Phylogeny of the Pteraspidiformes (Heterostraci), Silurian–Devonian jawless vertebrates

The Pteraspidiformes are an order of armoured agnathans of Silurian and Devonian age composed of five families: the Anchipteraspididae, Protopteraspididae, Pteraspididae, Protaspididae and Psammosteidae. Relationships within the order are poorly known and although past attempts have been made to represent the state of knowledge in this area none have attempted a rigorous computer-based analysis. Here we present the results of the cladistic analysis on a matrix comprising 25(+1) taxa and 59 characters using W inclada . The first analysis was run without any representative of the Psammosteidae and supports the presence of five groups within the order although one, the 'Protopteraspididae', is paraphyletic and a second, the Gigantaspididae, is newly recognized. In a second analysis the addition of the psammosteid Drepanaspis gemuendenensis results in a better resolved tree in which the basal family, the Anchipteraspididae, are clearly monophyletic and in which the Psammosteidae, as represented by Drepanaspis , is the next less inclusive. This is contrary to the previous view that the psammosteids were an advanced clade within the Pteraspidiformes.     

Bone vascularization and growth in placoderms (Vertebrata): The example of the premedian plate of Romundina stellina Ørvig, 1975

The Placodermi (armored jawed fishes), which appeared during the Lower Silurian and disappeared without leading any descendants at the end of the Famennian (Latest Devonian), have the highest diversity of known Devonian vertebrate groups. As phylogenetically basal gnathostomes (jawed vertebrates), they are potentially informative about primitive jawed vertebrate anatomy and origins. Until recently, the study of their internal or histological structures has required destructive methods such as sectioning or serial grinding. Recent advances in tomography and imaging technologies, especially through the increasing use of synchrotron phase contrast imaging for the study of fossils, allow us to reveal the inner structures of the fossil nondestructively and with unprecedented three-dimensional level of detail. Here, we present for the first time the prerostral anatomy of the small acanthothoracid Romundina stellina, one of the earliest and most basal placoderms. Phase contrast imaging allows us to reconstruct the vascularization and nerve canals of the premedian plate and adjacent parts of the skeleton three-dimensionally in great detail, providing important clues to the growth modes and biology of the animal.     

Chromium(VI) and apparent phenotypic reversion in Salmonella TA100

After treatment with potassium chromate at concentrations causing ultramicroscopic cellular lesions, a significant proportion (up to 75%) of TA100 colonies fail to replicate on fresh minimal plates containing biotin. This suggests that chromium(VI) may not always induce his- reversion to his+ in Salmonella TA100. The terms 'false' or phenotypic reversion have been used to distinguish such instances from 'true' or genotypic reversion, where progeny his+ cells readily grow on biotin replica plates. Results of the present study indicate that the majority of chromate-exposed colonies, initially scored as his-, are identifiable as his+ after 24 h culture on nutrient agar. Moreover, chromate exerts a cytostatic effect on TA100 since early colony development is suppressed at high chromate concentrations. A gradual chemical reduction of chromium(VI) ions by normal media compounds is probably responsible for the re-emergence of colony growth during prolonged incubation of test plates. Thus, temporary growth inhibition at high chromate concentration appears to be responsible for most of the non-replicating colonies detected in mutagenicity assays of chromium(VI).     

From Carlquist’s ecological wood anatomy to Carlquist’s Law: why comparative anatomy is crucial for functional xylem biology

All students of xylem structure–function relations need to be familiar with the work of Sherwin Carlquist. He studies xylem through the lens of the comparative method, which uses the appearance of similar anatomical features under similar conditions of natural selection to infer function. “Function” in biology implies adaptation; maximally supported adaptation inferences require experimental and comparative xylem scientists to work with one another. Engaging with comparative inferences of xylem function will, more likely sooner rather than later, bring one to the work of Sherwin Carlquist. To mark his 90th birthday, I highlight just a few examples of his extraordinarily perceptive and general comparative insights. One is “Carlquist’s Law”, the pervasive tendency for vessels to be solitary when background cells are conductive. I cover his pioneering of “ecological” wood anatomy, viewing xylem variation as reflecting the effects of selection across climate and habit variation. Another is the embolism vulnerability–conduit diameter relationship, one of the most widely invoked structure–function relationships in xylem biology. I discuss the inferential richness within the notion of Carlquistian paedomorphosis, including detailed functional inferences regarding ray cell orientation. My final example comes from his very recent work offering the first satisfactory hypothesis accounting for the geographical and histological distribution of scalariform perforation plates as an adaptation, including “Carlquist’s Ratchet”, why scalariform plates are adaptive but do not re-evolve once lost. This extraordinarily rich production over six decades is filled with comparative inferences that should keep students of xylem function busy testing for decades to come.     

Stimulation of lactobacilli by an aqueous extract of the green alga Scenedesmus acutus 276-3a

Summary The hot-water extract of Scenedesmus acutus 276-3a enhances acid formation by Lactobacillus casei var. sbirota, Streptococcus lactis and Streptococcus thermophilus appreciably. At least in S. lactis the stimulation is not caused by mineral constituents such as Mn²⁺. In order to facilitate screening, a quick test in tubes was used. Stimulation of lactobacilli by algal extract is also demonstrated in tests on agar plates containing TTC. Bioautography of algal extract fractions on TTC plates enabled adenine and hypoxanthine to be identified as growth factors in algal extract which contributed towards the stimulation of S. lactis.Dedicated to Professor Dr. Wilhelm Halbsgut on the occasion of his 65th birthday     

Robert Koch: the grandfather of cloning?

This year marks the centenary of Robert Koch's Nobel Prize for discovering the cause of tuberculosis. Koch was also the first scientist to isolate the anthrax and cholera microbes. Yet perhaps one of his greatest contributions to biology is the least appreciated: his method for propagating individual colonies of bacteria on plates, a technique that came to be called cloning.     

Distribution of scalariform and simple perforation plates within the vessel network in secondary xylem of Araliaceae and its implications for wood evolution

The distribution of scalariform and simple perforation plates along vessels in Arthrophyllum otopyrenum, Meryta tenuifolia, and Polyscias multijuga (Araliaceae) is examined. In all three species, most vessels bear simple perforation plates only, but the combination of simple and scalariform perforation plates in variable ratios also occurs. Aggregated arrangement of scalariform perforation plates along the vessels was statistically confirmed in some vessel portions. The scalariform perforation plates occur mostly in narrow vessels that are grouped in multiples. Within the clade represented by Polyscias and Arthrophyllum, the evolutionary transition from scalariform to simple perforation plates is realized as the gradual elimination of vessels or vessel portions with scalariform perforation plates, but is not accompanied by a gradual decrease of the number of bars per perforation plate. The narrow vessels that are grouped in vessel multiples are likely to retain the ability to develop scalariform plates, which could promote the evolution from simple to scalariform perforation plates as is the case within Meryta.     

Experimental morphology of coronar growth in regular echinoids

Summary The coronar growth of a cidaroid and an aulodont echinoid are investigated by means of tetracycline labelling. The results are compared with earlier investigations on a stirodont and on a camarodont echinoid in order to evaluate the general features of coronar growth. In all echinoids new coronar plates are added at the apical end of the corona throughout the life cycle. The plates are shifted towards the peristome and they grow peripherically.In cidaroids ambulacral (A-) plates are detached from the firm corona. They are transformed into scales covering the peristomial field. The interambulacral (IA-) plates, however, are partially reabsorbed at the peristomial margin. In this manner the oldest solitary interambulacral plates are lost. The subsequent plates are arranged in pairs. The cidaroids thus show interradial growth even at their peristomial margin. This is unique to echinoids.In non-cidaroids there is a perignathic girdle made up of paired ambulacral auricles with interambulacral ridges in between. In some species the ridge is a solitary element. Therefore interradial growth cannot occur in the peristomial margin. In other species the ridge consists of several elements, but it also grows as a whole. Slight resorption of calcite occurs in places at the peristomial margin. In other places, however, calcite is added onto the peristomial edge. In non-cidaroids, therefore, the widening of the peristome is achieved solely by means of lateral growth in the plates bordering the peristome. The shift of the coronar plates from apicad to orad in noncidaroids is a relative shift only.In all echinoids the coronar plates are arranged in meridional columns. All plates grow up to the peristome. Their growth rates are relatively uniform towards the adambulacral sutures (which run between A- and IA-columns). Their growth rates towards the perradius and the interradius respectively are high in younger plates which are positioned above the ambitus, and decrease rapidly in plates located below the ambitus. Near the peristome the interradiad and perradiad growth rates are always considerably lower than adradiad growth rates. Perradial and interradial growth serve to adjust the plates in size and shape to their respective position in the corona.     

鹅掌楸属(木兰科)次生木质部导管穿孔板的比较研究

利用扫描电子显微镜对鹅掌楸属仅存的2个自然种鹅掌楸和北美鹅掌楸的次生木质部导管穿孔板特征进行了详细的研究。结果显示,鹅掌楸属的2个种均以梯状穿孔板为主,同时存在网状-梯状混合穿孔板。鹅掌楸和北美鹅掌楸的导管穿孔板具有明显差异:(1)鹅掌楸具网状穿孔板,而北美鹅掌楸没有观察到;(2)北美鹅掌楸具单穿孔板,而鹅掌楸在该实验中未发现;(3)北美鹅掌楸具有横隔较粗的梯状穿孔板且横隔数目较多;(4)鹅掌楸的导管穿孔板多数横隔较少;(5)北美鹅掌楸的穿孔板倾斜角度较大;(6)北美鹅掌楸具麻黄式穿孔板的存在,且有纹孔膜残留存在。研究认为,北美鹅掌楸导管分子穿孔板分化较鹅掌楸更为剧烈。     

Isolation of alveolar plates from Coleps hirtus

In the ciliate Coleps hirtus, the alveoli contain rigid alveolar plates that are almost unstudied so far. Neither the exact composition nor the genesis and function are known. A necessary step to study the alveolar plates is to isolate these structures in an adequate amount. Therefore, culture conditions of C. hirtus were optimized to obtain an axenic and dense long-time culture. The protocol we developed to isolate C. hirtus alveolar plates is presented and clean alveolar plates were documented via scanning electron microscopy. The described procedure delivers alveolar plates of very good structure and integrity with preserved filigree details in sufficient amount. They can be analysed via a range of different material and biological characterisations. Since there are indications of a mineral phase within the alveolar plates, the presented results will allow to study C. hirtus alveolar plates also in the context of biomineralisation.     

Micromorphology of epicuticular waxes in Centrosperms

Epidermal surfaces of about 500 species from some 250 genera of centrospermous families plus some possibly related families were examined by scanning electron microscopy. The micromorphology of their epicuticular waxes is described under taxonomic aspects. In general, Centrosperms tend to develop wax platelets on their cuticle. Shape and size of these platelets are highly diverse, but specific for some taxa. Particular forms of rodlets and thick wax plates occur only in few taxa. The systematic and taxonomic applicability of wax micromorphology is limited, but tentatively family characterizations are given. The data presented provide additional information concerning the familiar and suprafamiliar classification ofCaryophyllales. Dedicated to the enthusiast of succulent Centrosperms, Prof. DrK. E. Wohlfarth-Bottermann (Director of the Institute of Cytology and Micromorphology, University of Bonn) on the occasion of his 65th birthday in May 1988.     

Morphology and growth of lepidosirenid lungfish tooth plates (Pisces: Dipnoi)

The structure of the tooth plates of Protopterus and Lepidosiren was investigated to determine the causes and consequences of postlarval shape change. During growth, the basal area of the tooth plates increases, some cusps become more prominent, and shearing surfaces are sharpened. The jaw articulation restricts the range of movements of the lower jaw, and causes the tooth plates to occlude precisely; the resulting wear patterns are regular. The tooth plates are composed of enamel, trabecular dentine, and petrodentine. A petrodentine column forms the core of a tooth plate; it is flanked by trabecular dentine. Microhardness measurements show that trabecular dentine is comparable in hardness to mammalian dentine, whereas the petrodentine is comparable to enamel. The location and differential wear of these tissues produce the prominent cusps and self-sharpened blades of the adult tooth plates.     

Aptychopsid plates - jaw elements or protective operculum

The three plates characteristic of Aptychopsis have been described as a jaw apparatus in this orthocone cephalopod as well as an operculum for it. Due to the limited material, interpretations have in various cases been made from photographic illustrations and those results are discussed in this article. The area of the aptychopsid plates is compared with the apertural area of the cephalopod and the results show a great similarity. Arguments for and against soft parts outside the aptychopsid plates are discussed as well as the position of the plates. Material from a Silurian shale in southern Sweden is described. ? Aptychopsis, aptychopsid plates. Cephalopoda, operculum, jaw apparatus, Silurian.     

Effects of amount and type of agar on the number of spontaneous revertants in the Ames test

It has been shown that the spontaneous revertants in the Ames test can depend on the amount and type of bottom agar on the plates. The most clear-cut effect was found with the his G46 strains, carrying the delta uvrB mutation, and with the new hisG428 strain, TA102. Evidence of mutagenic impurities in agar has been found.     

Zebra mussels and polystyrene

The growth of settled and metamorphosed larvae of the zebra mussel (Dreissena polymorpha) is clearly retarded when polystyrene plates are used as a substrate compared with the growth of those forms attached to PVC plates. Possibly, low molecular weight compounds are released into the aquatic environment by the polystyrene and these materials may have a strongly adverse effect upon the growth of young zebra mussels. There is no difference in colonization of young mussels between PVC and polystyrene plates if these plates are sufficiently overgrown with bacteria and algae.     

Dense chromatin plates in metaphase chromosomes

In a previous work we observed multilayered plate-like structures surrounding partially denatured HeLa chromosomes at metaphase ionic conditions. This unexpected finding has led us to carry out an extensive investigation of these structures. Our results show that plates can also be found in metaphase chromosomes from chicken lymphocytes. We have used atomic force microscopy (AFM) to image and investigate the mechanical properties of plates in aqueous solution. Plates are thin (~6.5 nm each layer) but compact and resistant to penetration by the AFM tip: their Young’s modulus is ~0.2 GPa and the stress required for surface penetration is ~0.03 GPa in the presence of Mg²⁺ (5–20 mM). Low-ionic strength conditions produce emanation of chromatin fibers from the edges of uncrosslinked plates. These observations and AFM results obtained applying high forces indicate that the chromatin filament is tightly tethered inside the plates. Images of metal-shadowed plates and cryo-electron microscopy images of frozen-hydrated plates suggest that nucleosomes are tilted with respect to the plate surface to allow an interdigitation between the successive layers and a thickness reduction compatible with the observed plate height. The similarities between denatured plates from chicken chromosomes and aggregates of purified chromatin from chicken erythrocytes suggest that chromatin has intrinsic structural properties leading to plate formation. Scanning electron micrographs and images obtained with the 200-kV transmission microscope show that plates are the dominant component of compact chromatids. We propose that metaphase chromosomes are formed by many stacked plates perpendicular to the chromatid axis.     

Patterns of comb row development in young and adult stages of the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus

The development of comb rows in larval and adult Mnemiopsis leidyi and adult Pleurobrachia pileus is compared to regeneration of comb plates in these ctenophores. Late gastrula embryos and recently hatched cydippid larvae of Mnemiopsis have five comb plates in subsagittal rows and six comb plates in subtentacular rows. Subsagittal rows develop a new (sixth) comb plate and both types of rows add plates at similar rates until larvae reach the transition to the lobate form at ～5 mm size. New plate formation then accelerates in subsagittal rows that later extend on the growing oral lobes to become twice the length of subtentacular rows. Interplate ciliated grooves (ICGs) develop in an aboral‐oral direction along comb rows, but ICG formation itself proceeds from oral to aboral between plates. New comb plates in Mnemiopsis larvae are added at both aboral and oral ends of rows. At aboral ends, new plates arise as during regeneration: local widening of a ciliated groove followed by formation of a short split plate that grows longer and wider and joins into a common plate. At oral ends, new plates arise as a single tuft of cilia before an ICG appears. Adult Mnemiopsis continue to make new plates at both ends of rows. The frequency of new aboral plate formation varies in the eight rows of an animal and seems unrelated to body size. In Pleurobrachia that lack ICGs, new comb plates at aboral ends arise between the first and second plates as a single small nonsplit plate, located either on the row midline or off‐axis toward the subtentacular plane. As the new (now second) plate grows larger, its distance from the first and third plates increases. Size of the new second plate varies within the eight rows of the same animal, indicating asynchronous formation of plates as in Mnemiopsis. New oral plates arise as in Mnemiopsis. The different modes of comb plate formation in Mnemiopsis versus Pleurobrachia are accounted for by differences in mesogleal firmness and mechanisms of ciliary coordination. In both cases, the body of a growing ctenophore is supplied with additional comb plates centripetally from opposite ends of the comb rows. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Resistances to fluid flow of model xylem vessels with simple and scalariform perforation plates

The resistances of xylem vessel walls and perforation plates has been investigated using 18 large-scale physical models made of plastic tubing into which scale models of plates were inserted. Flow of water through vessels was modelled using glycerol instead of water to keep the Reynolds number below 0.1. The technique proved easy, cheap and reliable.Results showed that perforation plate resistance is low compared with the resistance of the walls, whatever the plate morphology; plates only provided 0.6-18.6% extra resistance. Simple plates provided less resistance than scalariform plates, but because they are arranged closer together in vessels, resistance values (1.7-5.1%) overlap with those of scalariform plates. The resistance of scalariform plates varied in a systematic way with their morphology. For a given plate angle, increasing the number of bars increased resistance. For a given bar number, increasing the angle of the plate to the vessel axis also increased the resistance. However, for a given gap between bars, increasing the angle of the plate to the vessel axis decreased resistance. These results are discussed in the light of theories about the function of perforation plates.Keywords: Flow, xylem vessel, perforation plate, models.      

An appraisal of methods used in coral recruitment studies

 A new method for attaching individual artificial settlement plates directly to the reef surface using small stainless steel base plates is described. Recruitment of corals to settlement plates attached to the reef substratum and to steel mesh racks is compared. The effects of differences in depth, settlement plate angle, and local topography on recruitment of corals were also investigated. No significant difference in mean recruit density was found between settlement plates deployed using the two attachment methods. Small differences in depth and plate angle among replicate plates explained less than 6% of the variability in coral recruitment on replicate settlement plates. The direct-attachment method is less obtrusive, more cost and time efficient, and settlement plates can be deployed at precise locations. Additionally, because settlement plates are deployed individually rather than grouped on racks or frames, the direct-attachment method avoids complications associated with assumptions of independence implicit in most statistical procedures. Accepted: 24 November 1999