Extinction debt in a common grassland species: immediate and delayed responses of plant and population fitness

Changes in landscape structure and environmental conditions due to habitat fragmentation can have significant effects on plant populations. Decreasing genetic diversity and changing population structure can reduce plant fitness and influence the long-term persistence of populations. Dry calcareous grasslands in Estonia have witnessed a large decline in area within the last 80 years, but due to extinction debt, the species richness in these grasslands has not yet responded to this decline. In these calcareous grasslands, we studied genetic diversity, phenotypic performance and population characteristics of a common habitat-specialist grass, Briza media. A decrease in genetic diversity was associated with a decrease in plant reproductive output. In addition, we found that some fitness components of B. media showed a delayed response to landscape changes. Specifically, plant height and germination success were related to historical rather than to current landscape parameters, indicating a time-lagged response of plant performance to habitat fragmentation. Dependence on historical landscape structure may thus result in a future decline in population fitness even if habitat loss and fragmentation no longer continue. The documented effect of current environmental conditions, however, shows that fitness-related traits are already slowly adapting to the changing conditions. Our results indicate that even common habitat-specialist species can be susceptible to landscape changes and be threatened by decreased population performance in the future.     

Novel Galanin Receptor Subtype Specific Ligand in Depression Like Behavior

Neuropeptide galanin and its three receptors, galanin receptor type 1–galanin receptor type 3, are known to be involved in the regulation of numerous psychological processes, including depression. Studies have suggested that stimulation of galanin receptor type 2 (GalR2) leads to attenuation of the depression-like behavior in animals. However, due to the lack of highly selective galanin subtype specific ligands the involvement of different receptors in depression-like behavior is yet not fully known. In the present study we introduce a novel GalR2 selective agonist and demonstrate its ability to produce actions consistent with theorized GalR2 functions and analogous to that of the anti-depressant, imipramine.     

Measuring carbon and N2 fixation in field populations of colonial and free‐living unicellular cyanobacteria using nanometer‐scale secondary ion mass spectrometry1

Unicellular cyanobacteria are now recognized as important to the marine N and C cycles in open ocean gyres, yet there are few direct in situ measurements of their activities. Using a high‐resolution nanometer scale secondary ion mass spectrometer (nanoSIMS), single cell N₂ and C fixation rates were estimated for unicellular cyanobacteria resembling N₂ fixer Crocosphaera watsonii. Crocosphaera watsonii‐like cells were observed in the subtropical North Pacific gyre (22°45′ N, 158°0′ W) as 2 different phenotypes: colonial and free‐living. Colonies containing 3–242 cells per colony were observed and cell density in colonies increased with incubation time. Estimated C fixation rates were similarly high in both phenotypes and unexpectedly for unicellular cyanobacteria 85% of the colonial cells incubated during midday were also enriched in ¹⁵N above natural abundance. Highest ¹⁵N enrichment and N₂ fixation rates were found in cells incubated overnight where up to 64% of the total daily fixed N in the upper surface waters was attributed to both phenotypes. The colonial cells retained newly fixed C in a sulfur‐rich matrix surrounding the cells and often cells of both phenotypes possessed areas (<1 nm) of enriched ¹⁵N and ¹³C resembling storage granules. The nanoSIMS imaging of the colonial cells also showed evidence for a division of N₂ and C fixation activity across the colony where few individual cells (<34%) in a given colony were enriched in both ¹⁵N and ¹³C above the colony average. Our results provide new insights into the ecophysiology of unicellular cyanobacteria.     

Tree diversity and species identity effects on soil fungi,protists and animals are context dependent

Plant species richness and the presence of certain influential species (sampling effect) drive the stability and functionality of ecosystems as well as primary production and biomass of consumers. However, little is known about these floristic effects on richness and community composition of soil biota in forest habitats owing to methodological constraints. We developed a DNA metabarcoding approach to identify the major eukaryote groups directly from soil with roughly species-level resolution. Using this method, we examined the effects of tree diversity and individual tree species on soil microbial biomass and taxonomic richness of soil biota in two experimental study systems in Finland and Estonia and accounted for edaphic variables and spatial autocorrelation. Our analyses revealed that the effects of tree diversity and individual species on soil biota are largely context dependent. Multiple regression and structural equation modelling suggested that biomass, soil pH, nutrients and tree species directly affect richness of different taxonomic groups. The community composition of most soil organisms was strongly correlated due to similar response to environmental predictors rather than causal relationships. On a local scale, soil resources and tree species have stronger effect on diversity of soil biota than tree species richness per se.     

Comparative analysis detects dependencies among the 5' splice-site positions

Human-mouse comparative genomics is an informative tool to assess sequence functionality as inferred from its conservation level. We used this approach to examine dependency among different positions of the 5' splice site. We compiled a data set of 50,493 homologous human-mouse internal exons and analyzed the frequency of changes among different positions of homologous human-mouse 5' splice-site pairs. We found mutual relationships between positions +4 and +5, +5 and +6, -2 and +5, and -1 and +5. We also demonstrated the association between the exonic and the intronic positions of the 5' splice site, in which a stronger interaction of U1 snRNA and the intronic portion of the 5' splice site compensates for weak interaction of U1 snRNA and the exonic portion of the 5' splice site, and vice versa. By using an ex vivo system that mimics the effect of mutation in the 5' splice site leading to familial dysautonomia, we demonstrated that U1 snRNA base-pairing with positions +6 and -1 is the only functional requirement for mRNA splicing of this 5' splice site. Our findings indicate the importance of U1 snRNA base-pairing to the exonic portion of the 5' splice site.     

Immune response is energetically costly in white cabbage butterfly pupae

Parasite-driven coevolution has led hosts to develop a complicated and potentially costly defence machinery, consisting mainly of the immune system. Despite the evidence for the trade-offs between immune function and life-history traits, it is still obscure how the costs of using and maintaining the immune function are paid. We tested whether immune challenge is energetically costly for white cabbage butterfly (Pieris brassicae L.) diapausing pupa. Individuals challenged with nylon implant raised their standard metabolic rate nearly 8% compared to the controls. Hence, costs of activation of immune system in insect pupa can be expressed in energetic currency.     

Ragweed plants and airborne pollen in the Baltic states

Presence of pollen in the atmosphere was determined inTartu in 1989–1997, in Kuressaare in 1996–1997 and iniauliai in 1997. Ragweed airpollen was found in latesummer in three years. The distribution, abundance andflowering of local ragweed plants were estimated. Itappeared that the number of local sources did notexceed twenty per country per year. Majority of thesesources consisted of a small number of pollinating A. artemisiifolia individuals. The largest localsources, consisting of several hundreds ofindividuals, were exclusively rare. Transport ofragweed pollen by air masses from distant sources wasstudied. It was found that incursions of ragweedpollen were determined by air fluxes originating fromthe Ukraine as well as from the southeastern andsouthern regions of the European part of Russia. Theseincursions occurred in extensive high-pressure areaswhose centre was located in the central region of theEuropean part of Russia with a periphery extending tothe Baltic countries.     

An intersubunit zinc binding site in rat P2X2 receptors

P2X receptors are ATP-gated ion channels made up of three similar or identical subunits. It is unknown whether ligand binding is intersubunit or intrasubunit, either for agonists or for allosteric modulators. Zinc binds to rat P2X2 receptors and acts as an allosteric modulator, potentiating channel opening. To probe the location of this zinc binding site, P2X2 receptors bearing mutations of the histidines at positions 120 and 213 were expressed in Xenopus oocytes. Studies of H120C and H213C mutants produced five lines of evidence consistent with the hypothesis that the residues in these positions bind zinc. Mixing of subunits containing the H120A or H213A mutation generated receptors that showed zinc potentiation, even though neither of these mutant receptors showed zinc potentiation on its own. Furthermore, expression of trimeric concatamers with His --> Ala mutations at some but not all six positions showed that zinc potentiation correlated with the number of intersubunit histidine pairs. These results indicate that zinc potentiation requires an interaction across a subunit interface. Expression of the H120C/H213C double mutant resulted in the formation of ectopic disulfide bonds that could be detected by changes in the physiological properties of the receptors after treatment with reducing and oxidizing agents. Immunoblot analysis of H120C/H213C protein separated under nonreducing conditions demonstrated that the ectopic bonds were between adjacent subunits. Taken together, these data indicate that His120 and His213 sit close to each other across the interface between subunits and are likely to be key components of the zinc binding site in P2X2 receptors.     

Factor X activator from Vipera lebetina venom is synthesized from different genes

Vipera lebetina venom contains specific coagulant Factor X activator (VLFXA) that cleaves the Arg52-Ile53 bond in the heavy chain of human factor X. VLFXA is a glycoprotein that is composed of a heavy chain (HC) and two light chains (LC) linked by disulfide bonds. The complete amino acid sequences of the three chains of the factor X activator from V. lebetina snake venom are deduced from the nucleotide sequences of cDNAs encoding these chains. The full-length cDNA (2347 bp) sequence of the HC encodes an open reading frame (ORF) of 612 amino acids that includes signal peptide, propeptide and mature metalloproteinase with disintegrin-like and cysteine-rich domains. The light chain LC1 contains 123 and LC2 135 amino acid residues. Both light chains belong to the class of C-type lectin-like proteins. The N-termini of VLFXA chains and inner sequences of peptide fragments detected by liquid chromatography-electrospray ionization tandem mass spectrometry (LC MS/MS) from protein sequence are 100% identical to the sequences deduced from the cDNA. The molecular masses of tryptic fragments of VLFXA chains analyzed by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) also confirm the protein sequences deduced from the cDNAs. These are the first cloned factor X activator heavy and light chains. We demonstrate that the heavy and light chains are synthesized from different genes.