The occurrence of polysety in relation to the number of archegonia in the female inflorescences of Phascum cuspidatum Hedw.

Abstract

In Phascum cuspidatum the number of sporophytes per inflorescence was found to increase, up to a certain limit, with increase in the number of archegonia present. The number of archegonia present varies with the age of the inflorescence, and fertilization terminates the production of archegonia. The common occurrence of solitary sporophytes is due to fertilization at a time when only a small number of archegonia is present in most inflorescences. Delayed fertilization, leading to an increase in the average number of archegonia per inflorescence, is a necessary precondition for increased occurrence of polysety. As many as five sporophytes in a single inflorescence formed capsules with spores without significant reduction in the size of capsules. Variation in the frequency of abortive embryos gave evidence of competition amongst sporophytes and this was most severe in the smaller inflorescences. The occurrence of polysety in Tortula muralis appears to be governed by the same rules.     

Occurrence and distribution of free flavonoid aglycones in plants

Flavonoids are widely present in plants as water-soluble glycosides but the lipophilic free aglycones are far less abundant. The 462 flavonoids reported so far to be present in the free state and their plant sources are listed. Evaluation of these data reveals a correlation in most cases between the occurrence of flavonoid aglycones, the presence of secretory structures and the production of other lipophilic plant products. Their accumulation in some plant organs and in certain taxa is discussed. Special attention is given to their occurrence in materials deposited externally on leaves and buds.     

Distribution pattern of the epiphyte Neckera pennata on three spatial scales – importance of past landscape structure, connectivity and local conditions

We tested which factors explain the distribution pattern of the epiphytic moss Neckera pennata on three spatial scales using the framework of generalized linear models. First, we tested which factors explained its occurrence in forest stands in a 2500 ha landscape. At this scale, we also tested the effect of the historic landscape structure. We recorded its occurrence in all suitable stands. The occurrence probability increased with increasing present quantity of Acer platanoides, and with increasing present and past quantity of Fraxinus excelsior. The probability also increased with increasing connectivity to occupied stands. However, the connectivity to stands present in 1977 (recorded from infra‐red aerial photographs) explained more of the variation. This suggests that the regional metapopulation size of N. pennata has decreased during the past decades, and that its present distribution pattern reflects the age of the remaining stands, and the distribution of past dispersal sources in the landscape. Second, we tested which factors explained the occurrence and abundance on individual trees in three forest stands. Neckera pennata mainly occurred on Acer and Fraxinus stems. The most important variable in explaining occurrence probability was connectivity to surrounding occupied trees, which probably reflects the restricted dispersal range in this species. The abundance on occupied trees was also explained by this variable. The occurrence probability and abundance also increased with increasing tree diameter, probably reflecting the time that a tree has been available for colonization and the time since colonization, respectively. The occurrence probability and abundance furthermore decreased on strongly leaning (and deteriorating) trees. The occurrence probability increased with increasing bark roughness, probably reflecting increasing suitability regarding bark chemistry and moisture. Third, we tested its vertical distribution on occupied trees. The main distribution was below 1.6 m.     

Mobility and resource use influence the occurrence of pollinating insects in restored seminatural grassland fragments

After habitat restoration, species need to recolonize from existing populations. The ability of species to recolonize restored habitats likely depends on their traits. This study aimed to test if species traits and isolation from source habitat can explain the presence of insects in restored grasslands. We surveyed the occurrence of hoverflies and bees in 14 restored seminatural pastures as well as in intact seminatural grasslands in the surrounding landscape. We tested how connectivity, time since restoration, and species traits influence if species that are present in the surrounding landscape also occur in restored pastures. Solitary bee species present in the landscape were less likely to occur in restored pastures compared to bumblebees and hoverflies. The occurrence of bumblebees, but not solitary bees or hoverflies, decreased with time since restoration. The occurrence of solitary bees increased but the occurrence of hoverflies decreased with high connectivity. Migratory hoverflies were more likely to occur in restored pastures than nonmigratory hoverflies, especially in pastures with low connectivity. Among both bumblebees and solitary bees, the occurrence was influenced by nesting traits, with the lowest occurrence of parasitic species and of species digging nests in the ground. The subset of the landscape's species pool that occurs in restored pastures has a contrasting set of traits compared with species in intact source habitats. Both mobility and resource use act as filters that influence the assembly of pollinator communities after restoration. A full recovery of pollinator communities is more likely if source populations are available nearby.     

The occurrence of dicotyledonar embryos in Agave tequilana

Agave tequilana Weber is a monocot plant species member of the Asparagaceae family. One of the characteristics of monocot species is that their embryos show only one cotyledon. In this work, the occurrence of embryos with two cotyledons and fused cotyledons in A. tequilana is reported for the first time. The occurrence of dicotyledonar embryos in a species that by definition should have only one cotyledon could bring an opportunity to elucidate the mechanisms that have given the origin to the only one cotyledon present in monocots. Syncotyly is considered in this work as the possible mechanism that gave rise to the only cotyledon mostly present in this species.     

Wood of Tapirira (Anacardiaceae) from the paleogene Clarno Formation of Oregon

A new species of fossil wood, Tapirira clarnoensis, is described from a probable late Eocene deposit in the Clarno Formation of Oregon known locally as the Nut Beds. The wood represents, to the knowledge of the writer, the earliest occurrence of Tapirira in the fossil record and the only occurrence of the genus outside its present neutropical range of distribution.     

Co‐occurrence is not evidence of ecological interactions

There is a rich amount of information in co‐occurrence (presence–absence) data that could be used to understand community assembly. This proposition first envisioned by Forbes (1907) and then Diamond (1975) prompted the development of numerous modelling approaches (e.g. null model analysis, co‐occurrence networks and, more recently, joint species distribution models). Both theory and experimental evidence support the idea that ecological interactions may affect co‐occurrence, but it remains unclear to what extent the signal of interaction can be captured in observational data. It is now time to step back from the statistical developments and critically assess whether co‐occurrence data are really a proxy for ecological interactions. In this paper, we present a series of arguments based on probability, sampling, food web and coexistence theories supporting that significant spatial associations between species (or lack thereof) is a poor proxy for ecological interactions. We discuss appropriate interpretations of co‐occurrence, along with potential avenues to extract as much information as possible from such data.     

The Widespread Occurrence of Polyphosphate in Lower Plants

The widespread occurrence of polyphosphate (PoP) in lower plantsis described. PoP granules have been cytochemically detectedin algae, slime moulds, and mosses. A systematic survey is givenof lower plants in which the occurrence of PoP has been demonstratedwith both the present studies and previous investigations. The localization of PoP in cells has been studied. PoP granuleshave been observed to be present in the cytoplasm, the cytoplasmicvacuole, and in chloro-plasts of different algae. In Zygnemataceaeand in mosses PoP granules are localized in the chloroplastswhich also contain pentose nucleic acid. A relationship between PoP, pentose nucleic acid (PNA), andgrowth has been found and is discussed. A possible in situ synthesisof PoP in chloroplasts from phosphorylated intermediates ofthe photosynthetic process is suggested.     

Sterol composition and the classification of the demospongiae

The Demospongiae (Porifera) have yielded a wide range of novel and conventional sterols; a sample of 55 species screened and reported on have yielded 45 distinct sterol structures. The taxonomic relevance of the occurrence of particular sterols or overall sterol complement is evaluated and has proved to be informative in the case of the Verongida, Nepheliospongida, Axinellida and Hadromerida. A possible relationship between the occurrence of 26-methyl sterols and oviparous reproductive patterns within the Ceractinomorpha is noted. Sterol complement is observed to be qualitatively stable despite season and location of collection. High molecular weight sterols, present as major components, are probable membrane constituents. They afford an interesting parallel to the occurrence of diverse, high carbon fatty acids in sponge membranes.     

Factors influencing the etiology of cribra orbitalia in prehistoric Nubia

The present research represents an attempt to explain the occurrence of cribra orbitalia in Nubian skeletal remains associated with Meroitic, X-Group and Christian cultural horizons. The distribution of cribra orbitalia among 285 crania examined revealed a concentration of lesions among infants and aged individuals. While earlier studies have suggested cribra orbitalia may reflect the occurrence of abnormal hemoglobins such as sickle cell anemia or thalassemia, a consideration of the environmental context in which the lesions occurred makes an alternative hypothesis more likely. Particularly in Nubia (past and present), where parasitic infection is high, the diet is poor in iron, weanling diarrhea is frequent and multiparity is the norm, chronic iron deficiency anemia is a more likely causal factor. This interpretation is also compatable with clinical observations of cribra orbitalia among modern individuals suffering from chronic iron deficiency anemia.     

Differential apoptosis-like cell death in amastigote and trypomastigote forms from Trypanosoma cruzi-infected heart cells in vitro

Apoptosis, type-I of programmed cell death (PCD-I), is not restricted to multicellular organisms since many apoptotic features have been described in different trypanosomatids, including Trypanosoma cruzi. Our present aim was to monitor, by different morphological markers, the occurrence of apoptosis-like death in amastigotes and trypomastigotes of T.cruzi (Y strain) during the infection of heart culture cells. We documented the differential occurrence of PCD-I in amastigotes and trypomastigotes, with distinct death rates noticed between these two parasite-distinct forms. Fluorescence microscopy and flow cytometry analysis using different hall markers of apoptosis (phosphatidylserine exposure, collapse of mitochondrial membrane potential and DNA fragmentation) showed that amastigotes present higher levels of apoptosis-like cell death as compared to trypomastigotes. It is possible that the higher levels of PCD-I in these highly multiplicative forms may contribute to the control of the parasite burden within the host cells. On the other hand, the apoptosis-like occurrence in the infective but non-proliferative stage of the parasite (trypomastigotes) may play a role in parasite evasion mechanisms as suggested for other parasites.     

Does the presence of an observer affect a bird's occurrence rate or singing rate during a point count?

The approach or presence of an observer may affect the behavior of nearby birds, rendering them either more or less detectable than when no observer is present due to a change in singing rates. To test whether there are systematic detection biases associated with the presence of an observer during point count bird surveys, we compared the occurrence and singing rates of birds during a 10-min period immediately preceding the time when an observer arrived to conduct a count and during the formal count itself by extracting song information from autonomous sound recorders. We obtained recordings of 36 species of birds detected at ≥5 locations in one of three vegetation types, including burned conifer forest, green conifer/riparian streamside forest, and riparian bottomland/marshland. We found that species richness and both the probability of occurrence and singing rate for any of the species recorded were unaffected by the presence of an observer. In addition, the probability of occurrence did not differ significantly among four 2.5-min recording sessions during 10-min counts when an observer was present. Thus, the presence of an observer did not appear to introduce any detectable systematic bias that would make bird lists or unadjusted occurrence rates inaccurate on that basis alone. In addition, rates of bird occurrence across 2.5-min temporal subsets of a 10-min count did not vary in a systematic way that would violate the assumption of equal occupancy across adjacent time periods as sometimes used to build detection histories in occupancy modeling.     

Species-specific accumulation of ceramides in cerebrospinal fluid from encephalomyeloradiculoneurpathy patients associated with peripheral complement activation: A pilot study

Glycolipids are now known to be rapidly converted to mediators for inflammatory reactions or to signaling molecules that control inflammatory events in the nervous system. The present study aimed to explore whether disturbed glycolipids metabolism in the nervous system is present in patients with a neuroinflammatory disorder, encephalo-myelo-radiculo-neuropathy (EMRN), because most EMRN patients have been reported to exhibit autoantibodies against neutral glycolipids. Although molecular pathogenesis of this disorder remains unknown, we tried to search the immunochemical abnormalities in this disorder. ELISA for activated peripheral C5 complement and mass spectrometry analysis of cerebrospinal fluid clearly disclosed a significant upregulation of active C5 complement, C5a levels in sera as well as a significant accumulation of species-specific ceramides but not sphingomyelin in cerebrospinal fluid from EMRN patients. Furthermore, we confirmed the occurrence of anti-neutral glycolipids antibodies in all EMRN patients.Thus, the present study might indicate the pathophysiology of this disorder is the dysregulation of glycolipids metabolism and abnormal production of autoantibodies against neutral glycolipids resulting in the abnormal complement activation, although molecular basis for these sphingolipids dysregulation and the occurrence of autoantibodies against glycolipids remains to be elucidated at present. The present study implicates a new therapeutic strategy employing anti-ceramide and/or anti-complement therapy for this disorder.     

Trichocytes in Lithophyllum kotschyanum and Lithophyllum spp. (Corallinales,Rhodophyta) from the NW Indian Ocean

The current diagnosis of the genus Lithophyllum includes absent or rare trichocyte occurrence. After examining holotype material, single trichocytes have been revealed to occur abundantly in Lithophyllum kotschyanum Unger, and in freshly collected specimens of Lithophyllum spp. from the Red Sea, Gulf of Aden and Socotra Island (Yemen). Trichocyte occurrence is not considered a diagnostic character at specific or supraspecific levels in the Lithophylloideae, and the ecological significance of trichocyte formation is discussed. The generitype species, L. incrustans Philippi, does not show trichocytes nor do many other Lithophyllum species from diverse geographic localities, but the presence of abundant trichocytes in other congeneric taxa requires emendation of the genus diagnosis. Therefore, the diagnosis of Lithophyllum is here emended by eliminating the adjective “rare” in the sentence concerning trichocyte occurrence, as follows: “Trichocytes present or absent, if present occurring singly.”     

The fine structure of the guinea-pig muscle spindle

Summary Nuclear bag and nuclear chain intrafusal fibres are present in guinea-pig muscle spindles. Unlike muscle spindles in other species two types of nuclear chain fibre seem to be present. The electron microscopical appearance of one type of nuclear chain fibre is similar to that of nuclear bag fibres.It is suggested that under tension the nuclei of small nuclear bag fibres become sufficiently displaced to form nuclear chain-like fibres. The frequent occurrence of fibres which combine some of the properties of both nuclear bag and nuclear chain fibres indicates the possible occurrence of a third type of intrafusal fibre.The sensory innervation of guinea-pig muscle spindles is similar to that of the cat and the rat. Three types of motor nerve ending which could be classified according to the complexity of their subneural apparatus were seen.     

Large-scale occurrence patterns of red-listed lichens and fungi on old oaks are influenced both by current and historical habitat density

Current occurrence patterns of species associated with ancient trees may reflect higher historical habitat densities, because the dynamics of the habitat and the colonisation-extinction processes for many inhabiting species are expected to be slow. We tested this hypothesis in southeast Sweden by analysing species occurrence per parish for twelve redlisted lichen species and nine redlisted fungus species in relation with current density of big oaks, the density of oaks in the 1830s and connectivity with parishes with the species present. For most species, the occurrence was positively related with current density of habitat (for 18 species out of 21) and parish area (for 16 species). Historical habitat density was positively related with occurrence for 11 species, while connectivity with current occurrences in the surroundings was positive for the occurrence of 12 species and negative for the occurrence of two. For lichen species the connectivity measure that best explained the variation was at a larger spatial scale as compared to fungus species. Even if the density of old oaks remains in the future, inhabiting species will most likely decline because their distribution patterns are not in equilibrium with the current habitat density. Therefore, to allow long-term persistence of inhabiting species the number of old oaks should be increased. Areas where such an increase is most urgent could be identified based on species occurrence data and current habitat density, but because species data will always be incomplete data on the historical habitat distribution is valuable.     

The presence and activity of progesterone in the plant kingdom

Steroids are present in living organisms as one of the most essential groups of compounds. Continuous research has led to new discoveries and the revision of existing information concerning the occurrence and the role of steroids, both in animals and plants. This article will focus on reviewing the literature studying progesterone in the plant kingdom, including its discovery, its occurrence in different plant species as well as its biological activity and molecular basis of action. This review will present and discuss the current data in addition to introducing potential directions for further research on the subject of progesterone in plants.     

Distribution of Streptomycin Resistant Strains of Erwinia amylovora in Egypt during 1988

A survey of the occurrence of strains of Erwinia amylovora resistant to streptomycin in certain Egyptian pear orchards was earned out during April and May 1988. Twenty-two isolates out of 604 isolates collected from 11 orchards showed resistance to streptomycin. All the streptomycin resistant (Str^r) strains isolated in the present work were resistant to high levels of streptomycin with minimal inhibitory concentrations ranging from 1000 to 3000 μg/ml. The occurrence of Str^r strains in Egypt is still limited and the population of resistant strains was at relatively low level. However, such occurrence of E. amylovora with resistance to streptomycin is a potentially serious situation.     

The present record of the occurrence of Astomiopsis julacea （Besch.）Yip&Snider（Musci）in Xizang，China， is based on misidentification

The present record of the occurrence of Astomiopsis julacea （Besch.）Yip&S nider（Musci）in Xizang,China, is based on misidentification JIAYu WANGMei-Zhi WUPeng-Cheng     

Distribution of phytoecdysteroids in the Caryophyllaceae

Certain genera within the Caryophyllaceae (especially Silene and Lychnis) have received a significant amount of attention with regard to the isolation and identification of ecdysteroids. However, the taxonomy of this family is difficult. Hence, the occurrence of phytoecdysteroids in members of the Caryophyllaceae is presented, and combined with new data on ecdysteroid agonist (phytoecdysteroid) and antagonist activities, in order to survey the distribution of phytoecdysteroid-containing species within this large family, and to assess the utility of phytoecdysteroids as chemotaxonomic markers. The new data presented (representing ca. 110 species) have been obtained by the application of sensitive biological/biochemical methods for the detection of ecdysteroid agonists and antagonists, using Drosophila melanogaster B(II) bioassay and ecdysteroid-specific immunoassays. In the antagonist version of the B(II) bioassay, only weak ecdysteroid antagonist activities were detected in a few of the extracts. From both new and previously available data, it was found that phytoecdysteroids were present predominantly in the Genera Lychnis, Petrocoptis, Sagina and Silene. Comparison of ecdysteroid occurrence with a molecular phylogeny for the tribe Sileneae [Taxon 44 (1995) 525] revealed close association of ecdysteroid occurrence with certain groups of this tribe. In 14 species of Silene examined, there is a reasonable, but not absolute, relationship between the presence of ecdysteroids in the seeds and in other plant parts. Where ecdysteroids are present in the plant, highest concentrations are generally present in the roots.