Author: Chong Chen

New paper on adaptation of vent/seep scale worms published!

New co-authored paper on the adaptation and evolution of vent scale worms (polynoid polychaetes) published in Scientific Reports! The article is open access and free to read here: http://www.nature.com/articles/srep46205

Scale worms inhabit a great variety of environments ranging from very shallow water down to kilometres deep and are often an important member of chemosynthetic ecosystems such as vents, often living in close proximity to hot black smokers. In this study, we sequenced the transcriptomes of two deep-sea scale worms inhabiting hydrothermal vents and hydrocarbon seeps and one shallow water counterpart that was rather closely related. By comparing the three transcriptomes, we were able to elucidate selective amino acid usage, positively selected genes, highly expressed genes, and potentially duplicated genes, thereby shedding light on how the scale worms evolved to become successful members of deep-sea chemosynthetic communities. These are the first deep-sea scale worm transcriptomes ever reported.

Highly expressed genes in B. pettiboneae (vent/seep), Lepidonotopodium sp. (vent) and H. imbricata (shallow water relative).(a) Percentage of genes participated in different cellular processes. (b) Expression level for gene groups participated in different cellular processes.

Most significant among our findings was the significance of genes related to haemoglobin. The two deep-sea polynoids chosen for this study, in the genera Branchipolynoe and Lepidonotopodium, are shown to have adopted different yet equally effective ways to cope with the oxygen-poor chemosynthetic ecosystems. Branchipolynoe rapidly evolved a novel tetra-domain haemoglobin which is highly effective in oxygen transport, whereas Lepidonotopodium increased the expression levels of standard single-domain haemoglobin to four times as high as Branchipolynoe. These results indicate that dealing with hypoxic environment is a key element in becoming successful in deep-sea vents and seeps.

Zhang Y [Yanjie], Sun J, Chen C, Watanabe HK, Feng D, Zhang Y [Yu], Chiu JMY, Qian P-Y, Qiu J-W (2017). Adaptation and evolution of polynoid scale-worms (Annelida: Polynoidae): insights from transcriptome comparison among two deep-sea and a shallow-water species. Scientific Reports, 7: 46205. http://doi.org/10.1038/srep46205

New paper on a chiton ‘cryptic species complex’ published!

New paper dealing with a ‘cryptic species complex’ of polyplacophoran molluscs (chitons) published in Marine Biodiversity! Open access, please read here: http://bit.ly/2okQQ56

In this work, we present a case study of a total-evidence approach to resolving difficult and perplexing ‘cryptic species complexes’. A Pacific shallow water chiton Leptochiton rugatus (Carpenter in Pilsbry, 1892) is supposed to have a very wide range from Japan to Baja California, but has been previously suggested to comprise several cryptic species. Our genetic haplotype network using specimens across the range revealed four discrete clusters. Most strikingly, the haplotype of L. rugatus sensu stricto (California to Baja California) was very different in structure from that of the cluster ranging from the panhandle of Alaska to Oregon. The latter was found to have extremely high side fidelity and patchy distribution, and we present evidence that it is likely a brooder. The difference in life-history strategies between these two clusters account for the differences in their genetic structure. Although morphological differences were observed, these were minor and insufficient to guarantee each as species-level lineages alone. Only with the difference in life-history strategy could they be confidently recognised as separate species, the latter we described as L. cascadiensis sp. nov. after the Cascadia costal bioregion which it inhabits.

L. cascadiensis harbouring putative eggs in the pallial cavity

Things without names are difficult to rationalise, and are difficult to conserve; assigning names to species is therefore critical to understanding and conserving biodiversity. This study shows that combining evidence from molecules, morphology, and importantly life-history, is key to untangling ‘cryptic species complexes’ which have become increasingly discovered in the recent years. The take-home message: if you want to solve cryptic species problems, don’t forget to look at their way of life!

This is my first time getting involved with describing a chiton, yay! Chitons are awesome.

Sigwart JD, Chen C (2017). Brooding behaviour explains patchy distribution in a shallow-water invertebrate (Mollusca: Polyplacophora: Lepidopleurida). Marine Biodiversity, First Online, DOI: 10.1007/s12526-017-0688-1

New paper on potential impacts of deep-sea mining published!

New co-authored paper published today in The Nautilus! [Link] The Nautilus is a peer-reviewed journal publishing articles on diverse aspects of the biology, ecology, and systematics of mollusks established in 1886.

In this new paper, we discuss the potential impacts of deep-sea mining to molluscan biodiversity, especially with regards to exploiting active hydrothermal sulfide deposits.


Take the famous scaly-foot gastropod Chrysomallon squamiferum as an example – it is only known from three hydrothermal vents in the Indian Ocean, each around 0.003 sq km or half the size of a football field. Two of the three scaly-foot sites are already under active mining exploration licenses from the International Seabed Authority (ISA), to China (2011-2026) and Germany (2015-2030); the last one is in the Mauritius exclusive economic zone and therefore not under ISA jurisdiction. In fact, only 37 vent sites have been detected (4 actually visited) in the Indian Ocean (area approx.. 73,550,000 sq km) and their total area adds up to a mere 0.27 sq km (check out the infographics)! Many of these are also within the areas licenced for mining. These explorations are due to begin very soon and no conservation measures are in place or proposed, whereas many terrestrial mollusks such as the two-lipped door snail Alinda biplicata have extensive reserves dedicated to their conservation. Economic and political pressures to exploit deep-sea vents are advancing far quicker than our scientific understanding of these ecosystems that unique animals such as the scaly-foot call home, putting them at risk. Conservation measures for vent animals are urgently needed, and seem warranted given their tiny, disjunct areas of distribution.

Infographics giving an idea of the total area of detected hydrothermal vents in the Indian Ocean.


The original idea of this work was presented at the “Mollusks in Peril” 2016 Forum at the Bailey-Matthews National Shell Museum.

Sigwart JS, Chen C, Marsh L (2017). Is mining the seabed bad for mollusks? The Nautilus 131(1): 43-50.

58th MEXT “Science and Technology Week” pamphlet

A photo I took aboard the JAMSTEC submersible “SHINKAI 6500“ is chosen as the cover of the 58th MEXT “Science and Technology Week” pamphlet. This photograph will be exhibited at the “Beauty” Panel Exhibition during the week (April 17-23, 2017). The “SHINKAI 6500″ is one of only six currently operational science manned deep-submergence vehicles capable of diving to extreme depths over 2000 m deep. For more information: http://stw.mext.go.jp/index.html

New paper demonstrates convergent adaptation in vent snails!

New first-authored paper published in BMC Evolutionary Biology! [Link]

In the new paper, we reveal that two neomphaline hydrothermal vent gastropods, Gigantopelta and the ‘scaly-foot’ Chrysomallon, convergently evolved the peculiar adaptation of housing endosymbiotic bacteria in their much enlarged oesophageal gland. We first confirmed the existence of endosymbionts in Gigantopelta using Transmision Electron Microscopy (TEM), and then carried out serial sectioning and 3D reconstruction for a juvenile specimen of Gigantopelta chessoia along with dissections of the adult. These revealed many key anatomical differences with the ‘scaly-foot gastropod’ pointing towards two independent origins of a similar way of life, confirmed by a 5-gene phylogenetic reconstruction clearly showing that the two are not sister within the known members of Peltospiridae. By comparing Gigantopelta and Chrysomallon, we show that metazoans are capable of rapidly and repeatedly evolving equivalent anatomical adaptations and close-knit relationships with chemoautotrophic bacteria, achieving the same end-product through parallel evolutionary trajectories.


The paper is open access and available freely: http://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-017-0917-z

We also included an interactive 3D anatomical model of Gigantopelta, you only need a PDF reader to play around with it! Have fun! It is available here: https://static-content.springer.com/esm/art%3A10.1186%2Fs12862-017-0917-z/MediaObjects/12862_2017_917_MOESM1_ESM.pdf

 

Chen C*, Uematsu K, Linse K, Sigwart JS (2017). By more ways than one: Rapid convergence in adaptations to hydrothermal vents shown by 3D anatomical reconstruction of Gigantopelta (Mollusca: Neomphalina). BMC Evolutionary Biology, 17:62. DOI: 10.1186/s12862-017-0917-z

 

The eccentric world of molluscs

An image I produced was selected to be the JAMSTEC Image of the Week. http://www.jamstec.go.jp/e/hot_pictures/?494

The molluscs are invertebrates belonging to the phylum Mollusca, a highly diverse group of animals. With approximately 100,000 species, Mollusca is second largest animal phylum only after arthropods (including insects), and the most species rich in the marine realm. From their initial appearance in the Cambrian, molluscs have adapted to various aquatic and terrestrial environments through their evolutionary history, resulting in their amazingly disparate morphology within a single phylum. How did peculiar molluscs such as the iron-coated ‘scaly-foot gastropod’ Chrysomallon squamiferum (centre) from deep-sea hydrothermal vents and the eight-plated chiton Craspedochiton producta (bottom right) inhabiting shallow rocky shores evolve to adapt to their environment, and how did they achieve their strange morphological forms? Our research at JAMSTEC combines morphological (e.g., histology, dissection, microscopy) and genetic (e.g., phylogeny, population genetics) methodologies in an attempt to understand the life history and evolutionary biology of these remarkable animals.

New paper reports chimneys from 5700m deep in Mariana forearc

New co-authored, open-access paper published in the journal Geochemistry, Geophysics, Geosystems! [Link]

This study reports three types of brucite-carbonate chimneys from the deepest known serpentinite-hosted vent in the world, the 5700 m deep Shinkai Seep Field in Mariana forearc. Although mainly a geochemistry/geology paper, the chimneys are inhabited by some megafaunal animals and brief descriptions of the colonies are included. Molluscs are also present, such as Provanna snails. The paper is open-access so anyone can read it for free!

Okumura T, Ohara Y, Stern RJ, Yamanaka T, Onishi Y, Watanabe H, Chen C, Bloomer SH, Pujana I, Sakai S, Ishii T, Takai K (2016). Brucite chimney formation and carbonate alteration at the Shinkai Seep Field, a serpentinite-hosted vent system in the Southern Mariana Forearc. Geochemistry, Geophysics, Geosystems, 75. DOI: 10.1002/2016GC006449

New paper names a snail from deep alkaline seep!

A new paper lead-authored by myself has been published in Molluscan Research! The paper describeds a new species of Desbruyeresia (Gastropoda: Provannidae), Desbruyeresia chamorrensis Chen, Ogura & Okutani in Chen et al., 2016. The family Provannidae is only known from chemosynthetic ecosystems, and genus Desbruyeresia was previously restricted to hydrothermal vents. The present new species, however, was discovered from an alkaline serpentinite-hosted seep more than 2900m deep on the South Chamorro Seamount (13°47’N, 146°00’E), southeastern Mariana Forearc. It is a deposit feeder and only three specimens have been collected so far. It is distinguished from all other described congeners by having much more numerous (17–20) axial ribs on the teleoconch and a broad shell for the genus (shell width to height ratio 0.6–0.65). It was a great pleasure working with the eminent Japanese malacologist Prof. Takashi Okutani during the course of this project.

Holotype of the new species:

Chen C*, Ogura T, Hirayama H, Watanabe HK, Miyazki J, Okutani T (2016). First seep-dwelling Desbruyeresia (Gastropoda: Abyssochrysoidea) species discovered from a serpentinite-hosted seep in the southeastern Mariana Forearc. Molluscan Research. DOI:10.1080/13235818.2016.1172547