Torben Riehl

Genetic and Morphological Divergences in the Cosmopolitan Deep-Sea Amphipod Eurythenes gryllus Reveal a Diverse Abyss and a Bipolar Species

Eurythenes gryllus is one of the most widespread amphipod species, occurring in every ocean with a depth range covering the bathyal, abyssal and hadal zones. Previous studies, however, indicated the existence of several genetically and morphologically divergent lineages, questioning the assumption of its cosmopolitan and eurybathic distribution. For the first time, its genetic diversity was explored at the global scale (Arctic, Atlantic, Pacific and Southern oceans) by analyzing nuclear (28S rDNA) and mitochondrial (COI, 16S rDNA) sequence data using various species delimitation methods in a phylogeographic context. Nine putative species-level clades were identified within E. gryllus. A clear distinction was observed between samples collected at bathyal versus abyssal depths, with a genetic break occurring around 3,000 m. Two bathyal and two abyssal lineages showed a widespread distribution, while five other abyssal lineages each seemed to be restricted to a single ocean basin. The observed higher diversity in the abyss compared to the bathyal zone stands in contrast to the depth-differentiation hypothesis. Our results indicate that, despite the more uniform environment of the abyss and its presumed lack of obvious isolating barriers, abyssal populations might be more likely to show population differentiation and undergo speciation events than previously assumed. Potential factors influencing species’ origins and distributions, such as hydrostatic pressure, are discussed. In addition, morphological findings coincided with the molecular clades. Of all specimens available for examination, those of the bipolar bathyal clade seemed the most similar to the ‘true’ E. gryllus. We present the first molecular evidence for a bipolar distribution in a macro-benthic deep-sea organism.

Conquered from the deep sea? A new deep-sea isopod species from the Antarctic shelf shows pattern of recent colonization.

The Amundsen Sea, Antarctica, is amongst the most rapidly changing environments of the world. Its benthic inhabitants are barely known and the BIOPEARL 2 project was one of the first to biologically explore this region. Collected during this expedition, Macrostylis roaldi sp. nov. is described as the first isopod discovered on the Amundsen-Sea shelf. Amongst many characteristic features, the most obvious characters unique for M. roaldi are the rather short pleotelson and short operculum as well as the trapezoid shape of the pleotelson in adult males. We used DNA barcodes (COI) and additional mitochondrial markers (12S, 16S) to reciprocally illuminate morphological results and nucleotide variability. In contrast to many other deep-sea isopods, this species is common and shows a wide distribution. Its range spreads from Pine Island Bay at inner shelf right to the shelf break and across 1,000 m bathymetrically. Its gene pool is homogenized across space and depth. This is indicative for a genetic bottleneck or a recent colonization history. Our results suggest further that migratory or dispersal capabilities of some species of brooding macrobenthos have been underestimated. This might be relevant for the species’ potential to cope with effects of climate change. To determine where this species could have survived the last glacial period, alternative refuge possibilities are discussed.

A new genus and new species of Desmosomatidae Sars, 1897 (Isopoda) from the eastern South Atlantic abyss described by means of integrative taxonomy

We used a combined morphological and genetic approach for species delineation within desmosomatid isopods in the eastern South Atlantic. Based on morphological data from light, scanning electron, and confocal laser scanning, microscopy as well as on mitochondrial (COI, 16S) and nuclear (18S) DNA markers, we describe two new species and a new genus. Chelator aequabilis is reported from the Guinea Basin and the Angola Basin. High intraspecific genetic variability did not allow final conclusions about relationships and species status of all analysed individuals. Due to the patterns of genetic variation and the subtle variation in some morphological characters, we conclude that more than one species might be hidden in C. aequabilis north of the Walvis Ridge. Chelator rugosus is described from the Cape Basin; the new monotypic genus Parvochelus is erected with the description of P. russus from the Guinea and the Brazil Basins. In Parvochelus, pereopod I bears a carpo-chela, especially the carpus is slender and long, its width is smaller than the merus width. The slender and long seta that is situated laterally to the carpo-propodal articulation is another characteristic feature. Despite the divergence within this species, shared lineages on both sides of the Mid-Atlantic Ridge suggest sporadic connectivity between populations on both sides. Our results document how molecular data can complement morphology in an integrative taxonomic approach elucidating biodiversity in the deep sea. Keys to the genera of Desmosomatidae and the species of Chelator are provided.

Descriptions of two new species in the genus Macrostylis Sars, 1864 (Isopoda, Asellota, Macrostylidae) from the Weddell Sea (Southern Ocean), with a synonymisation of the genus Desmostylis Brandt, 1992 with Macrostylis

Abstract Descriptions of Macrostylis antennamagna sp. n. and Macrostylis uniformis sp. n. are presented with notes on intraspecific variability and sexual dimorphism. Macrostylis uniformis sp. n. showes differences to Macrostylis antennamagna sp. n. in the length of the antenna 2, the shape of the pleotelson and length of uropods. The genus Desmostylis Brandt, 1992 (formerly including the two species Desmostylis obscurus Brandt, 1992 and Desmostylis gerdesi Brandt, 2002) is synonymised with the genus Macrostylis. Based on type material additional remarks and additions to the original descriptions are provided for both species. Results lead to following nomenclatorial changes: Macrostylis obscurus (Brandt, 1992), comb. n. and Macrostylis gerdesi (Brandt, 2002), comb. n. A setal nomenclature is proposed and the diagnosis for the family is revised.

The Community Structure of Deep-Sea Macrofauna Associated with Polymetallic Nodules in the Eastern Part of the Clarion-Clipperton Fracture Zone

Deep-sea areas characterized by the presence of polymetallic nodules are getting increased attention due to their potential commercial and strategic interest for metals such as nickel, copper and cobalt. The polymetallic nodules occur in areas beyond national jurisdiction, regulated by the International Seabed Authority (ISA). Under exploration contracts, contractors have the obligation to determine the environmental baseline in the exploration areas. Despite a large number of scientific cruises to the central east Pacific Ocean, few published data on the macrofaunal biodiversity and community structure are available for the abyssal fields of the Clarion-Clipperton Fracture Zone (CCFZ). This study focused on the macrofaunal abundance, diversity and community structure in three physically comparable, mineable sites located in the license area of Global Sea Mineral Resources N.V., at ~ 4500 m depth. A homogeneous but diverse macrofaunal community associated with the sediment from polymetallic nodule areas was observed at a scale of 10s to 100s of km. However, slight differences in the abundance and diversity of Polychaeta between sites can be explained by a decline in the estimated flux of particulate organic carbon (POC) along a southeast-northwest gradient, as well as by small differences in sediment characteristics and nodule abundance. The observed homogeneity in the macrofaunal community is an important prerequisite for assigning areas for impact and preservation reference zones. However, a precautionary approach regarding mining activities is recommended, awaiting further research during the exploration phase on environmental factors structuring macrofaunal communities in the CCFZ. For instance, future studies should consider habitat heterogeneity, which was previously shown to structure macrofauna communities at larger spatial scales. Acknowledging the limited sampling in the current study, a large fraction (59-85%; depending on the richness estimator used and the macrofaunal taxon of interest) of the macrofaunal genus/species diversity from the habitat under study was characterized.

Caught in the act: an abyssal isopod collected while feeding on Komokiaceae

Protists such as Komokiaceae represent a huge, unexplored diversity in the abyss (Gooday et al. 1992). They likely play a key role in the food web and structuring of deep-sea benthos (Sokolova 1972), where isopods are abundant and diverse. Deep-sea isopods were initially classified as detritus feeders, but gut-content analyses (e.g. Svavarsson et al. 1993) revealed tests of hard-shelled Foraminifera, suggesting that some isopods, additionally or instead, prey upon protists. Isopod foraminiferivory was inferred also by means of fatty acid biomarkers (Würzberg et al. 2011). However, in a diverse taxon like Isopoda, feeding specialisation and plasticity can be expected, given temporal and spatial variations in food availabil i ty in the deep sea (Sokolova 1972). Hence, isopod feeding selectivity is likely complex, although it is not obvious from the often dominant materials in their guts: unidentifiable organic mucus, indicating that important food sources may be overlooked. Nevertheless, in addition to hard foraminiferan shells, some gut contents of Acanthocope and Betamorpha (Isopoda) were interpreted as remains of Komokiacea (Brökeland et al. 2010), a largely unexplored group of large-sized protists that often dominate the abyssal megabenthos. Vema-TRANSIT samples from the North Atlantic (see Supplementary material) contained a specimen of Betamorpha cf. profunda (Menzies & George, 1972) (ZMH K-45805) with parts of a komokiacean (cf. Lana Tendal & Hessler 1977) (Fig. 1) projecting out of the oral cavity. Between the mandible incisors, the komokiacean branches had been macerated to a pulp that can be further traced into the oral cavity and oesophagus, and is enriched in the stomach. To our knowledge, this is the first observation of an isopod directly feeding on a komokiacean. This evidence solidifies previous ideas of a komokiacean role in the diets of Betamorpha (Brökeland et al. 2010) and isopods in general. Given that both groups are abundant and diverse in abyssal settings, our observation yields the hypothesis that Komokiaceae may be an important food source for isopods. Communicated by C. Smith

Adding depth to line artwork by digital stippling—a step-by-step guide to the method

Vector-based software has revolutionized scientific illustrating and is well established in taxonomy. However, simple line drawings lack depth information. Shading techniques, such as stippling—the application of dots to generate shade—are the methods of choice for simulating shade, structure, shape, and texture. In this paper, a step-by-step guide for digital stippling is presented. Manual stippling offers great flexibility to achieve highly realistic results. A round brush is applied to the line art by tapping. To drastically reduce time consumption and generate homogeneous tinges, a semiautomation was developed: the smallest units of symmetric stippling patterns are stored in a brush library. Using macroinstructions (macros), such stored raw patterns are converted into symmetric repetitive patterns. This way, stippling can be applied quickly and evenly across large areas of the underlying line drawing. These methods come with all the advantages of vector illustrations, such as high scalability, reproducibility and easy correction of strokes that have turned out imperfect.

Multiple origins of subsociality in crab spiders (Thomisidae).

Determining factors that facilitate the transition from a solitary to a social lifestyle is a major challenge in evolutionary biology, especially in taxa that are usually aggressive towards conspecifics. Most spiders live solitarily and few species are known to be social. Nevertheless, sociality has evolved multiple times across several families and nearly all studied social lineages have originated from a periodically social (subsocial) ancestor. Group-living crab spiders (Thomisidae) are exclusively found in Australia and differ from most other social spiders because they lack a communal capture web. Three of the group-living species were placed in the genus Diaea and another in the genus Xysticus. Most Australian thomisids are, however, difficult to identify as most descriptions are old and of poor quality, and the genera Diaea and Xysticus may not correspond to monophyletic groups. Here, we clarify the phylogenetic relationships of the four group-living Australian thomisids and conclude that amongst these subsociality has evolved two to three times independently. The subsocial Xysticus bimaculatus is not closely related to any of the social Diaea and an independent origin of subsociality is likely in this case. The presented data indicates that within Diaea two origins of subsociality are possible. Our results help to understand the evolution of sociality in thomisids and support the hypothesis that permanent sociality in spiders has evolved multiple times relatively recently from subsocial ancestors.

Re-description of Xysticus bimaculatus L. Koch, 1867 (Araneae, Thomisidae) and characterization of its subsocial lifestyle.

Abstract Spiders have become an important model to study the evolution of sociality, but a lack of their detailed natural history and taxonomy hinders broader comparative studies. Group-living crab spiders (Thomisidae) provide an excellent contrast to other social spiders since they lack a communal capture web, which was thought to be a critical factor in the evolution of sociality. Only three non-webbuilding crab-spider species are known to be subsocial or social, all of which belong to the genus Diaea Thorell, 1869. The aim of this study is to describe the social lifestyle of Xysticus bimaculatus L. Koch, 1867 for the first time. Furthermore, we present a detailed re-description of this species and discuss its taxonomic implications. Like other subsocial crab spiders, X. bimaculatus builds nests from tree leaves. Nests contain up to 38 spiders and sometimes several adult females, indicating the species may be at a transitory stage between subsociality and permanent sociality.

Paradise lost already? A naturalist interpretation of the pelagic avian and marine mammal detection database of the IceAGE cruise off Iceland and Faroe Islands in fall 2011

We present naturalist sightings of seabirds and marine mammals made during a research cruise with the IceAGE project off Iceland and the Faroe Islands during September 2011. Our findings from the obtained pelagic database are in-line with many other, more in-depth studies, showing major declines for pelagic seabirds and likely sea mammals, thus revising the role that Iceland now plays for such species. Northern Fulmar (Fulmarus glacialis) was the most recorded species, followed by different gulls, Black-legged Kittiwake (Rissa tridactyla) and Northern Gannet (Morus bassanus). However, Atlantic Puffin (Fratercula arctica) and Common Murre (Uria aalge) were only seen very rarely, and no observations were made of Dovekie (Alle alle) or Thick-billed Murre (U. lomvia). These observations were surprising since Iceland is known, so far, to host globally relevant populations of these auk species. A surprising high number of thirteen species of passerines were also detected offshore, mostly Wheatear (Oenanthe oenanthe), Meadow Pipit (Anthus pratensis) and Reed Bunting (Emberiza schoeniclus). Only a few marine mammals (Balaenoptera and Megaptera sp.) were encountered. Our detections present underestimates but are discussed in relation to ongoing and recently reported but dramatic anthropogenic changes of Iceland and in the North Atlantic overall. These include the substantial decrease in bird populations, overfishing and subsequent trophic cascades, as well as climate change, Arctic shipping and more industrial development to come. In light of these dramatic ecological changes, we conclude with an urgent request for an improved effective conservation management for Iceland, the North Atlantic and its stakeholders for directly related global governance to handle problems proactively.