Grazer control and nutrient limitation of phytoplankton biomass in two Australian reservoirs

1. Grazer and nutrient controls of phytoplankton biomass were tested on two reservoirs of different productivity to assess the potential for zooplankton grazing to affect chlorophyll/phosphorus regression models under Australian conditions. Experiments with zooplankton and nutrients manipulated in enclosures, laboratory feeding trials, and the analysis of in-lake plankton time series were performed. 2. Enclosures with water from the more productive Lake Hume (chlorophyll a = 3–17.5 μg l^–1), revealed significant zooplankton effects on chlorophyll a in 3/6, phosphorus limitation in 4/6 and nitrogen limitation in 1/6 of experiments conducted throughout the year. Enclosures with water from the less productive Lake Dartmouth (chlorophyll a = 0.8–3.5 μg l^–1), revealed significant zooplankton effects in 5/6, phosphorus limitation in 5/6 and nitrogen limitation in 2/6 of experiments. 3. While Lake Hume enclosure manipulations of the biomass of cladocerans (Daphnia and Diaphanosoma) and large copepods (Boeckella) had negative effects, small copepods (Mesocyclops and Calamoecia) could have positive effects on chlorophyll a. 4. In Lake Hume, total phytoplankton biovolume was negatively correlated with cladoceran biomass, positively with copepod biomass and was uncorrelated with total crustacean biomass. In Lake Dartmouth, total phytoplankton biovolume was negatively correlated with cladoceran biomass, copepod biomass and total crustacean biomass. 5. In both reservoirs, temporal variation in the biomass of Daphnia carinata alone could explain more than 50% of the observed variance in total phytoplankton biovolume. 6. During a period of low phytoplankton biovolume in Lake Hume in spring–summer 1993–94, a conservative estimate of cladoceran community grazing reached a maximum of 0.80 day^–1, suggesting that Cladocera made an important contribution to the development of the observed clear-water phase. 7. Enclosure experiments predicted significant grazing when the Cladocera/Phytoplankton biomass ratio was greater than 0.1; this threshold was consistently exceeded during clear water phase in Lake Hume. 8. Crustacean length had a significant effect on individual grazing rates in bottle experiments, with large Daphnia having highest rates. In both reservoirs, mean crustacean length was negatively correlated with phytoplankton biovolume. The observed upper limit of its variation was nearly twice as high compared to other world lakes.     

Tumulduria incomperta and the case for Tommotian trilobites

The enigmatic fossil Tumulduria incomperta Missanhevsky 1969 from the basal Tommotian Stage at 'Dvortsy' on the Aldan River, Siberian Platform, is reinvestigated in light of the report (Fedorov et al. 1979, Dokl. AN SSSR 249) of trilobite remains from the same beds. Comparisons of these supposed trilobites with old and new collections from 'Dvortsy' leave no doubt that they are identical to Tumulduria incomperta. Tumulduria is represented by phosphatic plates with a crude bilateral symmetry, consisting of a central longitudinal rounded ridge flanked by flat lateral portions. They are built of growth lamellae overlapping each other along the axis of symmetry. The surface carries prominent transverse folds and lamellar terminations. There is considerable morphological variation, and the similarity of some specimens to trilobites is only superficial. Tumulduria is interpreted as a bilaterally symmetrical metazoan with a dorsal protective plate; it probably represents a short-lived group that left no descendants.     

Molecular Mechanisms of Pigment Transport in Melanophores

We present an overview of the research on intracellular transport in pigment cells, with emphasis on the most recent discoveries. Pigment cells of lower vertebrates have been traditionally used as a model for studies of intracellular transport mechanisms, because these cells transport pigment organelles to the center or to the periphery of the cell in a highly co-ordinated fashion. It is now well established that both aggregation and dispersion of pigment in melanophores require two elements of the cytoskeleton: microtubules and actin filaments. Melanosomes are moved along these cytoskeletal tracks by motor proteins. Recent studies have identified the motors responsible for pigment dispersion and aggregation in melanophores. We propose a model for the possible roles of the two cytoskeletal transport systems and how they might interact. We also discuss the putative mechanisms of regulation of pigment transport, especially phosphorylation. Last, we suggest areas of research that will receive attention in the future in order to elucidate the mechanisms of organelle transport.     

A new diploid species of Hieracium sect. Pannosa (Asteraceae) from Bulgaria

Hieracium petrovae Vladimirov & Szeląg sp. nov. , a new diploid (2 n  = 18) species in H. sect. Pannosa Zahn, is described and illustrated from the Rhodope Mountains, South Bulgaria, and compared with related taxa. It grows in relict habitats in crevices of limestone rock together with many Balkan endemics. H. petrovae is morphologically similar to taxa from the H. pannosum , H. pilosissimum and H. heldreichii groups (collective species sensu Zahn) to some of which it is a presumed ancestral species.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 261–265.     

Genital primordium of the free-living marine nematode Halichoanolaimus sonorus (Chromadoria,Chromadorida)

Summary

The genital primordium of the first stage juvenile (J1) of the free-living marine nematode Halichoanolaimus sonorus (Chromadorida: Selachinematidae) was studied using transmission electron microscopy. The primordium consists of four undifferentiated cells: two primordial germ cells (PGC) 5–6 μm in diameter and two somatic cells. The PGC have a large nucleus with nucleolus. The centriole was detected in close vicinity of the PGC nucleus. Most of the cell mitochondria are in close contact with the nuclear envelope. The mitochondria are interspersed by 0.2–0.3 μm particles of an electron-dense diffuse substance devoid of surrounding membrane. Both PGC are closely attached to each other and to the neighboring somatic cells of the genital primordium. The elongated somatic cells contain nuclei devoid of nucleoli; the cytoplasm is filled with free ribosomes and contains occasional cisternae of rough endoplasmatic reticulum (RER), Golgi bodies, mitochondria, and transparent vesicles. The genital primordium is separated by a narrow space from of the intestine (dorsally) and the somatic muscles (ventrally). The PGC of H. sonorous are devoid of typical P granules known for previously studied nematodes as distinct markers of germ line cell lineage. Perinuclear particles of dense diffuse substance found in PGC of H. sonorous could be considered as germ determinants analogous to P granules.     

Floristic richness of three perhumid New Zealand alpine plant communities in comparison with other regions

Abstract Results are presented on vascular species richness in three representative alpine plant communities at 1040–1410 m on Mt Burns in the perhumid Fiordland region, a hotspot of alpine plant diversity, in south‐western South Island, New Zealand. Overall species richness was not dissimilar between the three communities in any of the eight plot sizes (mean values of 20.8–24.4 species in the largest plots of 100 m²), even though coefficients of floristic similarity were small (17.9; 23.5) between both low‐alpine communities (snow tussock‐shrubland and snow tussock grassland) and the high‐alpine cushion fellfield. Vascular species richness was generally similar to that in the few other oceanic New Zealand alpine communities for which data are available. The decline in richness from the low‐alpine to high‐alpine zones, revealed in more comprehensive records from two other regions with generally similar oceanic environments, was not recorded, indeed was reversed, on Mt Burns. Whether the recognized biodiversity hotspot of Fiordland has a generally richer high‐alpine flora than other regions in New Zealand needs further examination. The general pattern of alpine floristic richness in relation to elevation, in New Zealand, also prevails in most alpine regions abroad, usually under much more extreme continental environments. This pattern is usually ascribed to the associated decrease in temperature. Both the small size of the land mass and/or associated environmental conditions may be implicated but clarification awaits further data, preferably collected with standardized procedures.     

Effects of silicon on growth processes and adaptive potential of barley plants under optimal soil watering and flooding

Barley (Hordeum vulgare L.) was grown in pots with brown loess soil and highly soluble amorphous silicon dioxide as the source of monosilicic acid to examine its influence on plant growth and adaptive potential under optimal soil watering and flooding. The adaptive potential of plants was estimated by the concentration of the thiobarbituric acid reactive substances (TBARs) as well as superoxide dismutase (SOD), guaiacol peroxidase (GPX) and ascorbate peroxidase (AsP) activities. Application of amorphous silica to the soil increased the Si content in barley shoots and roots and stimulated their growth and biomass production under optimal soil watering. Soil flooding suppressed the growth both of the (−Si)- and (+Si)-plants. The intensity of oxidative destruction estimated by the concentration of TBARs was lower in the roots and leaves of the (+Si)-plants. Soil flooding induced SOD activity in the roots and in the leaves of the (−Si;+flooding) and (+Si;+flooding)-plants, but no significant differences were observed due to the Si treatment. GPX activity in the roots of (+Si)-plants was higher than in the (−Si)-ones under optimal soil watering, but under soil flooding no differences between (+Si)- and (−Si)-treatments were observed. AsP activity was not influenced by Si treatment neither under optimal soil watering nor under flooding. Thus, application of Si stimulates growth processes of barley shoots and roots under optimal soil watering and decreases intensity of oxidative destruction under soil flooding without significant changes in the activities of antioxidant enzymes.     

Assessment of genetic and pheromonal diversity of the Cydia strobilella species complex (Lepidoptera: Tortricidae)

Combining pheromone trapping and genetic analyses can be useful when trying to resolve complexes of closely related insect taxa that are difficult to distinguish based on morphological characters. Nearctic and Palearctic populations of the spruce seed moth, Cydia strobilella L., have been considered taxonomically synonymous since 1983, but more recent work revealing distinct sex pheromones for Canadian and Swedish moths suggest that populations in the two regions belong to different species. In order to test this hypothesis, we performed field trapping using different pheromone lures at ten sites in North America, Europe and Asia, and reconstructed phylogenetic relationships among trapped moths using mitochondrial (cytochrome oxidase subunit I) and nuclear (elongation factor 1 alpha) DNA sequence data. Trapping data and tree topologies for both genes revealed distinct pherotypes in North America and Eurasia. A genetically distinct population from China was investigated further with respect to its sex pheromone. Electrophysiological data indicated that Chinese females produce a deviant ratio of the sex pheromone components (dienic acetates) compared to Swedish females. However, trapping experiments in both areas revealed a similar broad response profile in males to a wide range of acetate ratios, and these populations should be considered taxonomically synonymous. A previous suggestion of an agonistic effect on the attraction of C. strobilella males in Sweden when adding the corresponding alcohols to the binary acetate blend was also tested in Sweden as well as in China, with no observed effect on attraction of males. In conclusion, our study demonstrates the great potential of using pheromone trapping as a tool for identification and delimitation of taxa within cryptic species complexes. Based on our data, Nearctic and Palearctic populations of C. strobilella should be considered different species, and C. youngana Kearfott stat. rev. is resurrected here as valid name for North American populations, which was the case before the revision in 1983.