Condition-dependent reproductive effort in frogs infected by a widespread pathogen

To minimize the negative effects of an infection on fitness, hosts can respond adaptively by altering their reproductive effort or by adjusting their timing of reproduction. We studied effects of the pathogenic fungus Batrachochytrium dendrobatidis on the probability of calling in a stream-breeding rainforest frog (Litoria rheocola). In uninfected frogs, calling probability was relatively constant across seasons and body conditions, but in infected frogs, calling probability differed among seasons (lowest in winter, highest in summer) and was strongly and positively related to body condition. Infected frogs in poor condition were up to 40% less likely to call than uninfected frogs, whereas infected frogs in good condition were up to 30% more likely to call than uninfected frogs. Our results suggest that frogs employed a pre-existing, plastic, life-history strategy in response to infection, which may have complex evolutionary implications. If infected males in good condition reproduce at rates equal to or greater than those of uninfected males, selection on factors affecting disease susceptibility may be minimal. However, because reproductive effort in infected males is positively related to body condition, there may be selection on mechanisms that limit the negative effects of infections on hosts.     

Molecular cloning and characterization of murine and human N-acetylglucosamine kinase.

N-Acetylglucosamine is produced by the endogenous degradation of glycoconjugates and by the degradation of dietary glycoconjugates by glycosidases. It enters the pathways of aminosugar metabolism by the action of N-acetylglucosamine kinase. In this study we report the isolation and characterization of a cDNA clone encoding the murine enzyme. An open reading frame of 1029 base pairs encodes 343 amino acids with a predicted molecular mass of 37.3 kDa. The deduced amino-acid sequence contains matches of the sequences of eight peptides derived from tryptic cleavage of rat N-acetylglucosamine kinase. The recombinant murine enzyme was functionally expressed in Escherichia coli BL21 cells, where it displays N-acetylglucosamine kinase activity as well as N-acetylmannosamine kinase activity. The complete cDNA sequence of human N-acetylglucosamine kinase was derived from the nucleotide sequences of several expressed sequence tags. An open reading frame of 1032 base pairs encodes 344 amino acids and a protein with a predicted molecular mass of 37.4 kDa. Similarities between human and murine N-acetylglucosamine kinase were 86.6% on the nucleotide level and 91.6% on the amino-acid level. Amino-acid sequences of murine and human N-acetylglucosamine kinase show sequence similarities to other sugar kinases, and all five sequence motifs necessary for the binding of ATP by sugar kinases are present. Tissue distribution of murine N-acetylglucosamine kinase revealed an ubiquitous occurrence of the enzyme and a very high expression in testis. The size of the murine mRNA was 1.35 kb in all tissues investigated, with the exception of testis, where it was 1.45 kb mRNA of the murine enzyme was continuously expressed during mouse development. mRNA of the human enzyme was expressed in all investigated human tissues, as well as in cancer cell lines. In both the tissues and the cancer cell lines, the human mRNA was 1.35 kb in size.     

The neural correlates of crowding-induced changes in appearance

Object recognition in the peripheral visual field is limited by crowding: the disruptive influence of nearby clutter. Despite its severity, little is known about the cortical locus of crowding. Here, we examined the neural correlates of crowding by combining event-related fMRI adaptation with a change-detection paradigm. Crowding can change the appearance of objects, such that items become perceptually matched to surrounding objects; we used this change in appearance as a signature of crowding and measured brain activity that correlated with the crowded percept. Observers adapted to a peripheral patch of noise surrounded by four Gabor flankers. When crowded, the noise appears oriented and perceptually indistinguishable from the flankers. Consequently, substitution of the noise for a Gabor identical to the flankers ("change-same") is rarely detected, whereas substitution for an orthogonal Gabor ("change-different") is rarely missed. We predicted that brain areas representing the crowded percept would show repetition suppression in change-same trials but release from adaptation in change-different trials. This predicted pattern was observed throughout cortical visual areas V1-V4, increasing in strength from early to late visual areas. These results depict crowding as a multistage process, involving even the earliest cortical visual areas, with perceptual consequences that are increasingly influenced by later visual areas.     

Development of real-time assays for impedance-based detection of microbial double-stranded DNA targets: optimization and data analysis

A real-time, label free assay was developed for microbial detection, utilizing double-stranded DNA targets and employing the next generation of an impedimetric sensor array platform designed by Sharp Laboratories of America (SLA). Real-time curves of the impedimetric signal response were obtained at fixed frequency and voltage for target binding to oligonucleotide probes attached to the sensor array surface. Kinetic parameters of these curves were analyzed by the integrated data analysis package for signal quantification. Non-specific binding presented a major challenge for assay development, and required assay optimization. For this, differences were maximized between binding curve kinetic parameters for probes binding to complementary targets versus non-target controls. Variables manipulated for assay optimization included target concentration, hybridization temperature, buffer concentration, and the use of surfactants. Our results showed that (i) different target-probe combinations required optimization of specific sets of variables; (ii) for each assay condition, the optimum range was relatively narrow, and had to be determined empirically; and (iii) outside of the optimum range, the assay could not distinguish between specific and non-specific binding. For each target-probe combination evaluated, conditions resulting in good separation between specific and non-specific binding signals were established, generating high confidence in the SLA impedimetric dsDNA assay results.     

An endangered bird calls less when invasive birds are calling

Novel noises can affect various animal behaviours, and changes to vocal behaviour are some of the most documented. The calls of invasive species are an important source of novel noise, yet their effects on native species are poorly understood. We examined the effects of invasive bird calls on the vocal activity of an endangered Australian finch to investigate whether: 1) native finch calling behaviour was affected by novel invasive bird calls, and 2) the calls of the finches overlapped in frequency with those of invasive birds. We exposed a wild population of black‐throated finch southern subspecies Poephila cincta cincta to the vocalisations of two invasive birds, nutmeg mannikins Lonchura punctulata and common mynas Acridotheres tristis, a synthetic ‘pink' noise, and a silent control. To determine whether the amount of black‐throated finch calling differed in response to treatments, we recorded and quantified black‐throated finch vocalisations, and assessed the amount of calling using a generalised linear mixed model followed by pairwise comparisons. We also measured, for both black‐throated finches and the stimulus noises: dominant, minimum and maximum frequency, and assessed the degree of frequency overlap between black‐throated finch calls and stimulus noises. Compared to silent controls, black‐throated finches called less when exposed to common myna calls and pink noise, but not to nutmeg mannikin calls. We also found that pink noise overlapped most in frequency with black‐throated finch calls. Common myna calls also somewhat overlapped the frequency range of black‐throated finch calls, whereas nutmeg mannikin calls overlapped the least. It is possible that masking interference is the mechanism behind the reduction in calling in response to common myna calls and pink noise, but more work is needed to resolve this. Regardless, these results indicate that the calls of invasive species can affect the behaviour of native species, and future research should aim to understand the scope and severity of this issue.     

Extending the cost-benefit model of thermoregulation: high-temperature environments

The classic cost-benefit model of ectothermic thermoregulation compares energetic costs and benefits, providing a critical framework for understanding this process (Huey and Slatkin 1976 ). It considers the case where environmental temperature (T(e)) is less than the selected temperature of the organism (T(sel)), and it predicts that, to minimize increasing energetic costs of thermoregulation as habitat thermal quality declines, thermoregulatory effort should decrease until the lizard thermoconforms. We extended this model to include the case where T(e) exceeds T(sel), and we redefine costs and benefits in terms of fitness to include effects of body temperature (T(b)) on performance and survival. Our extended model predicts that lizards will increase thermoregulatory effort as habitat thermal quality declines, gaining the fitness benefits of optimal T(b) and maximizing the net benefit of activity. Further, to offset the disproportionately high fitness costs of high T(e) compared with low T(e), we predicted that lizards would thermoregulate more effectively at high values of T(e) than at low ones. We tested our predictions on three sympatric skink species (Carlia rostralis, Carlia rubrigularis, and Carlia storri) in hot savanna woodlands and found that thermoregulatory effort increased as thermal quality declined and that lizards thermoregulated most effectively at high values of T(e).     

Comparative studies on Ureide Permeases in Arabidopsis thaliana and analysis of two alternative splice variants of AtUPS5

The recovery of free purine and pyrimidine bases and their degradation products represent alternative pathways in plant cells either to synthesize nucleotides (salvage pathways) by low energy consumption or to reuse organic nitrogen. Such recycling of metabolites often requires their uptake into the cell by specialized transport systems residing in the plasma membrane. In plants, it has been suggested that several protein families are involved in this process, but only a few transporters have so far been characterized. In this work, gene expression, substrate specificities, and transport mechanisms of members of the Ureide Permease family in Arabidopsis (AtUPS) were analyzed and compared. Promoter-GUS studies indicated that the members of the family have distinct and partially overlapping expression patterns with regard to developmental stages or tissue specific localization. In addition, two alternative splice variants of AtUPS5, a novel member of the transporter family, were identified and investigated. The abundance of both alternative mRNAs varied in different organs, while the relative amounts were comparable. AtUPS5l (longer isoform) shares similar structural prediction with AtUPS1 and AtUPS2. In contrast, AtUPS5s (shorter isoform) lacks two transmembrane domains as structural consequence of the additional splice event. When expressed in yeast, AtUPS5l mediates cellular import of cyclic purine degradation products and pyrimidines similarly to AtUPS1 and AtUPS2, but differences in transport efficiencies were observed. AtUPS5s, however, could not be shown to mediate uptake of these compounds into yeast cells and might therefore be defective or have a different function.     

Probing lethal damage expression in cytochalasin B-induced polykaryons by radiation quality

The polykaryon-forming unit (PFU) cell survival assay is based on the postirradiation flow cytometric analysis of the DNA content accumulated in high-ploidy cells (polykaryons) induced by the cytokinesis inhibitor cytochalasin B and can provide a meaningful measure of cell radiosensitivity. In this assay, cell survival is defined as the ability to form a polykaryon of a given ploidy after irradiation. The slope of the polykaryon dose response has been shown to be highly correlated with the initial slope of the clonogenic survival curves after gamma irradiation, which implies a common subset of lethal lesions. We reported previously on an apoptotic mode of cell death in the polykaryon system and on the heritability of small variations in polykaryon radioresponse. We now show that exposure of PFUs to a given dose of alpha particles results in a greater reduction in the proportion of cells able to reach at least 16C when compared to the same dose of low-LET radiation. This reduction is less than that observed in the low-dose (alpha term) region of the clonogenic curve. On the basis of published LET-dependent spectra of radiation-induced DNA damage, we suggest that this behavior reflects a differential expression of lethal damage that can be probed by varying the LET of the radiation and that base damages contributing additional complexity to clustered DNA lesions may be more deleterious in PFUs than in clonogens.