Xenomorphic growth in ostreids

Attachment surfaces of ostreids preserve the (negative) imprint of the substrate morphology while the right (upper, free) valve may reflect its positive form (xenomorphism or xenomorphic sculpture). The substrate may be an invertebrate skeleton which is dissolved during diagenesis. The imprint of such skeletons on ostreid valves has often a greater biostratigraphic significance than the ostreid itself. Fossil examples are described.     

Chaetetid growth form and its controlling factors

Chactetid sponge morphology is examined to provide details on growth styles and their controlling factors. Chactetid growth forms range from laminar to domical. bulbous. columnar and complex branching in a variety of sizes. The chactetid skeleton began as a laminar unit comprising growth of many calicles across the substrate at the same time. Several styles of early growth. involving differential calicle growth rates and varying directions of adjacent calicle growth. are recognized. and result in complex arrangements of caliclcs in the skeleton. Despite this. the cross-sectional protile of the gross morphology at any stage of growth is usually a simple outline. implying that internal complexities of calicle development are modulated to produce an optimum cross-sectional outline for the individual chactetid. The morphological range of chactetids is similar to stromatoporoids. some tabulate. heliolitid and colonial rugose corals. some bryozoans. stromatolites. encrusting foraminifera and calcareous algae: the common environmental controlling factors of sedimentation and turbulence profoundly influenced growth form in all these organisms by virtue of their common sessile shallow marine habit. Chactetid growth forms show a general relationship to the environment: columnar and branching forms grew in quiet water. while laminar and domical were better adapted to environments of higher energies. The environmental adaptations of laminar forms. however. remain problematic. because they are found in both high and low energy facies. and interpretation depends strongly on facies study. Also. interpretation of all growth forms is suspected to relate to taxonomic aspects. as has been recognized for other groups. Unfortunately. chaetetid taxonomy is in need of revision. and at present no certain relationship has been demonstrated between taxonomy and growth form. Some modern calcareous sponges with a chaetetiform architccture also show similarities in growth form to fossil types. and may be subject to similar controls. □Chaetetid. calcified sponge. growth form. Pennsyloanian. North America.     

Pyritized radiolarians and siliceous sponges from oxygen-restricted deposits (Lower Toarcian,Jurassic)

In Lower Toarcian marls and marly limestone deposits from the South Iberia Paleomargin (Fuente Vidriera section, Betic Cordillera, southern Spain), siliceous skeletons of radiolarian and spicules of hexactinellid sponges are preserved in pyrite. The original siliceous skeletons (hydrated amorphous silica) were dissolved and totally replaced by pyrite. The radiolarians are locally very well preserved as independent remains or fused to pyrite framboids, in some cases distorted by the pyrite framboid growth. Pyritization of the remains and decay of the organic matter of these organisms by sulphate-reducing bacteria favored the early pyritization at the same time that silica dissolved. Pyrite formation was associated with organic matter decay through sulphate reduction; the amorphous silica skeleton acts either as a nucleation substrate or induces precipitation of pyrite precursors during biogenic silica dissolution. The organic matter may also help to stabilize colloids that are important for framboid precipitation. Pyritization occurred soon after the death of the organism, taking place in the upper sediment column just below the sediment–water interface, at the redox boundary where oxygen-bearing and hydrogen sulphide-bearing waters are in contact. The size of pyritized radiolaria (>40 μm) and the mean size of pyrite framboids (6.3–7.1 μm) are compatible with pyritization within the sediment–water interface under dysoxic conditions. The presence of trace fossils and benthic foraminifera exclude anoxic and euxinic conditions during the early Toarcian in this setting.     

Taphonomy of coral reefs: a review

This review summarises the major factors that affect the post-mortem history of skeletons in a coral reef environment. Skeletal material is traced from life, through death, breakdown, transport, burial and diagenesis to its final fossil form. The fact that most reef sediments are of skeletal composition poses problems of concentration or dilution of individual grain types in taphonomic analysis of reefs. Rates of supply of grains vary, not only with organism abundance and skeletal growth rates, but also with rates of physical and biological breakdown to transportable sediment. Physical and organic processes affect sedimentary structures and textures by mixing or segregating skeletal grains, though biogenic processes normally dominate in the protected setting of reef lagoons. The soft and hard substrates associated with reefs present different media for calcium carbonate accumulation and post-depositional disturbance, for example, loose sediments suffer bioturbation and rocks surfaces suffer bioerosion. The wide range of durability of skeletons and their susceptibility to diagenesis contribute further to the complexities of the preservation of coral reefs.     

Spicule and flagellated chamber formation in a growth zone of Aphrocallistes vastus (Porifera,Hexactinellida)

Three species of glass sponges (Class Hexactinellida) form massive deep‐water reefs by growing on the skeletons of past generations, with new growth largely vertical and away from sediment that buries the lower portions. Growth is therefore essential for reef health, but how glass sponges produce new skeleton or tissue is not known. We used fluorescence, light, and electron microscopy to study skeletal and tissue growth in the reef‐forming glass sponge Aphrocallistes vastus. The sponge consists of a single large tube (the osculum), usually with several side branches, each of which can function as an effective excurrent vent. New tissue forms at the tips of each of these extensions, but how this occurs in a syncytial animal, and how the tubes expand laterally as the sponge gets larger, are both unknown. The fluorescent dye PDMPO labeled more spicule types in the tips of the sponge than elsewhere, indicating growth that was concentrated at the edge of the osculum. New tissue production was tracked using the thymidine analog EdU. EdU‐labeled nuclei were found predominantly at the edge or lip of the osculum. In that region new flagellated chambers were formed from clusters of choanoblasts that spread out around the enlarging chamber. In cellular sponges clusters of choanocytes form flagellated chambers through several rounds of mitotic divisions, and also by immigration of mesohyl cells, to expand the chamber to full size. By contrast, chambers in glass sponges expand as choanoblasts produce enucleate collar bodies to fill them out. Growing chambers with enucleate structures may be an adaptation to life in the deep sea if chambers with cells, and therefore more nuclei, are costly to build.     

Fine-scale phosphorus distribution in coral skeletons: combining X-ray mapping by electronprobe microanalysis and LA-ICP-MS

Increased terrestrial phosphorus runoff is a major environmental problem that has been linked to deteriorating reef health. Unfortunately, long-term records of phosphorus are limited. Whilst phosphorus captured in coral skeletons could provide us with an archive of phosphorus variability, the mode of incorporation is poorly understood. In order to document phosphorus levels, we used laser ablation inductively coupled plasma mass spectrometry, followed by X-ray mapping of phosphorus in the skeleton at micron scale (~3–5 microns) using Electronprobe microanalysis. We recorded high phosphorus (≤8,700 ppm) in the living tissue zone associated with phosphorus-rich residues lining the internal pore network surfaces. The skeleton in the tissue zone had low, uniform levels of phosphorus, similar to older sections of the core (<50 ppm). Below the organic tissue layer, P was incorporated homogenously in the skeleton for extended periods (e.g., 5 mm growth bands). However, sections of the core (~1 cm down-core) displayed fine-scale elevated phosphorus concentrations associated with the presence of phosphorus-rich, often elongate (10–100 μm long), heterogeneities within the skeleton, the origin of these phosphorus-rich heterogeneities and their mode of incorporation requires further attention. In conclusion, these results support the continued development of this promising potential nutrient proxy.     

Stable isotopic records of bleaching and endolithic algae blooms in the skeleton of the boulder forming coral Montastraea faveolata

Within boulder forming corals, fixation of dissolved inorganic carbon is performed by symbiotic dinoflagellates within the coral tissue and, to a lesser extent, endolithic algae within the coral skeleton. Endolithic algae produce distinctive green bands in the coral skeleton, and their origin may be related to periods of coral bleaching due to complete loss of dinoflagellate symbionts or “paling” in which symbiont populations are patchily reduced in coral tissue. Stable carbon isotopes were analyzed in coral skeletons across a known bleaching event and 12 blooms of endolithic algae to determine whether either of these types of changes in photosynthesis had a clear isotopic signature. Stable carbon isotopes tended to be enriched in the coral skeleton during the initiation of endolith blooms, consistent with enhanced photosynthesis by endoliths. In contrast, there were no consistent δ¹³C patterns directly associated with bleaching, suggesting that there is no unique isotopic signature of bleaching. On the other hand, isotopic values after bleaching were lighter 92% of the time when compared to the bleaching interval. This marked drop in skeletal δ¹³C may reflect increased kinetic fractionation and slow symbiont recolonization for several years after bleaching.     

The stromatoporoid animal revisited: Building the skeleton

Modern coralline sponges secrete a skeleton by means of a basal pinacoderm, intracellularly, or inside the soft tissue on an organic matrix The examination of terminal growth surfaces of stromatoporoids indicates that soft tissue in laminate and amalgamate forms occupied the upper galleries and that the skeletal elements were secreted within the soft tissue on an organic matrix. The stromatoporellids and clathrodictyids secreted the skeleton in modules that are homologous to the chambers of a sphinctozoan. In stromatoporellids the module was bounded by a floor that formed the upper layer of the tripatite lamina below and a roof that became the lower layer of the next lamina; it further included the intervening pillars. In clathrodictyids the module had only a roof and pillars, and the laminae are single layers. other stromatoporoids may have secreted their skeletons at the base of the soft tissue and had minimal occupation of the skeleton. *** Stromatoporoid, sphinctozoa, sclerospongiae, sponge, paleobiology.     

Can model species be used to advance the field of invasion ecology?

Hypotheses for explaining plant invasions have focused on a variety of factors that may influence invasion success, including propagule pressure, interactions of the introduced species with the biotic, abiotic, or disturbance properties of the new ecosystem, or the genetic characteristics of the invader itself. Evaluating the relative importance of these factors has been difficult because for most invaders key information about the introduced population or the introduction event is not available. We propose that natural experiments using model species is an important tool to test multiple invasion hypotheses at the same time, providing a complementary approach to meta-analysis and literature review. By focusing on a single candidate species, Pinus contorta, we explore several attributes that we propose constitute a good model, including: (a) intentional and relatively well documented introduction into a wide range of environments and countries across the world during the past century, where invasion success or failure has already occurred, (b) conspicuous growth form that simplifies assessment of growth rates, and comparisons across native and introduced ecosystems around the world, and, (c) documented and replicated variability of introduction intensity, genetic characteristics of the introduced populations, contrasting biotic communities present at sites of introduction, and abiotic conditions within and across introduced ecosystems. We propose that identifying model species with these characteristics will provide opportunities to disentangle the relative importance of different mechanisms hypothesized to influence invasion success, and thereby advance the field of invasion ecology.     

The ‘biomineralization toolkit’ and the origin of animal skeletons

Biomineralized skeletons are widespread in animals, and their origins can be traced to the latest Ediacaran or early Cambrian fossil record, in virtually all animal groups. The origin of animal skeletons is inextricably linked with the diversification of animal body plans and the dramatic changes in ecology and geosphere–biosphere interactions across the Ediacaran–Cambrian transition. This apparent independent acquisition of skeletons across diverse animal clades has been proposed to have been driven by co‐option of a conserved ancestral genetic toolkit in different lineages at the same time. This ‘biomineralization toolkit’ hypothesis makes predictions of the early evolution of the skeleton, predictions tested herein through a critical review of the evidence from both the fossil record and development of skeletons in extant organisms. Furthermore, the distribution of skeletons is here plotted against a time‐calibrated animal phylogeny, and the nature of the deep ancestors of biomineralizing animals interpolated using ancestral state reconstruction. All these lines of evidence point towards multiple instances of the evolution of biomineralization through the co‐option of an inherited organic skeleton and genetic toolkit followed by the stepwise acquisition of more complex skeletal tissues under tighter biological control. This not only supports the ‘biomineralization toolkit’ hypothesis but also provides a model for describing the evolution of complex biological systems across the Ediacaran–Cambrian transition.     

Biological affinity, phenotypic variation and palaeoecology of Tetradium Dana, 1846

Comparisons of morphologies and modes of life of the Ordovician fossil Tetradium Dana, 1846, with chaetetid sponges, tabulate corals, and Recent rhodophytes show that several defining Tetradium characteristics are incompatible with its chaetetid and tabulate classifications. All Tetradium characteristics fit a rhodophyte identification, however, as a calcified uniaxial corticated florideophyte. It is argued from functional morphology that the fundamental subsquare cross-section of the Tetradium tube is an adaptation for close packing, which implies that the basic growth form is compact and should have developed where conditions were optimal. More open forms are derived from it and probably occupied less-favourable environments.
Palaeoecological studies from the Ottawa Valley, Canada, show that the Tetradium growth form is correlated with environmental stress and became more open as salinity increased: i.e. the compact T. fibratum form lived in normal marine conditions, radiating bundles of T. cellulosum tubes in low to middle hypersalinity and single T. syringoporoides tubes in high hypersalinity. Different Tetradium growth forms from the study area are phenotypic variants of a single species, rather than different species and genera. Therefore, classifications that divide Tetradium into different species and genera based only on growth form have no biological basis. There is little evidence of interspecific interactions with Tetradium .     

Evolution of calcium-carbonate skeletons in the Hydractiniidae

Biomineralization has mostly been studied in the class Anthozoa (Phylum Cnidaria), but very little is known about the evolution of the calcified skeleton in the class Hydrozoa or about the processes leading to its formation. The evolution of the calcified skeleton is here investigated in the hydrozoan family Hydractiniidae. A phylogenetic analysis of ribosomal, mitochondrial, and nuclear-protein-coding DNA sequences supported two independent origins of the calcified skeleton within the Hydractiniidae and indicates a case of parallel evolution, as suspected in the Anthozoa. Neither of the two origins of skeleton in the Hydractiniidae has led to either speciose or numerically abundant species, in contrast with other skeletonized hydrozoan families. Finally, we show that the origin of calcified skeletons in the Hydractiniidae is significantly correlated with the distribution of species with calcium carbonate granules within a polyp's gastrodermal cells. This suggests that the presence of these granules precedes the origin of a full skeleton.     

Skeletal microstructure of Galaxea fascicularis exsert septa: a high-resolution SEM study

The deposition of four crystal types at the growth surface of the septa of several color morphs of the coral Galaxea fascicularis was investigated over a 24-h period. Results suggest that nanocrystals, on denticles at the apices of exsert septa, may be the surface manifestation of centers of calcification. These crystals were also found on the septa of the axial corallite of Acropora formosa. The deposition of nanocrystals appears to be independent of diurnal rhythms. Internally and proximal to the septal apices, distinct clusters of polycrystalline fibers originate from centers of calcification and form fanlike fascicles. Upon these fascicles, acicular crystals grow and extend to form the visible fasciculi at the skeletal surface. Deposition of aragonitic fusiform crystals in both G. fascicularis and A. formosa occurs without diurnal rhythm. Nucleation of fusiform crystals appears to be independent of centers of calcification and may occur by secondary nucleation. Formation of semi-solid masses by fusiform crystals suggests that the crystals may play a structural role in septal extension. Lamellar crystals, which have not been reported as a component of scleractinian coral skeletons before, possess distinct layers of polyhedral plates, although these layers also do not appear to be associated with daily growth increments. The relationship of lamellar crystals to other components of the scleractinian coral skeleton and their involvement in skeletal growth is unknown.     

Abrupt burial imparts persistent changes to the bacterial diversity of turbidite‐associated sediment profiles

The emplacement of subaqueous gravity‐driven sediment flows imposes a significant physical and geochemical impact on underlying sediment and microbial communities. Although previous studies have established lasting mineralogical and biological signatures of turbidite deposition, the response of bacteria and archaea within and beneath debris flows remains poorly constrained. Both bacterial cells associated with the underlying sediment and those attached to allochthonous material must respond to substantially altered environmental conditions and selective pressures. As a consequence, turbidites and underlying sediments provide an exceptional opportunity to examine (i) the microbial community response to rapid sedimentation and (ii) the preservation and identification of displaced micro‐organisms. We collected Illumina MiSeq sequence libraries across turbidite boundaries at ~26 cm sediment depth in La Jolla Canyon off the coast of California, and at ~50 cm depth in meromictic Twin Lake, Hennepin County, MN. 16S rRNA gene signatures of relict and active bacterial populations exhibit persistent differences attributable to turbidite deposition. In particular, both the marine and lacustrine turbidite boundaries are sharply demarcated by the abundance and diversity of Chloroflexi, suggesting a characteristic sensitivity to sediment disturbance history or to differences in organic substrates across turbidite profiles. Variations in the abundance of putative dissimilatory sulfate‐reducing Deltaproteobacteria across the buried La Jolla Canyon sediment–water interface reflect turbidite‐induced changes to the geochemical environment. Species‐level distinctions within the Deltaproteobacteria clearly conform to the sedimentological boundary, suggesting a continuing impact of genetic inheritance distinguishable from broader trends attributable to selective pressure. Abrupt, <1‐cm scale changes in bacterial diversity across the Twin Lake turbidite contact are consistent with previous studies showing that relict DNA signatures attributable to sediment transport may be more easily preserved in low‐energy, anoxic environments. This work raises the possibility that deep subsurface microbial communities may inherit variations in microbial diversity from sediment flow and deformation events.     

A posttranslational modification of beta-actin contributes to the slow dissociation of the spectrin-protein 4.1-actin complex of irreversibly sickled cells

Irreversibly sickled cells (ISCs) remain sickled even under conditions where they are well oxygenated and hemoglobin is depolymerized. In our studies we demonstrate that triton extracted ISC core skeletons containing only spectrin, protein 4.1, and actin also retain their sickled shape; while reversibly sickled cell (RSC) skeletons remodel to a round or biconcave shape. We also demonstrate that these triton extracted ISC core skeletons dissociate more slowly upon incubation at 37 degrees C than do RSC or control (AA) core skeletons. This observation may supply the basis for the inability of the ISC core skeleton to remodel its shape. Using an in vitro ternary complex dissociation assay, we demonstrate that a modification in beta-actin is the major determinant of the slow dissociation of the spectrin-protein 4.1-actin complex isolated from the ISC core skeleton. We demonstrate that the difference between ISC and control beta-actin is the inaccessibility of two cysteine residues in ISC beta-actin to labeling by thiol reactive reagents; due to the formation of a disulfide bridge between cysteine284 and cysteine373 in ISC beta-actin, or alternatively another modification of cysteine284 and cysteine373 which is reversible with DTT and adds less than 100 D to the molecular weight of beta-actin.     

Ossification sequence of the avian order anseriformes,with comparison to other precocial birds

Ossification sequences are poorly known for most amniotes, and yet they represent an important source of morphogenetic, phylogenetic, and life history information. Here, the author describes the ossification sequences of three ducks, the Common Eider Somateria mollissima dresseri, the Pekin Duck Anas platyrhynchos, and the Muscovy Duck Cairina moschata. Sequence differences exist both within and among these species, but are generally minor. The Common Eider has the most ossified skeleton prior to hatching, contrary to what is expected in a subarctic migrant species. This may be attributed to a tradeoff between growth rate and locomotory performance. Growth rate is higher in hatchlings with more cartilaginous skeletons, but this may compromise locomotion. No major ossification sequence differences were observed in the craniofacial skeleton when compared with Galliformes, which suggests that the influence of adult morphology on ossification sequence might be relatively minor in many taxa. Galliformes and Anseriformes, while both highly ossified at hatching, differ in the location of their late‐stage ossification centers. In Anseriformes, these are most often located in the appendicular skeleton, whereas in Galliformes they are in the thoracic region and form the ventilatory apparatus. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Interpreting the autopodia of tetrapods: interphalangeal lines hinge on too many assumptions

Recently Peters proposed the concept of ‘interphalangeal lines’, defined as sub-parallel lines that could supposedly be drawn across the joints of the digits of all tetrapods. The lines were viewed as potential axes of rotation, and it was suggested that they could be used to determine the resting position of the digits, reconstruct missing digital elements of fossil tetrapods, and provide information on systematic relationships. Evidence was adduced from the skeletons of recent and fossil vertebrates and from footprints. However, detailed analysis shows that these claims are largely unfounded. Linear alignments of joints on neighbouring digits are not consistently present in tetrapods, especially across locomotor cycles. Even if present, interphalangeal (IP) lines would rarely be in an appropriate orientation to facilitate joint movements during locomotion. There is no reason to believe that IP lines would be homologous across different taxa, so they cannot be used to infer systematic relationships. Finally, the alleged support from the ichnological record is undermined by the uncertain relationship between the joint structure of the skeleton and the form of the print. We conclude that IP lines cannot be consistently constructed on tetrapod extremities, and would have minimal functional relevance or predictive power in any case.     

Life history variation across a riverine landscape: intermediate levels of disturbance favor sexual reproduction in the ant‐dispersed herb Ranunculus ficaria

Global climate change can fundamentally alter disturbance regimes across landscapes, but little is known about how species adjust their life histories to shifts in disturbance regimes. In plants, dispersal by seeds may permit rapid re‐colonization under frequent disturbances, but often seed‐dispersing animals may be absent and local dispersal by vegetative diaspores may be a more efficient means of occupying open space in the vicinity of the plant. We tested the effect of disturbances due to inundation on the investment in seed production by the ant‐dispersed plant, Ranunculus ficaria ssp. bulbifer. During seed ripening we collected 392 plants within a landscape mosaic of 39 sites with different levels of inundation. We measured the mass of fruits and other tissues (leafs, roots, bulbils, stalks) and described plant growth form. We found that fruit numbers and masses were more variable among plants than numbers and masses of other tissues. We then standardized fruit mass against the mass of other tissues and other growth‐form parameters. Standardized fruit mass showed a highly significantly hump‐shaped relationship with the level of inundation disturbances. This pattern was consistent across 12 small‐scale transects and thus not confounded by spatial autocorrelation within landscapes. The pattern was also confirmed by analyses that simultaneously accounted for disturbance and morphological co‐variables. We thus conclude that plants invested most heavily into reproduction by seeds under intermediate levels of disturbance. Under intermediate disturbance, seeds are beneficial for rapidly re‐colonizing open space after disturbance while the seed‐dispersers are still available. The life history of mutualists such as ant‐dispersed plants and ants may thus change across a landscape, reflecting small‐scale variation in the disturbance regime.