Cannibalism can drive the evolution of behavioural phase polyphenism in locusts

During outbreaks, locust swarms can contain millions of insects travelling thousands of kilometers while devastating vegetation and crops. Such large-scale spatial organization is preceded locally by a dramatic density-dependent phenotypic transition in multiple traits. Behaviourally, low-density solitarious individuals avoid contact with one another; above a critical local density, they undergo a rapid behavioural transition to the gregarious phase whereby they exhibit mutual attraction. Although proximate causes of this phase polyphenism have been widely studied, the ultimate driving factors remain unclear. Using an individual-based evolutionary model, we reveal that cannibalism, a striking feature of locust ecology, could lead to the evolution of density-dependent behavioural phase-change in juvenile locusts. We show that this behavioural strategy minimizes risk associated with cannibalistic interactions and may account for the empirically observed persistence of locust groups during outbreaks. Our results provide a parsimonious explanation for the evolution of behavioural plasticity in locusts.

Severe diffraction anisotropy, rotational pseudosymmetry and twinning complicate the refinement of a pentameric coiled-coil structure of NSP4 of rotavirus

The crystal structure of the region spanning residues 95-146 of the rotavirus nonstructural protein NSP4 from the asymptomatic human strain ST3 was determined at a resolution of 2.5 angstrom. Severe diffraction anisotropy, rotational pseudo-symmetry and twinning complicated the refinement of this structure. A systematic explanation confirming the crystal pathologies and describing how the structure was successfully refined is given in this report.

Optical frequency metrology with an Rb-stabilized ring-cavity resonator-study of cavity-dispersion errors

We have developed a technique to measure the absolute frequencies of optical transitions by using an evacuated Rb-stabilized ring-cavity resonator as a transfer cavity. The absolute frequency of the Rb D-2 line (at 780 nm) used to stabilize the cavity is known and allows us to determine the absolute value of the unknown frequency. We study wavelength-dependent errors due to dispersion at the cavity mirrors by measuring the frequency of the same transition in the Cs D-2 line (at 852 nm) at three cavity lengths. The spread in the values shows that dispersion errors are below 30 kHz, corresponding to a relative precision of 10(-10). We give an explanation for reduced dispersion errors in the ring-cavity geometry by calculating errors due to the lateral shift and the phase shift at the mirrors, and show that they are roughly equal but occur with opposite signs. We have earlier shown that diffraction errors (due to Guoy phase) are negligible in the ring-cavity geometry compared to a linear cavity; the reduced dispersion error is another advantage. Our values are consistent with measurements of the same transition using the more expensive frequency-comb technique. Our simpler method is ideally suited for measuring hyperfine structure, fine structure, and isotope shifts, up to several hundreds of gigahertz.

ZnO/Poly(3,4-ethylenedioxythiophene) Poly(styrenesulfonate) Based Ultraviolet and Visible Photodetectors: Role of Defects

Here, we report the ZnO/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) based photodetectors that can response to ultraviolet as well as visible light. The temporal response of the heterostructures for various excitations in the ultraviolet (UV) and visible range are performed. The time constants are found to be excitation-dependent, the response to visible light is better as compared to UV. The reason behind the better response to UV light is the high level of defects present in ZnO as confirmed by the photoluminescence (PL) measurements. This is corroborated by the time resolved fluorescence (TRF) measurements which provides sufficient information behind the slow response time under the UV excitations. The possible explanation being the non-radiative recombinations occurring due to the traps or impurities present in the film which slows down the photoresponse.

Narrowing of resonances in electromagnetically induced transparency and absorption using a Laguerre-Gaussian control beam

We study the phenomenon of electromagnetically induced transparency and absorption (EITA) using a control laser with a Laguerre-Gaussian (LG) profile instead of the usual Gaussian profile, and observe significant narrowing of the resonance widths. Aligning the probe beam to the central hole in the doughnut-shaped LG control beam allows simultaneously a strong control intensity required for high signal-to-noise ratio and a low intensity in the probe region required to get narrow resonances. Experiments with an expanded Gaussian control and a second-order LG control show that transit time and orbital angular momentum do not play a significant role. This explanation is borne out by a density-matrix analysis with a radially varying control Rabi frequency. We observe these resonances using degenerate two-level transitions in the D-2 line of Rb-87 in a room temperature vapor cell, and an EIA resonance with width up to 20 times below the natural linewidth for the F = 2 -> F' = 3 transition. Thus the use of LG beams should prove advantageous in all applications of EITA and other kinds of pump-probe spectroscopy as well.

Hydrolysis of aromatic beta-glucosides by non-pathogenic bacteria confers a chemical weapon against predators

Bacteria present in natural environments such as soil have evolved multiple strategies to escape predation. We report that natural isolates of Enterobacteriaceae that actively hydrolyze plant-derived aromatic beta-glucosides such as salicin, arbutin and esculin, are able to avoid predation by the bacteriovorous amoeba Dictyostelium discoideum and nematodes of multiple genera belonging to the family Rhabditidae. This advantage can be observed under laboratory culture conditions as well as in the soil environment. The aglycone moiety released by the hydrolysis of beta-glucosides is toxic to predators and acts via the dopaminergic receptor Dop-1 in the case of Caenorhabditis elegans. While soil isolates of nematodes belonging to the family Rhabditidae are repelled by the aglycone, laboratory strains and natural isolates of Caenorhabditis sp. are attracted to the compound, mediated by receptors that are independent of Dop-1, leading to their death. The b-glucosides-positive (Bgl(+)) bacteria that are otherwise non-pathogenic can obtain additional nutrients from the dead predators, thereby switching their role from prey to predator. This study also offers an evolutionary explanation for the retention by bacteria of `cryptic' or `silent' genetic systems such as the bgl operon.

Sea-level changes and its impact on coastal archaeological monuments: seven pagodas of Mahabalipuram, a case study

The name `Seven Pagodas' has served as a nickname for the south Indian port of Mahabalipuram since the early European explorers used it as landmark for navigation as they could see summits of seven temples from the sea. There are many theories concerning the name Seven Pagodas. The present study has compared coastline and adjacent seven monuments illustrated in a 17th century Portolan Chart (maritime map) with recent remote sensing data. This analysis throws new light on the name ``Seven Pagodas'' for the city. This study has used DEM of the site to simulate the coastline which is similar to the one depicted in the old portolan chart. Through this, the then sea level and corresponding flooding extent according to topography of the area and their effect on monuments could be analyzed. Most importantly this work has in the process identified possibly the seven monuments that constituted the name Seven Pagodas and this provides an alternative explanation to one of the mysteries of history. This work has demonstrated unique method of studying coastal archaeological sites. As large numbers of heritage sites around the world are on coastlines, this methodology has potential to be very useful for coastal heritage preservation and management.

Nucleation of a Stable Solid from Melt in the Presence of Multiple Metastable Intermediate Phases: Wetting, Ostwald's Step Rule, and Vanishing Polymorphs

In many systems, nucleation of a stable solid may occur in the presence of other (often more than one) metastable phases. These may be polymorphic solids or even liquid phases. Sometimes, the metastable phase might have a lower free energy minimum than the liquid but higher than the stable-solid-phase minimum and have characteristics in between the parent liquid and the globally stable solid phase. In such cases, nucleation of the solid phase from the melt may be facilitated by the metastable phase because the latter can ``wet'' the interface between the parent and the daughter phases, even though there may be no signature of the existence of metastable phase in the thermodynamic properties of the parent liquid and the stable solid phase. Straightforward application of classical nucleation theory (CNT) is flawed here as it overestimates the nucleation barrier because surface tension is overestimated (by neglecting the metastable phases of intermediate order) while the thermodynamic free energy gap between daughter and parent phases remains unchanged. In this work, we discuss a density functional theory (DFT)-based statistical mechanical approach to explore and quantify such facilitation. We construct a simple order-parameter-dependent free energy surface that we then use in DFT to calculate (i) the order parameter profile, (ii) the overall nucleation free energy barrier, and (iii) the surface tension between the parent liquid and the metastable solid and also parent liquid and stable solid phases. The theory indeed finds that the nucleation free energy barrier can decrease significantly in the presence of wetting. This approach can provide a microscopic explanation of the Ostwald step rule and the well-known phenomenon of ``disappearing polymorphs'' that depends on temperature and other thermodynamic conditions. Theory reveals a diverse scenario for phase transformation kinetics, some of which may be explored via modem nanoscopic synthetic methods.

Structural Insights into Saccharomyces cerevisiae Msh4-Msh5 Complex Function Using Homology Modeling

The Msh4-Msh5 protein complex in eukaryotes is involved in stabilizing Holliday junctions and its progenitors to facilitate crossing over during Meiosis I. These functions of the Msh4-Msh5 complex are essential for proper chromosomal segregation during the first meiotic division. The Msh4/5 proteins are homologous to the bacterial mismatch repair protein MutS and other MutS homologs (Msh2, Msh3, Msh6). Saccharomyces cerevisiae msh4/5 point mutants were identified recently that show two fold reduction in crossing over, compared to wild-type without affecting chromosome segregation. Three distinct classes of msh4/5 point mutations could be sorted based on their meiotic phenotypes. These include msh4/5 mutations that have a) crossover and viability defects similar to msh4/5 null mutants; b) intermediate defects in crossing over and viability and c) defects only in crossing over. The absence of a crystal structure for the Msh4-Msh5 complex has hindered an understanding of the structural aspects of Msh4-Msh5 function as well as molecular explanation for the meiotic defects observed in msh4/5 mutations. To address this problem, we generated a structural model of the S. cerevisiae Msh4-Msh5 complex using homology modeling. Further, structural analysis tailored with evolutionary information is used to predict sites with potentially critical roles in Msh4-Msh5 complex formation, DNA binding and to explain asymmetry within the Msh4-Msh5 complex. We also provide a structural rationale for the meiotic defects observed in the msh4/5 point mutations. The mutations are likely to affect stability of the Msh4/5 proteins and/or interactions with DNA. The Msh4-Msh5 model will facilitate the design and interpretation of new mutational data as well as structural studies of this important complex involved in meiotic chromosome segregation.

Mesoporous bioactive glass and glass-ceramics: Influence of the local structure on in vitro bioactivity

Mesoporous quaternary bioactive glasses and glass-ceramic with alkali-alkaline-earth oxide were successfully synthesized by using non-ionic block copolymer P123 and evaporation induced self assembly (EISA) process followed by acid treatment assisted sal-gel method. As prepared samples has been characterized for the structural, morphological and textural properties with the various analytical techniques. Glass dissolution/ion release rate in simulated body fluid (SBF) was monitored by inductively coupled plasma (ICP) emission spectroscopy, whereas the formation of apatite phase and its crystallization at the glass and glass-ceramic surface was examined by structural, textural and microscopic probes. The influence of alkaline-earth oxide content on the glass structure followed by textural property has become more evident. The pristine glass samples exhibit a wormhole-like mesoporous structure, whereas the glass-ceramic composition is found to be in three different phases, namely crystalline hydroxyapatite, wollastonite and a residual glassy phase as observed in Cerabone (R) A/W. The existence of calcium orthophosphate phase is closely associated with the pore walls comprising nanometric-sized ``inclusions''. The observed high surface area in conjunction with the structural features provides the possible explanation for experimentally observed enhanced bioactivity through the easy access of ions to the fluid. On the other hand, presence of multiple phases in glass-ceramic sample inhibits or delays the kinetics of apatite formation. (C) 2013 Elsevier Inc. All rights reserved.

Nestmate discrimination in the social wasp Ropalidia marginata: chemical cues and chemosensory mechanism

Nestmate discrimination plays an important role in preserving the integrity of social insect colonies. It is known to occur in the primitively eusocial wasp Ropalidia marginata in which non-nestmate conspecifics are not allowed to come near a nest. However, newly eclosed females are accepted in foreign colonies, suggesting that such individuals may not express the cues that permit differentiation between nestmates and non-nestmates. As cuticular hydrocarbons (CHCs) have been implicated as chemosensory cues used in nestmate recognition in other species, we investigated, using bioassays and chemical analyses, whether CHCs can play a role in nestmate recognition in R. marginata. We found that individuals can be differentiated according to colony membership using their CHC profiles, suggesting a role of CHCs in nestmate discrimination. Non-nestmate CHCs of adult females received more aggression than nestmate CHCs, thereby showing that CHCs are used as cues for nestmate recognition. Contrarily, and as expected, CHCs of newly eclosed females were not discriminated against when presented to a foreign colony. Behavioural sequence analysis revealed the behavioural mechanism involved in sensing nestmate recognition cues. We also found that newly eclosed females had a different CHC profile from that of adult females, thereby providing an explanation for why young females are accepted in foreign colonies. (C) 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Group behaviour in physical, chemical and biological systems

Groups exhibit properties that either are not perceived to exist, or perhaps cannot exist, at the individual level. Such `emergent' properties depend on how individuals interact, both among themselves and with their surroundings. The world of everyday objects consists of material entities. These are, ultimately, groups of elementary particles that organize themselves into atoms and molecules, occupy space, and so on. It turns out that an explanation of even the most commonplace features of this world requires relativistic quantum field theory and the fact that Planck's constant is discrete, not zero. Groups of molecules in solution, in particular polymers ('sols'), can form viscous clusters that behave like elastic solids ('gels'). Sol-gel transitions are examples of cooperative phenomena. Their occurrence is explained by modelling the statistics of inter-unit interactions: the likelihood of either state varies sharply as a critical parameter crosses a threshold value. Group behaviour among cells or organisms is often heritable and therefore can evolve. This permits an additional, typically biological, explanation for it in terms of reproductive advantage, whether of the individual or of the group. There is no general agreement on the appropriate explanatory framework for understanding group-level phenomena in biology.

Evaluating competing theories of street entrepreneurship

Conventionally, street entrepreneurs were either seen as a residue from a pre-modern era that is gradually disappearing (modernisation theory), or an endeavour into which marginalised populations are driven out of necessity in the absence of alternative ways of securing a livelihood (structuralist theory). In recent years, however, participa-tioninstreetentrepreneurshiphas beenre-read eitherasa rationaleconomicchoice(neo-liberal theory) or as conducted for cultural reasons (post-modern theory). The aim of this paper is to evaluate critically these competing explanations for participation in street entrepreneurship. To do this, face-to-face interviews were conducted with 871 street entrepreneurs in the Indian city of Bangalore during 2010 concerning their reasons for participation in street entrepreneurship. The finding is that no one explanation suffices. Some 12 % explain their participation in street entrepreneurship as necessity-driven, 15 % as traditional ancestral activity, 56 % as a rational economic choice and 17 % as pursued for social or lifestyle reasons. The outcome is a call to combine these previously rival explanations in order to develop a richer and more nuanced theorisation of the multifarious motives for street entrepreneurship in emerging market economies.

Polarization-rotation resonances with subnatural widths using a control laser

We demonstrate extremely narrow resonances for polarization rotation in an atomic vapor. The resonances are created using a strong control laser on the same transition, which polarizes the atoms due to optical pumping among the magnetic sublevels. As the power in the control laser is increased, successively higher-order nested polarization-rotation resonances are created, with progressively narrower linewidths. We study these resonances in the D-2 line of Rb in a room temperature vapor cell, and demonstrate a width of 0.14 G for the third-order rotation. The physical basis for the observed resonances is that optical pumping results in a simplified. AV-type level structure with differential dressing of the levels by the control laser, which is why the control power has to be sufficiently high for each resonance to appear. This explanation is borne out by a density-matrix analysis of the system. The dispersive lineshape and subnatural width of the resonance lends itself naturally to applications such as laser locking to atomic transitions and precision measurements. Copyright (c) EPLA, 2014

Turing and animal coat patterns

The present article describes a beautiful contribution of Alan Turing to our understanding of how animal coat patterns form. The question that Turing posed was the following. A collection of identical cells (or processors for that matter), all running the exact same program, and all communicating with each other in the exact same way, should always be in the same state. Yet they produce nonhomogeneous periodic patterns, like those seen on animal coats. How does this happen? Turing gave an elegant explanation for this phenomenon, namely that differences between the cells due to small amounts of random noise can actually be amplified into structured periodic patterns. We attempt to describe his core conceptual contribution below.