Diet preference in the House Sparrow Passer domesticus: hooked on millet?

Capsule House Sparrows preferred millet over seeds of prairie forbs and grasses native to the USA. By reducing the abundance and availability of some grains, changing agricultural practices may contribute to the population declines of House Sparrows seen in some parts of their range.     

Kinase-mediated trapping of bi-functional conjugates of paclitaxel or vinblastine with thymidine in cancer cells

In the present work, we explore the possibility of introducing selectivity to existing chemotherapeutics via the design of non-pro-drug, bi-functional molecules comprising a microtubule-binding agent and a substrate for a disease-associated kinase. The design, synthesis, and in vitro biological evaluation of paclitaxel-thymidine and vinblastine-thymidine bi-functional conjugates are reported here. This work provides the first account of 'kinase-mediated trapping' of cancer therapeutics.     

Plasticity of size and growth in fluctuating thermal environments: comparing reaction norms and performance curves

Ectothermic animals exhibit two distinct kinds of plasticityin response to temperature: Thermal performance curves (TPCs),in which an individual's performance (e.g., growth rate) variesin response to current temperature; and developmental reactionnorms (DRNs), in which the trait value (e.g., adult body sizeor development time) of a genotype varies in response to developmentaltemperatures experienced over some time period during development.Here we explore patterns of genetic variation and selectionon TPCs and DRNs for insects in fluctuating thermal environments.First, we describe two statistical methods for partitioningtotal genetic variation into variation for overall size or performanceand variation in plasticity, and apply these methods to availabledatasets on DRNs and TPCs for insect growth and size. Our resultsindicate that for the datasets we considered, genetic variationin plasticity represents a larger proportion of the total geneticvariation in TPCs compared to DRNs, for the available datasets.Simulations suggest that estimates of the genetic variationin plasticity are strongly affected by the number and rangeof temperatures considered, and by the degree of nonlinearityin the TPC or DRN. Second, we review a recent analysis of fieldselection studies which indicates that directional selectionfavoring increased overall size is common in many systems—thatbigger is frequently fitter. Third, we use a recent theoreticalmodel to examine how selection on thermal performance curvesrelates to environmental temperatures during selection. Themodel predicts that if selection acts primarily on adult sizeor development time, then selection on thermal performance curvesfor larval growth or development rates is directly related tothe frequency distribution of temperatures experienced duringlarval development. Using data on caterpillar temperatures inthe field, we show that the strength of directional selectionon growth rate is predicted to be greater at the modal (mostfrequent) temperatures, not at the mean temperature or at temperaturesat which growth rate is maximized. Our results illustrate someof the differences in genetic architecture and patterns of selectionbetween thermal performance curves and developmental reactionnorms.     

Negative density-dependent dispersal emerges from the joint evolution of density- and body condition-dependent dispersal strategies

Empirical studies have documented both positive and negative density-dependent dispersal, yet most theoretical models predict positive density dependence as a mechanism to avoid competition. Several hypotheses have been proposed to explain the occurrence of negative density-dependent dispersal, but few of these have been formally modeled. Here, we developed an individual-based model of the evolution of density-dependent dispersal. This model is novel in that it considers the effects of density on dispersal directly, and indirectly through effects on individual condition. Body condition is determined mechanistically, by having juveniles compete for resources in their natal patch. We found that the evolved dispersal strategy was a steep, increasing function of both density and condition. Interestingly, although populations evolved a positive density-dependent dispersal strategy, the simulated metapopulations exhibited negative density-dependent dispersal. This occurred because of the negative relationship between density and body condition: high density sites produced low-condition individuals that lacked the resources required for dispersal. Our model, therefore, generates the novel hypothesis that observed negative density-dependent dispersal can occur when high density limits the ability of organisms to disperse. We suggest that future studies consider how phenotype is linked to the environment when investigating the evolution of dispersal.     

Translational control in oocyte development

Translational control of specific mRNAs is a widespread mechanism of gene regulation, and it is especially important in pattern formation in the oocytes of organisms in which the embryonic axes are established maternally. Drosophila and Xenopus have been especially valuable in elucidating the relevant molecular mechanisms. Here, we comprehensively review what is known about translational control in these two systems, focusing on examples that illustrate key concepts that have emerged. We focus on protein-mediated translational control, rather than regulation mediated by small RNAs, as the former appears to be predominant in controlling these developmental events. Mechanisms that modulate the ability of the specific mRNAs to be recruited to the ribosome, that regulate polyadenylation of specific mRNAs, or that control the association of particular mRNAs into translationally inert ribonucleoprotein complexes will all be discussed.     

Energetic rationale for an unexpected and abrupt reversal of guanidinium chloride-induced unfolding of peptide deformylase

Peptide deformylase (PDF) catalyzes the removal of formyl group from the N-terminal methionine residues of nascent proteins in prokaryotes, and this enzyme is a high priority target for antibiotic design. In pursuit of delineating the structural-functional features of Escherichia coli PDF (EcPDF), we investigated the mechanistic pathway for the guanidinium chloride (GdmCl)-induced unfolding of the enzyme by monitoring the secondary structural changes via CD spectroscopy. The experimental data revealed that EcPDF is a highly stable enzyme, and it undergoes slow denaturation in the presence of varying concentrations of GdmCl. The most interesting aspect of these studies has been the abrupt reversal of the unfolding pathway at low to moderate concentrations of the denaturant, but not at high concentration. An energetic rationale for such an unprecedented feature in protein chemistry is offered.     

Patch Use in Free‐Ranging Goats: Does a Large Mammalian Herbivore Forage like Other Central Place Foragers?

Classic central place foraging theory does not focus on the foraging of central place herbivores. This is especially true with regard to large mammalian herbivores. To understand the foraging dynamics of these neglected foragers, we measured giving‐up densities (GUDs) in artificial food patches. We did this at different distances away from the central point (i.e. corral) for a herd of free‐ranging domestic goats. To determine temporal changes, we conducted the study over a 3‐mo period during an extended dry season. Throughout our study, goats foraged across a gradient of food availability where forage was more available farther away from the central point. In contrast to the prediction that predation risk and/or increased travel costs were the main drivers of foraging decisions, we found that the goats increased their feeding effort (i.e. achieved lower GUDs) the farther away they moved from the central point. This suggests that either metabolic or missed opportunity costs were the main factors that influenced foraging decisions. In addition, we suggest that social foraging may have also played a role. With increases in foraging opportunities away from the central point, a herd will likely move slowly while foraging. As a result, individuals can feed intensively from patches but remain part of the group. Ironically, owing to the sustained close proximity of other group members, individuals may perceive patches farther from the central point as being safer. Temporally, the goats increased their feeding effort throughout the dry season. This suggests there was a decline in food quality and/or availability across the environment as the study progressed. Despite this increase in feeding effort, the negative relationship with distance did not change. Ultimately, our results provide key insight into how metabolic, missed opportunity and perceived predation costs influence the feeding decisions of large central place herbivores.     

Delayed herbivory by migratory geese increases summer‐long CO2 uptake in coastal western Alaska

The advancement of spring and the differential ability of organisms to respond to changes in plant phenology may lead to “phenological mismatches” as a result of climate change. One potential for considerable mismatch is between migratory birds and food availability in northern breeding ranges, and these mismatches may have consequences for ecosystem function. We conducted a three‐year experiment to examine the consequences for CO₂ exchange of advanced spring green‐up and altered timing of grazing by migratory Pacific black brant in a coastal wetland in western Alaska. Experimental treatments represent the variation in green‐up and timing of peak grazing intensity that currently exists in the system. Delayed grazing resulted in greater net ecosystem exchange (NEE) and gross primary productivity (GPP), while early grazing reduced CO₂ uptake with the potential of causing net ecosystem carbon (C) loss in late spring and early summer. Conversely, advancing the growing season only influenced ecosystem respiration (ER), resulting in a small increase in ER with no concomitant impact on GPP or NEE. The experimental treatment that represents the most likely future, with green‐up advancing more rapidly than arrival of migratory geese, results in NEE changing by 1.2 µmol m^?2 s^?1 toward a greater CO₂ sink in spring and summer. Increased sink strength, however, may be mitigated by early arrival of migratory geese, which would reduce CO₂ uptake. Importantly, while the direct effect of climate warming on phenology of green‐up has a minimal influence on NEE, the indirect effect of climate warming manifest through changes in the timing of peak grazing can have a significant impact on C balance in northern coastal wetlands. Furthermore, processes influencing the timing of goose migration in the winter range can significantly influence ecosystem function in summer habitats.     

Activation of big MAP kinase 1 (BMK1/ERK5) inhibits cardiac injury after myocardial ischemia and reperfusion

Big MAP kinase 1 (BMK1/ERK5) plays a critical role in pre-natal development of the cardiovascular system and post-natal eccentric hypertrophy of the heart. Of the two isoforms upstream of MAPK-kinase 5 (MEK5) known to exist, only the longer MEK5alpha isoform potently activates BMK1. We generated cardiac-specific constitutively active form of the MEK5alpha (CA-MEK5alpha transgenic (Tg) mice), and observed a 3 to 4-fold increase in endogenous BMK1 activation and hyperphosphorylation of connexin 43 in the ventricles of the Tg compared to wild-type mice. The CA-MEK5alpha-Tg-mice demonstrated a profoundly accelerated recovery of left ventricular developed pressure after ischemia/reperfusion. We propose a novel role for BMK1 in protecting the heart from ischemia/reperfusion-induced cardiac injury.