, offer a relevant opportunity to investigate the role of natural selection in shaping genetic dominance: the high frequency of heterozygotes at these loci has been shown to enable the evolution of dominance among alleles. In the butterfly Heliconius numata, mimetic wing color variations are controlled by an inversion polymorphism of a circa 2 Mb genomic region (supergene P), with strong dominance between sympatric alleles. To test how differences in dominance observed on wing patterns correlate with variations in expression levels throughout the supergene region, we sequenced the complete transcriptome of heterozygotes at the prepupal stage and compared it to corresponding homozygotes. By defining dominance based on non-overlapping ranges of transcript expression between genotypes, we found contrasting patterns of dominance between the supergene and the rest of the genome; the patterns of transcript expression in the heterozygotes were more similar to the expression observed in the dominant homozygotes in the supergene region. Dominance also differed among the three subinversions of the supergene, suggesting possible epistatic interactions among their gene contents underlying dominance evolution. We found the expression pattern of the melanization gene cortex located in the P-region to predict wing pattern phenotype in the heterozygote. We also identify new candidate genes that are potentially involved in mimetic color pattern variations highlighting the relevance of transcriptomic analyses in heterozygotes to pinpoint candidate genes in non-recombining regions.

Factors determining the dorsal coloration pattern of aposematic salamanders

Aposematic bright colors have a key role for animal defense and can be expressed through metabolic production or by acquiring pigments from diet. Aposematic coloration can be related to both local adaptations and availability of trophic resources. The European fire salamander (Salamandra salamandra) shows significant color variability and occurs across a broad range of habitats. Here we combined field observations with common rearing experiments to disentangle the role of environmental conditions and local adaptations in determining aposematic coloration of salamander populations. We assessed color variation and measured habitat features and food availability in adults from 25 populations. Furthermore, we reared newborn larvae from 10 populations under different food availability and analyzed color of metamorphs. To assess color pattern, we measured the percentage of yellow covering the body, and the Hue, Saturation and Value of yellow coloration. Adult showed strong variation of color pattern; variation was strongly related to the individual's size, to habitat productivity and to food availability. Under common garden conditions, differences between populations were not anymore evident, and coloration was only affected by resource availability during larval development. Our results suggest that environmental conditions and food availability are more important than local adaptations in determining differences in aposematic color pattern.

Geographic variation in colour and spot patterns in Dwarf Caiman, Paleosuchus palpebrosus (Cuvier, 1807) in Brazil

Abstract Colour variation in crocodilians is associated with size, environment and genetic structure, but little is known about colour variation in the genus Paleosuchus (Alligatoridae). Different genetic lineages of Paleosuchus palpebrosus (Dwarf caiman) occupy different environments throughout the species extensive distribution, and all are cryptically coloured. We captured 187 P. palpebrosus and recorded their head colour from four genetically distinct geographic clades between 2008 and 2019. Additionally, we determined the jaw and belly spot pattern of a subsample of 95 individuals (22–109 cm snout-vent length). PERMANCOVA was used to investigate the relationships between head colour and spot patterns, to the caiman size, sex, and geographic lineage, as well as ambient temperature. Variation in head colour, and jaw and belly spot patterns, were related to genetic lineage, snout-vent length and temperature, but the model explained only ∼45.4% of the variance in the data. Sex was not significantly related to the head colour, or jaw and belly spot patterns. Dwarf caimans inhabiting cooler climates tend to be darker than individuals from warmer areas, and individuals from the “Cerrado-Pantanal” and “Bolivia” lineages generally darker than the “Amazon” and “Madeira” lineages. However, individuals of a given size in different lineages overlap greatly in colour patterns and colour alone could not be used to distinguish lineages. The Natterer’s hypothesis of head-colour as diagnose from “Cerrado-Pantanal” lineage, cannot be completely accepted according our quantitative analysis, although there are a variation in the geographic distribution of these phenotypic traits, and the “Cerrado-Pantanal” lineage had been the most distinct among the lineages.

A conserved molecular template underlies color pattern diversity in estrildid finches.

The color patterns that adorn animals’ coats not only exhibit extensive diversity linked to various ecological functions but also display recurrences in geometry, orientation, or body location. How processes of pattern formation shape such phenotypic trends remains a mystery. Here, we surveyed plumage color patterns in passerine finches displaying extreme apparent variation and identified a conserved set of color domains. We linked these domains to putative embryonic skin regions instructed by early developmental tissues and outlined by the combinatory expression of few genetic markers. We found that this embryonic prepattern is largely conserved in birds displaying drastic color differences in the adult, interspecies variation resulting from the masking or display of each domain depending on their coloration. This work showed that a simple molecular landscape serves as common spatial template to extensive color pattern variation in finches, revealing that early conserved landmarks and molecular pathways are a major cause of phenotypic trends.

Fluorescent colour patterns in the basal pectinid Pleuronectites from the Middle Triassic of Central Europe: origin, fate and taxonomic implications of fluorescence

AbstractUV light‐induced fluorescence is widely used as a key to reveal residual shell colour patterns of Neogene and Palaeogene molluscs. However, only few examples of fluorescent colour patterns are known from Mesozoic marine shells and little is known about the nature of fluorescence in fossils. Here, UV light‐induced fluorescence reveals previously unseen abundance and diversity in the colour patterns of the basal pectinid Pleuronectites laevigatus from the Middle Triassic Muschelkalk of Central Europe. In addition to known variations of radial bands, a multitude of zigzag and zigzag‐related patterns was found. The diversity of colour patterns is comparable to modern pectinids and is interpreted as colour pattern polymorphism. Raman spectra of the colour patterns indicated the preservation of residual organic pigments with aromatic moieties. The fluorescence properties of P. laevigatus and other basal pectinids from the Muschelkalk of Germany and France are described in detail, suggesting that colour pattern fluorescence is due to colourless diagenetic products of the pigments, not to the fossil pigments themselves. A remarkable feature of the colour patterns of P. laevigatus is the presence of different fluorescence colours. Because a gradual shift of the fluorescence colour from yellow to red with decreasing intensity to finally non‐fluorescent is observed, which correlates with the provenance of the specimens, the fluorescence properties are interpreted to reflect differences in diagenetic history. The results show that the fluorescence colour of fossil molluscs, especially of Mesozoic molluscs, may be affected by diagenesis and should only be used with caution for taxonomic purposes.