Juvenile salmonid populations in a temperate river system track synoptic trends in climate

Widespread declines among Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) over recent decades have been linked to pollution, exploitation and catchment modification, but climate change is increasingly implicated. We used long‐term, geographically extensive data from the Welsh River Wye, formerly a major salmon river, to examine whether climatically mediated effects on juveniles (>0+) might contribute to population change. Populations of Atlantic salmon and brown trout fell across the Wye catchment, respectively, by 50% and 67% between 1985 and 2004, but could not be explained by pollution because water quality improved during this time. Stream temperatures, estimated from calibrations against weekly air temperature at eight sites, increased by 0.5–0.7 °C in summer and 0.7–1.0 °C in winter, with larger tributaries warming more than shaded headwaters. Rates of winter warming were slightly greater after accounting for the effect of the North Atlantic Oscillation (1.1–1.4 °C). However, warming through time was smaller than measured variations among tributaries, and alone was insufficient to explain variations in salmonid density. Instead, population variations were best explained in multilevel mixed models by a synoptic variate representing a trend towards hotter, drier summers, implying interactions between climate warming, varying discharge and fluctuations in both brown trout and salmon. Taken alongside recent data showing effects of warming on survival at sea, these data suggest that Atlantic salmon might be jeopardized by future climatic effects in both their marine and freshwater stages. Effects on nondiadromous brown trout also imply climatically mediated processes in freshwaters or their catchments. Climate projections for the United Kingdom suggest that altered summer flow and increasing summer temperatures could exacerbate losses further in these species, and we advocate management actions that combine reduced abstraction with enhanced riparian shading.     

Mitochondrial gene diversity in Cepaea– population structure, history and positive selection

Previous studies on the geographical distributions of both shell polymorphisms and mitochondrial haplotypes in Cepaea land snails have suggested varying contributions of natural selection, random genetic drift and population history to the origin and persistence of variation. We combine previous studies of polymorphism within two species of Cepaea , with new molecular data from two mitochondrial genes. The distributions of mitochondrial variants suggest that elements of population history may have been influential in creating patterns of diversity. However, some patterns of amino acid substitution that are found in a protein coding gene are also consistent with the action of diversifying selection. This suggests the possibility that in addition to stochastic processes such as repeated founder events, local extinctions and random genetic drift within a structured population, adaptive molecular change may have affected mitochondrial diversity.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 167–184.     

Interaction of specialist root and shoot herbivores of Alliaria petiolata and their impact on plant performance and reproduction

Abstract.  1. This study explored interactions of two spatially and temporally separated weevils and their impact on Alliaria petiolata (garlic mustard) survival, growth, and reproduction at different herbivore densities.
2. The root-mining weevil Ceutorhynchus scrobicollis attacks A. petiolata rosettes from October to April, and larvae complete development in May. The shoot-mining weevil Ceutorhynchus alliariae attacks bolting plants in April/May with larvae completing development in June–July. Priority effects were expected, with early attack of C. scrobicollis affecting the later attacking C. alliariae , mediated through changes in plant growth or chemistry.
3. Attack by C. scrobicollis significantly increased plant mortality and changed plant architecture, while C. alliariae only significantly reduced plant height. Attack by C. scrobicollis also increased nitrogen content of stems.
4. Root feeding by C. scrobicollis affected the feeding niche of C. alliariae , but increased stem nitrogen content did not result in increased stem miner survival. While reduced height and stem diameters as a result of C. scrobicollis attack reduced C. alliariae attack at the stem level, attack at plant level and recruitment was unaffected.
5. Weevil density had no effect on plant performance, most likely due to strong intraspecific competition, and there were no synergistic effects between the two herbivores.
6. Overall, attack by C. scrobicollis was more detrimental to A. petiolata growth, seed output, and survival than attack by C. alliariae . Consequently, C. scrobicollis has been prioritised as a potential biocontrol agent for control of A. petiolata in North America.     

Characterization of a G Protein -Coupled Guanylyl Cyclase -B Receptor from Bovine Tracheal Smooth Muscle

A G protein-coupled natriuretic peptide-guanylyl cyclase receptor-B (NPR-B) located in plasma membranes from bovine tracheal smooth muscle shows complex kinetics and regulation. NPR-B was activated by natriuretic peptides (CNP-53 > ANP-28) at the ligand extracellular domain, stimulated by Gq-protein activators, such as mastoparan, and inhibited by Gi-sensitive chloride, interacting at the juxtamembrane domain. The kinase homology domain was evaluated by the ATP inhibition of Mn²⁺-activated NPR-B, which was partially reversed by mastoparan. The catalytic domain was studied by kinetics of Mn²⁺/Mg²⁺ and GTP, and the catalytic effect with GTP analogues with modifications of the /γ phosphates and ribose moieties. Most NPR-B biochemical properties remained after detergent solubilization but the mastoparan activation and chloride inhibition of NPR-B disappeared. Our results indicate that NPR-B is a highly regulated nano-machinery with domains acting at cross-talk points with other signal transducing cascades initiated by G protein-coupled receptors and affected by intracellular ligands such as chloride, Mn²⁺, Mg²⁺, ATP, and GTP.     

Indication of antagonistic interaction between climate change and erosion on plant species richness and soil properties in semiarid Mediterranean ecosystems

We analyzed the consequences of climate change and the increase in soil erosion, as well as their interaction on plant and soil properties in semiarid Mediterranean shrublands in Eastern Spain. Current models on drivers of biodiversity change predict an additive or synergistic interaction between drivers that will increase the negative effects of each one. We used a climatic gradient that reproduces the predicted climate changes in temperature and precipitation for the next 40 years of the wettest and coldest end of the gradient; we also compared flat areas with 20° steep hillslopes. We found that plant species richness and plant cover are negatively affected by climate change and soil erosion, which in turn negatively affects soil resistance to erosion, nutrient content and water holding capacity. We also found that plant species diversity correlates weakly with plant cover but strongly with soil properties related to fertility, water holding capacity and resistance to erosion. Conversely, these soil properties correlate weaker with plant species cover. The joint effect of climate change and soil erosion on plant species richness and soil characteristics is antagonistic. That is, the absolute magnitude of change is smaller than the sum of both effects. However, there is no interaction between climate change and soil erosion on plant cover and their effects fit the additive model. The differences in the interaction model between plant cover and species richness supports the view that several soil properties are more linked to the effect that particular plant species have on soil processes than to the quantity and quality of the plant cover and biomass they support. Our findings suggest that plant species richness is a better indicator than plant cover of ecosystems services related with soil development and protection to erosion in semiarid Mediterranean climates.     

Influence of quantity and lability of sediment organic matter on the biomass of two isoetids,Littorella uniflora and Echinodorus repens

1. Despite real improvement in the water quality of many previously eutrophic lakes, the recovery of submerged vegetation has been poor. This lack of recovery is possibly caused by the accumulation of organic matter on the top layer of the sediment, which is produced under eutrophic conditions. Hence, our objective was to study the combined effects of quantity and lability of sediment organic matter on the biomass of Echinodorus repens and Littorella uniflora and on the force required to uproot plants of L. uniflora. 2. Lake sediments, rich in organic matter, were collected from four lakes, two with healthy populations of isoetids and two from which isoetids had disappeared. The four lake sediments were mixed with sand to prepare a range of experimental sediments that differed in quantity and lability of sediment organic matter. Two isoetid species, E. repens and L. uniflora, were grown in these sediments for 8 weeks. Sediment quality parameters, including elemental composition, nutrient availability and mineralisation rates, were determined on the raw sources of sediment from the lakes. Porewater and surface water were analysed for the chemical composition in all mixtures. At the end of the experiment, plants were harvested and their biomass, tissue nutrient concentration and (for L. uniflora) uprooting force were measured. 3. For both species, all plants survived and showed no signs of stress on all types of sediment. The biomass of E. repens increased as the fraction of organic matter was increased (from 6 to 39% of organic content, depending upon sediment type). However, in some of the sediment types, a higher fraction of organic matter led to a decline in biomass. The biomass of L. uniflora was less responsive to organic content and was decreased significantly only when the least labile sediment source was used to create the gradient of organic matter. The increase in shoot biomass for both species was closely related to higher CO₂ concentrations in the porewater of the sediment. The force required to uproot L. uniflora plants over a range of sediment organic matter fitted a Gaussian model; it reached a maximum at around 15% organic matter and declined significantly above that. 4. Increasing organic matter content of the sediment increased the biomass of isoetid plants, as the positive effects of higher CO₂ production outweighed the negative effects of low oxygen concentration in more (labile) organic sediments. However, sediment organic matter can adversely affect isoetid survival by promoting the uprooting of plants.     

Chemical Composition of Viscin Mucilage from Three Mistletoe Species--A comparison

The viscin of mistletoes is a unique tissue which serves toprovide strong adherence of the seed of the parasite to thehost branch. The viscin mucilage of three species, Phoradendroncalifornicum and Arceuthobium americanum (Viscaceae) and Phthirusapyrifolia (Loranthaceae), was analysed. The major componentof the mucilage of Pho. californicum and A. americanum was polysaccharidic;of this, neutral sugars comprised the largest portion, but substantialamounts of uronic acids and proteins were also present. Xyloseand arabinose were the most abundant of the neutral sugars,and analysis showed glycine to be the most abundant amino acidas well as the presence of higher-than-average amounts of histidine.In contrast, in the mucilage of Pht. pyrifolia glucose was themost abundant neutral sugar and the protein content was substantiallyhigher. Based on the differences in composition observed amongthe different species the future use of viscin components astaxonomic markers is suggested. Viscin mucilage, mistletoes, Arceuthobium americanum, Phthirusa pyrifolia, Phoradendron californicum, g.l.c., amino acid analysis     

Influence of bacterial density and water temperature on the grazing activity of two freshwater ciliates

1. The influences of bacterial density and water temperature on the grazing activity of the ciliates Uronema sp. and Colpoda inflata were studied. The conditions assayed were two prey densities (10⁶ and 4 × 10⁷ bacteria ml^?1) and three water temperatures (10, 15 and 22 °C). 2. The response of the ciliates was measured from changes in protistan biovolumes and specific clearance rates. At high prey density, both ciliates showed lower biovolumes as water temperature increased, while at low prey density this tendency was minimized. 3. At the intermediate temperature of 15 °C both ciliates filtered ten times more body volume when bacteria were scarce; however, the ingested bacteria were fewer than at high prey density. At low prey density, a decrease from 15 to 10 °C evidenced different strategies of the two ciliates, which led to a similar ingestion of bacteria: C. inflata reduced its specific clearance rates and increased its biovolume, while Uronema sp. did not show changes. At high prey density, an increase from 15 to 22 °C caused lower biovolumes and a noticeable increase in specific clearance rates in both ciliates, indicating opportunist behaviour.