An alternative theoretical approach to escape decision-making: the role of visual cues

Escape enables prey to avoid an approaching predator. The escape decision-making process has traditionally been interpreted using theoretical models that consider ultimate explanations based on the cost/benefit paradigm. Ultimate approaches, however, suffer from inseparable extra-assumptions due to an inability to accurately parameterize the model's variables and their interactive relationships. In this study, we propose a mathematical model that uses intensity of predator-mediated visual stimuli as a basic cue for the escape response. We consider looming stimuli (i.e. expanding retinal image of the moving predator) as a cue to flight initiation distance (FID; distance at which escape begins) of incubating Mallards (Anas platyrhynchos). We then examine the relationship between FID, vegetation cover and directness of predator trajectory, and fit the resultant model to experimental data. As predicted by the model, vegetation concealment and directness of predator trajectory interact, with FID decreasing with increased concealment during a direct approach toward prey, but not during a tangential approach. Thus, we show that a simple proximate expectation, which involves only visual processing of a moving predator, may explain interactive effects of environmental and predator-induced variables on an escape response. We assume that our proximate approach, which offers a plausible and parsimonious explanation for variation in FID, may serve as an evolutionary background for traditional, ultimate explanations and should be incorporated into interpretation of escape behavior.     

Stigmastane derivatives from the roots of Vernonia guineensis and their antimicrobial activity

Chemical investigation of the roots of Vernonia guineensis (Asteraceae) afforded a new stigmastane derivative, vernoguinoside A (1) and the known vernoguinoside (2), stigmasterol 3-O-β-d-glucoside (3) and sitosterol 3-O-β-d-glucoside (4). Their structures were elucidated by spectroscopic analysis. Antimicrobial activities of 1–3 and CH₂Cl₂–MeOH (1:1) extract were evaluated against three bacteria species (Salmonella typhi, Staphylococcus aureus and Shigella flexneri) and three yeasts species (Candida albicans, Candida parapsilosis and Cryptococcus neoformans). Compounds 1 and 2 exhibited both antibacterial and antifungal activities that varied between the microbial species (MIC = 7.81–125 μg/mL) while S. flexneri and C. albicans were sensitive to all the tested compounds.     

The Fanconi anaemia components UBE2T and FANCM are functionally linked to nucleotide excision repair

The many proteins that function in the Fanconi anaemia (FA) monoubiquitylation pathway initiate replicative DNA crosslink repair. However, it is not clear whether individual FA genes participate in DNA repair pathways other than homologous recombination and translesion bypass. Here we show that avian DT40 cell knockouts of two integral FA genes--UBE2T and FANCM are unexpectedly sensitive to UV-induced DNA damage. Comprehensive genetic dissection experiments indicate that both of these FA genes collaborate to promote nucleotide excision repair rather than translesion bypass to protect cells form UV genotoxicity. Furthermore, UBE2T deficiency impacts on the efficient removal of the UV-induced photolesion cyclobutane pyrimidine dimer. Therefore, this work reveals that the FA pathway shares two components with nucleotide excision repair, intimating not only crosstalk between the two major repair pathways, but also potentially identifying a UBE2T-mediated ubiquitin-signalling response pathway that contributes to nucleotide excision repair.     

The role of initial spore adhesion in pellet and biofilm formation in Aspergillus niger

Fungi grow on a great variety of organic and inorganic materials. Colony establishment and growth on solid surfaces require adhesion of spores and hyphae to the substrate, while cell-to-cell interactions among spores and/or hyphae are a prerequisite for the development of three-dimensional mycelial structures such as pellets or biofilms. Surface adherence has been described as a two-step process, comprised of the initial attachment of ungerminated conidia followed by further adhesion of the forming germ tubes and growing hyphae. In the present study, we analyzed the contribution of adhesion of ungerminated spores to pellet and biofilm formation in Aspergillus niger. Mutants deficient in melanin biosynthesis were constructed by the deletion of the alb1 gene, encoding a polyketide synthase essential for pigment biosynthesis. Δalb1 conidia have an altered surface structure and changed physicochemical surface properties. Spore aggregation in liquid culture as well as spore surface attachment differ between the wild type and the mutant in a pH-dependent manner. In liquid culture further pellet formation is unaffected by altered spore-spore interactions, indicating that germ tube and hyphal adherence can compensate for deficiencies in the initial step of spore attachment. In contrast, under conditions promoting adhesion of Δalb1 conidia to polymer surfaces the mutant forms more stable biofilms than the wild type, suggesting that initial spore adhesion supports sessile growth.     

Sciadonic acid modulates prostaglandin E2 production by epithelial cells during infection with C. albicans and C. dubliniensis

Candida albicans is an important opportunistic pathogen in humans. During infection, arachidonic acid (ω6) is released from host phospholipids, leading to the production of host and yeast derived prostaglandin E(2) (PGE(2)). This stimulates yeast hyphal formation, is immunomodulatory and causes cell damage during infection. Although supplementation of mammalian cells with ω3 fatty acids has received attention due to their immunomodulatory and anti-inflammatory activities, increased production of ω3 fatty acid metabolites could lower the host's ability to combat infections. Since mammalian cells cannot produce PGE(2) from sciadonic acid (SA), a non-methylene interrupted ω6 fatty acid (NMIFA), supplementation of cells with SA may decrease the production of PGE(2) without increasing levels of ω3 fatty acid metabolites. Our study evaluated PGE(2) production by SA supplemented epithelial cells in response to Candida albicans and C. dubliniensis. We show that PGE(2) production during infection can be modulated by incorporation of SA into host lipids and that this does not influence the levels of ω3 fatty acids in the epithelial cells.     

Population structure, growth and production of Thoracophelia furcifera (Polychaeta: Opheliidae) on a sandy beach in Southern Brazil

This study investigates aspects of the life history of the polychaete Thoracophelia furcifera on a sandy beach in southern Brazil. Two fixed transects perpendicular to the shoreline in the intertidal zone were sampled fortnightly from May 2008 to April 2009 at low tide. Five T. furcifera samples were collected along each transect and sediment temperature and the salinity of interstitial water were recorded. The material was washed over 0.5- and 0.088-mm sieves, and the width of setiger 8 of each specimen was measured. A total of 5,870 organisms were examined and the estimated parameters of the von Bertalanffy growth curve were L _∞ 3.60?mm (Wd8S), K 0.63?year^?1, C 0.3 and WP 0.97 (Rn 0.132). Life span was 2.6?years, instantaneous mortality rate Z was 3.8?year^?1 and the growth index φ′ 0.91. Mean density ranged from 644.44?±?191.77 to 2,783.33?±?453.64 ind m^?2 and mean biomass ranged from 2.52?±?0.55 to 9.52?±?1.83?g?m^?2. Recruitment occurred from April to July and ovigerous females were found from June to November. Annual secondary production was 6.582?g?m^?2?year^?1, mean biomass was 5.638?g?m^?2 and turnover rate was 1.167. The high values for density, secondary production and biomass suggest that T. furcifera constitute an important food source. These features of T. furcifera’ life strategy demonstrate the significant role this species plays in ecosystem dynamics.     

RNF8 and RNF168 but not HERC2 are required for DNA damage-induced ubiquitylation in chicken DT40 cells

The ubiquitylation cascade plays an important role in the recruitment of repair factors at DNA double-strand breaks. The involvement of a growing number of ubiquitin E3 ligases adds to the complexity of the DNA damage-induced ubiquitin signaling. Here we use the genetically tractable avian cell line DT40 to investigate the role of HERC2, RNF8 and RNF168 in the DNA damage-induced ubiquitylation pathway. We show that formation of ubiquitin foci as well as cell survival after DNA damage depends on both RNF8 and RNF168. However, we find that RNF8 and RNF168 knockout cell lines respond differently to treatment with camptothecin indicating that they do not function in a strictly linear manner. Surprisingly, we show that HERC2 is required neither for survival nor for ubiquitin foci formation after DNA damage in DT40. Moreover, the E3 ubiquitin ligase activity of HERC2 is not redundant to that of RNF8 or RNF168.     

Simultaneous Simulations of Uptake in Plants and Leaching to Groundwater of Cadmium and Lead for Arable Land Amended with Compost or Farmyard Manure

The water budget of soil, the uptake in plants and the leaching to groundwater of cadmium (Cd) and lead (Pb) were simulated simultaneously using a physiological plant uptake model and a tipping buckets water and solute transport model for soil. Simulations were compared to results from a ten-year experimental field study, where four organic amendments were applied every second year. Predicted concentrations slightly decreased (Cd) or stagnated (Pb) in control soils, but increased in amended soils by about 10% (Cd) and 6% to 18% (Pb). Estimated plant uptake was lower in amended plots, due to an increase of K_d (dry soil to water partition coefficient). Predicted concentrations in plants were close to measured levels in plant residues (straw), but higher than measured concentrations in grains. Initially, Pb was mainly predicted to deposit from air into plants (82% in 1998); the next years, uptake from soil became dominating (30% from air in 2006), because of decreasing levels in air. For Cd, predicted uptake from air into plants was negligible (1–5%).