The Devonian land plant Protosalvinia

Gray, Jane&Boucot, ArthurJ. 197901 15: The Devonian land plant Protosalvinia. Lethaia . Vol. 12, pp. 57–63. Oslo. ISSN 0024–1164.
Protosalvinia (=Foerstia ) shows a number of morphological features which suggest that it was a land plant, possibly an emergent aquatic. Certain kinds of biochemical data, as presently interpreted, also support the morphological evidence. The weight of evidence supports neither a fucoid nor even an algal attribution for this enigmatic plant. Protosalvinia should be treated as the representative of a separate group of land plants, as previously advocated. Tracheid-like tubes with internal spiral thickenings appear on the basis of direct comparison to be morphologically identical to those of nematophytalean origin. They may have functioned in a capacity similar to the tracheids of vascular plants. The Nematophytales are non-marine plants of uncertain taxonomic position.     

The nature of pre-Devonian tracheid-like tubes

In the discussion on early vascular land plants an important part is played by different organic microfossils. One category comprises tube-like objects of pre-Devonian age, called tracheid-like tubes. Recognition of the taxonomic affinity of these microfossils is very important because tracheids are one of the fundamental elements of the xylem and are treated as a hallmark of the vascular plants. Banks (1975) was of the opinion that the tubes previously described as tracheid-like were of animal rather than plant origin. He suggested also that tracheid-like tubes presumably originated from graptolites or chi-tinozoans. Gray & Boucot (1977:166), following personal communications of A. Urbanek, W. B. N. Berry and K. M. Towe, stated that there was little likelihood that the tubes of the graptolites and tracheid-like tubes 'could be confused or that our tracheid-like tubes could have originated from graptolites'. Gray & Boucot claimed that tracheid-like tubes had a plant source.     

Evidence of land plant affinity for the Devonian fossil Protosalvinia (Foerstia)

The Devonian plant fossil Protosalvinia (Foerstia) has been examined by solid-state ¹³C nuclear magnetic resonance spectroscopy (NMR) and pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS). Results of these studies reveal that the chemical structure of Protosalvinia is remarkably similar to that of coalified wood. A well-defined phenolic carbon peak in the NMR spectra and the appearance of phenol and alkylated phenols in pyrolysis products are clearly indicative of lignin-like compounds. These data represent significant new information on the chemical nature of Protosalvinia and provide the first substantial organic geochemical evidence for land plant affinity. ▭ Protosalvinia, Foerstia, Upper Devonian, biostratigraphy, carbon-13 NMR, PY-GC-MS, lignin.     

Biogeography of the changing Phanerozoic world

Practically each one of the chapters in the book Historical Biogeography, Plate Tectonics, and the Changing Environment (Gray & Boucot 1979) would have deserved to be channelled to readers in the form of articles in periodicals, to be efficiently circulated among the most concerned specialists as offprints and to be abstracted and indexed by the secondary information services.     

Role of fungi in marine ecosystems

Marine fungi are an ecological rather than a taxonomic group and comprise an estimated 1500 species, excluding those that form lichens. They occur in most marine habitats and generally have a pantropical or pantemperate distribution. Marine fungi are major decomposers of woody and herbaceous substrates in marine ecosystems. Their importance lies in their ability to aggressively degrade lignocellulose. They may be important in the degradation of dead animals and animal parts. Marine fungi are important pathogens of plants and animals and also form symbiotic relationships with other organisms. The effect of disturbances on marine fungi is poorly investigated. Keystone marine species may exist, especially in mutualistic symbioses. However, as many saprophytes appear to carry out the same function simultaneously, they may be functionally redundant. The need for a concerted effort to investigate the biodiversity and role of marine fungi globally and on as many substrata as possible is presented.     

Observations on the ultrastructure, mode of infectivity and host range of xenosomes

Xenosomes are infectious bacterial-like symbionts that reside in the cytoplasm of certain strains of the marine hymenostome ciliate, Parauronema acutum. Ultrastructural studies of xenosomes of one such strain, P. acutum, 110/3, reveal that the particles possess a cell envelope whose outer membrane resembles that of Gramnegative bacteria. Unlike typical Gram-negative bacteria, however, xenosomes possess a much reduced ‘murein’ layer. The DNA is not located in a ‘nucleosome’ or ‘nuclear body’ as it is in most bacteria, but may be found dispersed throughout the internal contents of the particle. Xenosomes are capable of infecting several strains of Parauronema spp. and at least one other ciliate of marine origin, Miamiensis avidus, Ma. They are also capable of inhibiting the growth of certain marine ciliate strains, particularly those of the genus Uronema. Infectivity may be related to the fact that the particles are motile. When released from the host protozoan, they may be seen spinning or darting rapidly, suggesting the presence of a motile apparatus. Phosphotungstic acid staining of the released particles show that they do, indeed, possess bacterial-like flagella. The average number of flagella per particle observed was two, although some particles were seen with as many as five. A flagellum may occur at almost any point on the surface of the particle and is characteristically wider near its point of insertion into the cell envelope than it is near its tip. During normal growth in axenic culture, xenosomes are actively released into the ambient medium. Particles, thus released, rapidly lose their capacity to infect susceptible hosts, and this capacity parallels their ability to remain motile.     

黑龙江密山—宝清早泥盆世盾皮鱼类化石

<正>１９９３年,原地矿部沈阳地质矿产研究所苏养正先生将其在黑龙江省东北部密山及宝清下黑台组中采到的５件泥盆纪鱼化石送交王士涛鉴定。经过修理和观察后认为,这些骨片属于盾皮鱼类(Ｐｌａｃｏｄｅｒｍｓ)。这是迄今为止在东北地槽区内首次发现的泥盆纪鱼类化石,具有重要的生物地层学及古动物地理学意义。     

A fully fertile intergeneric hybrid derivative from Argyroxiphium sandwicense SSP. macrocephalum DUBAUTIA MENZIESII(Asteraceae) and its relevance to plant evolution in the Hawaiian Islands

Achenes collected from natural putative F₁ intergeneric hybrids involving Argyroxiphium sandwicense DC. ssp. macrocephalum (A. Gray) Meyrat and Dubautia menziesii (A. Gray) Keck were germinated and grown in cultivation. One of these apparent B₁ hybrids that approached D. menziesii in morphology exhibited greatly increased fertility over the F₁ (79% vs. 9% pollen stainability), and was used as a female parent to generate a B₂ progeny by backcrossing a second time to D. menziesii. The B₂ was surprisingly uniform. One individual that flowered was fully fertile (99% pollen stainability). Its floral and vegetative features were extremely similar to those of the recurrent parent, D. menziesii. Observations suggest that plants of similar origin may exist under natural conditions and that the close relatives, D. platyphylla (A. Gray) Keck and D. dolosa (Degener & Sherff) G. Carr, may have originated from the same or a similar intergeneric hybrid combination. Because many other analogous situations occur in the silversword alliance and elsewhere in the Hawaiian flora, it is concluded that hybridization is an evolutionarily important phenomenon, especially in unstable geological systems. Although the Hawaiian archipelago is a premier example of such instability, continents are not immune to natural perturbations. Therefore, hybridization, as a mechanism that greatly extends the size of gene pools available for recombination, should also be expected to play an important evolutionary role in continental floras.     

A fundamental plant evolutionary problem: the origin of land-plant sporophyte; is a new hypothesis possible?

The origin of the sporophyte in land plants represents a fundamental phase in the plant evolution. Today this subject is controversial and, in my opinion, scarcely considered in our textbooks and journals of botany, in spite of its importance. There are two conflicting theories concerning the origin of the alternating generations in land plants: the "antithetic" and the "homologous" theory. These have never been fully resolved. The antithetic theory maintains that the sporophyte and gametophyte generations are fundamentally dissimilar and that the sporophyte originated in an ancestor organism with haplontic cycle by the zygote dividing mitotically rather than meiotically, and with a developmental pattern not copying the developmental events of the gametophyte. The sporophyte generation was an innovation of critical significance for the land-plant evolution. By contrast, the homologous theory simply stated that a mass of cells forming mitotically from the zygote adopted the same developmental plan of the gametophyte, but giving origin to a diploid sporophyte. In this context, a very important question concerns the possible ancestor or ancestors of the land plants. Considerable evidences at morphological, cytological, ultrastructural, biochemical and, especially, molecular level, strongly suggest that the land plants or Embryophyta (both vascular and non-vascular) evolved from green algal ancestor(s), similar to those belonging to the genus Coleochaete, Chara and Nitella, living today. Their organism is haploid for most of their life cycle, and diploid only in the zygote phase (haplontic cycle). On the contrary, the land plants are characterized by a diplo-haplontic life cycle. Several questions are implied in these theories, and numerous problems remain to be solved, such as, for example, the morphological difference between gametophyte and sporophyte (heteromorphism, already present in the first land plants, the bryophytes), and the strong gap existing between these last with a sporophyte dependent on the gametophyte, and the pteridophytes having the gametophyte and sporophyte generations independent. On the ground of all of the evidences on the ancestors of the land plants, the antithetic theory is considered more plausible than the homologous theory. Unfortunately, no phylogenetic relationship exists between some green algae with diplontic life cycle and the land plants. Otherwise, perhaps, it should be possible to hypothesize another scenario in which to place the origin of the alternating generations of the land plants. In this case, could the gametophyte be formed by gametes produced from the sporophyte, through their mitoses or a delayed fertilization process?     

Plant Proteus: brown algal morphological plasticity and underlying developmental mechanisms

Brown algae are multicellular photosynthetic marine organisms, ubiquitous on rocky intertidal shores at cold and temperate latitudes. Nevertheless, little is known about many aspects of their biology, particularly their development. Given their phylogenetic distance (1.6 billion years) from other plant organisms (land plants, and green and red algae), brown algae harbor a high, as-yet undiscovered diversity of biological mechanisms governing their development. They also show great morphological plasticity, responding to specific environmental constraints, such as sea currents, reduced light availability, grazer attacks, desiccation and UV exposure. Here, we show that brown algal morphogenesis is rather simple and flexible, and review recent genomic data on the cellular and molecular mechanisms known to date that can possibly account for this developmental strategy.     

ACTIN GENE DUPLICATION AND THE EVOLUTION OF MORPHOLOGICAL COMPLEXITY IN LAND PLANTS

Actin is a highly conserved cytoskeletal protein that is a key component of cells. Genes encoding actin occur in single copies in most green algae, in 2–3 copies in bryophytes, and in increasingly more complex gene families in ferns and seed plants. We use the well-resolved phylogenetic frameworks of the Streptophyta as a guide to reconstruct the patterns of actin gene duplication in early diverging land plants. Our working hypothesis is that the origin of novel tissues in the bryophytes (e.g. multicellular sporophyte) may be reflected in the functional diversification of duplicate actin genes in these taxa. Actin is used as a model cytoskeletal protein with the assumption that its evolutionary history represents those of other cytoskeletal elements and the coevolved binding proteins. Here we provide a phylogenetic perspective on the origin of green algal and land plant actin genes and use this information to speculate on the role of plant actin in early plant evolution.     

Origin and evolution of green plants in the light of key evolutionary events

Green plants (Viridiplantae) are ancient photosynthetic organisms that thrive both in aquatic and terrestrial ecosystems, greatly contributing to the changes in global climates and ecosystems. Significant progress has been made toward understanding the origin and evolution of green plants, and plant biologists have arrived at the consensus that green plants first originated in marine deep-water environments and later colonized fresh water and dry land. The origin of green plants, colonization of land by plants and rapid radiation of angiosperms are three key evolutionary events during the long history of green plants. However, the comprehensive understanding of evolutionary features and molecular innovations that enabled green plants to adapt to complex and changeable environments are still limited. Here, we review current knowledge of phylogenetic relationships and divergence times of green plants, and discuss key morphological innovations and distinct drivers in the evolution of green plants. Ultimately, we highlight fundamental questions to advance our understanding of the phenotypic novelty, environmental adaptation, and domestication of green plants.     

Trophic amplification of climate warming

Ecosystems can alternate suddenly between contrasting persistent states due to internal processes or external drivers. It is important to understand the mechanisms by which these shifts occur, especially in exploited ecosystems. There have been several abrupt marine ecosystem shifts attributed either to fishing, recent climate change or a combination of these two drivers. We show that temperature has been an important driver of the trophodynamics of the North Sea, a heavily fished marine ecosystem, for nearly 50 years and that a recent pronounced change in temperature established a new ecosystem dynamic regime through a series of internal mechanisms. Using an end-to-end ecosystem approach that included primary producers, primary, secondary and tertiary consumers, and detritivores, we found that temperature modified the relationships among species through nonlinearities in the ecosystem involving ecological thresholds and trophic amplifications. Trophic amplification provides an alternative mechanism to positive feedback to drive an ecosystem towards a new dynamic regime, which in this case favours jellyfish in the plankton and decapods and detritivores in the benthos. Although overfishing is often held responsible for marine ecosystem degeneration, temperature can clearly bring about similar effects. Our results are relevant to ecosystem-based fisheries management (EBFM), seen as the way forward to manage exploited marine ecosystems.     

Pollen embryogenesis: atavism or totipotency?

Summary The origins of pollen embryogenesis are still in doubt. Totipotency of plant cells has traditionally been put forward as an explanation for this phenomenon but we have found this interpretation to involve some shortcomings. The pollen grain is a highly differentiated structure which should have a very reduced capability of regenerating a whole plant, whereas in some species the induction of androgenesis appears to occur with greater facility than somatic embryogenesis. Furthermore, some microspores seem to have a tendency to morphogenesis and organogenesis; spontaneous androgenesis occurs naturally in various species and many examples also occur of pollen dimorphism. Totipotency would seem to be insufficient to explain androgenesis and we propose that its origin might be found in the phenomenon of atavism. According to studies published on ancestral precursors of pollen, these structures appear to have had high proliferation capacity. The ability to form a multicellular structure from a single haploid cell is shared by the meiocytes of ancestral algae, of the first land plants, and of present-day ferns, which are evolutionarily related to pollen. Atavism is only expressed under certain circumstances, as indeed is androgenesis, normally as a consequence of an environmental stress. Our conclusion is that there is evidence enough to suggest that androgenesis may well be the expression of archaic genes of meiocytes with morphogenic capacity which were naturally expressed in the ancestors of flowering plants.     

Molecular genetic analyses of species boundaries in the sea

The tools of molecular genetics have enormous potential for clarifying the nature and age of species boundaries in marine organisms. Below I summarize the genetic implications of various species concepts, and review the results of recent molecular genetic analyses of species boundaries in marine microbes, plants, invertebrates and vertebrates. Excessive lumping, rather than excessive splitting, characterizes the current systematic situation in many groups. Morphologically similar species are often quite distinct genetically, suggesting that conservative systematic traditions or morphological stasis may be involved. Some reproductively isolated taxa exhibit only small levels of genetic differentiation, however. In these cases, large population sizes, slow rates of molecular evolution, and relatively recent origins may contribute to the difficulty in finding fixed genetic markers associated with barriers to gene exchange. The extent to which hybridization blurs species boundaries of marine organisms remains a subject of real disagreement in some groups (e.g. corals). The ages of recently diverged species are largely unknown; many appear to be older than 3 million years, but snails and fishes provide several examples of more recent divergences. Increasingly sophisticated genetic analyses make it easier to distinguish allopatric taxa, but criteria for recognition at the species level are highly inconsistent across studies. Future molecular genetic analyses should help to resolve many of these issues, particularly if coupled with other biological and paleontological approaches.     

Identification of suitable location to cultivate grape based on disease infestation using multi-criteria decision-making (MCDM) and remote sensing

This study aims to identify suitable regions for grape cultivation and the areas where diseases are likely to occur in Fars Province, Iran. The study employs a multi-criteria decision-making (MCDM) model based on the Analytic Hierarchy Process (AHP) and fuzzy logic methods, taking into account the ecological requirements of grape plants. Fourteen essential parameters for grape cultivation are prepared, and interpolation maps are created for each parameter. Fuzzy maps are generated by defining membership functions, and AHP is utilized to compare and determine the importance of each factor to produce a final map of grape cultivation land suitability. The study reveals that grape cultivation is most suitable in the southern regions of Fars Province. Furthermore, the research identifies the areas where Powdery mildew, Gray mold, and GFLV diseases may occur based on rainfall and temperature levels. The study recommends against grape cultivation in the southern region due to the possibility of these diseases developing. The study employs a highly accurate regression method (R² = 0.968 and F = 0.00001) and principal component analysis (PCA) to determine that land suitability class strongly correlates with Tmin, NDVI, LST, Total disease, Tmean, and RH. By identifying the areas suitable for grape cultivation and where pests may flourish, the necessary management can be implemented to ensure maximum harvest in the best suitable locations for grape planting.     

Heterogeneous genomic molecular clocks in primates

Using data from primates, we show that molecular clocks in sites that have been part of a CpG dinucleotide in recent past (CpG sites) and non-CpG sites are of markedly different nature, reflecting differences in their molecular origins. Notably, single nucleotide substitutions at non-CpG sites show clear generation-time dependency, indicating that most of these substitutions occur by errors during DNA replication. On the other hand, substitutions at CpG sites occur relatively constantly over time, as expected from their primary origin due to methylation. Therefore, molecular clocks are heterogeneous even within a genome. Furthermore, we propose that varying frequencies of CpG dinucleotides in different genomic regions may have contributed significantly to conflicting earlier results on rate constancy of mammalian molecular clock. Our conclusion that different regions of genomes follow different molecular clocks should be considered when inferring divergence times using molecular data and in phylogenetic analysis.     

Tropical freshwater ecotones: their formation,functions and use

Tropical water-terrestrial ecotones play important roles in regulating the flow of materials from and to land and water ecosystems. Ecotones exist where active interactions between two or more adjacent ecosystems occur with the appearance of processes that do not exist in either of the adjacent ecosystems.They occur naturally depending on the hydrological and geomorphological structure of the location. External and internal processes can influence the origin and persistence of ecotones. Ecotones regulate the landscape mosaic, affect energy flow between adjacent systems and intervene in landscape connectivity.The literature on geological and climatic origins of wetlands and open waters, internal influences on their creation and destruction and, finally, their use by society is reviewed.     

中国农业生态系统外来种入侵及其管理现状

农业生态系统极易遭受外来生物入侵。作者根据文献资料和多年工作观察统计出入侵我国农业生态系统的外来生物共计92科175属239种, 其中植物155种, 动物55种, 微生物29种, 植物多为有意引入后逸生, 而动物和微生物则主要是无意引入。外来入侵种发生数量呈现从南到北、从东到西逐渐减少的趋势。这些入侵种中, 来源于美洲的最多(占45.04%), 其次是欧洲(22.90%); 菜地(包括温室大棚)和果园入侵种最多, 分别达64.85%和66.53%, 而半年期的秋熟旱地和夏熟旱地分别占34.31%和23.85%。其中17种外来杂草、10种害虫、7种病原菌为恶性有害生物, 应作为防除的重点目标。目前农业生态系统外来入侵物种的控制以化学防治为主, 但由于长期施用化学农药, 在侵入我国农田的入侵种中, 已有51种在世界不同地区演化出抗药性生物型, 因而需重视生物防治、农业和生态防治以及检疫等的综合应用。今后外来种对农业生态系统的入侵格局、机制和趋势, 入侵途径以及生物入侵和抗药性生物型对农业生态系统中有害生物群落演替的影响、转基因作物导致的生物入侵等问题值得关注。     

Molecular evidence for a terrestrial origin of snakes

Biologists have debated the origin of snakes since the nineteenth century. One hypothesis suggests that snakes are most closely related to terrestrial lizards, and reduced their limbs on land. An alternative hypothesis proposes that snakes are most closely related to Cretaceous marine lizards, such as mosasaurs, and reduced their limbs in water. A presumed close relationship between living monitor lizards, believed to be close relatives of the extinct mosasaurs, and snakes has bolstered the marine origin hypothesis. Here, we show that DNA sequence evidence does not support a close relationship between snakes and monitor lizards, and thus supports a terrestrial origin of snakes.