The functional morphology of feeding in three species of maldanid polychaetes

The functional morphology of deposit feeding relative to proboscideal morphology of the maldanid polychaetes Axiothella rubrocincta (Johnson, 1901), Clymenella californica Blake & Kudenov, 1974, and Praxillella affinis pacifica (Berkeley, 1929) from central California is presented. The proboscides of these species are externally and internally similar. They consist of a cuticulatized buccal mass, a bucco-pharyngeal junction and ciliated pharynx. A functional unit of the feeding process is the palpode because its secretions enable the proboscis to be effectively everted. These worms exploit die physical properties of the substratum by changing its dilatancy (and thixotropy) while feeding. The rapidly emerging buccal mass increases the dilatancy of the sediment and provides a penetration anchor. The buccal mass partially deflates and loosens the substratum just prior to the forceful extrusion of the bucco-pharyngeal junction. Sediment about the latter region becomes dilatant. The proboscis then shortens and widens, causing the substratum about the pharynx to become thixotropic while it becomes dilatant about the region of the proboscis proximal to the pharynx. The worms push their proboscides into the loosened sediment while pharyngeal ciliary currents and the undulating bucco-pharyngeal margin draw food into the pharynx. Pharyngeal cilia and the buccal mass function in particle selection.
The maldanids and arenicolids examined to date share similar and basic proboscideal morphologies and activities. It is suggested that the feeding mechanism described for the maldanids, A. rubrocincta, C. californica and P. affinis pacifica , will be found in some members of both families.     

Protein Polymorphism and Evolution in the Genus Tetrahymena1

ABSTRACT. Immunoblotting tests involving cytoskeletal protein arrays and fluorescence microscopical examinations of whole cells using monoclonal antibody 424A8 gave substantially different results in three evolutionary subgroups within the genus Tetrahymena. These responses are described and some implications of the evolutionary divergence indicated in this ciliated protozoan are discussed.     

Germination behaviour of Astroloma xerophyllum (Ericaceae), a species with woody indehiscent endocarps

The dispersal unit of many Ericaceae comprises an ovoid drupe with a woody indehiscent endocarp, and diaspores of this type are notoriously difficult to germinate for most members of this widely distributed family. Within the biodiverse south‐west of Western Australia, more than 200 drupaceous species of Ericaceae have been described, more than 50 of which are considered to be rare and threatened, requiring significant conservation action in the near future. In this paper, we investigate the germination ecology of the common Australian endemic, Astroloma xerophyllum, as a proxy for closely related threatened taxa, focusing on the ex situ and in situ germination requirements of seeds and indehiscent endocarps. Each endocarp possessed up to seven locules and means of 2.0–3.4 seeds per endocarp from the two collections used in this study. Seeds were up to 2.74 mm in length and 100% viable. Embryos were linear, differentiated and approximately 1.3 mm in length. Seeds within endocarps imbibed water to 28%, whereas excised seeds became hydrated to 44%. Fifty‐five per cent of seeds extracted from endocarps germinated on water agar alone and 100% germinated when presoaked in gibberellic acid. Seeds remaining inside intact endocarps failed to germinate unless treated with a germination promoter and incubated for more than 20 weeks. Rapid germination of seeds in intact endocarps was promoted by soaking endocarps in gibberellic acid and incubating them in 100% O₂. Embryos grew substantially in length within seeds prior to germination, and thus seeds have morphophysiological dormancy. Seeds under natural conditions required several seasons to germinate to any degree. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 299–311.     

Effect of temperature on toxicity of three pyrethroids to horn flies

Predictive models describing best-fit regression equations for per cent mortality of horn flies as a function of temperature were determined for each of three pyrethroid insecticides (fenvalerate, flucythrinate and permethrin) over the temperature range 20-35 degrees C. Susceptible horn flies, Haematobia irritans (L.), were exposed to c. an LC70 dose of each pyrethroid using a residue-on-glass method. This technique used confined exposure in chambers with temperatures of 20, 25, 30 and 35 degrees C. Within this range, mortality was greatest at 25 degrees C with all three insecticides. Estimated temperature-mortality equations for each pyrethroid revealed different responses of horn flies to each of these insecticides. Horn flies exposed to flucythrinate demonstrated a linear mortality response that varied inversely with temperature. The response to permethrin was described by a quadratic equation, while the response to fenvalerate was best fitted by a cubic equation.     

Translation of Globin Messenger RNA in a Heterologous Cell-free System

MESSENGER-SPECIFIC initiation factors, capable of discriminating between classes of messenger RNAs (mRNAs) or different cistrons in viral RNA, have been implicated in the regulation of protein synthesis in bacteria^1–5. Comparable but less detailed observations have also been made in eukaryotic systems^6–10. For example, RNA extracted from a mammalian virus (encephalomyocarditis virus, EMC) cannot be translated in a reticulocyte cell-free system unless the system is fortified with an extract from responsive cells—in this case, Krebs II ascites cells⁶. Such results imply the existence of tissue-specific factors and lead to questions whether this incompatibility is reciprocated by an inability of the Krebs II ascites cell system to respond to the mRNA for globin.     

Filtering mechanism of the honey bee proventriculus

ABSTRACT. The fine structure and function of a honey bee's ( Apis mellifera Linn.) proventriculus were studied by scanning electron microscopy and video-recording. Our observations revealed that the proventriculus is used to engulf pollen and other particles which contaminate the nectar carried into the crop. The four lips are closed and opened, pulled backwards and straightened by the external circular muscles and internal longitudinal muscles. Combs of filiform-hairs (70 μm in length) located on the margins of the lips 'catch' and filter particles from the fluid. By repeated filtering, opening and closing actions of the hairs and lips, particles are filtered and collected in pouches between the ventricular folds to form boluses and are eventually passed into the midgut. In the present experiment, particle sizes ranging from 0.5 to 100 μm in diameter, including dandelion pollen ( Taraxacum officinale Web.), Torula yeast ( Candida utilis Lodder et Kreger-Van Rij), bee disease spores of Nosema apis Zander and Bacillus larvae White, and man-made particles can be filtered by the hairs. Small particles (0.23 μm in diameter) filter through the hair and return back to the fluid. Large particles (100–200 μm in diameter) are caught between the stylets of the mouthparts and are not ingested. These observations suggest that the particle size plays an important role in determining what can be taken by the mouthparts and the proventriculus and what can later be utilized as a food source by the bee. The role of the proventriculus in disease transmission is also discussed.     

Strontium-substitution for Calcium and Algal Cell Size

Mature cells of several algal species (Protosiphon bo-tryoides, Chlorococcum echinozygotum, Asterococcus superbus, Chlamydomonas reinhardtii, Chlorella pyrenoidota) that will grow in a strontium-substitution for calcium are larger and more highly vacuolated than control cells in calcium. In logarithmic phase cultures average cell size of cells in strontium-replacement medium is greater than for control cells in calcium. The water content of strontium-replacement cells is indicated to be greater than of control cells. Mechanisms whereby water content and cell size differences may become established are discussed.     

The importance of climate and soils for estimates of net primary production: a sensitivity analysis with the terrestrial ecosystem model

We used the Terrestrial Ecosystem Model (TEM) to investigate how alternative input data sets of climate (temperature/precipitation), solar radiation, and soil texture affect estimates of net primary productivity (NPP) for the conterminous United States. At the continental resolution, the climates of Cramer and Leemans (C&L) and of the Vegetation/ Ecosystem Modelling and Analysis Project (VEMAP) represent cooler and drier conditions for the United States in comparison to the Legates and Willmott (L&W) climate, and cause 5.2% and 2.3% lower estimates of NPP. Solar radiation derived from C&L and given in VEMAP is 32% and 60% higher than the solar radiation data derived from Hahn cloudiness. These differences cause ～ 8% and 10% lower NPP because of radiation-induced water stress. In comparison to the FAO/CSRC soil texture, which represents most biomes with loam soils, the soil textures are finer (more silt and clay) in the Zobler and VEMAP data sets. The use of VEMAP soil textures instead of FAO/CSRC soil textures causes ～ 3% higher NPP because enhanced volumetric soil moisture causes higher rates of nitrogen cycling, but use of the Zobler soil textures has little effect. In general, NPP estimates of TEM are more sensitive to alternative data sets at the biome and grid cell resolutions than at the continental resolution. At all spatial resolutions, the sensitivity of NPP estimates represents the impact of uncertainty among the alternative data sets we used in this study. The reduction of uncertainty in input data sets is required to improve the spatial resolution of NPP estimates by process-based ecosystem models, and is especially important for improving assessments of the regional impacts of global change.