Colour reverse learning and animal personalities: the advantage of behavioural diversity assessed with agent-based simulations

Foraging bees use colour cues to help identify rewarding from unrewarding flowers, but as conditions change, bees may require behavioural flexibility to reverse their learnt preferences. Perceptually similar colours are learnt slowly by honeybees and thus potentially pose a difficult task to reverse-learn. Free-flying honeybees (N = 32) were trained to learn a fine colour discrimination task that could be resolved at ca. 70% accuracy following extended differential conditioning, and were then tested for their ability to reverse-learn this visual problem multiple times. Subsequent analyses identified three different strategies: ‘Deliberative-decisive’ bees that could, after several flower visits, decisively make a large change to learnt preferences; ‘Fickle- circumspect’ bees that changed their preferences by a small amount every time they encountered evidence in their environment; and ‘Stay’ bees that did not change from their initially learnt preference. The next aim was to determine if there was any advantage to a colony in maintaining bees with a variety of decision-making strategies. To understand the potential benefits of the observed behavioural diversity agent-based computer simulations were conducted by systematically varying parameters for flower reward switch oscillation frequency, flower handling time, and fraction of defective ‘target’ stimuli. These simulations revealed that when there is a relatively high frequency of reward reversals, fickle-circumspect bees are more efficient at nectar collection. However, as the reward reversal frequency decreases the performance of deliberative-decisive bees becomes most efficient. These findings show there to be an evolutionary benefit for honeybee colonies with individuals exhibiting these different strategies for managing resource change. The strategies have similarities to some complex decision-making processes observed in humans, and algorithms implemented in artificial intelligence systems

Involvement of Plasmodium falciparum protein kinase CK2 in the chromatin assembly pathway

<p>Abstract</p> <p>Background</p> <p>Protein kinase CK2 is a pleiotropic serine/threonine protein kinase with hundreds of reported substrates, and plays an important role in a number of cellular processes. The cellular functions of <it>Plasmodium falciparum </it>CK2 (PfCK2) are unknown. The parasite's genome encodes one catalytic subunit, PfCK2α, which we have previously shown to be essential for completion of the asexual erythrocytic cycle, and two putative regulatory subunits, PfCK2β1 and PfCK2β2.</p> <p>Results</p> <p>We now show that the genes encoding both regulatory PfCK2 subunits (PfCK2β1 and PfCK2β2) cannot be disrupted. Using immunofluorescence and electron microscopy, we examined the intra-erythrocytic stages of transgenic parasite lines expressing hemagglutinin (HA)-tagged catalytic and regulatory subunits (HA-CK2α, HA-PfCK2β1 or HA-PfCK2β2), and localized all three subunits to both cytoplasmic and nuclear compartments of the parasite. The same transgenic parasite lines were used to purify PfCK2β1- and PfCK2β2-containing complexes, which were analyzed by mass spectrometry. The recovered proteins were unevenly distributed between various pathways, with a large proportion of components of the chromatin assembly pathway being present in both PfCK2β1 and PfCK2β2 precipitates, implicating PfCK2 in chromatin dynamics. We also found that chromatin-related substrates such as nucleosome assembly proteins (Naps), histones, and two members of the Alba family are phosphorylated by PfCK2α <it>in vitro</it>.</p> <p>Conclusions</p> <p>Our reverse-genetics data show that each of the two regulatory PfCK2 subunits is required for completion of the asexual erythrocytic cycle. Our interactome study points to an implication of PfCK2 in many cellular pathways, with chromatin dynamics being identified as a major process regulated by PfCK2. This study paves the way for a kinome-wide interactomics-based approach to elucidate protein kinase function in malaria parasites.</p

Lateral composition modulation in short period superlattices: The role of growth mode

The role of the growth mode on lateral composition modulation is studied in short period superlattices of AlAs/InAs and GaAs/InAs. Reflection high energy electron diffraction and scanning tunneling microscopy are used to monitor the growth mode and the quality of the interfaces. Cross-sectional transmission electron microscopy indicates that samples that grow via the layer-by-layer growth mode do not exhibit lateral composition modulation and the superlattice structure is well defined. Lateral composition modulation forms when roughening occurs during growth. However, too much roughening, i.e., three-dimensional island nucleation destroys the regularity of the composition modulation in both the lateral and vertical directions. These results are in general agreement with theoretical predictions. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70098/2/APPLAB-79-25-4118-1.pd

Plasma Resonance in Layered Normal Metals and Superconductors

A microscopic theory of the plasma resonance in layered metals is presented. It is shown that electron-impurity scattering can suppress the plasma resonance in the normal state and sharpen it in the superconducting state. Analytic properties of the conductivity for the electronic transport perpendicular to the layers are investigated. The dissipative part of the electromagnetic response in c-direction has been found to depend on frequency in a highly non-trivial manner. This sort of behavior cannot be incorporated in the widely used phenomenological Gorter-Kazimir model.Comment: 34 pages including 12 figures in uuencoded.file. A revised version. Several formulas and a number of misprints are corrected. A problem with printing of figures is fixe

Multiplet Effects in the Quasiparticle Band Structure of the f1−f2f^1-f^2 Anderson Model

In this paper, we examine the mean field electronic structure of the $f^1-f^2$ Anderson lattice model in a slave boson approximation, which should be useful in understanding the physics of correlated metals with more than one f electron per site such as uranium-based heavy fermion superconductors. We find that the multiplet structure of the $f^2$ ion acts to quench the crystal field splitting in the quasiparticle electronic structure. This is consistent with experimental observations in such metals as $UPt_3$.Comment: 9 pages, revtex, 3 uuencoded postscript figures attached at en

Kondo effect and anti-ferromagnetic correlation in transport through tunneling-coupled double quantum dots

We propose to study the transport through tunneling-coupled double quantum dots (DQDs) connected in series to leads, using the finite-$U$ slave-boson mean field approach developed initially by Kotliar and Ruckenstein [Phys. Rev. Lett. {\bf 57}, 1362 (1986)]. This approach treats the dot-lead coupling and the inter-dot tunnelling $t$ nonperturbatively at arbitrary Coulomb correlation $U$, thus allows the anti-ferromagnetic exchange coupling parameter $J=4t^2/U$ to appear naturally. We find that, with increasing the inter-dot hopping, the DQDs manifest three distinct physical scenarios: the Kondo singlet state of each dot with its adjacent lead, the spin singlet state consisting of local spins on each dot and the doubly occupied bonding orbital of the coupled dots. The three states exhibit remarkably distinct behavior in transmission spectrum, linear and differential conductance and their magnetic-field dependence. Theoretical predictions agree with numerical renormalization group and Lanczos calculations, and some of them have been observed in recent experiments.Comment: 5 pages, 5 figures. Physics Review B (Rapid Communication) (in press