Head shape disparity of the cod icefishes Trematominae (Notothenioidei, Teleostei)

The suborder Notothenioidei (Teleostei) has undergone a remarkable adaptive radiation in the Southern Ocean. Within this suborder, the subfamily Trematominae is endemic to Antarctic waters and represents a dominant component of the shelf fish fauna. After recent advances in molecular phylogenetics, 14 species of Trematomus are currently recognized (including Pagothenia and Cryothenia spp.) comprising both considerable morphological and ecological diversity. Here, we aim to illustrate the main axes of shape variation in Trematomus and explore the evolution of their morphology. A dataset of 96 specimens representing 10 species of Trematomus from the collection of the Natural History Museum of Paris was assembled, and landmark-based geometric morphometrics was applied to quantify head shape disparity. Regular regression analysis revealed significant interspecific allometry while a low percentage of shape variation was explained by size (R2 = 0.11; P < 0.001). Main shape variation across species was explored using a principal component (PC) analysis on shape variables. Two groups diverged along PC1: (1) T. bernacchii, T. hansoni, T. pennellii and T. tokarevi have short cephalic profiles with larger cheeks (lowest values along PC1); and (2) T. lepidorhinus, T. eulepidotus and T. newnesi show lengthened cephalic profiles with larger eyes (highest values along PC1). Trematomus scotti differed from all other species mainly along PC3 indicating more elongated cheeks. Phenogram based on Procrustes shape distances will be compared to molecular phylogenetic trees and morphometric data will be mapped onto phylogenetic trees in order to illustrate the mode of phenotypic diversification of Trematomus during evolution.Refugia and Ecosystem Tolerance in the Southern Ocea

Diet composition and gut microbiome of 0-group European plaice Pleuronectes platessa L. - Strong homogeneity and subtle spatial and temporal differences

© 2018 Elsevier B.V. This study presents the first case of the joint DNA metabarcoding of prey items and microbiome community analysis in wild juvenile fish. Juvenile European plaice (Pleuronectes platessa) were caught at 11 locations in the southern North Sea and eastern English Channel. Stomach fullness varied ontogenetically in time and space. Food uptake seemed to be slightly limited for the smallest plaice individuals up to a size of 20 to 30 mm. Furthermore, strong homogeneity for microbiome and prey item composition prevailed. Little seasonal, annual and regional (on-offshore/depth) variation was observed in prey item composition. Brown shrimp Crangon crangon made up >70% of the reads in all stomachs, length classes, regions, seasons and years. Offshore samples differentiated with a distinct lack of β-Proteobacteria in the gut microbiome. Based on a visual similarity network analysis, there was no observable correlation between prey item and microbiome composition, indicating that the microbiome composition wasn't driven by diet, but might be determined by the benthic bacterial community. DNA metabarcoding yields clear insights in the prey and microbiome composition of plaice, even for seemingly empty stomachs, and should therefore be considered for future dietary and microbiome studies.status: publishe

Repeated morphological diversification in endemic Antarctic fishes of the genus Trematomus

peer reviewedThe iterative nature of ecomorphological diversification is observed in various groups of animals. However, studies explicitly testing the consistency of morphological variation across and within species are scarce. Antarctic notothenioids represent a textbook example of adaptive radiation in marine fishes. Within Nototheniidae, the endemic Antarctic genus Trematomus consists of 15 extant species, some with documented large intraspecific variability. Here, we quantify head shape disparity in 11 species of Trematomus by landmark-based geometric morphometrics, and we illustrate repeated events of divergence and convergence of their head morphology. Taking advantage of the polymorphism observed in some species of Trematomus, we also show that two closely related species or clades (e.g., Trematomus bernacchii and T. hansoni) are characterised by the same level of morphological disparity as observed at the level of the entire genus. Interestingly, the same main axes of shape variation are shared between and within species, indicating repeated morphological diversification. Overall, we illustrate a similarity of intra- and interspecific patterns of phenotypic diversity providing new insights into the mechanisms that underlie the diversification of Antarctic fishes.Refugia and ecosystem tolerance in the Southern Ocea

Nimble vessel cruises as a complementary platform for Southern Ocean biodiversity research: concept and preliminary results from the Belgica 121 expedition.

International audienceThe western Antarctic Peninsula is facing rapid environmental changes and many recent publications stress the need to gain new knowledge regarding ecosystems responses to these changes. In the framework of the Belgica 121 expedition, we tested the use of a nimble vessel with a moderate environmental footprint as an approach to tackle the urgent needs of the Southern Ocean research community in terms of knowledge regarding the levels of marine biodiversity in shallow areas and the potential impacts of retreating glaciers on this biodiversity in combination with increasing tourism pressure. We discuss the strengths and drawbacks of using a 75’ (23 m) sailboat in this research framework, as well as its sampling and environmental efficiency. We propose that the scientific community considers this approach to 1) fill specific knowledge gaps and 2) improve the general coherence of the research objectives of the Antarctic scientific community in terms of biodiversity conservation and the image that such conservation conveys to the general public

Historical DNA Metabarcoding of the Prey and Microbiome of Trematomid Fishes Using Museum Samples

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Diversity of Mesopelagic Fishes in the Southern Ocean - A Phylogeographic Perspective Using DNA Barcoding

International audienc

Diversity of Mesopelagic Fishes in the Southern Ocean - A Phylogeographic Perspective Using DNA Barcoding (vol 6, 120, 2018)

© 2018 Christiansen, Dettai, Heindler, Collins, Duhamel, Hautecoeur, Steinke, Volckaert and Van de Putte. However, we highlight potential (pseudo-)cryptic or unrecognized species in Gymnoscopelus bolini, Lampanyctus achirus, and the non-myctophid genus Bathylagus. A correction has been made to the Discussion, Sub-section Phylogeny and Phylogeography of Southern Ocean Mesopelagic Fishes, Paragraph 6: The available sequences identified as Symbolophorus boops (BOLD references DSFSE476-08 to DSFSE480-08 and DSFSG260-10) cluster apart from the two other Symbolophorus clades resolved in our COI tree (one composed of S. californiensis, S. reversus, S. evermanni, Symbolophorus sp., and S. rufinus and the other composed of S. barnardi and S. veranyi; Figure 2). Instead these sequences settle within the Diaphinae (sensu Martin et al., 2017). Unfortunately we discovered a posteriori that the COI sequences included here as S. boops were likely misidentified on BOLD. These sequences are probably from a Diaphus species (P. A. Hulley, pers. comm.) currently also not present on BOLD, but the specimens are in poor condition, preventing definite identification. The correction has been transmitted to the BOLD database. Other studies that included genetic data proposed that Symbolophorus is closer related to Myctophum, Hygophum, and other genera, as opposed to Diaphinae, but they all lacked specimens of S. boops (Poulsen et al., 2013; Denton, 2014; Martin et al., 2017). Therefore, we highly recommend the collection of further samples/sequences in order to resolve the phylogenetic position of S. boops, and to re-identify the specimens erroneously labeled as Symbolophorus boops. In fact, the entire genus would benefit from a detailed systematic revision as already noted by Wisner (1976).status: publishe

Corrigendum: Diversity of Mesopelagic Fishes in the Southern Ocean – A Phylogeographic Perspective Using DNA Barcoding

© 2018 Christiansen, Dettai, Heindler, Collins, Duhamel, Hautecoeur, Steinke, Volckaert and Van de Putte. However, we highlight potential (pseudo-)cryptic or unrecognized species in Gymnoscopelus bolini, Lampanyctus achirus, and the non-myctophid genus Bathylagus. A correction has been made to the Discussion, Sub-section Phylogeny and Phylogeography of Southern Ocean Mesopelagic Fishes, Paragraph 6: The available sequences identified as Symbolophorus boops (BOLD references DSFSE476-08 to DSFSE480-08 and DSFSG260-10) cluster apart from the two other Symbolophorus clades resolved in our COI tree (one composed of S. californiensis, S. reversus, S. evermanni, Symbolophorus sp., and S. rufinus and the other composed of S. barnardi and S. veranyi; Figure 2). Instead these sequences settle within the Diaphinae (sensu Martin et al., 2017). Unfortunately we discovered a posteriori that the COI sequences included here as S. boops were likely misidentified on BOLD. These sequences are probably from a Diaphus species (P. A. Hulley, pers. comm.) currently also not present on BOLD, but the specimens are in poor condition, preventing definite identification. The correction has been transmitted to the BOLD database. Other studies that included genetic data proposed that Symbolophorus is closer related to Myctophum, Hygophum, and other genera, as opposed to Diaphinae, but they all lacked specimens of S. boops (Poulsen et al., 2013; Denton, 2014; Martin et al., 2017). Therefore, we highly recommend the collection of further samples/sequences in order to resolve the phylogenetic position of S. boops, and to re-identify the specimens erroneously labeled as Symbolophorus boops. In fact, the entire genus would benefit from a detailed systematic revision as already noted by Wisner (1976).status: publishe

Historical DNA metabarcoding of the prey and microbiome of trematomid fishes using museum samples.

Antarctic specimens collected during various research expeditions are preserved in natural history collections around the world potentially offering a cornucopia of morphological and molecular data. Historical samples of marine species are, however, often preserved in formaldehyde which may render them useless for genetic analysis. We sampled stomachs and hindguts from 225 Trematomus specimens from the Natural History Museum London. These samples were initially collected between 20 and 100 years ago and fixed in either formaldehyde or ethanol. A 313 bp fragment of the cytochrome c oxidase subunit I (COI) was amplified and sequenced for prey item identification in the stomach and a 450 bp region of the 16S rRNA gene to investigate microbiome composition in the gut system. Both data sets were characterized by large dropout rates during extensive quality controls. Eventually, no unambiguous results regarding stomach content (COI) were retained, possibly due to degraded DNA, inefficient primers and contamination. In contrast, reliable microbiome composition data (16S rRNA) was obtained from 26 samples. These data showed a correlation in change of microbiome composition with fish size as well as year of the catch, indicating a microbiome shift throughout ontogeny and between samples from different decades. A comparison with contemporary samples indicated that the intestinal microbiome of Trematomus may have drastically changed within the last century. Further extensive studies are needed to confirm these patterns with higher sample numbers. Molecular analyses of museum stored fish can provide novel micro evolutionary insights that may benefit current efforts to prioritize conservation units in the Southern Ocean.Refugia and ecosystem tolerance in the Southern Ocean (RECTO) - Research project BR/154/A1/RECT

Diversity of Mesopelagic Fishes in the Southern Ocean - A Phylogeographic Perspective Using DNA Barcoding

© 2018 Christiansen, Dettai, Heindler, Collins, Duhamel, Hautecoeur, Steinke, Volckaert and Van de Putte. Small mesopelagic fish are ubiquitous in the ocean, representing an important trophic link between zooplankton and tertiary consumers such as larger fish, marine mammals and birds. Lanternfishes (Myctophidae) are common worldwide as well as in the Southern Ocean. However, only 17 of the approximately 250 myctophid species occur exclusively in sub-Antarctic or Antarctic waters. It is unclear whether they colonized these latitudes once and diversified from there, or whether multiple colonization events took place in which multiple ancestral phenotypes entered the Southern Ocean at various times. Phylogeographic patterns have been investigated for individual myctophid species, but so far no study has compared species across the Southern Ocean. Here, we present a dataset with previously unpublished cytochrome c oxidase I (COI; n = 299) and rhodopsin (rh1; n = 87) gene sequences from specimens collected at various locations in the Southern Ocean. Our data extend the DNA barcode library of Antarctic mesopelagic fish substantially. Combined morphological and molecular taxonomy lead to confident species level identification in 271 out of 299 cases, providing a robust reference dataset for specimen identification, independently of incomplete morphological characters. This is highly topical in light of prospective ecological metabarcoding studies. Unambiguous sequences were subsequently combined with publicly available sequences of the global DNA barcode library yielding a dataset of over 1,000 individuals for phylogenetic and phylogeographic inference. Maximum likelihood trees were compared with results of recent studies and with the geographical origin of the samples. As expected for these markers, deep phylogenetic relationships remain partially unclear. However, COI offers unmatched sample and taxon coverage and our results at the subfamily to genus level concur to a large extent with other studies. Southern Ocean myctophids are from at least three distant subfamilies suggesting that colonization has occurred repeatedly. Overall, spatial divergence of myctophids is rare, potentially due to their enormous abundance and the homogenizing force of ocean currents. However, we recommend further investigation of the phylogenetic position of Symbolophorus boops and highlight potential (pseudo-)cryptic or unrecognized species in Gymnoscopelus bolini, Lampanyctus achirus, and the non-myctophid genus Bathylagus.status: publishe