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.     

Trends in Menarcheal Age between 1955 and 2009 in the Netherlands

Aim

To assess and compare the secular trend in age at menarche in Dutch girls (1955–2009) and girls from Turkish and Moroccan descent living in the Netherlands (1997–2009).

Methods

Data on growth and maturation were collected in 20,867 children of Dutch, Turkish and Moroccan descent in 2009 by trained health care professionals. Girls, 9 years and older, of Dutch (n = 2138), Turkish (n = 282), and Moroccan (n = 295) descent were asked whether they had experienced their first period. We compared median menarcheal age in 2009 with data from the previous Dutch Nationwide Growth Studies in 1955, 1965, 1980 and 1997. Age specific body mass index (BMI) z-scores were calculated to assess differences in BMI between pre- and postmenarcheal girls in different age groups.

Results

Median age at menarche in Dutch girls, decreased significantly from 13.66 years in 1955 to 13.15 years in 1997 and 13.05 years in 2009. Compared to Dutch girls there is a larger decrease in median age of menarche in girls of Turkish and Moroccan descent between 1997 and 2009. In Turkish girls age at menarche decreased from 12.80 to 12.50 years and in Moroccan girls from 12.90 to 12.60 years. Thirty-three percent of Turkish girls younger than 12 years start menstruating in primary school. BMI-SDS is significantly higher in postmenarcheal girls than in premenarcheal girls irrespective of age.

Conclusion

There is a continuing secular trend in earlier age at menarche in Dutch girls. An even faster decrease in age at menarche is observed in girls of Turkish and Moroccan descent in the Netherlands.     

Computational techniques for using insole pressure sensors to analyse three-dimensional joint kinetics

This study evaluated the feasibility of using insole pressure sensors together with whole body dynamics to analyse joint kinetics while running. Local affine transformations of shoe kinematics were first used to track the position of insole sensors during locomotion. Centre of pressure estimates derived from the insoles were within 10 mm of forceplate measures through much of stance, while vertical force estimates were within 15% of peak forceplate recordings. Insole data were then coupled with a least squares whole body dynamic model to obtain shear force estimates that were comparable to forceplate records during running. We demonstrated that these techniques provide a viable approach for analysing joint kinetics when running on uninstrumented surfaces.     

Toxin-antitoxin modules as bacterial metabolic stress managers

Bacterial genomes frequently contain operons that encode a toxin and its antidote. These 'toxin-antitoxin (TA) modules' have an important role in bacterial stress physiology and might form the basis of multidrug resistance. The toxins in TA modules act as gyrase poisons or stall the ribosome by mediating the cleavage of mRNA. The antidotes contain an N-terminal DNA-binding region of variable fold and a C-terminal toxin-inhibiting domain. When bound to toxin, the C-terminal domain adopts an extended conformation. In the absence of toxin, by contrast, this domain (and sometimes the whole antidote protein) remains unstructured, allowing its fast degradation by proteolysis. Under silent conditions the antidote inhibits the toxin and the toxin-antidote complex acts as a repressor for the TA operon, whereas under conditions of activation proteolytic degradation of the antidote outpaces its synthesis.     

Characterization of Dystrophin Deficient Rats: A New Model for Duchenne Muscular Dystrophy

A few animal models of Duchenne muscular dystrophy (DMD) are available, large ones such as pigs or dogs being expensive and difficult to handle. Mdx (X-linked muscular dystrophy) mice only partially mimic the human disease, with limited chronic muscular lesions and muscle weakness. Their small size also imposes limitations on analyses. A rat model could represent a useful alternative since rats are small animals but 10 times bigger than mice and could better reflect the lesions and functional abnormalities observed in DMD patients. Two lines of Dmd mutated-rats (Dmd^mdx) were generated using TALENs targeting exon 23. Muscles of animals of both lines showed undetectable levels of dystrophin by western blot and less than 5% of dystrophin positive fibers by immunohistochemistry. At 3 months, limb and diaphragm muscles from Dmd^mdx rats displayed severe necrosis and regeneration. At 7 months, these muscles also showed severe fibrosis and some adipose tissue infiltration. Dmd^mdx rats showed significant reduction in muscle strength and a decrease in spontaneous motor activity. Furthermore, heart morphology was indicative of dilated cardiomyopathy associated histologically with necrotic and fibrotic changes. Echocardiography showed significant concentric remodeling and alteration of diastolic function. In conclusion, Dmd^mdx rats represent a new faithful small animal model of DMD.     

FUNGI FROM THE LOWER DEVONIAN RHYNIE CHERT: CHYTRIDIOMYCETES

Several different chytridiomycetes are described from the Lower Devonian (Siegenian) Rhynie chert. Included are both eucarpic and apparently holocarpic forms that occur in Palaeonitella, Aglaophyton, Lyonophyton, Horneophyton, and clusters of algal cells, as well as in the surrounding chert matrix. Holocarpic types consist of endobiotic sporangia, each characterized by one discharge tube. Sporangia can be traced from the thallus stage to the discharge of zoospores. Monocentric and polycentric eucarpic chytrids are associated with the miospores of Aglaophyton and various thick-walled fungal spores. In these forms the sporangia are variable in size and shape ranging up to 30 μm. Most appear to be inoperculate and there is evidence that the sporangium ruptured on the distal surface. Some contain zoospores with flagella. One operculate eucarpic form had parasitized the cellular gametophyte emerging from the proximal surface of an Aglaophyton spore. Several of the Rhynie chert chytrids are comparable with a number of extant forms (e.g., Olpidiaceae and Spizellomycetaceae), while others possess features that encompass several groups. These fossil fungi are discussed in the context of their interactions with other organisms in this Lower Devonian freshwater paleoecosystem.     

Rapid typing of Coxiella burnetii

Coxiella burnetii has the potential to cause serious disease and is highly prevalent in the environment. Despite this, epidemiological data are sparse and isolate collections are typically small, rare, and difficult to share among laboratories as this pathogen is governed by select agent rules and fastidious to culture. With the advent of whole genome sequencing, some of this knowledge gap has been overcome by the development of genotyping schemes, however many of these methods are cumbersome and not readily transferable between institutions. As comparisons of the few existing collections can dramatically increase our knowledge of the evolution and phylogeography of the species, we aimed to facilitate such comparisons by extracting SNP signatures from past genotyping efforts and then incorporated these signatures into assays that quickly and easily define genotypes and phylogenetic groups. We found 91 polymorphisms (SNPs and indels) among multispacer sequence typing (MST) loci and designed 14 SNP-based assays that could be used to type samples based on previously established phylogenetic groups. These assays are rapid, inexpensive, real-time PCR assays whose results are unambiguous. Data from these assays allowed us to assign 43 previously untyped isolates to established genotypes and genomic groups. Furthermore, genotyping results based on assays from the signatures provided here are easily transferred between institutions, readily interpreted phylogenetically and simple to adapt to new genotyping technologies.     

Inhibitory Control of Linear and Supralinear Dendritic Excitation in CA1 Pyramidal Neurons

The transformation of dendritic excitatory synaptic inputs to axonal action potential output is the fundamental computation performed by all principal neurons. We show that in the hippocampus this transformation is potently controlled by recurrent inhibitory microcircuits. However, excitatory input on highly excitable dendritic branches could resist inhibitory?control by generating strong dendritic spikes and?trigger precisely timed action potential output. Furthermore, we show that inhibition-sensitive branches can be transformed into inhibition-resistant, strongly spiking branches by intrinsic plasticity of branch excitability. In addition, we demonstrate that the inhibitory control of spatially defined dendritic excitation is strongly regulated by network activity patterns. Our findings suggest that dendritic spikes may serve to transform correlated branch input into reliable and temporally precise output even in the presence of inhibition.     

Loss of Slc4a1b Chloride/Bicarbonate Exchanger Function Protects Mechanosensory Hair Cells from Aminoglycoside Damage in the Zebrafish Mutant persephone

Mechanosensory hair cell death is a leading cause of hearing and balance disorders in the human population. Hair cells are remarkably sensitive to environmental insults such as excessive noise and exposure to some otherwise therapeutic drugs. However, individual responses to damaging agents can vary, in part due to genetic differences. We previously carried out a forward genetic screen using the zebrafish lateral line system to identify mutations that alter the response of larval hair cells to the antibiotic neomycin, one of a class of aminoglycoside compounds that cause hair cell death in humans. The persephone mutation confers resistance to aminoglycosides. 5 dpf homozygous persephone mutants are indistinguishable from wild-type siblings, but differ in their retention of lateral line hair cells upon exposure to neomycin. The mutation in persephone maps to the chloride/bicarbonate exchanger slc4a1b and introduces a single Ser-to-Phe substitution in zSlc4a1b. This mutation prevents delivery of the exchanger to the cell surface and abolishes the ability of the protein to import chloride across the plasma membrane. Loss of function of zSlc4a1b reduces hair cell death caused by exposure to the aminoglycosides neomycin, kanamycin, and gentamicin, and the chemotherapeutic drug cisplatin. Pharmacological block of anion transport with the disulfonic stilbene derivatives DIDS and SITS, or exposure to exogenous bicarbonate, also protects hair cells against damage. Both persephone mutant and DIDS-treated wild-type larvae show reduced uptake of labeled aminoglycosides. persephone mutants also show reduced FM1-43 uptake, indicating a potential impact on mechanotransduction-coupled activity in the mutant. We propose that tight regulation of the ionic environment of sensory hair cells, mediated by zSlc4a1b activity, is critical for their sensitivity to aminoglcyoside antibiotics.