An integrated population model sheds light on the complex population dynamics of a unique colonial breeder

Climate models forecast increasing climatic variation and more extreme events, which could increase the variability in animal demographic rates. More variable demographic rates generally lead to lower population growth and can be detrimental to wild populations, especially if the particular demographic rates affected are those to which population growth is most sensitive. We investigated the population dynamics of a metapopulation of 25 colonies of a semi-arid bird species, the sociable weaver Philetairus socius, and how it was influenced by seasonal weather during 1993–2014. We constructed an integrated population model which estimated population sizes similar to observed population counts, and allowed us to estimate annual fecundity and recruitment. Variance in fecundity contributed most to variance in population growth, which showed no trend over time. No weather variables explained overall demographic variation at the population level. However, a separate analysis of the largest colony showed a clear decline with a high extinction probability (0.05 to 0.33) within 5 years after the study period. In this colony, juvenile survival was lower when summers were hot, and adult survival was lower when winters were cold. Rainfall was also negatively correlated with adult survival. These weather effects could be due to increased physiological demands of thermoregulation and rainfall-induced breeding activity. Our results suggest that the dynamics of the population on the whole are buffered against current weather variation, as individual colonies apparently react in different ways. However, if more and increasingly extreme weather events synchronize colony dynamics, they are likely to have negative effects.     

Maturation of rat brain is accompanied by differential expression of the long and short splice variants of G(s)alpha protein: identification of cytosolic forms of G(s)alpha

Distribution of the alpha subunit of the stimulatory G protein (G(s)alpha) was analyzed in membrane and cytosolic (supernatant 200 000 g) fractions from rat cortex, thalamus and hippocampus during the course of post-natal development. In parallel, changes in beta-adrenoceptor density and adenylyl cyclase activity were determined. Long (G(s)alphaL) and short (G(s)alphaS) variants of G(s)alpha were assessed by immunoblotting using specific polyclonal antisera reacting with both G(s)alpha isoforms. Post-natal development was associated with an increase in the total amount of brain G(s)alpha. G(s)alphaL was the dominant isoform of G(s)alpha in the membrane fractions of all studied brain regions and its amount increased markedly between post-natal day (PD) 1 and 90. The level of membrane-bound G(s)alphaS also elevated during post-natal development, but more pronounced changes were found in cytosolic G(s)alphaS. Although only a small amount of G(s)alphaS (much smaller than G(s)alphaL) was detected among soluble proteins shortly after birth, G(s)alphaS prevailed over G(s)alphaL at PD90. The G(s)alphaL/G(s)alphaS ratio decreased, respectively, from 3.2 to 1.2 and from 5.0 to 1.5 in the membrane fractions of cortex and hippocampus, but remained almost constant in thalamus between PD1 and 90. More dramatic changes were found in the cytosolic fractions of all studied brain regions: the G(s)alphaL/G(s)alphaS ratio decreased sharply in cortex (from 14.1 to 0.9), hippocampus (from 3.7 to 0.8), and also in thalamus (from 9.5 to 0.5). These results demonstrate that the membrane-cytosol balance of G(s)alpha proteins alters dramatically during the course of brain development. Both G(s)alphaL and G(s)alphaS were expressed in a region- and age-specific manner, which suggests different roles in the maturation of the brain tissue. A cyc(-) reconstitutive assay of cytosolic G(s)alpha indicated that only approximately 20% of this protein was functional, compared with membrane-bound G(s)alpha, and its ability to reconstitute adenylyl cyclase activity increased during the course of maturation. The number of beta-adrenoceptors increased sharply during early post-natal development but only slightly in adulthood, and both GTP- and isoproterenol-stimulated adenylate cyclase activity reached peak values around PD12.     

Mannan changes induced by 3-methyl-5-aminoisoxazole-4-thiocyanate,a new azole derivative,on Epidermophyton floccosum

The antifungal activity of 3-methyl-5-aminoisoxazole-4-thiocyanate, a new azole derivative, was studied on the dermatophyte Epidermophyton floccosum. The compound strongly inhibited the in vitro growth of two different strains of the fungus and even induced profound morphogenetic anomalies. Optical and electron microscopy showed that such treatment targets the endomembrane system, particularly the plasmalemma, causing abnormal extrusion of the wall mannans. This results in improper arrangement of the different parietal materials; the walls are thus weak and subject to subapical rupture which terminates cell growth and elongation of the hypha. The morphological results and the preliminary biochemical data on fungal sterols suggest that this compound employs an action mechanism similar to that of other azoles used in therapy.     

Are acute changes after status epilepticus in immature rats persistent?

Early consequences of lithium-pilocarpine convulsive status epilepticus (SE) were studied six days after this status had been induced in rat pups at the age of either 12 or 25 days. Studies of spontaneous EEG activity demonstrated the presence of epileptic phenomena (isolated spikes) in both hippocampus and cortex (cortical spikes were more expressed in the older group). There were no marked behavioral correlates of spikes and transition into the ictal phase was exceptional. The motor performance on a rotorod and a horizontal bar was the same in experimental and control rats of both ages. Behavior in the open field was changed in a reverse manner in the two age groups: the locomotor activity of rats with induced seizures at the age of 12 days was significantly lower than that of their control siblings, whereas animals undergoing status at the age of 25 days were hyperactive. In addition, they also exhibited increased exploratory activity (rearing) and their habituation to the open field was deranged. Nissl-stained brain sections demonstrated extensive brain damage in the older group in contrast to the negative findings in younger animals. EEG, behavioral and morphological changes induced by status epilepticus in developing rats persisted for 6 days after the status. They markedly differed according to the age of animals.     

Subcellular targets of mercaptoborate (BSH), a carrier of 10B for neutron capture therapy (BNCT) of brain tumors

The transformed C6 glial cells in cultures were treated with sodium mercaptoborate (Na(2)B(12)H(11)SH, BSH), a carrier of atomic targets ((10)B) of thermal neutrons for the neutron capture therapy of brain tumors. As shown by light microscopy, the therapeutic dose of BSH (100 microg/ml) did not alter the gross morphology and growth of the population of cells within a 72 h treatment interval. Electron microscopic analysis of these cells revealed activation of nucleoli and, occasionally, enlarged and bifurcated mitochondria. After 200 microg BSH/ml and 72 h treatment, growth of the cell population was inhibited and ultrastructural changes became more profound. They included condensation of chromatin and its allocation to the nuclear envelope which formed deeper invaginations. Mitochondria further increased in size and were characterized by slim or angular cristae. Moreover, in circumscribed segments of some of the slightly swollen mitochondria their cristae disappeared or were reduced to fine pouch-like structures localized near the continuous outer membrane, suggestive for a non-destructive restructuring of the inner mitochondrial membrane. The smooth pinocytotic vesicles near the plasma membrane, lysosomes and heterogeneous dense bodies were more frequent. The revealed subcellular targets of BSH may initiate the development of pharmacological protocols aimed to further improve the tolerance to BSH by the healthy tissues of patients undergoing BNCT of brain tumors, e.g. by intervention into the oxidative stress triggered likely by the altered mitochondria.     

Identification of Electric-Field-Dependent Steps in the Na,K-Pump Cycle

The charge-transporting activity of the Na⁺,K⁺-ATPase depends on its surrounding electric field. To isolate which steps of the enzyme’s reaction cycle involve charge movement, we have investigated the response of the voltage-sensitive fluorescent probe RH421 to interaction of the protein with BTEA (benzyltriethylammonium), which binds from the extracellular medium to the Na⁺,K⁺-ATPase’s transport sites in competition with Na⁺ and K⁺, but is not occluded within the protein. We find that only the occludable ions Na⁺, K⁺, Rb⁺, and Cs⁺ cause a drop in RH421 fluorescence. We conclude that RH421 detects intramembrane electric field strength changes arising from charge transport associated with conformational changes occluding the transported ions within the protein, not the electric fields of the bound ions themselves. This appears at first to conflict with electrophysiological studies suggesting extracellular Na⁺ or K⁺ binding in a high field access channel is a major electrogenic reaction of the Na⁺,K⁺-ATPase. All results can be explained consistently if ion occlusion involves local deformations in the lipid membrane surrounding the protein occurring simultaneously with conformational changes necessary for ion occlusion. The most likely origin of the RH421 fluorescence response is a change in membrane dipole potential caused by membrane deformation.     

Serosurvey of Brucella spp. infection in the Kafue lechwe (Kobus leche kafuensis) of the Kafue flats in Zambia

One of the diseases of veterinary and public health importance affecting the Kafue lechwe (Kobus leche kafuensis) on the Kafue flats is brucellosis, for which only scant information is available. During the 2003 (October), 2004 (December), and 2008 (July-December) hunting seasons in the Kafue flats, we conducted a study to determine the seroprevalence of Brucella spp. in the Kafue lechwe and to evaluate serologic tests for detection of Brucella spp. antibodies in lechwe. The Rose Bengal Test (RBT), competitive enzyme-linked immunosorbent assay (cELISA), and fluorescence polarization assay (FPA) were used. A total of 121 Kafue lechwe were hunted for disease investigations in 2003, 2004, and 2008 in the Kafue Flat Game Management Area. Of these, 21.6%, (95% confidence interval [CI]: 14.2-29.1%) had detectable antibodies to Brucella spp. The Kafue lechwe in Lochnivar National Park had higher antibody results than those in Blue Lagoon National Park (odds ratio=3.0; 95% CI: 0.94-9.4). Infection levels were similar in females (21.6%) and males (21.7%). Results were similar among RBT, FPA, cELISA tests, suggesting that these could effectively be used in diagnosing brucellosis in the Kafue lechwe. Our study demonstrates the presence of Brucella infections in the Kafue lechwe in two national parks located in the Kafue flats and further highlights the suitability of serologic assays for testing the Kafue lechwe. Because the Kafue lechwe is the most hunted wildlife species in Zambia, hunters need to be informed of the public health risk of Brucella spp. infection.     

Insertional mutagenesis combined with an inducible filamentation phenotype reveals a conserved STE50 homologue in Cryptococcus neoformans that is required for monokaryotic fruiting and sexual reproduction

Cryptococcus neoformans typically grows in a yeast-like morphology; however, under specific conditions the fungus can produce hyphae that are either dikaryotic or monokaryotic. In this study, we developed a simple method for inducing robust monokaryotic fruiting and combined the assay with Agrobacterium tumefaciens insertional mutagenesis to screen for hyphal mutants. A C. neoformans homologue of the Saccharomyces cerevisiae STE50 gene was identified and characterized. STE50 was found to be required for sexual reproduction and monokaryotic fruiting. Ste50p has conserved SAM and RA domains, as well as two SH3 domains specific to basidiomycetous Ste50 proteins. Analysis of protein-protein interaction showed that Ste50p can interact with Ste11p and Ste20p, and epistasis experiments placed STE50 between STE20 and STE11. Genetic analysis of the role of STE50 in sexual reproduction showed that it was required for all steps, from response to pheromone to production of hyphae. Analysis of the effect of individual Ste50p domains on sexual reproduction and monokaryotic fruiting revealed domain-specific effects for both processes. This study revealed that the C. neoformans STE50 gene has both conserved and novel functions during sexual reproduction and monokaryotic fruiting, and these functions are domain-dependent.     

Differential elicitation of two processing proteases controls the processing pattern of the trypsin proteinase inhibitor precursor in Nicotiana attenuata

Trypsin proteinase inhibitors (TPIs) of Nicotiana attenuata are major antiherbivore defenses that increase dramatically in leaves after attack or methyl jasmonate (MeJA) elicitation. To understand the elicitation process, we characterized the proteolytic fragmentation and release of TPIs from a multidomain precursor by proteases in MeJA-elicited and unelicited plants. A set of approximately 6-kD TPI peptides was purified from leaves, and their posttranslational modifications were characterized. In MeJA-elicited plants, the diversity of TPI structures was greater than the precursor gene predicted. This elicited structural heterogeneity resulted from differential fragmentation of the linker peptide (LP) that separates the seven-domain TPI functional domains. Using an in vitro fluorescence resonance energy transfer assay and synthetic substrates derived from the LP sequence, we characterized proteases involved in both the processing of the TPI precursor and its vacuolar targeting sequence. Although both a vacuolar processing enzyme and a subtilisin-like protease were found to participate in a two-step processing of LP, only the activity of the subtilisin-like protease was significantly increased by MeJA elicitation. We propose that MeJA elicitation increases TPI precursor production and saturates the proteolytic machinery, changing the processing pattern of TPIs. To test this hypothesis, we elicited a TPI-deficient N. attenuata genotype that had been transformed with a functional NaTPI gene under control of a constitutive promoter and characterized the resulting TPIs. We found no alterations in the processing pattern predicted from the sequence: a result consistent with the saturation hypothesis.