Annual carbon fixation in terrestrial populations of Nostoc commune (Cyanobacteria) from an Antarctic dry valley is driven by temperature regime

Nostoc commune Vaucher (a cyanobacterium) is a very conspicuous terrestrial primary producer in Victoria Land, continental Antarctica. Because polar ecosystems are considered to be especially sensitive to environmental changes, understanding the environmental constraints on net carbon (C) fixation by N. commune is necessary to determine the effects of environmental changes on the ecological functioning of ice‐free areas of the continent. A model describing net C fixation in terrestrial populations of N. commune in an Antarctic dry valley was constructed using field and laboratory measurements in which N. commune colonies were exposed to different combinations of incident irradiance (400–700 nm), temperature, and degree of desiccation. For desiccated N. commune mats with water content ≤ 30% saturation, net C fixation was highly variable between replicates and could not be modelled. However, for colonies at > 30% saturation, rates of net C fixation and dark respiration depended strongly on irradiance and temperature. Net C fixation reached a maximum rate of 21.6 μg C m^{− 2} s^{− 1} at irradiance of approximately 250 μmol m^{− 2} s^{− 1} and the optimum temperature of 20.5 °C. Agreement between predicted short‐term net C fixation and field and laboratory measurements allowed estimation of total seasonal fixation, using previously published environmental data. Annual net C fixation was estimated in the range 14.5–21.0 g C fixed m^{− 2}Nostoc mat, depending on year/season. Estimates for different seasons correlated with thermal time (accumulated hours above 0 °C during the year) rather than irradiance, in contrast to communities in local lacustrine environments, where irradiance is the main driver of primary productivity. In the terrestrial habitat, N. commune appears to compromise between an ability to capitalize on short periods of higher temperature and efficient utilization of lower irradiance at low temperature. The relationship between thermal time and net annual C fixation by N. commune is strongly linear.     

Transplantation of an indigenous neural stem cell population leading to hyperplasia and atypical integration

Astrocytes exhibit neural stem cell characteristics in vitro by generating multipotent clones of cells. In order to see if normal cues are present in vivo that can direct these astrocytes to generate cells of neuronal lineage, the astrocytes were transplanted into the persistently neurogenic mouse subependymal zone/rostral migratory stream. Grafted astrocytes assumed migratory profiles, joined chains of indigenous neuroblasts, and migrated into the olfactory bulb. Additionally, however, some grafted astrocytes "homed" to the lateral ventricle where they became hyperplastic, forming spherical structures composed of cells of mixed phenotype that attached to the ventricular wall, and eventually penetrated and dispersed within surrounding brain parenchyma. It is proposed that, with an interest in the use of stem cell transplants for neurological disease, findings of hyperplasia and apparent atypical integration of a native population of multipotent astrocytic stem cells suggest the need for caution before beginning even autologous neural stem cell transplants.     

Traction force on a kinetochore at metaphase acts as a linear function of kinetochore fiber length

We are investigating the relation between the force pulling a kinetochore poleward and the length of the corresponding kinetochore fiber. It was recognized by Ostergren in 1950 (Hereditas 36:1-19) that the metaphase position of a chromosome could be achieved by a balance of traction forces were proportional to the distance from kinetochore to pole. For the typical chromosome (i.e., a meiotic bivalent or mitotic chromosome) with a single kinetochore fiber extending to each pole, the resultant force (RF) would equal zero when the chromosome lay at the midpoint between the two poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles. For special chromosomes that have unequal numbers of kinetochore fibers extending towards opposite poles, Ostergren’s proposal suggests that RF = 0 when the chromosome is shifted closer to the pole toward which the greater number of kinetochore fibers are pulling. We have measured the force-length relationship in living spindles by analyzing the metaphase positions of experimentally generated multivalent chromosomes having three or four kinetochore fibers. Multivalent chromosomes of varied configurations were generated by γ-irradiation of nymphs of the grasshopper melanoplus differentialis, and their behavior was analyzed in living first meiotic spermocytes. The lengths of kinetochore fibers were determined from time-lapse photographs by measuring the kinetochore-to-pole distances for fully congressed chromosomes just before the onset of anaphase. In our analysis, force (F) along a single kinetochore fiber is expressed by: F = kL(exp), where k is a length-independent proportionality constant, L represents the kinetochore fiber length, and exp is an unknown exponent. The RF on a chromosome is then given by: RF = σk(i)L(i)(exp), where kinetochore fiber lengths in opposite half- spindles are given opposite sign. If forces on a metaphase chromosome are at equilibrium (RF = 0), then for asymmetrical orientations of multivalents we can measure the individual kinetochore fiber lengths (L(i)) and solve for the exponent that yields a resultant force of zero. The value of the exponent relates how the magnitude of force along a kinetochore fiber varies with its length. For six trivalents and one naturally occurring quadrivalent we calculated an average value of exp = 1.06 +/- 0.18. This result is consistent with Ostergren’s hypothesis and indicates that the magnitude of poleward traction force along a kinetochore fiber is directly proportional to the length of the fiber. Our finding suggests that the balance of forces along a kinetochore fiber may be a major factor regulating the extent of kinetochore microtubule assembly.     

Vivid molecular divergence over volcanic remnants: the phylogeography of Megadromus guerinii on Banks Peninsula,New Zealand

Megadromus guerinii, an endemic carabid beetle (Carabidae), is the most common carabid throughout its restricted range on Banks Peninsula, a formation of extinct volcanoes in Canterbury, New Zealand. This study characterises the small-scale phylogeographic patterns of M. guerinii across the formerly volcanically active Banks Peninsula using mitochondrial and ribosomal genes. Between the eastern and western areas of the peninsula, the mitochondrial, but not nuclear, DNA has a well-defined geographic distribution. Specifically, mitochondrial cytochrome c oxidase subunit I (CO1) identifies two distinct groups (> 6% divergence between eastern and western beetles) while ribosomal genes show no discernible pattern. Whether such a pattern represents male-biased dispersal, Wolbachia infection, a recent range expansion of a divergent lineage, or a deeper historic separation is explored. There is potential that male-biased dispersal could have occurred. Wolbachia infection was not detected. We conclude that historical processes have likely separated taxa in the eastern and western peninsula.     

Construction and evaluation of multisite recombinatorial (Gateway) cloning vectors for Gram-positive bacteria

Background  

The Gateway recombinatorial cloning system allows easy and rapid joining of DNA fragments. Here we report the construction and evaluation of three different Gram-positive vectors that can be used with the Multisite Gateway cloning system to rapidly produce new gene arrangements in plasmid constructs for use in a variety of Gram-positive bacteria.     

Assessing Compensatory Versus Additive Harvest Mortality: An Example Using Greater Sage-Grouse

ABSTRACT We used band-recovery data from 2 populations of greater sage-grouse (Centrocercus urophasianus), one in Colorado, USA, and another in Nevada, USA, to examine the relationship between harvest rates and annual survival. We used a Seber parameterization to estimate parameters for both populations. We estimated the process correlation between reporting rate and annual survival using Markov chain Monte Carlo methods implemented in Program MARK. If hunting mortality is additive to other mortality factors, then the process correlation between reporting and survival rates will be negative. Annual survival estimates for adult and juvenile greater sage-grouse in Nevada were 0.42±0.07 (x̄±SE) for both age classes, whereas estimates of reporting rate were 0.15±0.02 and 0.16±0.03 for the 2 age classes, respectively. For Colorado, average reporting rates were 0.14±0.016, 0.14±0.010, 0.19±0.014, and 0.18±0.014 for adult females, adult males, juvenile females, and juvenile males, respectively. Corresponding mean annual survival estimates were 0.59±0.01, 0.37±0.03, 0.78±0.01, and 0.64±0.03. Estimated process correlation between logit-transformed reporting and survival rates for greater sage-grouse in Colorado was ρ = 0.68±0.26, whereas that for Nevada was ρ = 0.04±0.58. We found no support for an additive effect of harvest on survival in either population, although the Nevada study likely had low power. This finding will assist mangers in establishing harvest regulations and otherwise managing greater sage-grouse populations.     

Disentangling stocking introgression and natural migration in brown trout: survival success and recruitment failure in populations with semi‐supportive breeding

1. Introgression into natural salmonid populations from stocked conspecifics has been widely studied. Outcomes vary from no effect even after decades of stocking, to population replacement after only a couple of generations. Potential introgression caused by semi‐supportive breeding (i.e. using a mixture of local strains as brood stock) is, however, less well studied. 2. We investigated population structure of brown trout (Salmo trutta) in a regulated alpine lake with three natural, environmentally contrasting tributaries used as spawning and rearing habitat. Massive semi‐supportive breeding of admixed local strains has been implemented for decades. Stocked trout represented c. 17% of the total lake population, and a substantial post‐release survival reflects a considerable potential for introgression. However, the mark‐recapture studies indicate no spawning runs of stocked fish. 3. Using 13 polymorphic microsatellite loci, we found natural straying and non‐native reproduction, especially among wild populations inhabiting environmentally unstable habitat. Retained genetic structure across tributaries indicated low reproductive success of wild‐born non‐natives. Moreover, the genetic structure among tributaries has probably not been influenced by semi‐supportive breeding, because of recruitment failure of stocked trout.     

GM1-ganglioside-mediated activation of the unfolded protein response causes neuronal death in a neurodegenerative gangliosidosis

GM1-ganglioside (GM1) is a major sialoglycolipid of neuronal membranes that, among other functions, modulates calcium homeostasis. Excessive accumulation of GM1 due to deficiency of lysosomal beta-galactosidase (beta-gal) characterizes the neurodegenerative disease GM1-gangliosidosis, but whether the accumulation of GM1 is directly responsible for CNS pathogenesis was unknown. Here we demonstrate that activation of an unfolded protein response (UPR) associated with the upregulation of BiP and CHOP and the activation of JNK2 and caspase-12 leads to neuronal apoptosis in the mouse model of GM1-gangliosidosis. GM1 loading of wild-type neurospheres recapitulated the phenotype of beta-gal-/- cells and activated this pathway by depleting ER calcium stores, which ultimately culminated in apoptosis. Activation of UPR pathways did not occur in mice double deficient for beta-gal and ganglioside synthase, beta-gal-/-/GalNAcT-/-, which do not accumulate GM1. These findings suggest that the UPR can be induced by accumulation of the sialoglycolipid GM1 and this causes a novel mechanism of neuronal apoptosis.     

The T-Cell Antigen Receptor: A Logical Response to an Unknown Ligand

The immune system can be roughly divided into innate and adaptive compartments. The adaptive compartment includes the B and T lymphocytes, whose antigen receptors are generated by recombination of gene segments. The consequence is that the creation of self-reactive lymphocytes is unavoidable. For the host to remain viable, the immune system has evolved a strategy for removing autoimmune lymphocytes during development. This review discusses how T lymphocytes are generated, how they recognize antigens, and how their antigen receptor directs the removal of self-reactive T cells.     

Indirect sperm transfer and male mating strategies in soil invertebrates

Summary

Many soil invertebrates transfer their sperm indirectly by means of spermatophores. Among the different taxa there is great variation in spermatophore architecture, auxiliary structures and behaviour. The behaviour, ranging from elaborate courtship rituals to seemingly indifferent scattering of spermatophores, can roughly be classified as association and dissociation. Which of the two is adaptive depends on many factors which can be summarized in a simple functional response model showing that in some cases the best choice depends on density.