The origins of graptolites and other pterobranchs: a journey from ‘Polyzoa’

The graptolites, known only from fossils, have been convincingly allied to the pterobranch hemichordates, a group of tiny, mostly colonial marine invertebrates bearing feeding arms. The phylogenetic position of pterobranchs has been subject to debate and revision for over a century. Their colonial lifestyle and feeding arms were originally seen as evidence placing them among the bryozoans, until later and more careful anatomical studies revealed more characters in common with acorn worms. Pterobranchs and acorn worms are now grouped as the phylum Hemichordata. For many decades, it was thought that pterobranchs were closer to the ancestral form of hemichordates, particularly because ‘lophophorate’ invertebrates also possess feeding arms, notably the phoronids and bryozoans, as do crinoid echinoderms. This traditional view has been challenged by recent molecular evidence. First, there is strong molecular evidence to indicate that lophophorates are very distant from hemichordates and echinoderms, in a different major branch of the animal phylogenetic tree. Therefore, similarities between the feeding structures must be due to convergent evolution. Second, there is strong evidence that hemichordates and echinoderms form a clade (Ambulacraria) within the deuterostomes, rather than hemichordates being closer to chordates. Third, there is weaker evidence that pterobranchs may be derived from acorn worms, and hence that the vermiform body plan may be ancestral within hemichordates. This suggestion warrants further testing. Here we review the evidence for these conclusions, highlight strengths and weaknesses in the data and analyses, and consider the implications for the origins of pterobranchs and graptolites.     

Population structure of graptolite assemblages

Graptolite rhabdosomes display a diverse suite of morphologies. The range of morphotypes present within most moderate- to high-diversity assemblages from the Ordovician and Silurian is similar, despite the different taxonomic composition of the faunas at different times. Survivorship analyses of graptolite faunas from the Ordovician and Silurian demonstrate strong similarities in the mortality rates of unrelated graptolites of similar functional morphology. They also show a strong correlation between decreasing mortality rates among more mature colonies with increasing rhabdosome complexity. This similarity in both functional morphology and life history of graptolites suggests that they lived within a very stable planktic community structure.     

Discovery of Anticostia uniformis from the Xiazhen Formation at Zhuzhai,South China and its stratigraphic implication

The Xiazhen Formation is an Upper Ordovician lithostratigraphic unit in the Jiangshan-Changshan-Yushan (JCY) area, which contains series of Late Ordovician reef successions. The reef successions of the Xiazhen Formation at Zhuzhai are critical for evaluation of the Late Ordovician marine diversity and palaeoecology. However, their age has long been uncertain and generally is regarded as of upper Katian, based on the occurrences of shelly fossils and correlation with the stratigraphic equivalent Changwu Formation. The newly discovered graptolite species Anticostia uniformis, in the Xiazhen Formation, together with the combined evidence of brachiopods and sedimentology, indicates an age range for the graptolite locality from the Dicellograptus complanatus Biozone to the Diceratograptus mirus Subzone of late Katian, but the graptolites do not rule out the possibility that it is Hirnantian.     

Shell bone histology indicates terrestrial palaeoecology of basal turtles

The palaeoecology of basal turtles from the Late Triassic was classically viewed as being semi-aquatic, similar to the lifestyle of modern snapping turtles. Lately, this view was questioned based on limb bone proportions, and a terrestrial palaeoecology was suggested for the turtle stem. Here, we present independent shell bone microstructural evidence for a terrestrial habitat of the oldest and basal most well-known turtles, i.e. the Upper Triassic Proterochersis robusta and Proganochelys quenstedti. Comparison of their shell bone histology with that of extant turtles preferring either aquatic habitats or terrestrial habitats clearly reveals congruence with terrestrial turtle taxa. Similarities in the shell bones of these turtles are a diploe structure with well-developed external and internal cortices, weak vascularization of the compact bone layers and a dense nature of the interior cancellous bone with overall short trabeculae. On the other hand, 'aquatic' turtles tend to reduce cortical bone layers, while increasing overall vascularization of the bone tissue. In contrast to the study of limb bone proportions, the present study is independent from the uncommon preservation of appendicular skeletal elements in fossil turtles, enabling the palaeoecological study of a much broader range of incompletely known turtle taxa in the fossil record.     

Silurian carbonate platforms and extinction events—ecosystem changes exemplified from Gotland, Sweden

Recent and ancient carbonate platforms are major marine ecosystems, built by various carbonate-secreting organisms with different sensitivity for environmental change. For this reason, carbonate platforms are excellent sensors for changes in contemporaneous marine environments. A variety of ecosystem changes in carbonate platforms have previously been recognised in the aftermath of mass extinction events. This paper addresses how two Silurian extinction events among graptolites, conodonts, and pentamerid brachiopods can be related to changes in the style of carbonate production and general evolution of low latitude carbonate platforms in a similar way as previously reported from the major five mass extinctions of the Phanerozoic. Strata formed on Gotland during the Mulde and Lau events share remarkably many similarities but are strikingly different in composition compared to other strata on the island. The event-related strata is characterised by the sudden appearance of widespread oolites, deviating reef composition, flat-pebble conglomerates, abundant micro- and macro-oncoids, stromatolites, and other microbial facies suggesting decreased bioturbation levels in contemporaneous shelf seas. Importantly, these changes can be tied to high-resolution biostratigraphic frameworks and global stable isotope excursions. The anomalous intervals may therefore be searched for elsewhere in order to test their regional or global significance.     

Evolution of filamentous plant pathogens: gene exchange across eukaryotic kingdoms

Filamentous fungi and oomycetes are eukaryotic microorganisms that grow by producing networks of thread-like hyphae, which secrete enzymes to break down complex nutrients, such as wood and plant material, and recover the resulting simple sugars and amino acids by osmotrophy. These organisms are extremely similar in both appearance and lifestyle and include some of the most economically important plant pathogens . However, the morphological similarity of fungi and oomycetes is misleading because they represent some of the most distantly related eukaryote evolutionary groupings, and their shared osmotrophic growth habit is interpreted as being the result of convergent evolution . The fungi branch with the animals, whereas the oomycetes branch with photosynthetic algae as part of the Chromalveolata . In this report, we provide strong phylogenetic evidence that multiple horizontal gene transfers (HGT) have occurred from filamentous ascomycete fungi to the distantly related oomycetes. We also present evidence that a subset of the associated gene families was initially the product of prokaryote-to-fungi HGT. The predicted functions of the gene products associated with fungi-to-oomycete HGT suggest that this process has played a significant role in the evolution of the osmotrophic, filamentous lifestyle on two separate branches of the eukaryote tree.     

Ecology of a Late Silurian fauna of graptolites and associated organisms

The Ludlow Series of Wales and the Welsh Borderland represents an ocean-bordering basin and shelf which received a shoaling sequence of sediments in the late Silurian. Graptolites grade from highest diversity and density in basin areas to lowest diversity and density on the nearshore shelf. By analogy with modern zooplankton, this distribution is attributed to differentiation of surface water masses over basin and shelf. During Ludlow time, the center of graptolite abundance shifted northward, indicating a restriction and seaward movement of the basin water mass. Small nektic cephalopods and phyllocarids parallel distribution trends of the graptolites, as does a fauna of small bivalves and brachiopods which may have lived on floating plants. The water mass model accounts for most distributional patterns of pelagic organisms in this local area, and has broader application to the distribution and evolution of graptolites.     

Linking taxonomical and functional biodiversity of saproxylic fungi and beetles in broad‐leaved forests in southern Italy with varying management histories

Abstract

The fundamental ecological significance of deadwood decomposition in forests has been highlighted in several reviews, some conclusions regarding silviculture being drawn. Old‐growth forests are natural centres of biodiversity. Saproxylic fungi and beetles, which are vital components of these ecosystems, occupy a variety of spatial and trophic niches. Fungal and beetle diversity on coarse woody debris (CWD) was analysed in 36 forest sites in the Cilento and Vallo di Diano National Park, Italy. The data were analysed by DCA and Spearman’s rank correlation. The results provide empirical evidence of the existence of a pattern of joint colonization of the woody substrate by fungi and beetles, which includes an assemblage of reciprocal trophic roles within fungal/beetle communities. These organisms act together to form a dynamic taxonomical and functional ecosystem component within the complex set of processes involved in wood decay. The variables most predictive of correlations between management‐related structural attributes and fungal/beetle species richness and their trophic roles for old‐growth forest are: number of logs, number of decay classes and CWD total volume. Deadwood spatio‐temporal continuity should be the main objective of forest planning to stop the loss of saproxylic fungal and insect biodiversity.     

Feinstrukturen und Verwandtschaftsbeziehungen der Graptolithen

Pterobranchs and graptolites exhibit essentially the same skeletal structure, namely a primary skeleton composed of regularly stacked bands and a later thickening made up of irregulary arranged, thinner elements. Both parts of the skeleton were most likely secreted via the individuals' cephalic discs. The most notable structural difference between the pterobranchs and graptolites can be seen in the secondary skeletal layers. In the graptolites it is made up of closely packed parallel fibers. The long distal thread (nema) of the planktonic graptolites is constructed and probably also secreted in a manner similar to that in which the skeleton is formed. Some sessile graptolites have more in common with recent pterobranchs than “normal” graptolites. The Crustoidea seem to be particulary well suited as model for the transition from pterobranch to graptolite structure. The minute structures of various pterobranchs and graptolites are depicted here, arranged approximately according to their probable evolution.     

Lower Devonian biostratigraphic correlation in Eastern Australia and Western North America

Savage, N. M.: Lower Devonian biostratigraphic correlation in Eastern Australia and Western North America.
Correlation of Lower Devonian marine strata of Eastern Australia and Western North America can be attempted using several fossil groups. In general the faunas are similar, with many species common to both areas. Graptolites occur infrequently, but are of great value because of their precise zonal significance. Several of these graptolites occur in the classic type sequences of Bohemia but are absent from the Rhineland stages. For this reason, and because of the Bohemian affinities of the shelly faunas, the Bohemian stage names are preferable to the Rhenish names for use in Eastern Australia and Western North America. Cono-donts are less precise index fossils than graptolites, but are considerably more abundant and therefore have greater application. Brachiopods are valuable if viewed as assemblages. In terms of the Rhenish stages, most Eastern Australian and Western North American early Lower Devonian formations appear to have been placed too high. Recent evidence from northern Canada throws new light on the problem of correlating Rhenish and Bohemian classic early Lower Devonian stages.     

PALAEOECOLOGY OF THE GRAPTOLITHINA, AN EXTINCT CLASS OF THE PHYLUM HEMICHORDATA

1. Whatever heirarchical system of classifying graptolites is adopted, perhaps even raising them to the rank of phylum, the hemichordates including Rhabdopleura and Cephalodiscus remain their closest relatives. 2. Benthonic graptolites preceded and outlasted the planktonic graptolites which exhibited spectacular morphological changes related to a change to a holoplanktonic mode of life and a probable hermaphroditism. 3. The resorption of the narrow-end of the larval skeleton (prosicular cauda) enabled the construction by an outer layer of secreting tissue (extrathecal tissue) of a hollow nema, the dark hollow rod which supported gas-filled tissue and which in turn conferred buoyancy on the colony. 4. The nema provided access to the exterior of the colony for extrathecal tissue which began to strengthen the outside of the prosicular and metasicular parts of the larval skeleton with laminated cortical deposits before the first non-sicular individual of the colony was budded. 5. Attachment of the larval stage in those graptolites having a basal disc or ‘roots’ was by the first-formed extrathecal tissue through a resorbed cauda. 6. Initial attachment of the larval stage in certain encrusting graptolites such as Idiotubus may have been by a larval individual lacking any scleroprotein periderm as a skeletal sheath. 7. After initial attachment the extrathecal tissue continued to secrete additional layers of cortical tissue mostly for the purposes of strengthening the colony. 8. Feeding in graptolites was by ciliated lophophore often positioned so as to take maximum advantage of currents flowing from the dorsal to the ventral side of the colony, for example in Dictyonema and Monograptus. 9. The main function of the nema, particularly of those nemata bearing vanes, was as a support for vacuolated tissue which imparted a holoplanktonic mode of life to planktonic (sensu Zato) graptolites. 10. Attachment of colonies (rhabdosomes) as groups of colonies (synrhabdosomes) was by the extrathecal tissue issuing from the tips of the nemata: such associations were probably sexual rather than for reasons of buoyancy. 11. Attachment of planktonic graptolites to floating algal fronds is an unnecessary hypothesis. Although an undoubted occurrence of graptolites in rocks containing large quantities of carbonaceous matter is beyond dispute, the plant or animal nature of this material has never been established. A symbiotic relationship of planktonic graptolites with a marine, formless alga, perhaps involving the extrathecal tissue, remains a possibility. 12. Although different species may have lived at different depths, the full vertical range of the holoplanktonic graptolites was probably small. The evidence advanced for depth zonation is considered inadequate. 13. Planktonic graptolites were essentially tropical to temperate in distribution with the bulk of the species and individuals in the former environment. 14. Automobility of graptolite rhabdosomes was an unlikely mechanism and does not readily account for the morphology and distribution of the graptolites. 15. Most planktonic graptolites were suspended beneath a nema coated in extrathecal, vacuolated (gas-filled) tissue: changes of position in the water were by passive response to ocean currents. 16. The nature of the graptolite zooid is considered unsolved, although it may have been essentially like that of the extant Rhabdopleura in having paired lophophores. 17. It is possible that a modified pre-oral lobe was capable of secreting both fusellar (inner) and cortical (outer) layers of the periderm. 18. The extrathecal tissue itself would in that case have been derived both from the nemal tube and the thecal individuals.     

Closing the gap between plant ecology and Quaternary palaeoecology

Ecology and Quaternary palaeoecology have largely developed as parallel disciplines. Although both pursue related questions, information exchange is often hampered by particularities of the palaeoecological data and a communication gap has been perceived between the disciplines. Based on selected topics and developments mainly in Quaternary palaeoecology, we show that both disciplines have converged somewhat during recent years, while we still see untapped potential for closer interactions. Macroecology is probably the discipline that most easily combines different time scales and where co‐operations between palaeoecologists, geneticists and vegetation modellers have been inspiring. Quantitative vegetation reconstructions provide robust estimates of tree composition and land cover at different spatial scales, suitable for testing hypotheses about long‐term vegetation changes or as quantitative background data in studies on contemporary vegetation patterns. Palaeo data also hold yet unexplored potential to study the drivers of long‐term diversity, and aspects of functional diversity may facilitate comparisons between continents and over glacial–interglacial cycles.     

Out of the woods: forest biotechnology enters the genomic era

Trees represent a unique life form of upmost importance for mankind, as these organisms have developed a perennial lifestyle that produces the majority of terrestrial biomass. The difference between trees and annual plants is one of the main arguments behind the effort to sequence the entire genome of the poplar tree. This initiative is being backed up with a full-scale functional genomics effort on trees that will set a completely new agenda for forest research.     

白垩纪中期缅甸琥珀昆虫行为生态学研究进展

缅甸琥珀生物群产自距今约98.8Ma的白垩纪中期,该生物群是世界上物种多样性很高的琥珀生物群之一,为了解白垩纪中期生物多样性和古生态提供了重要窗口。文中以近年来缅甸琥珀地层学、琥珀生物学研究为依据,总结缅甸琥珀形成环境,并对缅甸琥珀揭示的昆虫与植物的协同演化、昆虫的捕食、社会性证据、寄生、求偶和结构色等方面的研究结果进行总结,以期较全面地综述缅甸琥珀的古环境和昆虫行为生态学特征。     

Decay and composition of the hemichordate Rhabdopleura: implications for the taphonomy of graptolites

Although the graptolites lacked biomineralised tissue, their skeletons are abundantly preserved in deeper-water mudstones. Decay experiments and observations on the closely related living hemichordate Rhabdopleura demonstrate that the periderm and stolon are highly resistant to decay, remaining intact for months, whereas the zooids are unrecognizable within days. The extreme rarity of the preservation of traces of the zooids in graptoloids reflects their planktic lifestyle; the zooids had normally decayed before burial. Curie-point-gas-chromatography (Py-GC) and Curie-point-gas-chromatography-mass spectrometry (Py-GC-MS) of the periderm of Rhabdopleura confirms that proteinaceous organic matter is a major constituent. Ultrastructurally preserved graptolite periderm (Ordovician, Oklahoma; Silurian, Arctic Canada), on the other hand, is a highly altered kerogen-like substance rich in aliphatic biomacromolecules. The composition of the preserved graptolite periderm reflects diagenetic replacement by components probably mainly derived from algal cell walls.     

Medical Application of Synthetic Phospholipids as Liposomes and Drugs

Abstract

Synthetic phospholipids or analogues having well-defined purities are useful and stable carriers of drugs for a variety of medical therapies. Synthetic phospholipids possess the additional quality of being powerful drugs in the therapy of cancer and protozoaen diseases. In the last decade we have developed several different strategies for the large scale synthesis of phospholipids (50 to 100 kg). Here we describe methods involving the recombination of nonpolar and polar regions of phospholipid molecules which permit the creation of an unlimited variety of well-defined and characterizable phospholipids and of analogues. As an example for medical application we describe hexadecylphosphocholine (HePC) which in 1992 was approved and registered as a drug by the German Bundesgesundheitsamt. Recent studies have provided compelling evidence that erucylphosphocholine (ErPC) is an even more selective drug than HePC for systemic i.v. treatment of cancer.     

Role of linkers in communication between protein modules

Multidomain proteins are common in a variety of cellular processes. Their domains are interconnected through short stretches of amino acid residues referred to as linkers. Recent studies on many systems have provided compelling evidence that linkers are more than simple covalent connectors. They also perform the important task of establishing communication between the different functional modules that exist within such proteins.     

Intramolecular Telomeric G-Quadruplexes Dramatically Inhibit DNA Synthesis by Replicative and Translesion Polymerases,Revealing their Potential to Lead to Genetic Change

Recent research indicates that hundreds of thousands of G-rich sequences within the human genome have the potential to form secondary structures known as G-quadruplexes. Telomeric regions, consisting of long arrays of TTAGGG/AATCCC repeats, are among the most likely areas in which these structures might form. Since G-quadruplexes assemble from certain G-rich single-stranded sequences, they might arise when duplex DNA is unwound such as during replication. Coincidentally, these bulky structures when present in the DNA template might also hinder the action of DNA polymerases. In this study, single-stranded telomeric templates with the potential to form G-quadruplexes were examined for their effects on a variety of replicative and translesion DNA polymerases from humans and lower organisms. Our results demonstrate that single-stranded templates containing four telomeric GGG runs fold into intramolecular G-quadruplex structures. These intramolecular G quadruplexes are somewhat dynamic in nature and stabilized by increasing KCl concentrations and decreasing temperatures. Furthermore, the presence of these intramolecular G-quadruplexes in the template dramatically inhibits DNA synthesis by various DNA polymerases, including the human polymerase δ employed during lagging strand replication of G-rich telomeric strands and several human translesion DNA polymerases potentially recruited to sites of replication blockage. Notably, misincorporation of nucleotides is observed when certain translesion polymerases are employed on substrates containing intramolecular G-quadruplexes, as is extension of the resulting mismatched base pairs upon dynamic unfolding of this secondary structure. These findings reveal the potential for blockage of DNA replication and genetic changes related to sequences capable of forming intramolecular G-quadruplexes.     

Actin on disease--studying the pathobiology of cell motility using Dictyostelium discoideum

The actin cytoskeleton in eukaryotic cells provides cell structure and organisation, and allows cells to generate forces against membranes. As such it is a central component of a variety of cellular structures involved in cell motility, cytokinesis and vesicle trafficking. In multicellular organisms these processes contribute towards embryonic development and effective functioning of cells of all types, most obviously rapidly moving cells like lymphocytes. Actin also defines and maintains the architecture of complex structures such as neuronal synapses and stereocillia, and is required for basic housekeeping tasks within the cell. It is therefore not surprising that misregulation of the actin cytoskeleton can cause a variety of disease pathologies, including compromised immunity, neurodegeneration, and cancer spread. Dictyostelium discoideum has long been used as a tool for dissecting the mechanisms by which eukaryotic cells migrate and chemotax, and recently it has gained precedence as a model organism for studying the roles of conserved pathways in disease processes. Dictyostelium's unusual lifestyle, positioned between unicellular and multicellular organisms, combined with ease of handling and strong conservation of actin regulatory machinery with higher animals, make it ideally suited for studying actin-related diseases. Here we address how research in Dictyostelium has contributed to our understanding of immune deficiencies and neurological defects in humans, and briefly discuss its future prospects for furthering our understanding of neurodegenerative disorders.     

Phylogeny and palaeoecology of Polyommatus blue butterflies show Beringia was a climate-regulated gateway to the New World

Transcontinental dispersals by organisms usually represent improbable events that constitute a major challenge for biogeographers. By integrating molecular phylogeny, historical biogeography and palaeoecology, we test a bold hypothesis proposed by Vladimir Nabokov regarding the origin of Neotropical Polyommatus blue butterflies, and show that Beringia has served as a biological corridor for the dispersal of these insects from Asia into the New World. We present a novel method to estimate ancestral temperature tolerances using distribution range limits of extant organisms, and find that climatic conditions in Beringia acted as a decisive filter in determining which taxa crossed into the New World during five separate invasions over the past 11 Myr. Our results reveal a marked effect of the Miocene-Pleistocene global cooling, and demonstrate that palaeoclimatic conditions left a strong signal on the ecology of present-day taxa in the New World. The phylogenetic conservatism in thermal tolerances that we have identified may permit the reconstruction of the palaeoecology of ancestral organisms, especially mobile taxa that can easily escape from hostile environments rather than adapt to them.