Density dependence and environmental factors affect population stability of an agricultural pest and its specialist parasitoid

Host–parasitoid dynamics are intrinsically unstable unless the risk of parasitism is sufficiently heterogeneous among hosts. Spatial aggregation of parasitoids can contribute to this heterogeneity, stabilising host–parasitoid population dynamics and thereby reducing pest outbreaks. We examined the spatial distribution of mango gall fly (Procontarinia matteiana, Kiefer and Cecconi), a non-native pest of South African mango orchards, which is controlled by a single parasitoid (Chrysonotomyia pulcherrima, Kerrich). We assessed whether spatial aggregation of parasitoids is associated with proximity to natural vegetation and/or to host density-dependent and host density-independent factors at three spatial scales. We found evidence for higher parasitism rates near natural vegetation at the field scale, and inverse host-density dependent and density-independent parasitoid aggregation at both the leaf scale and field scale. Therefore, we conclude that natural vegetation plays a role in promoting stabilising aggregation of parasitoids, possibly through provision of non-host resources (nectar, pollen), in this system.     

Fifteen years of annual Cape Parrot Poicephalus robustus censuses: current population trends and conservation contributions

The Cape Parrot Poicephalus robustus is endemic to South Africa and numbers have reportedly declined since the early 1900s. It is a forest specialist and food nomadic, moving between patches depending on fruit availability. This makes it difficult to estimate numbers accurately and to determine its distribution. The annual Cape Parrot Big Birding Day was initiated in 1998 as a national census to determine a population estimate. Volunteers assist in monitoring and counting the Cape Parrot in the Eastern Cape, KwaZulu-Natal and Limpopo provinces in indigenous forests as well as sites where the parrots are known to feed outside of forests. Here, a summary of 15 years of census data is presented. In all years, with the exception of 2009, less than 1 600 Cape Parrots were recorded in the wild. The census data showed a slight increase in Cape Parrots, although this may be largely explained by an increase in coverage of suitable habitat and stabilisation in the population since 2005. A current distribution map for the Cape Parrot, based on census data, is presented. The distribution remains largely unchanged from that presented in the 1970s. This study highlights the value of public participation in monitoring an Endangered species and the need to conserve the forests where these parrots occur, due to their nomadic feeding behaviour.     

Stoichiometric and growth responses of a freshwater filamentous green alga to varying nutrient supplies: slow and steady wins the race

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Branched intermediate formation is the slowest step in the protein splicing reaction of the Ala1 KlbA intein from Methanococcus jannaschii

We report the first detailed investigation of the kinetics of protein splicing by the Methanococcus jannaschii KlbA (Mja KlbA) intein. This intein has an N-terminal Ala in place of the nucleophilic Cys or Ser residue that normally initiates splicing but nevertheless splices efficiently in vivo [Southworth, M. W., Benner, J., and Perler, F. B. (2000) EMBO J.19, 5019-5026]. To date, the spontaneous nature of the cis splicing reaction has hindered its examination in vitro. For this reason, we constructed an Mja KlbA intein-mini-extein precursor using intein-mediated protein ligation and engineered a disulfide redox switch that permits initiation of the splicing reaction by the addition of a reducing agent such as dithiothreitol (DTT). A fluorescent tag at the C-terminus of the C-extein permits monitoring of the progress of the reaction. Kinetic analysis of the splicing reaction of the wild-type precursor (with no substitutions in known nucleophiles or assisting groups) at various DTT concentrations shows that formation of the branched intermediate from the precursor is reversible (forward rate constant of 1.5 × 10(-3) s(-1) and reverse rate constant of 1.7 × 10(-5) s(-1) at 42 °C), whereas the productive decay of this intermediate to form the ligated exteins is faster and occurs with a rate constant of 2.2 × 10(-3) s(-1). This finding conflicts with reports about standard inteins, for which Asn cyclization has been assigned as the rate-determining step of the splicing reaction. Despite being the slowest step of the reaction, branched intermediate formation in the Mja KlbA intein is efficient in comparison with those of other intein systems. Interestingly, it also appears that this intermediate is protected against thiolysis by DTT, in contrast to other inteins. Evidence is presented in support of a tight coupling between the N-terminal and C-terminal cleavage steps, despite the fact that the C-terminal single-cleavage reaction occurs in variant Mja KlbA inteins in the absence of N-terminal cleavage. We posit that the splicing events in the Mja KlbA system are tightly coordinated by a network of intra- and interdomain noncovalent interactions, rendering its function particularly sensitive to minor disruptions in the intein or extein environments.     

Inhibitory mechanism of pure curcumin on Wilms' tumor 1 (WT1) gene expression through the PKCα signaling pathway in leukemic K562 cells

The aim of this study was to investigate the inhibitory mechanism of pure curcumin on WT1 expression in leukemic K562 cells. Pure curcumin suppressed WT1 expression, independent of effects on protein degradation or WT1 mRNA stability. Chromatin immunoprecipitation and reporter gene assays indicate that pure curcumin treatment attenuates WT1 auto-regulation. Interestingly, PKCα inhibition mimicks the repressive effects of pure curcumin in K562 cells. Conversely, myristoylated PKCα over-expression increased WT1 expression and reversed the inhibitory effect of pure curcumin. Our study indicates that pure curcumin attenuates WT1 auto-regulatory function through inhibition of PKCα signaling in K562 cells.     

Identification of neuronal RNA targets of TDP-43-containing ribonucleoprotein complexes

TAR DNA-binding protein 43 (TDP-43) is associated with a spectrum of neurodegenerative diseases. Although TDP-43 resembles heterogeneous nuclear ribonucleoproteins, its RNA targets and physiological protein partners remain unknown. Here we identify RNA targets of TDP-43 from cortical neurons by RNA immunoprecipitation followed by deep sequencing (RIP-seq). The canonical TDP-43 binding site (TG)(n) is 55.1-fold enriched, and moreover, a variant with adenine in the middle, (TG)(n)TA(TG)(m), is highly abundant among reads in our TDP-43 RIP-seq library. TDP-43 RNA targets can be divided into three different groups: those primarily binding in introns, in exons, and across both introns and exons. TDP-43 RNA targets are particularly enriched for Gene Ontology terms related to synaptic function, RNA metabolism, and neuronal development. Furthermore, TDP-43 binds to a number of RNAs encoding for proteins implicated in neurodegeneration, including TDP-43 itself, FUS/TLS, progranulin, Tau, and ataxin 1 and -2. We also identify 25 proteins that co-purify with TDP-43 from rodent brain nuclear extracts. Prominent among them are nuclear proteins involved in pre-mRNA splicing and RNA stability and transport. Also notable are two neuron-enriched proteins, methyl CpG-binding protein 2 and polypyrimidine tract-binding protein 2 (PTBP2). A PTBP2 consensus RNA binding motif is enriched in the TDP-43 RIP-seq library, suggesting that PTBP2 may co-regulate TDP-43 RNA targets. This work thus reveals the protein and RNA components of the TDP-43-containing ribonucleoprotein complexes and provides a framework for understanding how dysregulation of TDP-43 in RNA metabolism contributes to neurodegeneration.     

BBX32, an Arabidopsis B-Box protein, functions in light signaling by suppressing HY5-regulated gene expression and interacting with STH2/BBX21

A B-box zinc finger protein, B-BOX32 (BBX32), was identified as playing a role in determining hypocotyl length during a large-scale functional genomics study in Arabidopsis (Arabidopsis thaliana). Further analysis revealed that seedlings overexpressing BBX32 display elongated hypocotyls in red, far-red, and blue light, along with reduced cotyledon expansion in red light. Through comparative analysis of mutant and overexpression line phenotypes, including global expression profiling and growth curve studies, we demonstrate that BBX32 acts antagonistically to ELONGATED HYPOCOTYL5 (HY5). We further show that BBX32 interacts with SALT TOLERANCE HOMOLOG2/BBX21, another B-box protein previously shown to interact with HY5. Based on these data, we propose that BBX32 functions downstream of multiple photoreceptors as a modulator of light responses. As such, BBX32 potentially has a native role in mediating gene repression to maintain dark adaptation.     

The statistical mechanics of community assembly and species distribution

? Theoretically, communities at or near their equilibrium species number resist entry of new species. Such 'biotic resistance' recently has been questioned because of successful entry of alien species into diverse natural communities. ? Data on 10,409 naturalizations of 5350 plant species over 16 sites dispersed globally show exponential distributions both for species over sites and for sites over number of species shared. These exponentials signal a statistical mechanics of species distribution, assuming two conditions. First, species and sites are equivalent, either identical ('neutral') or so complex that the chance a species is in the right place at the right time is vanishingly small ('idiosyncratic'); the range of species and sites in our data disallows a neutral explanation. Secondly, the total number of naturalizations is fixed in any era by a 'regulator'. ? Previous correlation of species naturalization rates with net primary productivity over time suggests that the regulator is related to productivity. ? We conclude that biotic resistance is a moving ceiling, with resistance controlled by productivity. The general observation that the majority of species occur naturally at only a few sites, and only a few species occur at many sites, now has a quantitative (exponential) character, offering the study of species' distributions a previously unavailable rigor.     

Detection of the oyster herpesvirus in commercial bivalve in northern California, USA: conventional and quantitative PCR

The ostreid herpesvirus (OsHV-1) and related oyster herpesviruses (OsHV) are associated with world-wide mortalities of larval and juvenile bivalves. To quantify OsHV viral loads in mollusc tissues, we developed a SYBR Green quantitative PCR (qPCR) based on the A-region of the OsHV-1 genome. Reaction efficiency and precision were demonstrated using a plasmid standard curve. The analytical sensitivity is 1 copy per reaction. We collected Crassostrea gigas, C. sikamea, C. virginica, Ostrea edulis, O. lurida, Mytilus galloprovincialis, and Venerupis phillipinarum from Tomales Bay (TB), and C. gigas from Drakes Estero (DE), California, U.S.A., and initially used conventional PCR (cPCR) to test for presence of OsHV DNA. Subsequently, viral loads were quantified in selected samples of all tested bivalves except O. lurida. Copy numbers were low in each species tested but were significantly greater in C. gigas (p < 0.0001) compared to all other species, suggesting a higher level of infection. OsHV DNA was detected with cPCR and/or qPCR and confirmed by sequencing in C. gigas, C. sikamea, C. virginica, O. edulis, M. galloprovincialis, and V phillipinarum from TB and C. gigas from DE. These data indicate that multiple bivalve species may act as reservoirs for OsHV in TB. A lack of histological abnormalities in potential reservoirs requires alternative methods for their identification. Further investigation is needed to determine the host-parasite relationship for each potential reservoir, including characterization of viral loads and their relationship with infection (via in situ hybridization), assessments of mortality, and host responses.