Temporal population variability in local forest communities has mixed effects on tree species richness across a latitudinal gradient

Among the local processes that determine species diversity in ecological communities, fluctuation‐dependent mechanisms that are mediated by temporal variability in the abundances of species populations have received significant attention. Higher temporal variability in the abundances of species populations can increase the strength of temporal niche partitioning but can also increase the risk of species extinctions, such that the net effect on species coexistence is not clear. We quantified this temporal population variability for tree species in 21 large forest plots and found much greater variability for higher latitude plots with fewer tree species. A fitted mechanistic model showed that among the forest plots, the net effect of temporal population variability on tree species coexistence was usually negative, but sometimes positive or negligible. Therefore, our results suggest that temporal variability in the abundances of species populations has no clear negative or positive contribution to the latitudinal gradient in tree species richness.     

Temperature effects on fish production across a natural thermal gradient

Global warming is widely predicted to reduce the biomass production of top predators, or even result in species loss. Several exceptions to this expectation have been identified, however, and it is vital that we understand the underlying mechanisms if we are to improve our ability to predict future trends. Here, we used a natural warming experiment in Iceland and quantitative theoretical predictions to investigate the success of brown trout as top predators across a stream temperature gradient (4–25 °C). Brown trout are at the northern limit of their geographic distribution in this system, with ambient stream temperatures below their optimum for maximal growth, and above it in the warmest streams. A five‐month mark‐recapture study revealed that population abundance, biomass, growth rate, and production of trout all increased with stream temperature. We identified two mechanisms that contributed to these responses: (1) trout became more selective in their diet as stream temperature increased, feeding higher in the food web and increasing in trophic position; and (2) trophic transfer through the food web was more efficient in the warmer streams. We found little evidence to support a third potential mechanism: that external subsidies would play a more important role in the diet of trout with increasing stream temperature. Resource availability was also amplified through the trophic levels with warming, as predicted by metabolic theory in nutrient‐replete systems. These results highlight circumstances in which top predators can thrive in warmer environments and contribute to our knowledge of warming impacts on natural communities and ecosystem functioning.     

Dietary zinc deficiency has no effect on auditory brainstem responses in the rat

Zinc has been shown to effect--in vitro--a number of processes associated with neurotransmission. We have tested whether the rate of impulse conduction--in vivo--as measured from the latencies of auditory brainstem responses (ABR), is influenced by dietary zinc deficiency in the rat. Dietary zinc deficiency for up to 26 wk had no effect on the wave I-IV interval compared to zinc-adequate fed animals. The results are discussed in relation to the observed constancy of brain overall and extracellular fluid zinc concentrations under conditions of dietary zinc deficiency.     

Toxin depletion has no effect on antipredator responses in common toad (Bufo bufo) tadpoles

Antipredator responses often involve changes in several phenotypic traits and these changes interactively influence fitness. However, gaining insight into how the overall fitness effect of the overall response comes about is notoriously difficult. One promising avenue is to manipulate a single defensive trait and observe how that modifies fitness as well as the expression of other inducible responses. In chemically‐defended animals, toxins are likely to be costly to produce but it is still unknown how their depletion influences other characteristics. In the present study, we artificially depleted bufadienolide toxin stores in common toad (Bufo bufo) tadpoles, and assessed the effect of this with respect to the interaction with predator presence and limited food availability. We found that toxin depletion in tadpoles did not significantly affect any of the measured life‐history traits. Tadpoles in the predator treatment exhibited an elevated development rate, although this was only apparent when food availability was limited. Also, body mass at metamorphosis was lower in tadpoles exposed to chemical cues indicating a predation threat and when food availability was limited. These results provide evidence that, in larval common toads, the expression of inducible defences may incur fitness costs, whereas chemical defences are either expressed constitutively or, if inducible, elevated toxin production has negligible costs.     

Temperature acclimation has no effect on ryanodine receptor expression or subcellular localization in rainbow trout heart

In cardiomyocytes, ryanodine receptors (RYRs) mediate Ca²⁺-induced Ca²⁺-release (CICR) from the sarcoplasmic reticulum (SR) during excitation–contraction (e–c) coupling. In rainbow trout heart, the relative importance of CICR increases with cold-acclimation. Thus, the aim of this study was to investigate the effect of temperature acclimation (4, 11 and 18°C) on RYR intracellular localization and expression density. We used immunocytochemistry to assess intracellular localization in ventricular myocytes and Western blotting to assess RYR expression in both atrial and ventricular tissue. In ventricular myocytes, RYRs were localized peripherally in transverse bands aligning with sarcomeric m-lines and centrally around mitochondria and the nucleus. Localization did not change with temperature acclimation. RYR expression was also unaffected by temperature acclimation. The localization of RYRs at the m-line is similar to neonatal mammalian cardiomyocytes. We suggest this positioning is indicative of myocytes which rely predominantly on transsarcolemmal Ca²⁺-influx, rather than CICR, during e–c coupling.     

Effects of anthropogenic habitat disturbance on local pollinator diversity and species turnover across a precipitation gradient

Anthropogenic habitat disturbance can have profound effects on multiple components of forest biotas including pollinator assemblages. We assessed the effect of small-scale disturbance on local richness, abundance, diversity and evenness of insect pollinator fauna; and how habitat disturbance affected species turnover across the landscape and overall diversity along a precipitation gradient in NW Patagonia (Argentina). We evaluated the effect of disturbance on overall pollinator fauna and then separately for bees (i.e. Apoidea) and non-bee pollinators. Locally, disturbed habitats had significantly higher pollinator species richness and abundances than undisturbed habitats for the whole pollinator assemblage, but not for bees or non-bees separately. However, significant differences in species richness between habitats vanished after accounting for differences in abundance between habitat types. At a local scale Shannon–Weaver diversity and evenness did not vary with disturbance. A β diversity index indicated that, across forest types, species turnover was lower between disturbed habitats than between undisturbed habitats. In addition, rarefaction curves showed that disturbed habitats as a whole accumulated fewer species than undisturbed habitats at equivalent sample sizes. We concluded that small patches of disturbed habitat have a negligible effect on local pollinator diversity; however, habitat disturbance reduced β diversity through a homogenization of the pollinator fauna (in particular of bees) across the landscape.     

Relative influence of deterministic processes on structuring marsh plant communities varies across an abiotic gradient

Understanding the processes determining community structure is one of the major goals of ecological research. Both deterministic and stochastic processes may shape community structure. The challenge is to understand the relative influence of each type of process across different environmental conditions. We investigated the influence of deterministic and stochastic processes on plant community assembly in tidal marshes across a strong abiotic (salinity) gradient in three estuaries in Georgia, USA using probabilistic Raup–Crick community dissimilarity. Our results indicated that deterministic processes had an increasingly important influence on structuring plant communities in salt and brackish marshes, probably due to high heterogeneity of microhabitats produced by the interplay between abiotic stress and biotic interactions. In contrast, the influence of deterministic processes on plant community assembly decreased in tidal freshwater marshes, suggesting an increasingly important role of stochastic processes in plant community assembly in tidal freshwater marshes, probably due to the higher species richness, higher recruitment from seed, and lower levels of abiotic stress in these habitats. At the estuarine scale (across tidal freshwater, brackish and salt marshes in each estuary), our results suggested that deterministic processes also had a relatively important influence on shaping plant community structure. Our results illustrated that plant community structure in tidal marshes is influenced by both deterministic and stochastic processes, but that the relative influence of these two types of processes varies across estuarine landscapes.     

Human recombinant interleukin 1 beta has no effect on intracellular calcium or on functional responses of human neutrophils

The effect of human recombinant interleukin 1 beta (rIL 1 beta) on human neutrophils was examined. rIL 1 beta, even at concentrations of 100 ng/ml (100 half-maximal T cell stimulating U/ml) did not change significantly the intracellular free calcium concentration, [Ca++]i, whereas the control stimulus, fmet-leu-phe, significantly elevated [Ca++]i. rIL 1 beta also failed to stimulate production of superoxide, degranulation of lysosomal enzymes, phagocytosis of bacterial particles, chemotaxis, or chemokinesis of human neutrophils. This is substantial evidence that superphysiologic concentrations of interleukin 1 have no direct effect on [Ca++]i, as well as on functional responses of neutrophils.     

TPA has no influence on the expression of myosin heavy chain isoforms in cultured adult cardiac muscle cells.

The effect of a tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA), on the expression of myosin heavy chain isoforms in cultured rat cardiac ventricular muscle cells was studied. The previous preliminary report [Claycomb WC (1988): "Biology of Isolated Adult Cardiac Myocytes." In Clark WA, Decker RS, Borg TK (eds): New York: Elsevier, pp 284-287] indicated that TPA turns off the expression of myosin heavy chain genes in cultured adult cardiac myocytes. Electrophoretic and immunocytochemical analyses were carried out in the present studies. The myosin heavy chain isoform profiles of cardiac myocytes exposed to TPA at concentrations of 50-250 ng/ml culture medium for varying periods were similar to those of controls that were grown in the absence of TPA, showing predominant isoform V1. Immunofluorescence microscopy with monoclonal antibodies to cardiac ventricular isomyosin revealed the structural organization of myosin in TPA-treated cells. The organization of myosin was variable among different myocytes and within a single myocyte. Immunofluorescence microscopy was extended to the examination of the organization of alpha-actinin which did not differ from that of myosin in some myocytes. In contrast to the previous report [Claycomb, 1988], this study has demonstrated that TPA has no influence on the expression of myosin heavy chain isoforms in cultured adult ventricular cardiac muscle cells.     

Acute running stimulates hippocampal dopaminergic neurotransmission in rats, but has no influence on brain-derived neurotrophic factor

Hippocampal brain-derived neurotrophic factor (BDNF) protein is increased with exercise in rats. Monoamines seem to play a role in the regulation of BDNF, and monoamine neurotransmission is known to increase with exercise. The purpose of this study was to examine the influence of acute exercise on monoaminergic neurotransmission and BDNF protein concentrations. Hippocampal microdialysis was performed in rats that were subjected to 60 min of treadmill running at 20 m/min or rest. Two hours postexercise, the rats were killed, and the hippocampus was dissected. In experiments without microdialysis, hippocampus and serum samples were collected immediately after exercise. Exercise induced a twofold increase in hippocampal dopamine release. Noradrenaline and serotonin release were not affected. Hippocampal BDNF levels were not influenced, whether they were measured immediately or 2 h after the exercise protocol. Serum BDNF levels did not change either, but serum BDNF was negatively correlated to peripheral corticosterone concentrations, indicating a possible inhibitory reaction to the stress of running. Sixty minutes of exercise enhances dopamine release in the hippocampus of the rat in vivo. However, this increase is not associated with changes in BDNF protein levels immediately nor 2 h after the acute exercise bout. An increased corticosterone level might be the contributing factor for the absence of changes in BDNF.     

The influence of topical capsaicin on the local thermal control of skin blood flow in humans

To test whether heat-sensitive receptors participate in the cutaneous vascular responses to direct heating, we monitored skin blood flow (SkBF; laser Doppler flowmetry) where the sensation of heat was induced either by local warming (T(Loc); Peltier cooling/heating unit) or by both direct warming and chemical stimulation of heat-sensitive nociceptors (capsaicin). In part I, topical capsaicin (0.075 or 0.025%) was applied to 12 cm(2) of skin 1 h before stepwise local warming of untreated and capsaicin-treated forearm skin. Pretreatment with 0.075% capsaicin cream shifted the SkBF/T(Loc) relationship to lower temperatures by an average of 6 +/- 0.8 degrees C (P < 0.05). In part II, we used a combination of topical capsaicin (0.025%) and local warming to evoke thermal sensation at one site and only local warming to evoke thermal sensation at a separate site. Cutaneous vasomotor responses were compared when the temperatures at these two sites were perceived to be the same. SkBF differed significantly between capsaicin and control sites when compared on the basis of actual temperatures, but that difference became insignificant when compared on the basis of the perceived temperatures. These data suggest heat-sensitive nociceptors are important in the cutaneous vasodilator response to local skin warming.     

Maternal uniparental disomy 22 has no impact on the phenotype.

A 25-year-old normal healthy male was karyotyped because five of his wife's pregnancies terminated in spontaneous abortions at 6-14 wk of gestation. Cytogenetic investigation disclosed a de novo balanced Robertsonian t(22q;22q) translocation. Molecular studies revealed maternal only inheritance for chromosome 22 markers. Reduction to homozygosity for all informative markers indicates that the rearranged chromosome is an isochromosome derived from one of the maternal chromosomes 22. Except for the possibility of homozygosity for recessive mutations, maternal uniparental disomy 22 does not seem to have an adverse impact on the phenotype, apart from causing reproductive failure. It can be concluded that no maternally imprinted genes with major effect map to chromosome 22.     

Nicotinamide has no effect on the ethanol-induced decrease in testosterone biosynthesis

Administration of ethanol to Wistar rats in a dose of 3.5 g per 1 kg of the weight is accompanied by a decrease of testosterone concentration in the blood plasma. Nicotinamide, a NAD predecessor, exerts no effect on this index being applied in a dose of 200 mg/kg and does not modify the action of ethanol being administered in combination with the latter NAD concentration in the testicles as well as the rate of its utilization in the course of poly-ADP-ribose synthetase reaction remains unchanged. The data obtained contradict the hypothesis that ethanol effects in the testicles are determined by accessibility of oxidated NAD.     

The influence of Trypanosoma brucei infection on local immunoglobulin responses of rats to Nippostrongylus brasiliensis

Wedrychowicz H., Maclean J. M. and Holmes P. H., 1984. The influence of Trypanosoma brucei infection on local immunoglobulin responses of rats to Nippostrongylus brasiliensis. International Journalfor Parasitology14: 453–458. Serum, intestinal and lung immunoglobulin and antibody isotype responses to Nippostrongylus brasiliensis infection were studied in normal and trypanosome-infected Hooded Lister rats. Rats which received trypanosomes 7 days before N. brasiliensis infection had impaired responses of serum IgG and IgA. Bronchial and intestinal mucosal IgG was not reduced whilst IgA concentration in these sites was markedly diminished. Total immunoglobulin M levels in T. brucei parasitised rats were higher in both sera and mucosal sites. However, tests with radiolabelled adult nematode excretory-secretory antigens indicated that specific lung and intestinal IgM responses were reduced. Immunoglobulin A antibody responses were diminished most markedly in sera and lungs and also in the intestine while IgG antibodies were decreased in sera and intestine mucosae T. brucei infected rats had higher worm burdens than rats infected with N. brasiliensis alone but worm expulsion was not delayed. The results indicate that local as well as systemic antibody responses are reduced in trypanosome infected animals.     

Benzalkonium chloride (BAK) induces apoptosis or necrosis, but has no major influence on the cell cycle of Jurkat cells

Benzalkonium chloride (BAK) is a cationic detergent with a very slow turnover. Because of its strong antibacterial activities, BAK is widely used especially in dentistry and ophthalmology. It is the most commonly used preservative in topical ophthalmic medications. Due to chronicity and widespread use of such treatments, BAK's side effects are of great importance. BAK toxicity for adherent cells, probably related to its pro-oxidative activities, is time- and dose-dependent. Although lymphocytes often infiltrate superficial eye tissues, the BAK influence on them is yet to be established. The aim of this study was to check BAK cytotoxicity on T lymphocytic Jurkat line cells and to verify the suggestion that BAK can induce G2M cell blocks. A dose- and time-dependent cytotoxic effect of BAK on lymphoid cells in relatively low concentrations was shown in this study. In lower concentrations, it shows a moderate apoptotic and minimal antiproliferative effect on Jurkat cells, while in higher concentrations it shows a rapid necrotic effect. No G2M cell blocks were observed. Our findings could suggest lymphoid dysfunction during intensive, prolonged topical BAK treatment, even at dosages relatively non-toxic to epithelial eye cells.     

The effect of repeated mild cold water immersions on the adaptation of the vasomotor responses

There are several types of cold adaptation based on the alteration of thermoregulatory response. It has been thought that the temperature of repeated cold exposures during the adaptation period is one of the factors affecting the type of cold adaptation developed. This study tested the hypothesis that repeated mild cold immersions would induce an insulative cold adaptation but would not alter the metabolic response. Seven healthy male participants were immersed to their xiphoid process level repeatedly in 26°C water for 60 min, 3 days every week, for 4 weeks. During the first and last exposure of this cold acclimation period, the participants underwent body immersion tests measuring their thermoregulatory responses to cold. Separately, they conducted finger immersion into 5°C water for 30 min to assess their cold-induced vasodilation (CIVD) response before and after cold acclimation. During the immersion to xiphoid process, participants showed significantly lower mean skin temperature and skin blood flow in the forearm post-acclimation, while no adaptation was observed in the metabolic response. Additionally, blunted CIVD responses were observed after cold acclimation. From these results, it was considered that the participants showed an insulative-type of cold acclimation after the repeated mild cold immersions. The major finding of this study was the acceptance of the hypothesis that repeated mild cold immersion was sufficient to induce insulative cold adaptation but did not alter the metabolic response. It is suggested that the adaptation in the thermoregulatory response is specific to the response which is repeatedly stimulated during the adaptation process.     

Different responses of avian feeding guilds to spatial and environmental factors across an elevation gradient in the central Himalaya

Although elevational patterns of species richness have been well documented, how the drivers of richness gradients vary across ecological guilds has rarely been reported. Here, we examined the effects of spatial factors (area and mid‐domain effect; MDE) and environmental factors, including metrics of climate, productivity, and plant species richness on the richness of breeding birds across different ecological guilds defined by diet and foraging strategy. We surveyed 12 elevation bands at intervals of 300 m between 1,800 and 5,400 m a.s.l using line‐transect methods throughout the wet season in the central Himalaya, China. Multiple regression models and hierarchical partitioning were used to assess the relative importance of spatial and environmental factors on overall bird richness and guild richness (i.e., the richness of species within each guild). Our results showed that richness for all birds and most guilds displayed hump‐shaped elevational trends, which peaked at an elevation of 3,300–3,600 m, although richness of ground‐feeding birds peaked at a higher elevation band (4,200–4,500 m). The Normalized Difference Vegetation Index (NDVI)—an index of primary productivity—and habitat heterogeneity were important factors in explaining overall bird richness as well as that of insectivores and omnivores, with geometric constraints (i.e., the MDE) of secondary importance. Granivore richness was not related to primary production but rather to open habitats (granivores were negatively influenced by habitat heterogeneity), where seeds might be abundant. Our findings provide direct evidence that the richness–environment relationship is often guild‐specific. Taken together, our study highlights the importance of considering how the effects of environmental and spatial factors on patterns of species richness may differ across ecological guilds, potentially leading to a deeper understanding of elevational diversity gradients and their implications for biodiversity conservation.