Biogeographic and bathymetric ranges of Atlantic deep-sea echinoderms and ascidians: the role of larval dispersal

Dispersal plays an important role in the establishment and maintenance of biodiversity and, for most deep-sea benthic marine invertebrates, it occurs mainly during the larval stages. Therefore, the mode of reproduction (and thus dispersal ability) will affect greatly the biogeographic and bathymetric distributions of deep-sea organisms. We tested the hypothesis that, for bathyal and abyssal echinoderms and ascidians of the Atlantic Ocean, species with planktotrophic larval development have broader biogeographic and bathymetric ranges than species with lecithotrophic development. In comparing two groups with lecithotrophic development, we found that ascidians, which probably have a shorter larval period and therefore less dispersal potential, were present in fewer geographic regions than elasipod holothurians, which are likely to have longer larval periods. For asteroids and echinoids, both the geographic and bathymetric ranges were greater for lecithotrophic than for planktotrophic species. For these two classes, the relationships of egg diameter with geographic and bathymetric range were either linearly increasing or non-monotonic. We conclude that lecithotrophic development does not necessarily constrain dispersal in the deep sea, probably because species with planktotrophic development may be confined to regions of high detrital input from the sea surface. Our data suggest that more information is necessary on lengths of larval period for different species to accurately assess dispersal in the deep sea.     

Freeze-fracture electron microscopy of human erythrocytes lacking the major membrane sialoglycoprotein

Human erythrocytes of blood group En (a-), a rare homozygous condition involving a complete lack of the major sialoglycoprotein of the cell membrane (glycophorin A), were compared with erythrocytes from normal (En(a+)) individuals by freeze-fracture electron microscopy. No decrease in number, or variation in morphology, of the intramembranal particles of En (a-) cells was detectable. These results show that the erythrocyte sialoglycoprotein is not essential for the maintenance of the integrity of the intramembranal particles of the human erythrocyte membrane.     

CeleST: Computer Vision Software for Quantitative Analysis of C. elegans Swim Behavior Reveals Novel Features of Locomotion

In the effort to define genes and specific neuronal circuits that control behavior and plasticity, the capacity for high-precision automated analysis of behavior is essential. We report on comprehensive computer vision software for analysis of swimming locomotion of C. elegans, a simple animal model initially developed to facilitate elaboration of genetic influences on behavior. C. elegans swim test software CeleST tracks swimming of multiple animals, measures 10 novel parameters of swim behavior that can fully report dynamic changes in posture and speed, and generates data in several analysis formats, complete with statistics. Our measures of swim locomotion utilize a deformable model approach and a novel mathematical analysis of curvature maps that enable even irregular patterns and dynamic changes to be scored without need for thresholding or dropping outlier swimmers from study. Operation of CeleST is mostly automated and only requires minimal investigator interventions, such as the selection of videotaped swim trials and choice of data output format. Data can be analyzed from the level of the single animal to populations of thousands. We document how the CeleST program reveals unexpected preferences for specific swim “gaits” in wild-type C. elegans, uncovers previously unknown mutant phenotypes, efficiently tracks changes in aging populations, and distinguishes “graceful” from poor aging. The sensitivity, dynamic range, and comprehensive nature of CeleST measures elevate swim locomotion analysis to a new level of ease, economy, and detail that enables behavioral plasticity resulting from genetic, cellular, or experience manipulation to be analyzed in ways not previously possible.

This is a PLOS Computational Biology Software Article

     

Contrasting patterns of spread in interacting invasive species: Membranipora membranacea and Codium fragile off Nova Scotia

In the Northwest Atlantic, overgrowth of the competitively dominant, native kelps by an invasive bryozoan Membranipora membranacea increases frond erosion, which has facilitated the establishment and spread of the invasive macroalga Codium fragile ssp fragile. To document the spread of both introduced species along the Atlantic coast of Nova Scotia from initial introduction points (the ‘epicentre’) southwest of Halifax, we conducted video-surveys of shallow rocky habitats along the southwestern shore of Nova Scotia (100 km linear distance, encompassing the range of M. membranacea) in 2000, and then along the entire Atlantic coast in 2007 (650 km). Membranipora membranacea was observed continuously throughout the surveyed ranges in 2000 and 2007, wherever kelps were present, suggesting natural dispersal via planktonic larvae. Codium fragile was observed along 95 km of the surveyed range in 2000 and along 445 km in 2007, with a relatively patchy distribution beyond the epicentre, suggesting a combination of natural and anthropogenic dispersal mechanisms. Rockweed-dominated (Fucus spp.) or mixed algal assemblages common outside the epicentre may alter the interaction between M. membranacea and C. fragile, since seaweeds other than kelp are not subject to defoliation by the bryozoan. Percent cover of kelp at the epicentre generally increased from 2000 to 2007, while that of C. fragile generally decreased. Codium fragile was the dominant canopy alga at 54% of sites in 2000 and at only 15% of sites in 2007. These findings indicate that, at near decadal timescales, C. fragile does not prevent re-colonization by native kelps.     

Do Larval Supply and Recruitment Vary among Chemosynthetic Environments of the Deep Sea?

Background

The biological communities that inhabit chemosynthetic environments exist in an ephemeral and patchily distributed habitat with unique physicochemical properties that lead to high endemicity. Consequently, the maintenance and recovery from perturbation of the populations in these habitats is, arguably, mainly regulated by larval supply and recruitment.

Methodology/Principal Findings

We use data from the published scientific literature to: (1) compare the magnitudes of and variability in larval supply and settlement and recruitment at hydrothermal vents, seeps, and whale, wood and kelp falls; (2) explore factors that affect these life history processes, when information is available; and (3) explore taxonomic affinities in the recruit assemblages of the different chemosynthetic habitats, using multivariate statistical techniques. Larval supply at vents can vary across segments by several orders of magnitude for gastropods; for bivalves, supply is similar at vents on different segments, and at cold seeps. The limited information on larval development suggests that dispersal potential may be highest for molluscs from cold seeps, intermediate for siboglinids at vents and lowest for the whale-bone siboglinid Osedax. Settlement is poorly studied and only at vents and seeps, but tends to be highest near an active source of emanating fluid in both habitats. Rate of recruitment at vents is more variable among studies within a segment than among segments. Across different chemosynthetic habitats, recruitment rate of bivalves is much more variable than that of gastropods and polychaetes. Total recruitment rate ranges only between 0.1 and 1 ind dm⁻² d⁻¹ across all chemosynthetic habitats, falling above rates in the non-reducing deep sea. The recruit assemblages at vents, seeps and kelp falls have lower taxonomic breadth, and include more families and genera that have many species more closely related to each other than those at whale and wood falls. Vents also have the most uneven taxonomic structure, with fewer recruits represented by higher taxonomic levels (phyla, orders, classes) compared to seeps and wood and kelp falls, whereas the opposite is true at whale falls.

Conclusions/Significance

Based on our evaluation of the literature, the patterns and regulatory factors of the early history processes in chemosynthetic environments in the deep sea remain poorly understood. More research focused on these early life history stages will allow us to make inferences about the ecological and biogeographic linkages among the reducing habitats in the deep sea.     

Biodiversity of the deep-sea continental margin bordering the Gulf of Maine (NW Atlantic): relationships among sub-regions and to shelf systems

Background

In contrast to the well-studied continental shelf region of the Gulf of Maine, fundamental questions regarding the diversity, distribution, and abundance of species living in deep-sea habitats along the adjacent continental margin remain unanswered. Lack of such knowledge precludes a greater understanding of the Gulf of Maine ecosystem and limits development of alternatives for conservation and management.

Methodology/Principal Findings

We use data from the published literature, unpublished studies, museum records and online sources, to: (1) assess the current state of knowledge of species diversity in the deep-sea habitats adjacent to the Gulf of Maine (39–43°N, 63–71°W, 150–3000 m depth); (2) compare patterns of taxonomic diversity and distribution of megafaunal and macrofaunal species among six distinct sub-regions and to the continental shelf; and (3) estimate the amount of unknown diversity in the region. Known diversity for the deep-sea region is 1,671 species; most are narrowly distributed and known to occur within only one sub-region. The number of species varies by sub-region and is directly related to sampling effort occurring within each. Fishes, corals, decapod crustaceans, molluscs, and echinoderms are relatively well known, while most other taxonomic groups are poorly known. Taxonomic diversity decreases with increasing distance from the continental shelf and with changes in benthic topography. Low similarity in faunal composition suggests the deep-sea region harbours faunal communities distinct from those of the continental shelf. Non-parametric estimators of species richness suggest a minimum of 50% of the deep-sea species inventory remains to be discovered.

Conclusions/Significance

The current state of knowledge of biodiversity in this deep-sea region is rudimentary. Our ability to answer questions is hampered by a lack of sufficient data for many taxonomic groups, which is constrained by sampling biases, life-history characteristics of target species, and the lack of trained taxonomists.     

In vivo detection of amyloid-β deposits using heavy chain antibody fragments in a transgenic mouse model for Alzheimer's disease

This study investigated the in vivo properties of two heavy chain antibody fragments (V(H)H), ni3A and pa2H, to differentially detect vascular or parenchymal amyloid-β deposits characteristic for Alzheimer's disease and cerebral amyloid angiopathy. Blood clearance and biodistribution including brain uptake were assessed by bolus injection of radiolabeled V(H)H in APP/PS1 mice or wildtype littermates. In addition, in vivo specificity for Aβ was examined in more detail with fluorescently labeled V(H)H by circumventing the blood-brain barrier via direct application or intracarotid co-injection with mannitol. All V(H)H showed rapid renal clearance (10-20 min). Twenty-four hours post-injection (99m)Tc-pa2H resulted in a small yet significant higher cerebral uptake in the APP/PS1 animals. No difference in brain uptake were observed for (99m)Tc-ni3A or DTPA((111)In)-pa2H, which lacked additional peptide tags to investigate further clinical applicability. In vivo specificity for Aβ was confirmed for both fluorescently labeled V(H)H, where pa2H remained readily detectable for 24 hours or more after injection. Furthermore, both V(H)H showed affinity for parenchymal and vascular deposits, this in contrast to human tissue, where ni3A specifically targeted only vascular Aβ. Despite a brain uptake that is as yet too low for in vivo imaging, this study provides evidence that V(H)H detect Aβ deposits in vivo, with high selectivity and favorable in vivo characteristics, making them promising tools for further development as diagnostic agents for the distinctive detection of different Aβ deposits.     

Interactive effects of haloclines and food patches on the vertical distribution of 3 species of temperate invertebrate larvae

In laboratory experiments, we examined the effect of haloclines and determined whether the presence of food patches overrides this effect on larval vertical distribution of the sea star Asterias rubens, the sea urchin Strongylocentrotus droebachiensis and the mussel Mytilus edulis. We experimentally constructed haloclines in which the salinity of the bottom water layer was 35 and that of the top layer was 21, 24, 27, and 30 (21/35, 24/35, 27/35, and 30/35) for A. rubens and S. droebachiensis, and 24, 27, 30 and 32 (24/35, 27/35, 30/35, and 32/35) for M. edulis. For each species and stage, additional halocline treatments (A. rubens: 24/32 and 27/32; 4-arm S. droebachiensis: 21/29 and 24/32; 6-arm S. droebachiensis: 24/29 and 24/32; M. edulis: 27/32 and 30/32) were used to determine whether the larval response to inhibitory salinity gradients was due to the absolute salinity of the top layer or the relative salinity difference between the two layers. Also, we measured the density of A. rubens and M. edulis to determine whether the specific gravity of larvae can explain the observed vertical distributions. Larvae aggregated at and below the halocline and these aggregations were more pronounced with increasing strength of the vertical salinity gradient. Threshold salinities in the top layer which inhibited ~ 100% of the larvae from crossing the halocline were 24 for A. rubens and M. edulis, and 21 for S. droebachiensis. These distributional patterns were not the result of larval density, which was greater than all treatment water densities for M. edulis and S. droebachiensis and lower for A. rubens. The effect of the presence of a food patch at inhibitory haloclines (A. rubens: 24/35 and 27/35; 4-arm S. droebachiensis: 21/34 and 24/34; M. edulis: 27/35) was determined by using three algal densities: 0, 5000 or 10 000 cells ml^- 1Thalassiosira pseudonana in either the top or the bottom water layer. For both A. rubens and M. edulis, the number of larvae at the halocline increased in the presence of a food patch, but this effect did not depend on algal density in the patch. For 4-arm S. droebachiensis, there was no effect of the presence of a food patch on larval vertical distribution. Our results suggest that low salinity may act as a barrier to vertical movement and that the presence of food patches above the halocline may strengthen the larval aggregation response to inhibitory haloclines.     

Promoting inclusive metrics of success and impact to dismantle a discriminatory reward system in science

Success and impact metrics in science are based on a system that perpetuates sexist and racist “rewards” by prioritizing citations and impact factors. These metrics are flawed and biased against already marginalized groups and fail to accurately capture the breadth of individuals’ meaningful scientific impacts. We advocate shifting this outdated value system to advance science through principles of justice, equity, diversity, and inclusion. We outline pathways for a paradigm shift in scientific values based on multidimensional mentorship and promoting mentee well-being. These actions will require collective efforts supported by academic leaders and administrators to drive essential systemic change.

This Essay argues that success and impact metrics in science are based on a system that perpetuates sexist and racist ‘rewards’ by prioritizing citations and impact factors; the authors advocate shifting this outdated value system to advance science through principles of justice, equity, diversity, and inclusion.