RESEARCH ARTICLE Identification of Shell Colour Pigments in Marine Snails Clanculus pharaonius and C. margaritarius (Trochoidea; Gastropoda) S. T. Williams1*, S. Ito2, K. Wakamatsu2, T. Goral3, N. P. Edwards4, R. A. Wogelius4, T. Henkel4, L. F. C. de Oliveira5, L. F. Maia5, S. Strekopytov3, T. Jeffries3†, D. I. Speiser6,J. T. Marsden7 1 Natural History Museum, Department of Life Sciences, London, United Kingdom, 2 Department of Chemistry, Fujita Health University School of Health Sciences, 1–98 Dengakugakubo, Kutsukake-cho, a11111 Toyoake, Aichi, Japan, 3 Natural History Museum, Imaging and Analysis Centre, London, United Kingdom, 4 School of Earth, Atmospheric, and Environmental Sciences, University of Manchester, Manchester, United Kingdom, 5 NEEM Núcleo de Espectroscopia e Estrutura Molecular, Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Juiz de Fora, Juiz de Fora, MG, Brazil, 6 Department of Biological Sciences, University of South Carolina, Columbia, South Carolina, United States of America, 7 Viapath, Reference Biochemistry Laboratories, King's College Hospital, London, United Kingdom † Deceased. OPEN ACCESS * [email protected] Citation: Williams ST, Ito S, Wakamatsu K, Goral T, Edwards NP, Wogelius RA, et al. (2016) Identification of Shell Colour Pigments in Marine Snails Clanculus Abstract pharaonius and C. margaritarius (Trochoidea; Gastropoda). PLoS ONE 11(7): e0156664. Colour and pattern are key traits with important roles in camouflage, warning and attraction. doi:10.1371/journal.pone.0156664 Ideally, in order to begin to understand the evolution and ecology of colour in nature, it is Editor: Geerat J. Vermeij, University of California, important to identify and, where possible, fully characterise pigments using biochemical UNITED STATES methods. The phylum Mollusca includes some of the most beautiful exemplars of biological Received: March 17, 2016 pigmentation, with the vivid colours of sea shells particularly prized by collectors and scien- Accepted: May 17, 2016 tists alike. Biochemical studies of molluscan shell colour were fairly common in the last cen- Published: July 1, 2016 tury, but few of these studies have been confirmed using modern methods and very few shell pigments have been fully characterised. Here, we use modern chemical and multi- Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, modal spectroscopic techniques to identify two porphyrin pigments and eumelanin in the transmitted, modified, built upon, or otherwise used shell of marine snails Clanculus pharaonius and C margaritarius. The same porphyrins were by anyone for any lawful purpose. The work is made also identified in coloured foot tissue of both species. We use high performance liquid chro- available under the Creative Commons CC0 public matography (HPLC) to show definitively that these porphyrins are uroporphyrin I and uro- domain dedication. porphyrin III. Evidence from confocal microscopy analyses shows that the distribution of Data Availability Statement: All relevant data are porphyrin pigments corresponds to the striking pink-red of C. pharaonius shells, as well as within the paper and its Supporting Information files. pink-red dots and lines on the early whorls of C. margaritarius and yellow-brown colour of Funding: STW gratefully acknowledges financial later whorls. Additional HPLC results suggest that eumelanin is likely responsible for black support from the Department of Life Sciences, Natural History Museum. LFCO and LFM thank the spots. We refer to the two differently coloured porphyrin pigments as trochopuniceus (pink- Brazilian agencies CNPq, CAPES and FAPEMIG for red) and trochoxouthos (yellow-brown) in order to distinguish between them. Trochopuni- financial support. STW’s visit to the King Abdullah ceus and trochoxouthos were not found in the shell of a third species of the same superfam- University of Science and Technology was funded by ily, Calliostoma zizyphinum, despite its superficially similar colouration, suggesting that this KAUST awards CRG-1-2012-BER-002 and 59130357 (to M.L. Berumen). DIS acknowledges species has different shell pigments. These findings have important implications for the funding from the National Science Foundation (IOS- study of colour and pattern in molluscs specifically, but in other taxa more generally, since 1457148). We acknowledge the Diamond Light PLOS ONE | DOI:10.1371/journal.pone.0156664 July 1, 2016 1/25 Identification of Gastropod Shell Pigments Source for synchrotron access granted under this study shows that homology of visible colour cannot be assumed without identification of proposal SP9488 and NPE is funded by NERC grant pigments. NE/J023426/1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The remaining authors received no specific funding for this work. Introduction Competing Interests: The authors have declared that no competing interests exist. Colour plays an important role in the survival of many species, specifically in mate attraction, signalling, camouflage, thermoregulation, immunity and strengthening [1–4]. Colour can also offer a visible link between an external phenotype and its corresponding genotype, providing a model for the exploration of fundamental evolutionary processes [2]. In order to study how colour and pattern have evolved in any organism it is imperative to know which pigments are responsible for colouration and how these pigments originate [4–6]. There are several classes of biological pigments, and each can give rise to a range of colours that overlaps with those pro- duced by other pigment classes [4, 7]. As such, it is not possible to identify the pigment classes present in any organism purely by its visible colour, making it essential to identify pigments biochemically to avoid mistaking homoplasy for homology. Once a pigment is known, molecu- lar studies can be more targeted in identifying genes associated with its pigment [4]. Molluscs are often renowned for their highly colourful shells, and shell colour and pattern have proved to be highly tractable markers for use in studies on natural selection, in part because shells and shell fragments can be easily collected [4] (e.g. [8]). Recently, there has been growing interest in the molecular origins of shell colour (e.g. [9–12]). The biochemical nature of shell pigments was investigated by a number of researchers towards the end of the 1800s, reaching a peak in terms of number of studies in the mid-1900s (e.g. [5, 13–24]). Older studies identified two main classes of shell pigments: melanins and tetrapyrroles (which include por- phyrins and linear tetrapyrroles known as bile pigments or bilins) along with a number of other pigments that could not be fully characterised, some of which were complexed to pro- teins. More recent chemical studies are scarce, but have confirmed the presence of porphyrins, bilins and incompletely characterised pigments identified only as polyenes (organic com- pounds containing multiple double bonds) (e.g. [24–26]). However, the extraction and identification of pigments is extremely difficult. For example, in one recent study, more than 30 kg of shells of Haliotis discus hannai were required to obtain only 2.7 mg of purified pigment [24]. Such studies are likely only possible for species that are very large or the target of aquaculture (as in the case of Haliotis). In part because of the difficul- ties associated with chemical identification of shell pigments, many recent studies of shell pig- mentation have focused on using Resonance Raman Microspectrometry to examine whole shells. These studies have also found polyenes or polyenes bound to other molecules in shells, which are usually described as carotenoids, and occasionally as psittacofulvins (e.g. [7, 27–30]). Although little is known about the evolution of pigments in molluscs, it seems likely that pigment types are distributed in a phylogenetically relevant manner ([4, 15] and references therein). For instance, tetrapyrrole pigments such as porphyrins and bilins occur most com- monly in vetigastropods and have not been found in the shells of freshwater gastropods (other than some neritids) or land snails [20]. Conversely, polyenes (mostly thought to be caroten- oids) have been identified by Raman Microspectrometry primarily in shells of caenogastro- pods, hetereobranch gastropods and unionid bivalves [28, 29, 31–34]. In this study we use a variety of chemical and multi-modal spectroscopic techniques to iden- tify and characterise as fully as possible shell pigments in two nominal species of the vetigastro- pod genus, Clanculus (Trochoidea; Trochidae): Clanculus margaritarius (Philippi, 1846) (Fig 1A and 1B) and C. pharaonius (Linnaeus, 1758) (Fig 1C). Clanculus pharaonius shells are a PLOS ONE | DOI:10.1371/journal.pone.0156664 July 1, 2016 2/25 Identification of Gastropod Shell Pigments Fig 1. Photos of exemplar specimens. (A) Clanculus margaritarius A. Shell from Kitahama, Japan. Note that the specimen is sub adult. Specimen # 3. (B) Clanculus margaritarius B. Shell of an unlocalised specimen, NHMUK collection. Specimen # 10. (C) Clanculus pharaonius. Rose Reef, Thuwal, Saudi Arabia. Specimen # 4. (D) Calliostoma zizyphinum. Shetland Islands, United Kingdom. Specimen # 1. Scale bars = 5 mm, except in (D), where scale bar = 1 cm. doi:10.1371/journal.pone.0156664.g001 vivid pink-red with black and white spots and C. margaritarius