Characterization of the protein fraction of the temporary adhesive secreted by the tube feet of the sea star Asterias rubens

Sea stars are able to make firm but temporary attachments to various substrata by secretions released by their tube feet. After tube foot detachment, the adhesive secretions remain on the substratum as a footprint. Proteins presumably play a key role in sea star adhesion, as evidenced by the removal of footprints from surfaces after a treatment with trypsin. However, until now, characterisation was hampered by their high insolubility. In this study, a non-hydrolytic method was used to render most of the proteins constituting the adhesive footprints soluble. After analysis by SDS-PAGE, the proteins separated into about 25 bands, which ranged from 25 to 450 kDa in apparent molecular weight. Using mass spectrometry and a homology-database search, it was shown that several of the proteins are known intracellular proteins, presumably resulting from contamination of footprint material with tube foot epidermal cells. However, 11 protein bands, comprising the most abundant proteins, were not identified and might correspond to novel adhesive proteins. They were named ‘Sea star footprint proteins’ (Sfps). Tandem mass spectrometry analysis of the protein bands yielded 43 de novo-generated peptide sequences. Most of them were shared by several, if not all, Sfps. Polyclonal antibodies were raised against one of the peptides (HEASGEYYR from Sfp-115) and were used in immunoblotting. They specifically labelled Sfp-115 and other bands with lower apparent molecular weights. The different results suggest that all Sfps might belong to a single family of related proteins sharing similar motifs or, alternatively, they are the products of polymerization and/or degradation processes.     

Eutacticity in Sea Urchin Evolution

An eutactic star, in a n-dimensional space, is a set of N vectors which can be viewed as the projection of N orthogonal vectors in a N-dimensional space. By adequately associating a star of vectors to a particular sea urchin, we propose that a measure of the eutacticity of the star constitutes a measure of the regularity of the sea urchin. Then, we study changes of regularity (eutacticity) in a macroevolutive and taxonomic level of sea urchins belonging to the Echinoidea class. An analysis considering changes through geological time suggests a high degree of regularity in the shape of these organisms through their evolution. Rare deviations from regularity measured in Holasteroida order are discussed.     

Seasonality and 3D‐visualization of brooding in the hermaphroditic ophiuroid Amphiura capensis

This article describes the reproductive biology and developing young of Amphiura capensis, a small brooding brittle star found in the intertidal zones of Namibia and South Africa. Each month from October 2014 to September 2015, 20 specimens were collected from Mouille Point, Cape Town, South Africa, and dissected for internal examination of brooding characteristics. Disc diameters of 238 analyzed adults ranged 2.5–8.7 mm, with a mean of 6.15 mm (SD = 1.10 mm). Brooding was exhibited in 60.5% of all sampled individuals, of which 30.6% contained young of only one of six subjectively chosen size classes, 31.9% contained two size classes, and the rest (37.5%) contained more than two size classes at the same time. Young within the same bursa were commonly of the same size class, which suggests sequential brooding. However, multiple size classes of young were often present within different bursae of the same parent, which thus exhibited characteristics of both sequential and simultaneous brooding. Of 584 brooded young retrieved from dissections, an average of 2.5 (SD = 3.2) and a maximum of 14 young were recorded within a single parent. As no larval stages were observed, development was assumed to be direct. Three‐dimensional visualizations of μCT scans revealed the positions of the brooded young to be quite different from those in other species, facing with their mouths downwards instead of upwards, and not all pressed against the adult's bursal wall. Brooding occurred throughout the year, but numbers of young peaked in austral winter, coinciding with warmer water temperatures at this site. The duration of brooded development was estimated to be ~6 months, comparable with other species with similar reproductive biology.     

Elucidation of the origin of ‘agriocrithon’ based on domestication genes questions the hypothesis that Tibet is one of the centers of barley domestication

Wild barley forms a two‐rowed spike with a brittle rachis whereas domesticated barley has two‐ or six‐rowed spikes with a tough rachis. Like domesticated barley, ‘agriocrithon’ forms a six‐rowed spike; however, the spike is brittle as in wild barley, which makes the origin of agriocrithon obscure. Haplotype analysis of the Six‐rowed spike 1 (vrs1) and Non‐brittle rachis 1 (btr1) and 2 (btr2) genes was conducted to infer the origin of agriocrithon barley. Some agriocrithon barley accessions (eu‐agriocrithon) carried Btr1 and Btr2 haplotypes that are not found in any cultivars, implying that they are directly derived from wild barley through a mutation at the vrs1 locus. Other agriocrithon barley accessions (pseudo‐agriocrithon) carried Btr1 or Btr2 from cultivated barley, thus implying that they originated from hybridization between six‐rowed landraces carrying btr1Btr2 and Btr1btr2 genotypes followed by recombination to produce Btr1Btr2. All materials we collected from Tibet belong to pseudo‐agriocrithon and thus do not support the Tibetan Plateau as being a center of barley domestication. Tracing the evolutionary history of these allelic variants revealed that eu‐agriocrithon represents six‐rowed barley lineages that were selected by early farmers, once in south‐eastern Turkmenistan (vrs1.a1) and again in the eastern part of Uzbekistan (vrs1.a4).     

Apparent Selection Intensity for the Cytochrome Oxidase Subunit I Gene Varies with Mode of Reproduction in Echinoderms

When most amino acid substitutions in protein-coding genes are slightly deleterious rather than selectively neutral, life history differences can potentially modify the effective population size or the selective regime, resulting in altered ratios of non-synonymous to synonymous substitutions among taxa. We studied substitution patterns for the mitochondrial cytochrome oxidase subunit I (COI) gene in a sea star genus (Leptasterias spp.) with an obligate brood-protecting mode of reproduction and small-scale population genetic subdivision, and compared the results to available COI sequences in nine other genera of echinoderms with pelagic larvae: three sea stars, five sea urchins and one brittle star. We predicted that this life history difference would be associated with differences in the ratio of non-synonymous (dN) to synonymous (dS) substitution rates. Leptasterias had a significantly greater dN/dS ratio (both between species and within species), a significantly smaller transition/transversion rate ratio, and a significantly lower average nucleotide diversity within species, than did the non-brooding genera. Other explanations for the results, such as altered mutation rates or selective sweeps, were not supported by the data analysis. These findings highlight the potential influence of reproductive traits and other life history factors on patterns of nucleotide substitution within and between species.     

Bringing the Visible Universe into Focus with Robo-AO

The angular resolution of ground-based optical telescopes is limited by the degrading effects of the turbulent atmosphere. In the absence of an atmosphere, the angular resolution of a typical telescope is limited only by diffraction, i.e., the wavelength of interest, λ, divided by the size of its primary mirror''s aperture, D. For example, the Hubble Space Telescope (HST), with a 2.4-m primary mirror, has an angular resolution at visible wavelengths of ~0.04 arc seconds. The atmosphere is composed of air at slightly different temperatures, and therefore different indices of refraction, constantly mixing. Light waves are bent as they pass through the inhomogeneous atmosphere. When a telescope on the ground focuses these light waves, instantaneous images appear fragmented, changing as a function of time. As a result, long-exposure images acquired using ground-based telescopes - even telescopes with four times the diameter of HST - appear blurry and have an angular resolution of roughly 0.5 to 1.5 arc seconds at best.Astronomical adaptive-optics systems compensate for the effects of atmospheric turbulence. First, the shape of the incoming non-planar wave is determined using measurements of a nearby bright star by a wavefront sensor. Next, an element in the optical system, such as a deformable mirror, is commanded to correct the shape of the incoming light wave. Additional corrections are made at a rate sufficient to keep up with the dynamically changing atmosphere through which the telescope looks, ultimately producing diffraction-limited images.The fidelity of the wavefront sensor measurement is based upon how well the incoming light is spatially and temporally sampled¹. Finer sampling requires brighter reference objects. While the brightest stars can serve as reference objects for imaging targets from several to tens of arc seconds away in the best conditions, most interesting astronomical targets do not have sufficiently bright stars nearby. One solution is to focus a high-power laser beam in the direction of the astronomical target to create an artificial reference of known shape, also known as a ''laser guide star''. The Robo-AO laser adaptive optics system^2,3 employs a 10-W ultraviolet laser focused at a distance of 10 km to generate a laser guide star. Wavefront sensor measurements of the laser guide star drive the adaptive optics correction resulting in diffraction-limited images that have an angular resolution of ~0.1 arc seconds on a 1.5-m telescope.