Beyond simple habituation: Anthropogenic habitats influence the escape behaviour of spur-winged lapwings in response to both human and non-human threats

Habitat development may affect wildlife behaviour, favouring individuals or behaviours that cope better with perceived threats (predators). Bolder behaviours in human-dominated habitats (HDH; e.g. urban and rural settlements) may represent habituation specifically to humans, or a general reduction in predator-avoidance response. However, such carry-over effects across threat types (i.e. beyond humans) and phases of the escape sequence have not been well studied to date. Here we investigated escape behaviours of a locally common wader species, the spur-winged lapwing Vanellus spinosus. We assayed their flight initiation distance (FID) and subsequent escape behaviours in agricultural areas and in HDH. We found that lapwings in HDH were bolder, and that the difference was manifested in several phases of the predator-avoidance sequence (shorter FIDs, shorter distances fled, and a higher probability of escape by running vs. flying). When re-approached (by an observer) after landing, lapwings in HDH were also more repetitive in their FID than those in other habitats. To determine whether this apparent bolder behaviour in HDH areas is merely a consequence of habituation to humans or represents a broader behavioural change, we introduced an additional threat type-a remotely-operated taxidermic jackal ('Jack-Truck'). Finding bolder responses in the HDH to the human threat alone (and not to the Jack-Truck) could have supported the habituation hypothesis. In contrast, however, we found a bolder response in the HDH to both threat types, as well as a correlation between their FIDs across different sites. These bolder behaviours suggest that HDH impose a broader behavioural change on lapwings, rather than just simple habituation. Overall, our findings demonstrate how FID trials can reveal strong behavioural carry-over effects of HDH following human and non-human threats, including effects on the subsequent phases of escaping the predator. Further, FID assays may reveal consistent behavioural types when assessed under field conditions, and offer a direct way to differentiate among the various poorly understood and non-mutually exclusive mechanisms that lead to behavioural differences among organisms in HDH. The mechanistic perspective is essential for understanding how rapid urbanization impacts wildlife behaviour, populations, and the range of behaviours within them, even in species apparently resilient to such environmental changes.

Interior-point methodology for 3-D PET reconstruction

Interior-point methods have been successfully applied to a wide variety of linear and nonlinear programming applications. This paper presents a class of algorithms, based on path-following interior-point methodology, for performing regularized maximum-likelihood (ML) reconstructions on three-dimensional (3-D) emission tomography data. The algorithms solve a sequence of subproblems that converge to the regularized maximum likelihood solution from the interior of the feasible region (the nonnegative orthant). We propose two methods, a primal method which updates only the primal image variables and a primal-dual method which simultaneously updates the primal variables and the Lagrange multipliers. A parallel implementation permits the interior-point methods to scale to very large reconstruction problems. Termination is based on well-defined convergence measures, namely, the Karush-Kuhn-Tucker first-order necessary conditions for optimality. We demonstrate the rapid convergence of the path-following interior-point methods using both data from a small animal scanner and Monte Carlo simulated data. The proposed methods can readily be applied to solve the regularized, weighted least squares reconstruction problem.

Translation of chloroplast psbA mRNA is modulated in the light by counteracting oxidizing and reducing activities

Light has been proposed to stimulate the translation of Chlamydomonas reinhardtii chloroplast psbA mRNA by activating a protein complex associated with the 5' untranslated region of this mRNA. The protein complex contains a redox-active regulatory site responsive to thioredoxin. We identified RB60, a protein disulfide isomerase-like member of the protein complex, as carrying the redox-active regulatory site composed of vicinal dithiol. We assayed in parallel the redox state of RB60 and translation of psbA mRNA in intact chloroplasts. Light activated the specific oxidation of RB60, on the one hand, and reduced RB60, probably via the ferredoxin-thioredoxin system, on the other. Higher light intensities increased the pool of reduced RB60 and the rate of psbA mRNA translation, suggesting that a counterbalanced action of reducing and oxidizing activities modulates the translation of psbA mRNA in parallel with fluctuating light intensities. In the dark, chemical reduction of the vicinal dithiol site did not activate translation. These results suggest a mechanism by which light primes redox-regulated translation by an unknown mechanism and then the rate of translation is determined by the reduction-oxidation of a sensor protein located in a complex bound to the 5' untranslated region of the chloroplast mRNA.

Rate of retrograde transport of cholera toxin from the plasma membrane to the Golgi apparatus and endoplasmic reticulum decreases during neuronal development

Various glycolipid-binding toxins are internalized from the cell surface to the Golgi apparatus. Prominent among these is cholera toxin (CT), which consists of a pentameric B subunit that binds to ganglioside GM1 and an A subunit that mediates toxicity. We now demonstrate that rhodamine (Rh)-CT can be further internalized from the Golgi apparatus to the endoplasmic reticulum (ER) in cultured hippocampal neurons and in neuroblastoma N18TG-2 cells and that the A subunit is essential for retrograde transport to the ER. In addition, the rate of internalization of Rh-CT to the Golgi apparatus and ER decreases dramatically as hippocampal neurons mature. The Golgi apparatus was labeled in almost all 1-day-old neurons after < 1 h of incubation with Rh-CT but was labeled in < 10% of 14-day-old neurons after 1 h. During the first 14 days in culture, there was a 15-fold increase in the number of 125I-CT-binding sites per cell, indicating that the decrease in the rate of internalization of Rh-CT is not due to reduced levels of cell surface GM1 in older neurons. These results imply that the rate of retrograde transport of CT from the plasma membrane to the Golgi apparatus and ER is regulated during neuronal development and differentiation.

The internalization of a short acyl chain analogue of ganglioside GM1 in polarized neurons

In order to study the endocytosis of membrane lipids during the development of neuronal polarity, we examined the internalization of a short acyl chain fluorescent derivative of ganglioside GM1, N-(6-(4-nitrobenz-2-oxa-1,3-diazole-7-yl)-aminohexanoyl)-GM1 (C6-NBD-GM1), in hippocampal neurons cultured at low density. C6-NBD-GM1 was internalized by temperature- and energy-dependent mechanisms, and after short times of incubation, accumulated in endosomes in the axon, cell body and dendrites of neurons maintained for up to 4–5 days in culture. C6-NBD-GM1 was subsequently transported in a retrograde direction to a pool of recycling endosomes in the cell body, with little transport to lysosomes, as indicated by the lack of degradation of C6-NBD-GM1 even after long times, and the re-appearance of intact C6-NBD-GM1 at the cell surface after recycling; similarly, little degradation of C6-NBD-GM1 was detected in N18TG-2 neuroblastoma cells. In hippocampal neurons maintained for longer than 6 days in culture, there was little internalization of C6-NBD-GM1 along the length of axons, but the amount of endocytosis from dendrites was similar to that observed in younger neurons. These results demonstrate that gangliosides turnover rapidly in dendritic membranes at all stages of neuronal development, whereas ganglioside turnover in axons is much less rapid, at least in mature, polarized neurons.

Cationic amphiphilic drugs inhibit the internalization of cholera toxin to the Golgi apparatus and the subsequent elevation of cyclic AMP

Cholera toxin (CT) consists of a pentameric B subunit which binds with high affinity to ganglioside GM1, and an A subunit which stimulates adenylate cyclase, resulting in the elevation of cAMP. We now examine the effect of cationic amphiphilic drugs (CADs) on the internalization of rhodamine (Rh)-CT in cultured hippocampal neurons. CADs have recently been shown to inhibit receptor recycling by disrupting the assembly-disassembly of clathrin at the plasma membrane and on endosomes (Wang, L.-H., Rothberg, K. G., and Anderson, R. G. W. (1993) J. Cell Biol. 123, 1107-1117). Rh-CT was internalized by an energy- and temperature-dependent (presumably vesicular) mechanism to the Golgi apparatus. Internalization to the Golgi apparatus was completely but reversibly blocked by CADs, and the ability of CT to stimulate the elevation of cAMP was significantly reduced. In control cells, cAMP levels were elevated 2.3-fold after 20 min of incubation with CT, but in CAD-treated cells cAMP levels were only elevated 1.3-fold. The effect of CADs on CT internalization was not due to a direct effect of CADs on the Golgi apparatus. Our data demonstrate that CADs inhibit vesicular transport of CT to the Golgi apparatus and imply that the sorting of CT to the Golgi apparatus occurs in the same endosomal compartment involved in sorting recycling receptors to the plasma membrane, since both pathways are inhibited by CADs.