Lead isotopic evidence for an Australian source of aeolian dust to Antarctica at times over the last 170,000 years

Systematic analysis of Pb, Sr and Nd isotopes of 32 fluvial clay samples (< 2 µm fraction) from many of the major tributaries of the vast (1.10⁶ km²) Murray Darling Basin (MDB), located in semiarid southeastern Australia, displays similar isotopic values between some MDB clays and dust from several ice core samples from the EPICA Dome C in Antarctica. Close scrutiny of several ratios of the four Pb isotopes, and in particular ²⁰⁸Pb/²⁰⁷Pb versus ²⁰⁶Pb/²⁰⁷Pb, shows that several samples from the Darling-sub-basin of the MDB display similar values for the same isotopes for Dome C samples from different ages, and more particularly during wet phases in Australia [Marine Isotopic Stages 5e, 3 and 1]. The combination of Nd and Sr isotopic ratios from the same MDB fluvial clays clearly eliminates the Murray sub-basin, and supports the Darling sub-basin as a potential source of aeolian material to Antarctica. Overall, the Australian dust supply to Antarctica predominantly occurred during interglacial periods.The work presented here shows that aerosols generated in southeastern Australia can travel to parts of West Antarctica and this is supported by atmospheric observations and models. In addition, evidence of Australian dust in Antarctic ice cores further implies dust deposition in the Southern Ocean would have occurred in the past. Current meteorological observations also imply that the western Pacific and Indian Ocean sector of the Southern Ocean would frequently receive aeolian dust components originating from southeastern Australia.     

Memory Effects on Movement Behavior in Animal Foraging

An individual’s choices are shaped by its experience, a fundamental property of behavior important to understanding complex processes. Learning and memory are observed across many taxa and can drive behaviors, including foraging behavior. To explore the conditions under which memory provides an advantage, we present a continuous-space, continuous-time model of animal movement that incorporates learning and memory. Using simulation models, we evaluate the benefit memory provides across several types of landscapes with variable-quality resources and compare the memory model within a nested hierarchy of simpler models (behavioral switching and random walk). We find that memory almost always leads to improved foraging success, but that this effect is most marked in landscapes containing sparse, contiguous patches of high-value resources that regenerate relatively fast and are located in an otherwise devoid landscape. In these cases, there is a large payoff for finding a resource patch, due to size, value, or locational difficulty. While memory-informed search is difficult to differentiate from other factors using solely movement data, our results suggest that disproportionate spatial use of higher value areas, higher consumption rates, and consumption variability all point to memory influencing the movement direction of animals in certain ecosystems.     

Motion-guided attention promotes adaptive communications during social navigation

Animals are capable of enhanced decision making through cooperation, whereby accurate decisions can occur quickly through decentralized consensus. These interactions often depend upon reliable social cues, which can result in highly coordinated activities in uncertain environments. Yet information within a crowd may be lost in translation, generating confusion and enhancing individual risk. As quantitative data detailing animal social interactions accumulate, the mechanisms enabling individuals to rapidly and accurately process competing social cues remain unresolved. Here, we model how motion-guided attention influences the exchange of visual information during social navigation. We also compare the performance of this mechanism to the hypothesis that robust social coordination requires individuals to numerically limit their attention to a set of n-nearest neighbours. While we find that such numerically limited attention does not generate robust social navigation across ecological contexts, several notable qualities arise from selective attention to motion cues. First, individuals can instantly become a local information hub when startled into action, without requiring changes in neighbour attention level. Second, individuals can circumvent speed–accuracy trade-offs by tuning their motion thresholds. In turn, these properties enable groups to collectively dampen or amplify social information. Lastly, the minority required to sway a group''s short-term directional decisions can change substantially with social context. Our findings suggest that motion-guided attention is a fundamental and efficient mechanism underlying collaborative decision making during social navigation.     

Short‐term response of threatened small macropods and their predators to prescribed burns in subtropical Australia

Fire is an important ecological process that shapes vegetation structure and habitat for faunal assemblages globally. Prescribed burns are increasingly being used in conservation and management to restore fire regimes in fire‐suppressed vegetation communities. Small threatened macropods require structurally complex habitat that allows them to evade detection by predators. Given that fire can alter vegetation structure, it can be viewed as a strong ecological force in shifting the dynamics between predator and prey species. Previous studies in temperate Australia have shown that prescribed burns in the presence of European Red Fox (Vulpes vulpes) and feral Cat (Felis catus) can have negative impacts on small macropods and medium‐sized mammals. Post‐fire response of threatened small macropods and their predators has not been experimentally examined in subtropical Australia despite this region providing refugia for the Long‐nosed Potoroo (Potorous tridactylus) and Red‐legged Pademelon (Thylogale stigmatica). We conducted a before‐after‐control‐impact fire experiment at two paired sites after low–moderate intensity burns typical of cool season prescribed burns. We used camera trapping to investigate changes in activity of threatened small macropods and their predators. We also recorded vegetation change. Despite large reductions in ground and shrub cover, activity of small macropods and the Dingo (Canis dingo) did not change in response to fires. Therefore, the threat of dingo predation appears to have remained unchanged following the fires. Although feral cats and foxes were present, they showed negligible activity across our sites. Our study suggests that small‐scale patchy ecological burns may not lead to increased predation of small macropods in our landscape. We attribute this to sufficient post‐fire refugia and very low densities of foxes.     

The Effect of Container Surface Passivation on Aggregation of Intravenous Immunoglobulin Induced by Mechanical Shock

Aggregation of therapeutic proteins can result from a number of stress conditions encountered during their manufacture, transportation, and storage. This work shows the effects of two interrelated sources of protein aggregation: the chemistry and structure of the surface of the container in which the protein is stored, and mechanical shocks that may result from handling of the formulation. How different mechanical stress conditions (dropping, tumbling, and agitation) and container surface passivation affect the stability of solutions of intravenous immunoglobulin are investigated. Application of mechanical shock causes cavitation to occur in the protein solution, followed by bubble collapse and the formation of high‐velocity fluid microjets that impinged on container surfaces, leading to particle formation. Cavitation was observed after dropping of vials from heights as low as 5 cm, but polyethylene glycol (PEG) grafting provided temporary protection against drop‐induced cavitation. PEG treatment of the vial surface reduced the formation of protein aggregates after repeated dropping events, most likely by reducing protein adsorption to container surfaces. These studies enable the development of new coatings and surface chemistries that can reduce the particulate formation induced by surface adsorption and/or mechanical shock.     

SHORT NOTES

Earlé, R. A. 1981. Factors governing avian breeding in Acacia savanna, Pietermaritzburg, Part 3: Breeding success, recruitment and clutch size. Ostrich 52:235-243.

The clutch size and breeding success of eight species of birds were monitored over a two year period in Acacia savanna. The mean clutch size fluctuated within the breeding season and four patterns of clutch size variation were noted. A smaller proportion of large clutches were laid in the 1979 season when less food was available. Breeding success was higher in the dry 1979 season but fewer breeding attempts were made and the overall recruitment was thus lower. At the peak of the breeding season, in mid-November, breeding success was at its lowest. Predation on nests was the greatest factor reducing breeding success although rain and strong winds affected some species.     

scyllo-inositol and myo-inositol levels in tissues of the skate Raja erinacea.

1. Many organs of the skate Raja erinacea have been found to contain scyllo-inositol levels that are much higher than myo-inositol, the opposite to that found in mammals. 2. Both inositols were found in all skate organs studied. 3. myo-Inosose-2 was found to accompany the inositols in many of these organs.     

Demonstration of specific "high affinity" binding sites for [3H] imipramine on human platelets

High affinity and saturable binding sites for [³H] imipramine have been demonstrated on human platelet membranes. These binding sites appear to be specific for tricyclic antidepressants and their pharmacologically-active metabolites. In contrast, inactive tricyclic compounds such as the parent iminodibenzyl and iminostilbenes do not inhibit [³H] imipramine binding. The binding of [³H] imipramine to human platelets is of high affinity $\text{(}\text{Kd}\text{? 1.4}\text{nM}\text{)}$, saturable $\text{(}\text{Bmax}\text{? 625}\text{fmols/mg prot}\text{)}$, and sensitive to proteolytic degradation. The effects of various drugs and neurotransmitter agonists and antagonists suggests that these binding sites are pharmacologically distinct from the previously reported binding of tricyclic antidepressants to alpha-adrenergic, muscarinic-cholinergic, and histaminergic receptors. The binding characteristics of [³H] imipramine to platelets is similar to that in rat and human brain and may thus serve as a useful model in elucidating the pharmacological and physiological significance of these binding sites.     

Catalase-peroxidase active site restructuring by a distant and "inactive" domain

Catalase-peroxidases are composed of two peroxidase-like domains. The N-terminal domain contains the heme-dependent, bifunctional active site. The C-terminal domain does not bind heme, has no catalytic activity, and is separated from the active site by >30 A. Nevertheless, without the C-terminal domain, the N-terminal domain exhibits neither catalase nor peroxidase activity due to the apparent coordination of the distal histidine to the heme iron. Here we report the ability of the separately expressed and isolated C-terminal domain (KatG(C)) to restructure the N-terminal domain (KatG(N)) to its bifunctional conformation. Addition of equimolar KatG(C) to KatG(N) decreased the hexacoordinate low-spin heme complex and increased the high-spin species (pentacoordinate and hexacoordinate). EPR spectra of the domain mixture showed a distribution between high-spin species nearly identical to that of wild-type KatG. The CD spectrum for the 1:1 physical mixture of the domains was identical to an arithmetic composite of individual spectra for KatG(N) and KatG(C). Both physical and arithmetic mixtures were nearly identical to the spectrum for wild-type KatG, suggesting that major shifts in secondary structure did not accompany active site reconfiguration. With the shift in heme environment, the parallel return of catalase and peroxidase activity was observed. Inclusion of bovine serum albumin instead of KatG(C) produced no activity, indicating that specific interdomain interactions were required to reestablish the bifunctional active site. Apparent constants for reactivation (k(react) approximately 4 x 10(-3) min(-1)) indicate that a slow process like movement of established structural elements may precede the restructuring of the heme environment and return of catalytic activity.