Aggregated distribution of resources creates competition refuges for rainforest dung beetles

This study examines the effects of resource distribution on colonisation, intra- and interspecific aggregation, and the occurrence of low-density, competition refuges for tropical dung beetles. In field experiments from central Peru, using dung pats (resource patches) of different volumes, the numbers of interacting species and total beetle biomass at individual pats increased with increasing pat volume. In two of three separate experiments (including an experiment that also varied patch density), this represented a decrease in the biomass of beetles per unit volume (biomass-density) at larger patches. The numbers of interacting tunneller species and tunneller biomass-density were also related to the distance between pats (patch density) in one of two experiments with constant numbers of pats. Closely positioned pats had generally fewer interacting species and a lower biomass-density of beetles. For the most abundant Dichotomius species, interspecific associations increased as distances increased between dung pats. The numbers of interacting species and biomass-density declined linearly under the combined effects of increasing patch density and local patch abundance in 25 m² plots. In experimentally placed grids with large numbers of pats, colonisation of pats at the edge of the grids was generally higher than at the centre of the grids for tunnellers and Eurysternus spp. but not for ball rollers; however, at least tunnellers did not readjust to avoid patches with high densities of competitors. These results indicate that an aggregated distribution of dung and natural variability in patch size contribute to species coexistence by creating low-density refuges for weaker competitors.     

Rab11-FIP3 localises to a Rab11-positive pericentrosomal compartment during interphase and to the cleavage furrow during cytokinesis

The Rab11-family interacting protein 3 (Rab11-FIP3), also known as Arfophilin and Eferin, is a Rab11 and ADP-ribosylation factor (ARF) binding protein of unknown function. Here, we sought to investigate the subcellular localisation and elucidate the function of Rab11-FIP3 in eukaryotic membrane trafficking. Utilising a polyclonal antibody specific for Rab11-FIP3, we have demonstrated by immunofluorescence microscopy that Rab11-FIP3 colocalises with Rab11 in a distinctive pericentrosomal location in A431 cells. Additionally, we found that Rab11-FIP3 localises to punctate vesicular structures dispersed throughout A431 cells. We have demonstrated that both Rab11 and Rab11-FIP3 localise to the cleavage furrow during cytokinesis, and that Rab11-FIP3 localisation is dependent on both microtubule and actin filament integrity. We show that Rab11-FIP3 does not enter brefeldin A (BFA) induced membrane tubules that are positive for the transferrin receptor (TfnR). Furthermore, we show that expression of an amino-terminally truncated mutant of Rab11-FIP3 (Rab11-FIP3((244-756))) does not inhibit transferrin (Tfn) recycling in HeLa cells. It is likely that Rab11-FIP3 is involved in trafficking events other than Tfn trafficking; these may include the transport of endosomally derived membrane to the cleavage furrow during cytokinesis.     

A description of arterial wall mechanics using limiting chain extensibility constitutive models

Certain aspects of the mechanical response of arterial walls can be described using nonlinear elasticity theory. Uniaxial tests on vascular walls reveal nonlinear stress-strain behavior, with higher extensibility in the low stretch range and progressively lower extensibility with increasing stretch. This phenomenon is well known in the framework of rubber-like materials where it is called a strain-hardening or strain-stiffening effect. Constitutive models of incompressible hyperelasticity that take this into account include power-law models and limiting chain extensibility models. Our purpose in this paper is to bring to the attention of the biomechanics community some essential features of one such model of the latter type due to Gent. This model is compared with isotropic versions of biomechanical constitutive models by Takamizawa-Hayashi and Fung; the latter is a limiting version of a power-law material. Two particular problems are considered for which experimental data on arterial wall deformations are available. The first concerns small oscillations superposed on a large static stretch of a vertical string of arterial tissue. It is shown that the exponential model of Fung and the Gent model match well with the experimental data. The second problem is the extension of an internally pressurized circular cylindrical tube. It is shown that an inversion phenomenon observed experimentally for the human iliac artery can be described within a membrane theory by the Gent model whereas this cannot be described using the exponential model. The foregoing considerations are carried out for isotropic elastic materials in the absence of residual stress. Extensions to include anisotropy are also indicated.     

Ontogenetic Behavior, Migration, and Social Behavior of Pallid Sturgeon, Scaphirhynchus albus, and Shovelnose Sturgeon, S. platorynchus, with Notes on the Adaptive Significance of Body Color

We conducted laboratory studies on the ontogenetic behavior of free embryos (first life interval after hatching) and larvae (first feeding interval) of pallid and shovelnose sturgeon. Migration styles of both species were similar for timing of migration (initiation by embryos on day 0 after hatching and cessation by larvae on days 12–13 at 236–243 cumulative temperature degree units), migration distance (about 13km), life interval when most distance was moved (embryo), and diel behavior of embryos (diurnal). However, the species differed for two behaviors: movement characteristics of embryos (peak movement rate of pallid sturgeon was only one-half the peak rate of shovelnose sturgeon, but pallid sturgeon continued the lower rate for twice as long) and diel behavior of larvae (pallid sturgeon were diurnal and shovelnose sturgeon were nocturnal). Thus, the species used different methods to move the same distance. Migrating as poorly developed embryos suggests a migration style to avoid predation at the spawning site, but moving from spawning habitat to rearing habitat before first feeding could also be important. Migrants of both species preferred bright habitat (high illumination intensity and white substrate), a behavioral preference that may characterize the migrants of many species of sturgeon. Both species were remarkably similar for swimming height above the bottom by age, and day 7 and older migrants may swim far above the bottom and move far downstream. A migration of 12 or 13 days will probably not distribute larvae throughout the population's range, so an older life interval likely initiates a second longer downstream migration (2-step migration). By day 2, individuals of both species were a black-tail phenotype (light grey body with a black-tail that moved conspicuously during swimming). Aggregation behavior suggests that black-tail is a visual signal used for group cohesion.     

Changes in body water and plasma constituents during bullfrog development: effects of temperature and hormones

The osmoregulatory responses to warmer temperatures and hormone treatment in cold-adapted (5 degrees C) Rana catesbeiana tadpoles and newly metamorphosed frogs were examined. Tadpoles transferred to 11 degrees C and 18 degrees C and left for 5 days lost 7% and 10% of their body weight. Plasma [Na+] was elevated 28% and 21%, respectively. Control (5 degrees C) animals maintained their body weight and plasma [Na+] constant. Daily treatment with either ovine prolactin (oPRL) or ovine growth hormone (oGH) prevented the weight loss and the increase in extracellular [Na+] that occurred when tadpoles were transferred to 18 degrees C. Neither propylthiouracil (PTU) nor arginine vasotocin (AVT) were effective in countering temperature-induced weight loss in tadpoles. Newly metamorphosed frogs transferred to 18 degrees C also lost weight; this was not prevented by daily treatment with saline, oPRL, oGH or PTU. However, in frogs treated daily with AVT, initial BW was regained by day 6. When warm-adapted (18 degrees C) tadpoles were treated daily for 18 days with saline, bPRL, bGH, thyroxine (T4), ergocornine, cortisol, or cortisol + T4, bPRL was most effective in retarding weight loss and maintaining body water content, whereas T4 + cortisol caused the greatest loss of weight and body water. By day 20, the correlations between weight loss and both body water content and hematocrit were highly significant. These data suggest that reported increases in plasma solute concentrations in larval amphibians may actually reflect decreases in extracellular fluid volume, rather than increased amounts of solutes, per se.     

Apical localization of 1-aminocyclopropane-1-carboxylic acid and its conversion to ethylene in etiolated pea seedlings

The biosynthetic basis for the high rates of ethylene production by the apical region of etiolated pea (Pisum sativum L.) seedlings was investigated. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) was quantified in extracts of various regions of seedlings by measuring isotopic dilution of a ²H-labelled internal standard using selected-ion-monitoring gas chromatography/mass spectrometry. The ACC levels in the apical hook and leaves were much higher than in the expanded internodes of the epicotyl. The capacity of excised tissue sections to convert exogenous ACC to ethylene was also much greater in the apical region, reflecting the distribution of soluble protein in the epicotyl.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - FW fresh weight - GC/MS coupled gas chromatography/mass spectrometry - HPLC high-performance liquid chromatography     

Prey preferences of free‐ranging cheetahs on farmland: scat analysis versus farmers' perceptions

Human–predator conflict is one of the biggest threats to large carnivore species worldwide. Its intensity is closely linked to farmer's attitudes and perceptions of predators. As a result, farmers' estimates of the number of livestock or game‐stock animals killed by predators are often formed based on the perceived number of predators present and their perceivably favoured prey species. This study aims to examine the prey preferences of cheetahs Acinonyx jubatus in relation to farmers' perceptions and the relative contribution of livestock and game‐stock to the cheetahs' diet. Cheetahs' prey preferences were determined through the cross‐sectional analysis of prey hair, found in cheetah scat. Cheetahs were found to predominantly prey on free‐ranging abundant game species, primarily kudu Tragelaphus strepsiceros. Game ranchers overestimated the prominence of game‐stock to the cheetahs' diet, especially springbok Antidorcas marsupialis. Potential reasons for these discrepancies and the importance of abundant natural prey as a potential human–predator coexistence strategy are discussed.     

Effects of abscisic acid analogues on abscisic acid-induced gene expression in barley aleurone protoplasts: Relationship between structure and function of the abscisic acid molecule

The plant hormone abscisic acid (ABA) mediates gene expression in barley aleurone protoplasts. In order to elucidate the essential functional groups of the ABA molecule, the specificity of a number of ABA analogues for inducing ABA-regulated gene (e.g., RAB, BASI) expression in barley aleurone protoplasts was studied. These analogues have modifications at three different positions of the ABA molecule: (a) the 1-hydroxyl group (1-deoxy ABA), (b) the carboxyl group (ABA-methyl ester or ABA-glucose ester), and (c) both the 1-hydroxyl and 4-carbonyl groups (-ionylidene acetic acid). The importance of the different putative functional groups was analyzed. The dose-response analysis of ABA analogues upon the induction gene expression showed the following order: ABA > ABA methyl ester > 1-deoxy ABA > ABA glucose ester > -ionylidene acetic acid > --ionone.