Duration of strike-induced chemosensory searching in long-term captive rattlesnakes at national zoo,audubon zoo,and San Diego Zoo

Rattlesnakes typically strike and release adult rodent prey. Striking is followed by a sustained, high rate of tongue flicking that guides the snake to the envenomated, dead prey. Wild-caught rattlesnakes exhibited this chemosensory searching for about 2.5 h, and the present study demonstrated that long-term captive rattlesnakes (Crotalus atrox, C durissus, C horridus, C vegrandis, C unicolor) at three zoos did the same. Because these zoo-raised snakes had always been offered dead rodents and because the snakes had become accustomed to ingesting them without striking, the present snakes had rarely exercised their innate predatory repertoires. The duration of chemosensory searching in these snakes indicates that this important aspect of the predatory repertoire had not been degraded as a consequence of long-term captive husbandry.     

Detection of conformational changes in human chorionic gonadotropin upon binding to rat gonadal receptors

After binding to rat testicular or ovarian luteinizing hormone (LH) receptors, human chorionic gonadotropin (hCG) and mammalian LH can be detected with monoclonal antibodies directed against a conserved epitope on the beta subunit of the hormones. Two such anti-hCG/anti-LH monoclonal antibodies, known as B105 and B110, compete with one another for binding to this epitope region on free and receptor-bound hormone. By comparing the affinities of B105 and B110 for these two forms of hCG, we have detected apparent changes in the structure of the hormone which develop subsequent to receptor binding. Whereas the affinity of B105 for receptor-bound hCG is approximately 10-fold lower than that for free hCG, the affinity of B110 for receptor-bound hCG is nearly 20-fold greater than that for free hCG. Both B105.hCG and B110.hCG complexes bind to the receptor; however, they have approximately 25 and 50% lower affinity than hCG. Thus, although B110 binds better to the form of hCG which is bound to receptors, binding of B110 to hCG does not appear to induce a conformational change in the hormone which facilitates hormone-receptor binding. Consequently, both B105 and B110 partially inhibit binding of hCG to its receptors. Fab fragments of B105 and B110 are as effective as intact B105 and B110 in inhibiting the binding of labeled B105 and B110 to hCG-receptor complexes, suggesting that circular complexes which might be formed by the interaction of divalent antibody, two molecules of hCG, and two membrane-bound receptors or one divalent receptor are not contributing to the affinity of the antibodies for receptor-bound hCG. Alternatively, formation of circular complexes can explain an increase in apparent affinity of B105 for ovine or bovine LH-receptor complexes. Data obtained with B105 suggest either that the structure of the epitope is altered following binding or that a portion of the epitope is partially obscured when hCG binds to the receptor. In contrast, the data obtained using B110 are not explained by models in which steric factors reduce the affinity of the antibody for the hormone-receptor complex. Therefore, as a minimal explanation for these observations, we postulate that the conformation of the B105/B110 epitope region is altered following binding of the hormone to receptors. The nature of the conformational change and its relationship to LH/hCG action is unknown.     

A quantitative analysis of the interplay of environment,neighborhood, and cell state in 3D spheroids

Cells react to their microenvironment by integrating external stimuli into phenotypic decisions via an intracellular signaling network. To analyze the interplay of environment, local neighborhood, and internal cell state effects on phenotypic variability, we developed an experimental approach that enables multiplexed mass cytometric imaging analysis of up to 240 pooled spheroid microtissues. We quantified the contributions of environment, neighborhood, and intracellular state to marker variability in single cells of the spheroids. A linear model explained on average more than half of the variability of 34 markers across four cell lines and six growth conditions. The contributions of cell‐intrinsic and environmental factors to marker variability are hierarchically interdependent, a finding that we propose has general implications for systems‐level studies of single‐cell phenotypic variability. By the overexpression of 51 signaling protein constructs in subsets of cells, we also identified proteins that have cell‐intrinsic and cell‐extrinsic effects. Our study deconvolves factors influencing cellular phenotype in a 3D tissue and provides a scalable experimental system, analytical principles, and rich multiplexed imaging datasets for future studies.     

vFitness: a web-based computing tool for improving estimation of <Emphasis Type=Italic>in vitro</Emphasis> HIV-1 fitness experiments

Background  

The replication rate (or fitness) between viral variants has been investigated in vivo and in vitro for human immunodeficiency virus (HIV). HIV fitness plays an important role in the development and persistence of drug resistance. The accurate estimation of viral fitness relies on complicated computations based on statistical methods. This calls for tools that are easy to access and intuitive to use for various experiments of viral fitness.     

The cost of incubation in relation to clutch-size in the Collared Flycatcher Ficedula albicollis

This study examines the importance of avian incubation costs as determinants of clutch-size variation by performing clutch-size and brood-size manipulations in the same population of Collared Flycatchers Ficedula albicollis during the same breeding season. In 2 5 cases when three or more clutches of the same size were completed on the same day, we moved two eggs on the day after the last egg had been laid from one randomly selected clutch (C) to another (C) and moved two other eggs from this to a third clutch (C⁺). In 20 other cases of simultaneously completed clutches of the same size, we moved two randomly selected young from one brood to a second and from that moved two other young to a third (B, B and B⁺groups). Most females were weighed the day after completion of the clutch and 1–4 days before hatching of the young, and some of them also 10–14 days after hatching of the young. We measured the daily energy expenditure of females incubating manipulated clutches of 4, 6 and 8 eggs by means of the doubly-labelled water (D₂¹⁸O) technique and also recorded their nest attendance. Hatching success of fertilized eggs was reduced in the enlarged clutches compared with control and reduced clutches. Females expired on average 3142.6 ml CO₂ and expended 78.6 kJ per day while incubating, which corresponds to a metabolic intensity of 3.3 times BMR. Daily energy expenditure increased with clutch-size due to higher costs while incubating, and not because of changed activity patterns. There were no significant differences in length of incubation, female mass or mass changes between phases for the C, C and C⁺groups. In both the C and B groups, enlarged broods produced significantly more fledged young than control broods, and those significantly more than reduced broods. Fledgling tarsus-length and mass did not differ significantly between treatments in either the C or B groups. There was no significant difference in breeding success between clutch and brood manipulations. In this season, incubation costs did not entail significant fitness losses, expressed either as fledgling production or female condition. Also, control females could have raised more young to fledging age than they did with no apparent costs.     

Complementary seed dispersal by three avian frugivores in a fragmented Afromontane forest

Questions: To what extent does species‐specific variation in gut passage time (GPT), habitat use and mobility of three key avian frugivores synergistically affect the distribution of Xymalos monospora seeds within and among isolated forest fragments? Location: Three fragments of a severely fragmented cloud forest, Taita Hills, southeast Kenya. Methods: We experimentally determined GPTs of X. monospora seeds and recorded movements and habitat use by Turdus helleri, Andropadus milanjensis and Tauraco hartlaubi through radiotelemetry, and combined these data to generate species‐specific seed dispersal patterns. Results: Differences in mobility and habitat use among the three frugivores caused significant complementarity in seed dispersal, despite the fact that gut transit times were highly comparable. While the most sedentary and forest‐dependent species mainly led to short‐distance dispersal away from parent trees, two more mobile species dispersed seeds further away from the source trees, both within indigenous forest patches and towards exotic plantations and isolated fruiting trees in the landscape matrix. A. milanjensis inhabiting a very small forest fragment spent significantly more time in the landscape matrix than conspecifics residing in the two larger fragments. Conclusions: By varying distances over which seeds are carried away from parent trees and the habitat types in which they are ultimately deposited, avian frugivores affect the spatial distribution of seeds and early plant recruits in a distinct and complementary manner. Because landscape properties are expected to lead to different constraints on avian mobility for habitat specialists and for generalists, ecosystem processes such as avian seed dispersal are shaped by complex interactions between disperser behaviour and the environment.     

Effect of management on natural capital stocks underlying ecosystem service provision: a ‘provider group’ approach

Land management practices directly impact on the occurrence and condition of natural capital stocks, which can be measured using species diversity and abundance metrics. Species identity and abundance drive ecosystem service supply, either through effects of local diversity and/or through the presence of service providing species. However, the influence of management practices on the provision of ecosystem services is not adequately understood. We grouped grassland plant species into six groups according to desirable attributes (palatability and nutritional value to livestock; medicinal or aromatic compounds; nectar production; pollen production; nitrogen fixation; and endemic and red listed species), which we recognise as ecosystem service ‘provider groups’, and tested the influence of three land management practices (abandonment of mowing, grazing, and mowing) on diversity and abundance within these groups in upland temperate grasslands of Transylvania (Romania). All three management practices favoured at least one provider group, but hay making in upland grasslands favoured more provider groups than abandonment of mowing or grazing. The effects of management on diversity and abundance within several provider groups diverged from the effects on overall species diversity and abundance. Management, through changes in species composition, favours certain provider groups, and hence ecosystem services, over others. The provider group approach is more useful than overall species diversity metrics for assessing the provision of ecosystem services from landscapes and can be used to inform the development of agri-environment schemes and conservation policies aimed at meeting priorities for ecosystem service provision.     

Impairment of photosystem 2 activity at the level of secondary quinone electron acceptor in chloroplasts treated with cobalt, nickel and zinc ions

The toxicity of heavy metals on photosystem 2 photochemistry, was investigated by monitoring Hill activity, fluorescence, and thermoluminescence properties of photosystem 2 (PS 2) in pea (Pisum sativum L. cv. Bombay) chloroplasts. In Co²⁺-, Ni²⁺- or Zn²⁺-treated chloroplasts 2,6-dichlorophenolindophenol-Hill activity was markedly inhibited. Addition of hydroxylamine which donates electrons close to PS 2 reaction center did not restore the PS 2 activity. Co²⁺-, Ni²⁺ or Zn²⁺ also inhibited PS 2 activity supported by hydroxylamine in tris (hydroxymethyl)aminomethane (Tris)-inactivated chloroplasts. These observations were confirmed by fluorescence transient measurements. This implies that the metal ions inhibit either the reaction center or the components of PS 2 acceptor side. Flash-induced thermoluminescence studies revealed that the S₂Q^?_A charge recombination was insensitive to metal ion addition. The S₂Q^?_B charge recombination, however, was inhibited with increase in the level of Co²⁺, Ni²⁺ or Zn²⁺. The observed sensitivity of S₂^?_B charge recombination in comparison to the stability of S₂Q^?_A recombination suggests that the metal ions inhibit at the level of secondary quinone electron acceptor. Q_B. We suggest that Co²⁺, Ni²⁺ or Zn²⁺ do not block the electron flow between the primary and secondary quinone electron acceptor, but possibly, directly modify Q_B site, leading to the loss of PS 2 activity.