Effects of resource distribution, patch spacing, and preharvest information on foraging decisions of northern bobwhites

We investigated patch assessment by northern bobwhites (Collinusvirginianus) in an experimental arena where the distributionof resources in patches, preharvest information about thesepatches, and spacing of patches varied. We found that preharvestinformation about patch quality and a bimodal distribution ofpatch rewards allowed birds to selectively exploit patches highin resources. In contrast, uniform distribution of patch qualitiesand lack of preharvest information caused birds to forage nonselectivelyamong patches. Birds distinguished among patches of differentquality when these patches were spaced 13 m apart, but failedto react to patch quality differences when patches were 0 or3 m apart We also found a strong effect of the level of patchdepletion on foraging decisions: as resources in die arena becamescarce, birds increasingly foraged selectively in die most profitablepatches. Foraging decisions of bobwhites are biased by die waythey experience and memorize a spatially and temporally variableenvironment. The relative cost of this cognitive bias (i.e.,lost opportunity) is nonlinearty related to die mean resourcedensity in die environment and to die difference between thismean density and die resource density in die exploited patch.Cognitive bias should be considered when evaluating patch assessmentcapabilities of foragers in complex environments.     

Patch time allocation in male parasitoids

Abstract 1. Patch time allocation has been mostly studied in female parasitoids exploiting patches of hosts. Different parameters such as oviposition, host encounters, patch quality, etc. have been repeatedly shown to modify the time females invest on hosts. 2. Male parasitoids are expected to maximise their lifetime fitness by maximising the number of females inseminated during their life. Because they can be sperm and/or time limited, they should optimise their time allocation on emergence patches. 3. Patch time allocation thus appears to be an important question for both male and female parasitoids. 4. In this study, we determined the parameters used by males of the egg parasitoid Trichogramma turkestanica to decide when to leave the emergence patch. Among the different patch‐leaving parameters tested, only contacts with parasitised hosts and presence of virgin females significantly influenced the patch‐leaving tendency. 5. Our results suggest that males express behaviours that could enable them to optimise their patch exploitation time, as females do, but using different strategies.     

Local and global pyrogeographic evidence that indigenous fire management creates pyrodiversity

Despite the challenges wildland fire poses to contemporary resource management, many fire‐prone ecosystems have adapted over centuries to millennia to intentional landscape burning by people to maintain resources. We combine fieldwork, modeling, and a literature survey to examine the extent and mechanism by which anthropogenic burning alters the spatial grain of habitat mosaics in fire‐prone ecosystems. We survey the distribution of Callitris intratropica, a conifer requiring long fire‐free intervals for establishment, as an indicator of long‐unburned habitat availability under Aboriginal burning in the savannas of Arnhem Land. We then use cellular automata to simulate the effects of burning identical proportions of the landscape under different fire sizes on the emergent patterns of habitat heterogeneity. Finally, we examine the global extent of intentional burning and diversity of objectives using the scientific literature. The current distribution of Callitris across multiple field sites suggested long‐unburnt patches are common and occur at fine scales (<0.5 ha), while modeling revealed smaller, patchy disturbances maximize patch age diversity, creating a favorable habitat matrix for Callitris. The literature search provided evidence for intentional landscape burning across multiple ecosystems on six continents, with the number of identified objectives ranging from two to thirteen per study. The fieldwork and modeling results imply that the occurrence of long‐unburnt habitat in fire‐prone ecosystems may be an emergent property of patch scaling under fire regimes dominated by smaller fires. These findings provide a model for understanding how anthropogenic burning alters spatial and temporal aspects of habitat heterogeneity, which, as the literature survey strongly suggests, warrant consideration across a diversity of geographies and cultures. Our results clarify how traditional fire management shapes fire‐prone ecosystems, which despite diverse objectives, has allowed human societies to cope with fire as a recurrent disturbance.     

Myotube formation is affected by adipogenic lineage cells in a cell-to-cell contact-independent manner

Intramuscular adipose tissue (IMAT) formation is observed in some pathological conditions such as Duchenne muscular dystrophy (DMD) and sarcopenia. Several studies have suggested that IMAT formation is not only negatively correlated with skeletal muscle mass but also causes decreased muscle contraction in sarcopenia. In the present study, we examined w hether adipocytes affect myogenesis. For this purpose, skeletal muscle progenitor cells were transfected with siRNA of PPARγ (siPPARγ) in an attempt to inhibit adipogenesis. Myosin heavy chain (MHC)-positive myotube formation was promoted in cells transfected with siPPARγ compared to that of cells transfected with control siRNA. To determine whether direct cell-to-cell contact between adipocytes and myoblasts is a prerequisite for adipocytes to affect myogenesis, skeletal muscle progenitor cells were cocultured with pre- or mature adipocytes in a Transwell coculture system. MHC-positive myotube formation was inhibited when skeletal muscle progenitor cells were cocultured with mature adipocytes, but was promoted when they were cocultured with preadipocytes. Similar effects were observed when pre- or mature adipocyte-conditioned medium was used. These results indicate that preadipocytes play an important role in maintaining skeletal muscle mass by promoting myogenesis; once differentiated, the resulting mature adipocytes negatively affect myogenesis, leading to the muscle deterioration observed in skeletal muscle pathologies.     

Rationalization of poor solubility of TGF-β3 using MD simulation

Despite sequence and structural similarity, TGF-β3 has low solubility among other isoforms of TGF-β. We used nanosecond of molecular dynamic simulations (MD) with explicit solvent, alone and in presence of urea, to investigate the intermediates resulting from the unfolding process of TGF-β3 and TGF-β1. MD simulations of the full-length proteins show a very early loss of α-helix in TGF-β3 compared to the one in the TGF-β1. MD simulation of a small fragment consisting of H3 α-helix of TGF-β3 shows conversion of this segment to β-sheet. Relative instability of H3 α-helix in TGF-β3 and its propensity to form β-sheet may explain the poor solubility of TGF-β3 compared to TGF-β1. The other reasons for poor solubility of TGF-β3 may be the hydrophobic patches on its surface and low charge over the entire range of pH.     

Defensins play a crucial role in protecting mice against oral Shigella flexneri infection

An earlier study revealed that 4-day-old mice, but not older mice, were infected with invasive Shigella strains. Here we attempted to determine the underlying mechanism that induces inflammation in the intestines of neonate mice after oral Shigella infection. Wild-type BALB/c mice of different ages (7, 14, and 35 days old) were orally administered GFP-expressing Shigella flexneri 5a M90T strain (5 × 10⁹ CFU) and analyzed for colonization 6 h following infection. We found that Shigella localized in the epithelium, lamina propria, and crypt regions of the small intestines of 7-day-old BALB/c mice. Microarray analysis revealed that expression levels of cryptdin and various types of cryptdin-related mRNA (e.g., cryptrs-2, -5, -7, -12 and lysozyme) in the small intestines were significantly lower in 7-day-old than in older mice regardless of Shigella infection status. Interestingly, matrix metalloprotease-7 (matrilysin)-deficient (MAT^−/−) mice of B6 background had more colonies and more severe symptoms of inflammation in the intestines than did wild-type B6 mice after oral Shigella challenge. This suggests that cryptdin-related antimicrobial molecules are indispensable for efficient protection against oral Shigella infection.     

Extinction conditions for isolated populations affected by environmental stochasticity

We determine the critical patch size below which extinction occurs for populations living in one-dimensional habitats surrounded by completely hostile environments in the presence of environmental fluctuations. The population dynamics is reformulated in terms of a stochastic reaction–diffusion equation and is reduced to a deterministic equation that incorporates the systematic contributions of the noise. We obtain bifurcation diagrams and relations for the mean population density at the stationary state, the critical patch size, and the mean number of individuals in the habitat. The effect of the noise differs, depending on whether it affects the net growth rate or the intraspecific competition term. Fluctuations in the net growth rate decrease the critical patch size, whereas fluctuations in the competition term do not change the critical patch size. We compare our analytical results with numerical solutions of the stochastic partial differential equations and show that our procedure proves useful in dealing with reaction–diffusion equations with multiplicative noise.     

The chaotropic anions thiocyanate and nitrate inhibit the electric current through the tonoplast ATPase of isolated vacuoles from suspension cells of Chenopodium rubrum

Using the whole-vacuolar mode of the patch clamp technique, we studied the effect of the chaotropic anions thiocyanate and nitrate on the electric currents generated by the proton pumping tonoplast ATPase and pyrophosphatase (PPiase), respectively, in vacuoles from suspension cells of Chenopodium rubrum L. Addition of KNO₃ (150–250 m M ) or KSCN (70–150 m M ), and ATP (5 m M , obligatory) irreversibly inhibited the subsequent electric current through the tonoplast ATPase driven by 1 m M ATP, whereas PPiase-activity by 50 μ M PPi remained unaffected. The kinetics of inhibition, indicative of ATPase disintegration by the chaotropic anions, follows a single exponential (τ= 3.44 min). However, apparent ATPase disintegration did not measurably increase the tonoplast conductance. We conclude that, by contrast to organellar F-ATPases, upon disintegration the transmembrane proteolipid of the V-ATPase does not act as a proton conductor which, in the presence of chaotropic anions, like chloride or nitrate, would severely perturb solute compartmentation in the plant cell.     

Effects of plot vegetation diversity and spatial scale on Coccinella septempunctata movement in the absence of prey

The influence that vegetation diversity and the spatial scale of that diversity exert on insect behavior has increasingly been explored in the ecological literature, but relatively few experiments have explicitly incorporated both factors in experimental treatments. We conducted a field study designed to explore the effect of both of these factors on insect movement behavior in a broccoli agroecosystem. We caught and released seven‐spotted ladybird beetles (Coccinella septempunctata L.) in plots containing different degrees of vegetation diversity at two different spatial scales in which prey had been removed. Beetle movement was recorded at timed intervals, and move lengths and turning angles were used to generate discrete path maps for each beetle. Observed mean beetle net squared displacements were compared with predicted net squared displacements, and 95% confidence intervals were generated using a bootstrap method described by Turchin (1998 ) [Quantitative Analysis of Movement: Measuring and Modeling Population Redistribution in Animals and Plants. Sinauer Associates Inc., Sunderland, MA.]. Predicted net squared displacements underestimated beetle movement in smaller plots with both low and higher vegetation diversity for the first five move lengths, whereas no significant difference between observed and predicted net squared displacement for beetles in larger plots of either level of vegetation diversity were detected. These findings highlight the need for a better understanding of how natural enemies are influenced by vegetation diversity and the spatial scale of that vegetation in agroecosystems. The implications of these results for biological control are discussed.     

A genetically encoded indicator for monitoring intracellular chloride

Inhibitory drives in the nervous system are provided by synapses operating mostly through Cl⁻ ion channels. We describe a novel CFP-YFP-based fluorescence Cl⁻ indicator, Cl-sensor, characterized by a high sensitivity, which can be successfully used as a tool for monitoring intracellular Cl⁻ in various biological preparations. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 380–381, July–October, 2007.