Shell Colour Patterns Research Articles

Akoyazara, a new genus of limpet-shaped trochids, with redescription of Broderipia J.E. Gray, 1847 (Vetigastropoda: Trochidae: Fossarininae)

ABSTRACT The generic assignment of ‘Broderipia’ eximia has been problematic in the past, and here we propose a new trochid genus Akoyazara n. gen. for it and compare this with Broderipia. The type species of both genera have limpet-shaped shells, but they differ from each other in shell height, external shell sculpture, shell colour pattern, length of epipodial tentacles, shape of the cutting edge of the radular teeth, the presence or absence of a sensory organ at the base of each epipodial tentacle and a genitalia-like projection on the right side of the head. The strong radial ribs on the external shell surface of Akoyazara eximia are suggested to be an adaptation to highly exposed shores. The depressed limpet-shaped shell of Broderipia iridescens is likely to be adaptive, allowing access to narrow spaces in pits carved from rock, which have been bored and occupied by the sea urchins with which they live. Broderipia nitidissima is also transferred to Akoyazara (n. comb.), and this new genus currently includes only two species. New lectotypes of the type species of Broderipia, B. rosea and B. iridescens are designated herein based on specimens in the collection of the Natural History Museum, London.

Carapace Morphology Variations in Captive Tortoises: Insights from Three-Dimensional Analysis.

The carapace morphology of tortoises is a crucial characteristic used for species identification, with features such as shell shape, roughness, and color patterns varying among species. Understanding this morphological diversity is valuable not only for taxonomic classification but also for more specialized clinical approaches. This study investigated the morphological differences in the shells of Leopard tortoises (Stigmochelys pardalis), African spurred tortoises (Centrochelys sulcata), and Greek tortoises (spur-thighed tortoises; Testudo graeca) raised in captivity. Using 3D scanners, the carapaces were modeled, and a 3D geometric morphometric method was employed to analyze shape variations and dimensional features, with landmarks applied automatically. Among the species studied, African spurred tortoises had the largest carapace size. Principal component analysis (PCA) identified PC1 and PC3 as critical factors in distinguishing between species based on morphological characteristics. Positive PC1 values, associated with a shorter carapace height, indicated a flatter or more compact shell shape. A higher PC3 value corresponded to a raised shape at the back of the shell, while a lower PC3 value indicated a raised shape at the front. Specifically, Leopard tortoises exhibited a higher carapace shape than the other species, while African spurred tortoises had shorter carapaces. An allometric effect was observed in the carapaces, where smaller specimens tended to be proportionately higher-domed, whereas larger shells displayed a lower height in shape. These findings highlight the significance of shape variations in tortoise shells, which emerge during adaptation and have important implications for taxonomy and clinical practice. Such differences should be carefully considered in veterinary care and species identification.

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.

Identification of shell-color-related microRNAs in the Manila clam Ruditapes philippinarum using high-throughput sequencing of small RNA transcriptomes

Shell-color polymorphism is a common phenomenon in several mollusk species and has been associated with thermal capacity, developmental stability, shell strength, and immunity. Shell-color polymorphism has been related to the differential expression of genes in several signal transduction pathways; however, the functions of micro-RNAs (miRNAs) in shell-color formation remain unclear. In the present study, we compared high-quality, small-RNA transcriptomes in three strains of the Manila clam Ruditapes philippinarum with specific shell-color patterns, artificially selected for six generations. Totals of 114 known and 208 novel miRNAs were identified by high-throughput sequencing, of which nine known and one novel miRNA were verified by stem-loop quantitative real time-polymerase chain reaction. Predicted miRNA targets were subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. miR-137 and miR-216b and the Hedgehog signaling pathway and Wnt signaling pathway were identified as being potentially involved in pigment formation and regulation in R. philippinarum. These results may help to clarify the role of miRNAs in shell coloration and shed light on the mechanisms regulating color formation in bivalve shells.

Genome-wide identification and expression profiling of TYR gene family in Ruditapes philippinarum under the challenge of Vibrio anguillarum

Tyrosinase (EC1.14.18.1, TYR) is also called phenol oxidase, is not only involved in pigmentation but also plays an important role in modulating innate immunity in invertebrates. Tyrosinase is a copper containing metalloenzyme. The tyrosinase protein has two copper binding sites and three conserved histidines. In this study, 21 tyrosinase genes (RpTYR) were obtained from the whole genome of Ruditapes philippinarum. Their open reading frames were from 951 to 5424 aa, the range of predicted relative molecular weight from 36.72 to 203.81 kDa, and the range of isoelectric point from 4.72 to 9.88. Transcriptome analysis showed that RpTYR gene was expressed specifically in different developmental stages, adult tissues, four strains and two groups with different shell colors. Besides, the expression profiles of 21 RpTYRs were investigated against the immune response of R. philippinarum to a Vibrio challenge. The qPCR results showed that RpTYRs were involved in the immune response of R. philippinarum after Vibrio anguillarum challenge. This study provides preliminary evidence that the tyrosinases genes are involved in the immune defense and the potential immune function of R. philippinarum. Overall, these findings suggested that the expansion of TYR genes may play vital roles in larval development, the formation of shell color pattern, and immune response in R. philippinarum.

Genome-wide identification and transcriptome-based expression profiling of Wnt gene family in Ruditapes philippinarum

The Wnt genes encode a set of conserved glycoproteins regulating early development, cell proliferation and differentiation, and tissue regeneration in metazoans. In some mollusks, the knowledge of Wnt gene family has been limited because of the short of the genomic and transcriptomic resources. Ruditapes philippinarum is an economically important bivalve with a variety of shell coloration patterns and ability to regenerate its siphon. To gain a greater understanding of the evolutionary dynamics of Wnt gene family, we carried out a genome-wide identification and phylogenetic analysis of Wnt gene family in R. philippinarum and other four mollusks. A total of 12 Wnt genes were identified in the genome of R. philippinarum, and the dynamic patterns of gene conservation, loss and duplication of Wnt genes were analyzed in mollusks and model organisms. Furthermore, the transcriptome analyses demonstrated the expression profiles of the Wnt genes at different developmental stage, in adult tissues, during siphon regeneration, in four different shell color strains, and at uncolored and colored developmental stages in two different shell color strains. These findings suggest that the expansion of Wnt genes may play vital roles in the larval development, the formation of shell color pattern and siphon regeneration in R. philippinarum. This study provides a valuable insight into Wnt function and evolution in mollusks.

Unraveling Cryptic Morphological Diversity in a Marine Snail Species Complex Using Nuclear Genomic Data

Conus lividus (Hwass in Bruguiere, 1792) and Conus sanguinolentus (Quoy and Gaimard, 1834) are closely related Indo-West Pacific cone snails that have largely overlapping distributions. Previous population genetic analyses of these species found that some individuals that were identified as C. lividus possessed mitochondrial gene sequences that were similar or in some cases identical to those of C. sanguinolentus. While these species tend to be easily distinguished based on shell color patterns, it is possible that some individuals of C. sanguinolentus were misidentified as C. lividus. The result though could also be due to introgression of the mitochondrial genome of C. sanguinolentus into C. lividus. We used a ddRAD approach to obtain sequences of short fragments of more than 7,000 nuclear genomic loci to examine patterns of variation and evaluate these explanations. Results showed that the two parental species are genetically differentiated at nuclear loci and all putative hybrids were unambiguously assigned to C. sanguinolentus based on shared patterns of variation. These results demonstrate that variation in shell color patterns of C. sanguinolentus overlaps with that of C. lividus, and extend the distribution of C. sanguinolentus into the Hawaiian Archipelago. Additional analyses of patterns of genetic variation among populations of the two species revealed that while C. lividus shows no genetic population structure, the population of C. sanguinolentus from Hawaii is genetically differentiated from populations elsewhere as found in prior analyses based on mitochondrial sequence data.

Characteristics of a Novel Tyrosinase Gene Involved in the Formation of Shell Color in Hard Clam Meretrix meretrix

Hard clam (Meretrix meretrix) has a rich shell color variation among individuals from light yellow to bluish gray, brown red, and black, which may associating with melanin. Tyrosinase (Tyr) is a key rate-limiting enzyme for the biosynthesis of melanin, which affects the dark color of animal skin, hair, fur, scales and feathers. Here, we isolated and characterized the full-length cDNA sequence of M. meretrix tyrosinase gene (MmTyr) which encodes a protein with 689 amino acids. Sequence characteristics and phylogenetic analysis showed that there are a variety of Tyr genes in mollusks, which can be divided into different categories. The abundance of MmTyr transcript was detected in six tissues including mantle, adductor muscle, digestive gland, foot, gill and siphon of adult M. meretrix with qRT-PCR. The results showed a higher expression specifically in the mantle, digestive gland and siphon, which was consistent with the phenotypic color difference. In the embryos and larvae at different developmental stages, high expression was found in the trochophore larvae and juvenile clams. Among three M. meretrix strains with different shell colors, the expression level of MmTyr and total melanin content in the mantle edge both showed significant differences, suggesting that MmTyr is involved in the formation of shell color. The results obtained in this study will improve our understanding of molluscan tyrosinase gene function and molecular mechanism of shell color pattern determination.

A new species of Amoria (Gastropoda, Volutidae, Amoriinae) from the mid-east coast of Australia

A new species of Amoria Gray, 1855 (Gastropoda, Volutidae) is described from shells dredged off the Australian mid-east coast (Cape Moreton, Queensland and Tweed Heads, New South Wales). Amoria thorae sp. nov. shows a number of similarities in shell form and/or colour pattern to two other small Amoria, A. necopinata Darragh, 1983 and A. benthalis McMichael, 1964 and to the much larger A. undulata (Lamarck, 1804) but can be readily distinguished from these and all other members of the genus by the combination of small shell size, fusiform shape, high spire, equal-sized thick columellar plaits and a single, large undulation of the axial lines.

Genetic diversity and clonality of the Asian clam Corbicula fluminea are reflected by inner shell color pattern

Genetic diversity and clonality of the Asian clam Corbicula fluminea are reflected by inner shell color pattern

Discrete or indiscrete? Redefining the colour polymorphism of the land snail Cepaea nemoralis

Biologists have long tried to describe and name the different phenotypes that make up the shell polymorphism of the land snail Cepaea nemoralis. Traditionally, the view is that the ground colour of the shell is one of a few major colour classes, either yellow, pink or brown, but in practise it is frequently difficult to distinguish the colours, and define different shades of the same colour. To understand whether colour variation is in reality continuous, and to investigate how the variation may be perceived by an avian predator, we applied psychophysical models of colour vision to shell reflectance measures. We found that both achromatic and chromatic variation are indiscrete in Cepaea nemoralis, being continuously distributed over many perceptual units. Nonetheless, clustering analysis based on the density of the distribution did reveal three groups, roughly corresponding to human-perceived yellow, pink and brown shells. We also found large-scale geographic variation in the frequency of these groups across Europe, and some covariance between shell colour and banding patterns. Although further studies are necessary, the observation of continuous variation in colour is intriguing because the traditional theory is that the underlying supergene that determines colour has evolved to prevent phenotypes from “dissolving” into continuous trait distributions. The findings thus have significance for understanding the Cepaea polymorphism, and the nature of the selection that acts upon it, as well as more generally highlighting the need to measure colour objectively in other systems.

Growth, mortality and susceptibility of oyster Crassostrea spp. to Perkinsus spp. infection during on growing in northeast Brazil.

Crassostrea rhizophorae and C. gasar oysters are cultivated in the northeast region. Perkinsus parasites infect bivalves, and their effects on oysters from tropical regions are poorly understood. This study evaluated the impact of Perkinsus infection on the productive traits of native oysters. Oysters were sampled bimonthly during 7 months, from July 2010 to February 2011, to evaluate growth rate, mortality and shell color patterns (white and dark-gray) (n = 500), and to determine the prevalence and intensity of Perkinsus (n = 152). Perkinsus and Crassostrea species were determined using molecular tools. Results showed that most dark-gray (90%, n = 20) and white (67%, n = 18) oysters were C. gasar and C. rhizophorae, respectively. Oysters showed a high growth rate and moderate cumulative mortality (44%). C. gasar oysters grew better and showed lower mortality and lower incidence of Perkinsus compared to C. rhizophorae. The mean prevalence of Perkinsus was moderate (48%), but the infection intensity was light (2.2). Perkinsosis affected very small oysters (19.4 mm). In conclusion, native oysters, especially C. gasar, have a great potential for culture, mortality is not associated with perkinsosis, and the shell color of oysters can be used to improve selection for spats with better performance.

Land snails of Leptopoma Pfeiffer, 1847 in Sabah, Northern Borneo (Caenogastropoda: Cyclophoridae): an analysis of molecular phylogeny and geographical variations in shell form.

Leptopoma is a species rich genus with approximately 100 species documented. Species-level identification in this group has been based on shell morphology and colouration, as well as some anatomical features based on small sample sizes. However, the implications of the inter- and intra-species variations in shell form to the taxonomy of Leptopoma species and the congruency of its current shell based taxonomy with its molecular phylogeny are still unclear. There are four Leptopoma species found in Sabah, Borneo, and their taxonomy status remains uncertain due to substantial variation in shell forms. This study focuses on the phylogenetic relationships and geographical variation in shell form of three Leptopoma species from Sabah. The phylogenetic relationship of these species was first estimated by performing Maximum Likelihood and Bayesian analysis based on mitochondrial genes (16S rDNA and COI) and nuclear gene (ITS-1). Then, a total of six quantitative shell characters (i.e., shell height, shell width, aperture height, aperture width, shell spire height, and ratio of shell height to width) and three qualitative shell characters (i.e., shell colour patterns, spiral ridges, and dark apertural band) of the specimens were mapped across the phylogenetic tree and tested for phylogenetic signals. Data on shell characters of Leptopoma sericatum and Leptopoma pellucidum from two different locations (i.e., Balambangan Island and Kinabatangan) where both species occurred sympatrically were then obtained to examine the geographical variations in shell form. The molecular phylogenetic analyses suggested that each of the three Leptopoma species was monophyletic and indicated congruence with only one of the shell characters (i.e., shell spiral ridges) in the current morphological-based classification. Although the geographical variation analyses suggested some of the shell characters indicating inter-species differences between the two Leptopoma species, these also pointed to intra-species differences between populations from different locations. This study on Leptopoma species is based on small sample size and the findings appear only applicable to Leptopoma species in Sabah. Nevertheless, we anticipate this study to be a starting point for more detailed investigations to include the other still little-known (ca. 100) Leptopoma species and highlights a need to assess variations in shell characters before they could be used in species classification.

New observations of the enigmatic West African Cellana limpet (Mollusca: Gastropoda: Nacellidae)

Identification of limpets is often hampered by highly variable within-species shell morphologies and colour patterns. Since pre-Linnean times this has produced complex taxonomies with confusing nomenclatorial histories and uncertain distribution patterns. This is the case for a complex of taxa associated with Cymbula safiana (Lamarck, 1819) and with the rejected name Patella nigra. We DNA sequenced limpets from Nigeria that were originally identified as C. safiana. Comparisons with available cox1 data of patellogastropods show that the specimens actually belong to the genus Cellana Adams, 1869 which has been recorded only once before in the Atlantic Ocean with the finding of specimens from Ghana. We are reporting findings of Cellana sp. from the Gulf of Guinea for the second time. Specimens from Nigeria are 100 % similar to previously published cox1 sequences from Ghana. Due to variable shell characteristics we suspect that this species may have been confused with Cymbula safiana (Lamarck, 1819) in previous records. Inspection of the radula sack and radula demonstrates clear similarities with other Cellana species and contrasting differences in the organization of the teeth in Cymbula. Because Cellana is a possible candidate of invasive species in West Africa and Cymbula is considered as endangered, is seems particularly important to be able to distinguish between the two without being dependent on DNA analysis. When shell morphology seems to be of questionable diagnostic value, examination of the radula will help in future mapping and monitoring of these two species. A cox1 gene tree with Nigerian sequences included is in line with findings of previous authors and restates the need for taxonomic revision of the species clustering with Cellana toreuma (Reeve, 1854) and parts of a polyphyletic Cellana radiata von Born, 1778.

UV Light Reveals the Diversity of Jurassic Shell Colour Patterns: Examples from the Cordebugle Lagerstätte (Calvados, France).

Viewed under UV light the diverse and exceptionally well-preserved molluscs from the Late Jurassic Cordebugle Konservat Lagerstätte (Calvados, Normandy, France) reveal fluorescent fossil shell colour patterns predating the oldest previously known instance of such patterns by 100 Myr. Evidently, residual colour patterns are observable in Mesozoic molluscs by application of this non-destructive method, provided the shells are not decalcified or recrystallized. Among 46 species which are assigned to twelve gastropod families and eight bivalve families, no less than 25 species yielded positive results. Out of nine colour pattern morphologies that have been distinguished six occur in gastropods and three in bivalves. The presence of these variant morphologies clearly indicates a significant pre-Cenozoic diversification of colour patterns, especially in gastropods. In addition, the occurrence of two distinct types of fluorescence highlights a major difference in the chemical composition of the pigments involved in colour pattern formation in gastropods. This discovery enables us to discriminate members of higher clades, i.e. the Vetigastropoda emitting red fluorescence from the Caenogastropoda and Heterobranchia emitting whitish-beige to yellow fluorescence. Consequently, fluorescent colour patterns may help to allocate part of the numerous enigmatic Mesozoic gastropod taxa to their correct systematic position.

Transcriptome analysis of shell color-related genes in the clam Meretrix meretrix.

Color polymorphism has received much attention due to its strong implications for speciation and adaptation. In contrast to body color, little is currently known about the molecular mechanism of shell color formation. This study represents the first analysis of the relationship between whole-scale gene expression and shell color variations in the marine bivalve mollusks via comparative transcriptome analyses. Three clam Meretrix meretrix strains with different and monotonous shell color patterns, which were developed by our 10-year artificial selection, combined with clams with nearly white shell color were used in the analyses. The results supported the idea that there was a relationship between gene expression and shell pigmentation in the clam M. meretrix, and complex signal transduction were involved. It was proposed that Notch signaling pathway played a crucial role in shell pigmentation in a gene-dosage dependent pattern and also potentially involved in the shell color patterning. Calcium signaling process may equally be implicated in shell color formation via activation of Notch pathway. Other differentially expressed genes (e.g., Myl, Mitf) potentially implicated in shell color pigmentation were also noticed. This study provides information on the expression profiles of clams with different shell color morphs and sheds light on color formation mechanism of shell.

Tissue transaminase activities in the black-sea mollusc Mytilus galloprovincialis Lam. with different shell color

The tissue activities of aspartate aminotransferase (AST, EC 2.6.1.1) and alanine aminotransferase (ALT, EC 2.6.1.2) were studied in the bivalve molluscs differing in shell color. The shell color patterns were evaluated by photographing and computer image processing in Adobe Photoshop CS-3. The transaminase activities were determined by the Reitman-Frankel method. The four shell-color groups of molluscs were distinguished: black, intermediate, dark- and light brown. The AST and ALT activities were found to increase as shell color became lighter, probably reflecting different tolerance of molluscs to habitats with different oxygen concentration. The ALT distribution pattern differed appreciably in the foot of M. galloprovincialis where the highest values were found in the black-colored mussels, apparently due to the change of the predominant enzyme function. In this tissue, the transamination reaction was directed towards replenishing the pool of free amino acids required for the synthesis of byssus filaments.

Genetic population structure in Nacella magellanica: Evidence of rapid range expansion throughout the entire species distribution on the Atlantic coast

Nacella magellanica, the most abundant limpet in the Magellanic biogeographic Province of Argentina and Chile, is characterized by a noticeable variability in shell morphology and color patterns. Ecological as well as evolutionary features make this limpet an interesting species for evolutionary and population genetic studies. Here, arbitrary nuclear molecular markers, inter-simple sequence repeat-PCR, are used to analyze the population genetic structure in 14 localities of N. magellanica along 2900km on the Atlantic coast of the Magellanic Province. We compare the present results, based on nuclear markers, with previous findings of a phylogeographic study that used the mitochondrial COI gene. All the results presented here suggest little genetic structure within N. magellanica, with moderate to high genetic connectivity among populations. The short time elapsed since the expansion of this species plus a possible long larval lifespan and the oceanographic and environmental conditions of the Magellanic Province might explain the lack of genetic structuring and the low levels of genetic differentiation in the species throughout its distribution range along the Argentine coast.

Growth performance of the clam, Meretrix meretrix, breeding-selection populations cultured in different conditions

A breeding-selection program for the clam, Meretrix meretrix, was conducted since 2004. Two of the selection populationswere generated with the shell color pattern as an additional selection criterion and named as SP (purple stripes) population and SB (black dots) population. The third-generation SP and SB populations (08G3SP and 08G3SB, respectively) were cultured at two commercial clam farms and a nursery pond and their shell lengths were compared. 08G3SB clams had significantly larger sizes than 08G3SP clams at commercial clam farms (p < 0.05), yet 08G3SB individuals were significantly smaller than 08G3SP individuals at the nursery pond (p < 0.05). Then, we examined the growth of the fourth-generation SP and SB populations (10G4SP and 10G4SB, respectively) at a commercial farm, and found that the shell lengths of the 10G4SB clams increased at a significantly higher growth rate than the 10G4SP clams (p < 0.05) from May to September, when the water temperature was between 24.2-27.5A degrees C, while 10G4SB lost the growth advantage in the other months. These results indicated that SP and SB populations responded differently to environmental factors, so it is beneficial for the clam farmers to select a suitable population according to the culture environment. Furthermore, a diallel mating of the SB and SP populations was designed to investigate whether their hybrid population would show heterosis. However, the heterosis was not shown in this study, whichmight result from the slight genetic divergence between SB and SP populations.

Differential shell strength of Cepaea nemoralis colour morphs--implications for their anti-predator defence.

One of the most spectacular evolutionary forces is predation, evidenced to stimulate polymorphism in many prey species. Shell colour polymorphism of the land snail Cepaea nemoralis is a well-known model in evolutionary research. Nevertheless, the knowledge on the ecological causes driving its evolution remains incomplete and proximal factors shaping predatory pressure on C. nemoralis morphs are unknown. We evaluated shell crushing resistance and thickness, constituting crucial snail anti-predator defences in two shell areas (the apex and labium) of eight C. nemoralis morphotypes differing in shell colour and banding pattern. A GLM showed a significant effect of shell colour, banding pattern and shell thickness on shell strength. Pink shells were stronger than yellow ones, and banded forms had stronger shells than unbanded snails. The labium (usually attacked by mice) was generally thicker and more resistant than the apex (usually crushed by birds). Thicker shells were more resistant to crushing, and the rate of shell strength increase per unit of shell thickness was greater in pink and banded individuals compared to yellow and unbanded ones. Yellow and unbanded morphs have been found to be preferred by mice in the previous studies, which suggests that shell strength may be an important trait used in prey selection by these shell-crushing predators. The differences in potential anti-predator defences among snail morphs, found in the present study, justify future research on direct effect of C. nemoralis morphs shell strength on predator selectivity.