SCOLECODONTS VERSUS JAW APPARATUSES

Polychaete jaw apparatuses, until recently very rare in fossil state, have been discovered in large numbers in the Ordovician and Silurian limestone of the Baltic Region. Investigations on them (Kielan-Jaworowska 1966) have shown that the systematics of polychaete annelids based on jaw apparatuses is close to natural and that the jaw apparatuses are important as index fossils. It is stressed that combining the parataxonomy of scolecodonts with the systematics of jaw apparatuses in one system makes it impossible to carry out any meaningful scientific investigation in this field. An attempt is made to explain the scarcity of polychaete jaws in Mesozoic and Tertiary deposits.     

Commensal symbiosis between agglutinated polychaetes and sulfate‐reducing bacteria

Pendant bioconstructions occur within submerged caves in the Plemmirio Marine Protected Area in SE Sicily, Italy. These rigid structures, here termed biostalactites, were synsedimentarily lithified by clotted‐peloidal microbial carbonate that has a high bacterial lipid biomarker content with abundant compounds derived from sulfate‐reducing bacteria. The main framework builders are polychaete serpulid worms, mainly Protula with subordinate Semivermilia and Josephella. These polychaetes have lamellar and/or fibrillar wall structure. In contrast, small agglutinated terebellid tubes, which are a minor component of the biostalactites, are discontinuous and irregular with a peloidal micritic microfabric. The peloids, formed by bacterial sulfate reduction, appear to have been utilized by terebellids to construct tubes in an environment where other particulate sediment is scarce. We suggest that the bacteria obtained food from the worms in the form of fecal material and/or from the decaying tissue of surrounding organisms and that the worms obtained peloidal micrite with which to construct their tubes, either as grains and/or as tube encompassing biofilm. Peloidal worm tubes have rarely been reported in the recent but closely resemble examples in the geological record that extend back at least to the early Carboniferous. This suggests a long‐lived commensal relationship between some polychaete worms and heterotrophic, especially sulfate‐reducing, bacteria.     

Eridites undulatum壳体微细构造

利用偏光显微镜及扫描电子显微镜观察了假直角石类Ｅｒｉｄｉｔｅｓｕｎｄｕｌａｔｕｍ的体管沉积及气室沉积微细构造特征,体管沉积内部有机质层及矿物晶体层形态及厚度较稳定。气室沉积中有机质层及矿物晶体层形态及厚度变化大,晶体层内部具有柱状晶体。基于内部微细构造特征,推测体管沉积由软体上皮细胞直接分泌而成,气室沉积由体液渗透连接环在气室内表面上形成矿化基质后通过有机质层及矿物晶体层不断加积而成。另外,通过与石炭纪其它假直角石类内部沉积微细构造特征的比较,认为假直角石类内部沉积的微细构造特征不具有分类学意义。     

Taphonomic implications of polychaete jaws recovered from gut contents of the queen triggerfish

Remains of jawed polychaetes were recovered from stomach contents of queen triggerfish ( Balistes vetula L.) collected by spearing from Came Bow Cay, Belize, Central America. Jaws in the nereidids, glycerids, and arabellids recovered are perfectly preserved, and might be passed by the fish without noticeable alteration. Jaws in the onuphids are fully articulated, but the outer wall-layer has been digested away, leaving only the inner aragonitic layer intact. A low fossilization potential for onuphid jaws is indicated, consistent with laboratory studies of jaw composition. Based on literature accounts, fish predation may have a considerable influence on polychaete jaw (scolecodont) assemblages in sediment.     

Ordovician eunicid polychaetes of Estonia and surrounding areas: review of their distribution and diversification

Scolecodonts, the jaws of polychaete worms, are common and diverse palynomorphs in the Ordovician rocks of Estonia and surrounding areas. Some 120 apparatus-based species representing about 40 genera have been recorded thus far. Relatively long stratigraphical ranges of the majority of species reflect a low rate of evolution of jawed polychaetes. However, some individual species, as well as structural changes in the assemblages, appear to be useful for stratigraphical purposes. Environmental events like those in the middle Caradoc and late Ashgill had some impact on polychaete faunas, but less than on several other groups. In order to study the spatial distribution of eunicids, faunas of particular intervals of the Ordovician were investigated. Quantitative analysis revealed that polychaete assemblages with a very consistent qualitative and quantitative composition were widespread over long distances within the belts of similar facies conditions in the Baltoscandian Palaeobasin. On the other hand, it appears that species of Ordovician jawed polychaetes were strongly influenced by particular facies, and accordingly well differentiated along the palaeobasin gradient. The decrease in diversity and abundance towards the deeper-water part of the palaeobasin indicates that the majority of Ordovician eunicids preferred relatively shallow-water conditions. The increase in differentiation of environments is accompanied by an increase in differentiation of polychaete assemblages.     

Comparison of cranial form and function in association with diet in natricine snakes

The skull of squamates has many functions, with food acquisition and ingestion being paramount. Snakes vary interspecifically in the frequency, size, and types of prey that are consumed. Natural selection should favor phenotypes that minimize the costs of energy acquisition; therefore, trophic morphology should reflect a snake's primary prey type to enhance some aspect of feeding performance. I measured 19 cranial variables for six natricine species that vary in the frequency with which they consume frogs and fish. Both conventional and phylogenetically corrected analyses indicated that fish‐eating snakes have relatively longer upper and lower jaw elements than frog‐eating snakes, which tended to have broader skull components. I also compared the ratio of the in‐lever to the out‐lever lengths of the jaw‐closing mechanism [jaw mechanical advantage (MA)] among species. Fish‐eating snakes had significantly lower MAs in the jaws than did the frog‐eating snakes. This result suggests that piscivores have faster closing jaws and that the jaws of frog‐eating snakes have higher closing forces. Cranial morphology and the functional demands of prey capture and ingestion appear to be associated with primary prey type in natricine snakes. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Cutting edge structural protein from the jaws of Nereis virens

The fang-like jaws of the marine polychaete Nereis virens possess remarkable mechanical properties considering their high protein content and lack of mineralization. Hardness and stiffness properties in the jaw tip are comparable to human dentin and are achieved by extensive coordination of Zn (2+) by a histidine-rich protein framework. In the present study, the predominant protein in the jaw tip, Nvjp-1, was purified and characterized by partial peptide mapping and molecular cloning of a partial cDNA from a jaw pulp library. The deduced amino acid sequence revealed an approximately 38 kDa histidine-rich protein rich in glycine and histidine (approximately 36 and 27%, respectively) with no well-defined repetitive motifs. The effects of pH and metal treatment on aggregation, secondary structure, and hydrodynamic properties of recombinant Nvjp-1 are described. Notably, Zn treatment induced the formation of amyloid-like fibers.     

Microstructure of the linguliformean brachiopod Linnarssonia from the Lower Cambrian of Sichuan, China

Acrotretoids, one of the oldest brachiopod groups, are abundant in the Lower Cambrian Jiulaodong Formation. The shell of Linnarssonia sp. is composed of two layers: a primary layer and a columnar secondary layer. The primary layer is mostly exfoliated, resulting in exposure of the openings to the central canal of the columns. Filae are seen on the surface of the columnar layer, indicating that the columnar secondary layer has influenced changes in ornament on the shell surface. The larval shell has only very weak ripples; the post-larval shell has obvious concentric ribs. Small pits of variable shape cover almost the entire shell surface. The secondary layer is composed of several columnar laminations, each of which comprises both the upper and lower laminae and the cylindrical columns between them. On the inner side of shell the thin columnar laminations increase. The new microstructural data show that two shell layers are developed in Early Cambrian acrotretoid brachiopods; the columnar lamination may be a primitive feature of the microstructural development of the Brachiopoda and may help establish the affinity between different stem-group brachiopods.     

The oldest Gondwanan cephalopod mandibles (Hangenberg Black Shale,Late Devonian) and the mid‐Palaeozoic rise of jaws

It is widely accepted that the effects of global sea‐level changes at the transition from the Devonian to the Carboniferous are recorded in deposits on the shelf of northern Gondwana. These latest Devonian strata had been thought to be poor in fossils due to the Hangenberg mass extinction. In the Ma'der (eastern Anti‐Atlas), however, the Hangenberg Black Shale claystones (latest Famennian) are rich in exceptionally preserved fossils displaying the remains of non‐mineralized structures. The diversity in animal species of these strata is, however, low. Remarkably, the organic‐rich claystones have yielded abundant remains of Ammonoidea preserved with their jaws, both in situ and isolated. This is important because previously, the jaws of only one of the main Devonian ammonoid clades had been found (Frasnian Gephuroceratina). Here, we describe four types of jaws of which two could be assigned confidently to the Order Clymeniida and to the Suborder Tornoceratina. These findings imply that chitinous normal‐type jaws were likely to have already been present at the origin of the whole clade Ammonoidea, i.e. in the early Emsian (or earlier). Vertebrate jaws evolved prior to the Early Devonian origin of ammonoids. The temporal succession of evolutionary events suggests that it could have been the indirect positive selection pressure towards strong (and thus preservable) jaws since defensive structures of potential prey animals would otherwise have made them inaccessible to jawless predators in the course of the mid‐Palaeozoic marine revolution. In this respect, our findings reflect the macroecological changes that occurred in the Devonian. [Correction added on 28 July 2016 after first online publication: In the Abstract, the sentence “Vertebrate jaws probably … in the Early Devonian” was amended]     

A unique skeletal microstructure of the deep‐sea micrabaciid scleractinian corals

Micrabaciids are solitary, exclusively azooxanthellate deep‐sea corals belonging to one of the deepest‐living (up to 5,000 m) scleractinian representatives. All modern micrabaciid taxa (genera: Letepsammia, Rhombopsammia, Stephanophyllia, Leptopenus) have a porous and often very fragile skeleton consisting of two main microstructural components known also from other scleractinians: rapid accretion deposits and thickening deposits. However, at the microstructural level, the skeletal organization of the micrabaciids is distinctly different from that of other scleractinians. Rapid accretion deposits consist of alternations of superimposed “microcrystalline” (micrometer‐sized aggregates of nodular nanodomains) and fibrous zones. In contrast to all shallow‐water and sympatric deep‐water corals so far described, the thickening deposits of micrabaciids are composed of irregular meshwork of short (1–2 μm) and extremely thin (ca. 100–300 nm) fibers organized into small, chip‐like bundles (ca. 1–2 μm thick). Longer axes of fiber bundles are usually subparallel to the skeletal surfaces and oriented variably in this plane. The unique microstructural organization of the micrabaciid skeleton is consistent with their monophyletic status based on macromorphological and molecular data, and points to a diversity of organic matrix‐mediated biomineralization strategies in Scleractinia. J. Morphol.,2011. © 2010 Wiley‐Liss, Inc.     

Characterization of sea urchin primary mesenchyme cells and spicules during biomineralization in vitro

An in vitro culture system for primary mesenchyme cells of the sea urchin embryo has been used to study the cellular characteristics of skeletal spicule formation. As judged initially by light microscopy, these cells attached to plastic substrata, migrated and fused to form syncytia in which mineral deposits accumulated in the cell bodies and in specialized filopodial templates. Subsequent examination by scanning electron microscopy revealed that the cell bodies and the filopodia and lamellipodia formed spatial associations similar to those seen in the embryo and indicated that the spicule was surrounded by a membrane-limited sheath derived by fusion of the filopodia. The spicules were dissolved from living or fixed cells by a chelator of divalent cations or by lowering the pH of the medium. However, granular deposits found in the cell bodies appeared relatively refractory to such treatments, indicating that they were inaccessible to agents that dissolved the spicules. Use of rapid freezing and an anhydrous fixative to preserve the syncytia for transmission electron microscopy and X-ray microprobe analysis, indicated that electron-dense deposits in the cell bodies contain elements (Ca, Mg and S) common to the spicule. Examination of the spicule cavity after dissolution of the spicule mineral revealed openings in the filopodia-derived sheath, coated pits within the limiting membrane and a residual matrix that stained with ruthenium red. Concanavalin A--gold applied exogenously entered the spicule cavity and bound to matrix glycoproteins. Based on these observations, we conclude that components of the spicule initially are sequestered intracellularly and that spicule elongation occurs in an extracellular cavity. Ca2+ and associated glycoconjugates may be routed in this cavity via a secretory pathway.     

Forest Modification Affects Diversity (But Not Dynamics) of Speciose Tropical Pyraloid Moth Communities

We studied temporal and spatial dynamics of extremely diverse moth ensembles (Lepidoptera: Pyraloidea) along a gradient of forest disturbance ranging from undisturbed primary tropical rain forest to different kinds of modified forest and open cultivated land at the margin of Mount Kinabalu National Park (Sabah, East Malaysia). We sampled moths by light trapping during two periods (March‐May and August‐September 1997). We collected a total of 7724 individuals representing 680 species during 78 light‐trapping nights at six study sites. Species diversity (Fisher's α) of ensembles in undisturbed primary forest was distinctly higher than in disturbed or secondary forest. More pyraloid moths were attracted in undisturbed primary forest. Samples from disturbed primary or old‐growth secondary forest were statistically indistinguishable from the undisturbed primary forest ensemble in regard to species composition. Thus, pyraloid ensembles from disturbed forest with tall trees remaining appeared to represent impoverished subsets of the undisturbed primary forest community. The more heavily disturbed sites had a distinct fauna and showed a stronger faunal differentiation among each other. Four species of the genus Eoophyla, in which aquatic larvae feed on algae in fast‐running streams benefited prominently from forest disturbance. Temporal variation of ensembles was remarkably concordant across the disturbance gradient. Relative abundance variation of the commonest species was identical at all sites. Overall, pyraloid moths responded more sensitively to anthropogenic habitat alteration than most other moth taxa studied thus far in tropical regions and allowed for an analysis of diversity patterns at a high temporal resolution.     

Fruit,Minerals, and Forest Elephant Trails: Do All Roads Lead to Rome?

Tropical forests are among the most heterogeneous environments on earth, and food resources for many animals are patchy both in time and space. In Africa's equatorial forest, permanent trails created and maintained by forest elephants are conspicuous features. Trails may be several meters wide and continue for tens of kilometers. Speculation on which resources determine the distribution of trails has identified fruit, browse, and mineral deposits as candidates. In this study, the relationships between these habitat variables and elephant trails were investigated. The size of individual trails and the density of the trail system increased dramatically with proximity to mineral deposits. Fruit tree basal area decreased with perpendicular distance from trails, while that of non‐fruit trees did not. Fruit tree abundance and basal area were significantly higher on trail intersections than random sites and increased with intersection size. No relationship was found between monocotyledon browse abundance and elephant trail system characteristics. Clumped resources, which are at least partially reliable, provide a high nutritional payback, and are not rapidly depleted and can thus be visited repeatedly, appear to influence permanent trail formation by forest elephants. Permanent trails may allow naive individuals or those with imperfect knowledge to locate and acquire important resources.     

Evaluation de l’état diagénétique de tests de Mollusques du Pléistocène de la Mer Caspienne

A microstructural examination of some molluscan shells (bivalves and gastropods) collected in Pleistocene levels of the Kraynovka core (north-western coast of the Caspian Sea) shows that the shells are altered: exfoliated shell layers, abundant superficial cavities, disappearance of the organic matrix … Although the microstructures are apparent, chemical analyses show high Si, Al, K and Fe contents. These enrichments lack after a light etching of the shells. Very thin infiltrations and/or secondary deposits are present on the shells, without any structural or mineralogical changes in the hard parts. Shells are aragonitic. Alterations in these shells can be detected only by microstructural observations related to localized chemical analysis.     

Palaeoenvironmental significance of cool‐water microbialites in the Darriwilian (Middle Ordovician) of Sweden

Well‐developed oncoids and centimetre‐sized stromatolites are reported for the first time from the Darriwilian (Middle Ordovician) cool‐water ‘orthoceratite limestone’ at Kinnekulle, Västergötland, Sweden. The characteristics and stratigraphical distribution of these microbialites show an apparent relationship to fluctuations in relative sea level. The most abundant and well‐developed oncoids occur in stratigraphical intervals that are characterized by notable sea‐level lowstands. Stromatolites, which share many compositional characteristics with the oncoids, are essentially confined to a single bed associated with an especially prominent lowstand. Stromatolite‐like lamination also occurs in the uppermost part of the studied succession, but this feature may be of abiogenic origin. The microbialites appear to be originally calcareous, but synsedimentary iron‐ and/or phosphate‐enriched laminae are conspicuous, and secondary substitution by coarse calcite and barite is common. Iron staining is most prominent in poorly preserved specimens. Diagenesis has occluded the identity of the producers of these microbialites, but characteristics of associated endolithic borings suggest that they were formed in photic waters. The laminated fabrics of the documented microbialites record a depositional environment sensitive to high‐frequency environmental change. Most significantly, the microbialites have provided important information about the depositional environment of their enigmatic host limestone, and the collective observations challenge the notion that the studied strata were deposited in a deep shelf to basinal environment – rather, it appears that they are to a large extent, shallow‐water deposits, formed in waters only a few tens of metres deep.     

Abbreviation of larval development and extension of brood care as key features of the evolution of freshwater Decapoda

The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life‐history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean‐type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico‐chemical factors and phytoplankton availability in freshwater habitats. These life‐history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r‐ to K‐strategy in freshwater decapods are traded‐off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio‐temporal alteration of their socio‐ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs.     

Enrichment of metals in the jaws of fossil and extant polychaetes - distribution and function

Jawed polychaete annelids are successful in modern oceans, just as they were in early Palaeozoic oceans: the fossil evidence bears witness to abundant and taxonomically diverse faunas. The jaws are composed of sclerotized proteins and were used for grasping in sediment or capturing prey and therefore needed to be resistant to wear. A nuclear microprobe, Particle-Induced X-ray Emission (PIXE) and Scanning Transmission Ion Microscopy (STIM) techniques revealed an enrichment of metals, commonly Zn, Fe and Cu, concentrated mainly at the tips or delicate parts of the jaws. This suggests that accumulation was regulated by the animal and that these elements had functional significance. Similar enrichment was detected in the jaws of Recent Polychaeta and has also been reported in stress-related, 'tool-like' exoskeletal structures of other animal groups, including arthropods, chaetognaths and molluscs.     

The kinetics of siderophore‐mediated olivine dissolution

Silicate minerals represent an important reservoir of nutrients at Earth's surface and a source of alkalinity that modulates long‐term geochemical cycles. Due to the slow kinetics of primary silicate mineral dissolution and the potential for nutrient immobilization by secondary mineral precipitation, the bioavailability of many silicate‐bound nutrients may be limited by the ability of micro‐organisms to actively scavenge these nutrients via redox alteration and/or organic ligand production. In this study, we use targeted laboratory experiments with olivine and the siderophore deferoxamine B to explore how microbial ligands affect nutrient (Fe) release and the overall rate of mineral dissolution. Our results show that olivine dissolution rates are accelerated in the presence of micromolar concentrations of deferoxamine B. Based on the non‐linear decrease in rates with time and formation of a Fe³⁺‐ligand complex, we attribute this acceleration in dissolution rates to the removal of an oxidized surface coating that forms during the dissolution of olivine at circum‐neutral pH in the presence of O₂ and the absence of organic ligands. While increases in dissolution rates are observed with micromolar concentrations of siderophores, it remains unclear whether such conditions could be realized in natural environments due to the strong physiological control on microbial siderophore production. So, to contextualize our experimental results, we also developed a feedback model, which considers how microbial physiology and ligand‐promoted mineral dissolution kinetics interact to control the extent of biotic enhancement of dissolution rates expected for different environments. The model predicts that physiological feedbacks severely limit the extent to which dissolution rates may be enhanced by microbial activity, though the rate of physical transport modulates this limitation.     

Does the morphology of animal foraging pits influence secondary seed dispersal by ants?

Secondary seed dispersal by ants (myrmecochory) is an important process in semi‐arid environments where seeds are transported from the soil surface to an ant nest. Microsites from which ants often remove seeds are the small pits and depressions made by native and exotic animals that forage in the soil. Previous studies have demonstrated greater seed retention in the pits of native than exotic animals, but little is known about how biotic factors such as secondary seed dispersal by ants affect seed removal and therefore retention in these foraging pits. We used an experimental approach to examine how the morphology of burrowing bettong (Bettongia lesueur), greater bilby (Macrotis lagotis), short‐beaked echidna (Tachyglossus aculeatus) and European rabbit (Oryctolagus cuniculus) foraging pits and ant body size influenced ant locomotion and seed removal from pits along an aridity gradient. Ants took 3.7‐times longer to emerge from echidna pits (19.6 s) and six‐times longer to emerge from bettong pits (30.5 s) than from rabbit pits (5.2 s), resulting in lower seed removal from bettong pits than other pit types. Fewer seeds were removed from pits when cages were used to exclude large body‐sized (>2 mm) ants. Few seeds were removed from the pits or surface up to aridity values of 0.5 (humid and dry sub‐humid), but removal increased rapidly in semi‐arid and arid zones. Our study demonstrates that mammal foraging pit morphology significantly affects ant locomotion, the ability of ants to retrieve seeds, and therefore the likelihood that seeds will be retained within foraging pits.