A test of the preference–performance hypothesis with stream insects: selective oviposition affects the hatching success of caddisfly eggs

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Unlike effects of denervation on the rate of entry of inorganic phosphate into rat slow and fast muscles.

The increased inorganic phosphate flow, characteristic of denervated gastrocnemius muscle is shown to be present in additional denervated fast muscles, i.e. the plantaris, tibialis anterior and extensor digitorum longus muscles. The response of the soleus, a slow muscle, to denervation is biphasic. After an initial decrease of the phosphate flow at the end of the first postoperative day, there is a secondary rise which has the same general characteristics as the rise observed in fast muscles i.e. an exponential or hyperbolic increase to an asymptotic value reached after thirty days. The denervated fast and slow muscles are not converging to an intermediate metabolic pattern. The changes in phosphate flow induced by denervation are reversible in the soleus as well as in the gastrocnemius muscles.     

Morphological plasticity in a native freshwater fish from semiarid Australia in response to variable water flows

In fishes, alterations to the natural flow regime are associated with divergence in body shape morphology compared with individuals from unaltered habitats. However, it is unclear whether this morphological divergence is attributable to evolutionary responses to modified flows, or is a result of phenotypic plasticity. Fishes inhabiting arid regions are ideal candidates for studying morphological plasticity as they are frequently exposed to extreme natural hydrological variability. We examined the effect of early exposure to flows on the development of body shape morphology in the western rainbowfish (Melanotaenia australis), a freshwater fish that is native to semiarid northwest Australia. Wild fish were collected from a region (the Hamersley Ranges) where fish in some habitats are subject to altered water flows due to mining activity. The offspring of wild‐caught fish were reared in replicated fast‐flow or slow‐flow channels, and geometric morphometric analyses were used to evaluate variation in fish body shape following 3, 6, 9, and 12 months of exposure. Water flows influenced fish morphology after 6 and 9 months of flow exposure, with fish in fast‐flow environments displaying a more robust body shape than those in slow‐flow habitats. No effect of flow exposure was observed at 3 and 12 months. Fishes also showed significant morphological variation within flow treatments, perhaps due to subtle differences in water flow among the replicate channels. Our findings suggest that early exposure to water flows can induce shifts in body shape morphology in arid zone freshwater fishes. Morphological plasticity may act to buffer arid zone populations from the impacts of anthropogenic activities, but further studies are required to link body shape plasticity with behavioral performance in habitats with modified flows.     

Water velocity shapes juvenile salmonids

Phenotypic plasticity in morphology is often considered adaptive. Stream-living fish encounter considerable spatial and temporal environmental variation in their native habitats, and the ability to adapt to this variation is of utmost importance. We studied experimentally whether water velocity affects the body shape of juvenile Atlantic salmon (Salmo salar m. sebago Girard) and brown trout (Salmo trutta m. lacustris L.). The fish were reared in slow and fast water flow, and their morphology was studied by measuring a number of morphometric characters. We studied which characters differed between the environments in each species, and found that water velocity caused morphological differentiation in both salmon and brown trout. The differences occurred especially in body height as well as in fin sizes, characters that are very likely to be of functional importance for life in the stream environment. Salmon in fast flow became more robust, whereas brown trout in fast flow became slightly more streamlined. The observed variation in body morphology of salmon and brown trout indicates phenotypic plasticity, but the species differed in their response to environmental variation, which may be due to different energetics and cost reduction strategies. Morphological differentiation caused by water flow occurred very rapidly, within 1-month exposure to the different water flows. This revised version was published online in November 2006 with corrections to the Cover Date.     

Primary producers in a Pampean stream: temporal variation and structuring role

Low current velocities, high nutrient levels, the lack of riparian forest vegetation, and the development of dense and rich macrophyte communities characterize Pampean streams. The objective of this study was to describe the main physical, chemical, and biological characteristics of a headwater Pampean stream as well as to analyze the role of macrophytes and phytobenthos. The study was conducted in a stream considered to be not much disturbed by human activities. Samples of water and organisms (macrophytes, benthic algae and invertebrates) were taken monthly for 14 months in two sampling stations, in fast flow and slow flow sites. Macrophyte biomass and diversity increased in spring and summer, and they decreased in autumn, when the plant community was greatly affected by an important flood. Phytobenthos biomass was lower in late summer, possibly due to the establishment of a dense cover of the floating macrophyte Lemna gibba L. Density of amphipods and gastropods greatly increases in spring and summer, jointly with the macrophyte development. Analysis of correlation showed that current velocity is the most important factor influencing macrophyte biomass and phytobenthos structure, while depth, nutrients, and herbivores are linked factors. Pampean streams could be considered systems dynamically fragile, because habitat heterogeneity is generated by aquatic vegetation, a substratum that varies along time.     

Green crab (Carcinus maenas) foraging efficiency reduced by fast flows

Predators can strongly influence prey populations and the structure and function of ecosystems, but these effects can be modified by environmental stress. For example, fluid velocity and turbulence can alter the impact of predators by limiting their environmental range and altering their foraging ability. We investigated how hydrodynamics affected the foraging behavior of the green crab (Carcinus maenas), which is invading marine habitats throughout the world. High flow velocities are known to reduce green crab predation rates and our study sought to identify the mechanisms by which flow affects green crabs. We performed a series of experiments with green crabs to determine: 1) if their ability to find prey was altered by flow in the field, 2) how flow velocity influenced their foraging efficiency, and 3) how flow velocity affected their handling time of prey. In a field study, we caught significantly fewer crabs in baited traps at sites with fast versus slow flows even though crabs were more abundant in high flow areas. This finding suggests that higher velocity flows impair the ability of green crabs to locate prey. In laboratory flume assays, green crabs foraged less efficiently when flow velocity was increased. Moreover, green crabs required significantly more time to consume prey in high velocity flows. Our data indicate that flow can impose significant chemosensory and physical constraints on green crabs. Hence, hydrodynamics may strongly influence the role that green crabs and other predators play in rocky intertidal communities.     

Primary productivity and spatial structure of phytolithic growth in streams in the Great Smoky Mountains National Park,Tennessee

The purpose of this study was to examine the primary production rates of phytolithic communities found in the major different habitats of streams and determine the effects of physical and chemical parameters associated with each habitat on periphyton community spatial structure. The project was designed to study natural, intact communities within stream systems.A comparative analysis was made of phytolithic communities found in Camel Hump and Husky Branch streams in the Great Smoky Mountains National Park. Camel Hump flows through virgin forest area and Husky Branch flows through an area logged approximately 60 y ago. The effects of logging on Husky Branch stream and the surrounding watershed are discussed.Seasonal data were collected from July, 1981 through May, 1982 from fast flow, slow flow and pool areas within each stream. An incubation chamber designed for use in lotic systems was used for in situ measurements of ¹⁴C uptake. Rock samples collected at each site were used as substrates for community structure observations utilizing a scanning electron microscope.The algal communities of Camel Hump and Husky Branch streams were found to be predominantly composed of diatoms. The dominant genera in the fast, slow and pool areas included Achnanthes, Eunotia, Meridion, Navicula and Gomphonema. Fast flow areas were dominated by diatom species growing in a prostrate position. Slow flow areas were more densely populated by diatoms than the fast flow areas. Diatoms in the slow flow areas appeared mainly in prostrate position with a few stalked forms present. Pool area communities were less densely packed than slow flow areas and contained stalked and chain formations of diatoms.Results indicate that the physical and chemical parameters associated with each habitat affect the primary production rates and community structure found at the experimental sites. Measurements of carbon assimilation and chlorophyll a concentration were significantly greater in habitats of higher current velocity and light availability. Cell densities tend to increase with a decrease in current velocity. Habitats of high density showed a decrease in diversity and evenness. Correlations between productivity in the various habitats of each stream and other parameters measured in the study are discussed.     

The effect of charge density on the velocity and attenuation of ultrasound waves in human cancellous bone

Cancellous bone is a highly porous material, and two types of waves, fast and slow, are observed when ultrasound is used for detecting bone diseases. There are several possible stimuli for bone remodelling processes, including bone fluid flow, streaming potential, and piezoelectricity. Poroelasticity has been widely used for elucidating the bone fluid flow phenomenon, but the combination of poroelasticity with charge density has not been introduced. Theoretically, general poroelasticity with a varying charge density is employed for determining the relationship between wave velocity and attenuation with charge density. Fast wave velocity and attenuation are affected by porosity as well as charge density; however, for a slow wave, both slow wave velocity and attenuation are not as sensitive to the effect of charge density as they are for a fast wave. Thus, employing human femoral data, we conclude that charged ions gather on trabecular struts, and the fast wave, which moves along the trabecular struts, is significantly affected by charge density.     

Stream hydraulics and the distribution of microcrustacea: a role for refugia?

1. The relationship between microcrustacean abundance and flow habitat in three contrasting reaches of a single stream was examined. 2. Three methods of characterizing stream hydraulics (shear stress frequency distributions, Froude numbers and mean reach velocity) showed the same pattern among the three reaches, which were subsequently termed ‘fast’, ‘slow’ and ‘medium’. 3. Distributions of epibenthic microcrustacea matched flow characteristics of the three reaches, being most abundant in the slow reach and least abundant in the fast reach. In contrast, densities of three out of four species of interstitial Harpacticoida did not vary significantly with reach, and none of the parameters measured explained much of their between-patch variation in density. Hydraulic conditions at the substratum surface may not affect the distribution of species with interstitial habits. 4. Patterns in the abundance of organic matter (a possible food source) were examined. Measures of organic matter were highly correlated with hydraulic variables, with detritus being most abundant in the slow reach and least in the fast reach. Despite their strong response to reach, local densities of most microcrustacea (including many epibenthic species) did not vary with organic matter. Food for detritivorous microcrustacea may not be limiting in this highly retentive stream. 5. There was some evidence to suggest that different numbers of animals were retained in the three reaches during flow disturbances. One reach may function as a ‘flow refugium’. Models illustrating the processes by which lotic organisms may use flow refugia are presented and provide a framework for future empirical and theoretical studies.     

Morphological and biochemical correlates of skeletal muscle contractility in the cat. II. Physiological and biochemical studies.

Isometric twitch characteristics and biochemical parameters of isolated myosin and sarcoplasmic reticulum have been compared in three cat hind limb muscles. The fast twitch caudofemoralis and the slow twitch soleus are almost pure muscles as judged from histochemical studies. Isolated myosin from the caudofemoralis is not only 2- to 3-fold higher in its ATPase activities than that of the soleus, but also in non-dissociated forms has greater electrophoretic mobility than the soleus myosin. Purified myosins from fast muscles as well as soleus exhibited three light chains upon electrophoresis. However, the intact non-solubilized myosins differed in electrophoretic mobilities. The sarcoplasmic reticulum fraction isolated from caudfemoralis exhibits faster rates of Ca++ binding and uptake than soleus, and when fit to a two component model, the caudofemoralis SR exhibits a higher amount of a fast binding site than does soleus SR, features reflected in differences in the relaxation time of the two muscles. In contrast, the fast twitch tibialis anterior has been shown to be a gradient of fiber types and its isometric twitch may be separated by selective nerve stimulation, into a fast and a slow twitch component. Our findings that myosin fractions, as well as sarcoplasmic reticulum fractions isolated from these two components differ with respect to their biochemical characteristics add support to the possibility of a dual function in this muscle.     

Ultrastructure,encystment and cyst wall composition of the resting cyst of the peritrich ciliate Opisthonecta henneguyi

The cyst wall of Opisthonecta henneguyi has been studied ultrastructurally and cytochemically by light and electron microscopy, as well as by chemical and electrophoretic analyses, to examine the structure of the cyst wall and its composition. The cyst wall consists of four morphologically distinct layers. The ectocyst is a thin dense layer. The mesocyst is the thickest layer and is composed of a compact material. The endocyst is a thin layer like the ectocyst, but less dense. The granular layer varies in thickness and is composed of a granular material. In the resting cyst, kinetosomes of both oral apparatus and trochal band as well as the myoneme system are maintained, and only cilia are resorbed. The sugars present in the cyst wall are predominantly N-acetylglucosamine (90%) and glucose (10%). The mesocyst is composed of chitin, and the endocyst includes glycoproteins and acid mucopolysaccharides. During secretion of the cyst wall, the endocyst and granular layer are secreted from precursors synthesized "de novo". No cytoplasmic precursors of ectocyst and mesocyst have been detected.     

Decidual cells in the human ovary at term. I. Incidence, gross anatomy and ultrastructural features of merocrine secretion

Decidual tissue occurring within the human ovarian cortex was examined by light and electron microscopy. Of 21 ovarian specimens obtained at term (36-42 weeks of gestation), decidual cells were confirmed in each. Decidual cells were found within the tunica albuginea as single cells, in nodules, in polyps or in confluent sheets. Decidual cells exhibited several characteristics of cells engaged in secretory activity: abundant rough and smooth endoplasmic reticulum, numerous profiles of the Golgi complex and a large, euchromatic nucleus devoid of heterochromatin and displaying a prominent fibrous lamina. Peduncular protrusions at the periphery of the cell contained numerous dense bodies 0.4-0.9 micron in diameter. These dense bodies were bounded by a single membrane and contained granular subunits 30-60 nm in diameter. These granular subunits were observed in the process of apparent exocytosis, as well as free in the extracellular space. Secretory bodies and their granular content also were observed both in the region of the Golgi complex and partially extruded into peduncular processes. By far the greatest number of secretory bodies occurred within peduncular processes where they may be stored prior to release. Migration of a secretory body into a peduncular process and exocytosis from such a process appears to be an unusual mode of meocrine secretion, perhaps unique to decidual cells.     

Diffusion Boundary Layers Ameliorate the Negative Effects of Ocean Acidification on the Temperate Coralline Macroalga Arthrocardia corymbosa

Anthropogenically-modulated reductions in pH, termed ocean acidification, could pose a major threat to the physiological performance, stocks, and biodiversity of calcifiers and may devalue their ecosystem services. Recent debate has focussed on the need to develop approaches to arrest the potential negative impacts of ocean acidification on ecosystems dominated by calcareous organisms. In this study, we demonstrate the role of a discrete (i.e. diffusion) boundary layer (DBL), formed at the surface of some calcifying species under slow flows, in buffering them from the corrosive effects of low pH seawater. The coralline macroalga Arthrocardia corymbosa was grown in a multifactorial experiment with two mean pH levels (8.05 ‘ambient’ and 7.65 a worst case ‘ocean acidification’ scenario projected for 2100), each with two levels of seawater flow (fast and slow, i.e. DBL thin or thick). Coralline algae grown under slow flows with thick DBLs (i.e., unstirred with regular replenishment of seawater to their surface) maintained net growth and calcification at pH 7.65 whereas those in higher flows with thin DBLs had net dissolution. Growth under ambient seawater pH (8.05) was not significantly different in thin and thick DBL treatments. No other measured diagnostic (recruit sizes and numbers, photosynthetic metrics, %C, %N, %MgCO₃) responded to the effects of reduced seawater pH. Thus, flow conditions that promote the formation of thick DBLs, may enhance the subsistence of calcifiers by creating localised hydrodynamic conditions where metabolic activity ameliorates the negative impacts of ocean acidification.     

Three types of miniature inhibitory potentiaes in the frog spinal cord motoneurons: the possibility of GABA and glycine co-release

Miniature inhibitory postsynaptic potentials (mlPSPs) were recorded from motoneurons of the frog isolated spinal cord after blocking action potentials and ionotropic glutamate receptors (TTX 1 mcm: CNQX 25 mcm, D-AP5 50 mcm). Three types of mlPSPs were selected by their time characteristics) fast, slow and mlPSPs with two decay time constants. We classified 8.7% of mlPSPs as dual-component, 64.5% as fast mlPSPs, and 26.8% as slow mlPSPs. The GABA(A)R blocker bicuculline (20 mcm) diminished the number of the slow and dual-component events while the number of mlPSP with a fast kinetics was increased. The GlyR antagonist strychnine (1 mcm) reduced the frequency of fast mlPSPs and increased this parameter of slow mlPSPs. These data suggest existence of three different mlPSP groups distinguished by their kinetics and sensitivity to receptor antagonists: fast events mediated by glycine, slow events mediated by GABA and dual-component mlPSPs corresponding to glycine and GABA co-release.     

Three-dimensional rotational plasma flows near solid surfaces in an axial magnetic field

A rotational flow of a conducting viscous medium near an extended dielectric disk in a uniform axial magnetic field is analyzed in the magnetohydrodynamic (MHD) approach. An analytical solution to the system of nonlinear differential MHD equations of motion in the boundary layer for the general case of different rotation velocities of the disk and medium is obtained using a modified Slezkin–Targ method. A particular case of a medium rotating near a stationary disk imitating the end surface of a laboratory device is considered. The characteristics of a hydrodynamic flow near the disk surface are calculated within the model of a finite-thickness boundary layer. The influence of the magnetic field on the intensity of the secondary flow is studied. Calculations are performed for a weakly ionized dense plasma flow without allowance for the Hall effect and plasma compressibility. An MHD flow in a rotating cylinder bounded from above by a retarding cap is considered. The results obtained can be used to estimate the influence of the end surfaces on the main azimuthal flow, as well as the intensities of circulating flows in various devices with rotating plasmas, in particular, in plasma centrifuges and laboratory devices designed to study instabilities of rotating plasmas.     

REGENERATION OF PIGEON FAST AND SLOW MUSCLE FIBER TYPES AFTER PARTIAL EXCISION AND MINCING

The pigeon's metapatagialis muscles, containing fast fibers in two slips and slow fibers in another slip, were excised for a third of their length, minced, and replaced into their previous sites. After regeneration, the pattern of fiber types and their ATPase and oxidative enzymes were examined histochemically. Ultrastructural examination was carried out on the fast fibers. After 4–17 wk the muscles had regenerated into patterns histochemically similar to the controls only within the slip containing fast fibers. The slow slip was much less regenerated, and had a histochemically embryonic composition. Fiber types were characterized and their cross-sectional areas measured, and the degree of atrophy was greatest in the large fast fibers and the slow fibers. Ultrastructural studies revealed a number of alterations of the mitochondria, including dense and light areas in the matrix and an altered pattern of the cristae into parallel tubular or vesicular aggregations. Other changes included dilated sarcoplasmic reticulum, myofibril disorganization, and a compaction of filaments. The slow fibers were thought to be slower in their regeneration rates because of the pattern of multiple innervation's producing a more complex regenerative pattern.     

Modeling the hydraulic effect of transverse deep zones on the performance of short-circuiting constructed treatment wetlands

Short-circuiting, which occurs when a large fraction of water traveling through a system exits well before the residence time, reduces the performance of constructed treatment wetlands. Recent field and laboratory observations have shown that short-circuiting within vegetated marsh areas results from narrow, continuous fast flowpaths that experience longitudinal dispersion but do not exchange fluid with slow flowing regions of dense vegetation on either side. Based on these observations, this paper develops an analytic stream tube model with dispersion to represent flow through the marsh areas of a short-circuiting constructed treatment wetland under steady flow conditions. The model also includes transverse deep zones, which rapidly dissipate fast flowpath momentum and introduce lateral mixing through wind-driven circulation. Modeled results reveal that a transverse deep zone that replaces a portion of a wetland marsh can offset the adverse impact of short-circuiting flowpaths through two separate mechanisms. First, lateral mixing can dilute the water that has traveled through a fast flowpath. Second, deep zones reduce the probability that fast flowpaths align throughout the entire wetland. The model results suggest that deep zones may improve wetland performance when properly sized and located, even when they do not directly contribute to contaminant removal.     

Comparative analysis of circulating hemocytes of the freshwater snail Pomacea canaliculata

Molluscs are invertebrates of great relevance for economy, environment and public health. The numerous studies on molluscan immunity and physiology registered an impressive variability of circulating hemocytes. This study is focused on the first characterization of the circulating hemocytes of the freshwater gastropod Pomacea canaliculata, a model for several eco-toxicological and parasitological researches.Flow cytometry analysis identified two populations of hemocytes on the basis of differences in size and internal organization. The first population contains small and agranular cells. The second one displays major size and a more articulated internal organization. Light microscopy evidenced two principal morphologies, categorized as Group I (small) and II (large) hemocytes. Group I hemocytes present the characteristics of blast-like cells, with an agranular and basophilic cytoplasm. Group I hemocytes can adhere onto a glass surface but seem unable to phagocytize heat-inactivated Escherichia coli. The majority of Group II hemocytes displays an agranular cytoplasm, while a minority presents numerous granules. Agranular cytoplasm may be basophilic or acidophilic. Granules are positive to neutral red staining and therefore acidic. Independently from their morphology, Group II hemocytes are able to adhere and to engulf heat-inactivated E. coli. Transmission electron microscopy analysis clearly distinguished between agranular and granular hemocytes and highlighted the electron dense content of the granules. After hemolymph collection, time-course analysis indicated that the Group II hemocytes are subjected to an evident dynamism with changes in the percentage of agranular and granular hemocytes. The ability of circulating hemocytes to quickly modify their morphology and stainability suggests that P. canaliculata is endowed with highly dynamic hemocyte populations able to cope with rapid environmental changes as well as fast growing pathogens.     

Genesis of connective matrix of Veretillum cynomorium Pall. (Cnidaria-Anthozoa). Ultrastructural and autoradiographic study (author's transl)]

Ultrastructural study of the tissues of Veretillum cynomorium shows the presence of two mesenchymatous cellular states in the mesoglea: the nongranular mesenchymatous cells and the granular mesenchymatous cells. These latter possess, besides their cytoplasmic granules, some homogeneous fibrous inclusions, very similar to the fibrous material of the mesoglea. Granules and homogeneous fibrous inclusions are also present in the cytoplasm of some ectodermic and endodermic cells. These morphological results lead us to consider that mesoglea and epithelia can be occupied by the same granular cell type. Besides this, the digestive endodermic cells are sometimes very rich in heterogeneous fibrous inclusions histochemically identified as phagosomes. An autoradiographic study indicates two possible pathways for the synthesis of the mesoglea. The first involves the endoderm which elaborates the mesoglea at a fast rate but in small amounts. The second is due to the granular cells (mesenchymatous and epithelial) which show a slow rate of synthesis leading to the formation of the homogeneous fibrous inclusions. The heterogeneous fibrous inclusions of the digestive endodermic cell support the hypothesis of the involvement of these cells in mesogleal degradation.     

Effect of flow regime on the architecture of a Pseudomonas fluorescens biofilm

A comparison of the effects of laminar versus turbulent flow regime on the characteristics of a single-species biofilm is presented. The study was carried out by growing Pseudomonas fluorescens biofilms in a flow cell and studying the different layers of the biological matrix with a confocal laser-scanning microscope. The following conclusions were obtained: i) a higher concentration of cells was found in the upper layers of the microbial films than in their inner layers, regardless of the flow regime; ii) the fraction of cells in the overall biofilm mass decreased with time as the film grew; and iii) under laminar flow the total number of cells was higher than in biofilms formed under turbulent flow, but the latter had a higher number of cells per unit volume. Such conclusions, together with the fact that the biofilms were more dense and stable when formed in contact with turbulent flows, favor the design of more compact and efficient biofilm reactors operating in turbulent conditions.