bluuebunny/crossref_metadata_2025_split huggingface dataset:
A biomechanical hypothesis explaining upstream movements by the freshwater snail Elimia
Authors: HURYN A. D. , DENNY M. W. 
Published: November 2003

1. Many taxa of freshwater invertebrates show active upstream movements, particularly the snails. Hypotheses explaining this behaviour invoke the search for food or space, compensation for drift, avoidance of predation and hydrodynamic effects. The pervasiveness of upstream movements among remote lineages of snails (two subclasses, three orders, 10 families), however, suggests that snails may move upstream for mechanical rather than adaptive reasons. 2. It is proposed that upstream movements by snails are a function of torque on the snail’s foot generated by hydrodynamic drag on the shell. When subject to high broadside drag‐forces on their shells, snails are able to reduce torque and stabilize orientation only by directing their anterior aspect upstream. 3. Movements of the freshwater pleurocerid snail Elimia were studied by following marked free‐ranging individuals in six streams in Alabama, USA (four species, eight populations). 4. Populations showed either no net movement (two streams) or significant upstream movements ranging to a mean of ≈40 m over a 3‐month period (four streams). Movement patterns were stream specific rather than species or population specific. Within populations showing significant upstream movements, snails with shell lengths ≤10 mm showed little net movement. Larger snails showed movements from 0 to >200 m upstream. 5. A torque‐constrained random walk model was used to perform a post hoc test of the hypothesis that upstream movements were a function of torque on the snail’s foot generated by hydrodynamic drag on the shell. The model predicted upstream and size‐dependent movement patterns that approximated those observed for snails in the field.
Influence of pregnancy on the thermal biology of the lizard, Sceloporus jarrovi: why do pregnant females exhibit low body temperatures?
Authors: MATHIES T. , ANDREWS R. M. 
Published: November 2003

1. Selected body temperatures of female lizards, Sceloporus jarrovi, were measured on a photothermal gradient during late pregnancy and again when postpartum, and pregnant females were subjected to one of three fluctuating temperature regimes that simulated body temperatures of (1) pregnant females, (2) postpartum females or (3) allowed normal thermoregulation. 2. Overall, females selected lower body temperatures when pregnant (mean = 32·0°C) than when postpartum (mean = 33·5°C). 3. Females regulated body temperature more precisely when pregnant than when postpartum as judged by their smaller variances in body temperature throughout the day. 4. When pregnant, females selected a lower mean maximum body temperature (mean: pregnant = 32·8°C; postpartum = 34·5°C) than when postpartum, but selected mean minimum body temperatures did not differ. 5. None of the experimental temperature treatments was detrimental to pregnant females. Female body length increased during pregnancy but the rate of increase did not differ among treatments. Moreover, length‐adjusted body mass of postpartum females did not differ among treatments. 6. Pregnant females that experienced postpartum body temperatures produced neonates that were smaller in body mass and length than pregnant females that experienced pregnant body temperatures and females that were allowed to thermoregulate. 7. For neonates resulting from the postpartum body temperature treatment, the disparity in the body length, but not mass, was still observed at 9 days of age, although survival and growth of neonates was high and did not differ among treatments. 8. The results demonstrate that pregnant females could maintain higher postpartum body temperatures without compromising their physical condition, but select relatively low body temperatures, presumably to avoid decrements in offspring fitness.
The effect of nitrogen fertilization and rust fungus infection, singly and combined, on the leaf chemical composition of Rumex obtusifolius
Authors: HATCHER P. E. , PAUL N. D. , AYRES P. G. , WHITTAKER J. B. 
Published: November 2003

1. The chrysomelid beetle Gastrophysa viridula occurs on Rumex obtusifolius growing in a range of nutrient conditions and also on plants infected with the foliar fungus Uromyces rumicis. In a controlled environment, we investigated the effect of fertilizing plants with eight nitrate and four ammonium concentrations, with or without infection, on leaf nutritional quality. 2. Increasing nitrate fertilization increased leaf oxalate, total nitrogen and nitrate concentrations and water content, and decreased total non‐structural carbohydrate (NSC) concentrations. Increasing ammonium fertilization increased leaf nitrogen concentration and water content, decreased nitrate and NSC concentrations, and had no effect on oxalate concentrations. 3. Infection produced a mainly additive effect to fertilization, increasing NSC and oxalate, and decreasing nitrate and nitrogen concentration in whole plants fed nitrate, and increasing nitrate and NSC in whole plants fed ammonium. 4. Young leaves on infected plants remained uninfected and had greater nitrogen and NSC concentrations, and lower oxalate and nitrate concentrations, than infected leaves on the same plant. 5. These results are discussed in relation to changes in C:N and NSC:organic nitrogen ratios, the effect of nitrate and oxalate, and the known feeding and oviposition preferences of the beetle. The results suggest that there is an optimum nitrogen fertilization level for G. viridula development.
The influence of preformed defences on the dynamic wound response in Spruce bark
Authors: WAINHOUSE D. , ROSE D. R. , PEACE A. J. 
Published: November 2003

1. Two of the principal defences in conifer bark against attack by bark beetles and associated fungi, the flow of preformed resin and the dynamic wound response (DWR), are commonly regarded as separate, sequential responses to attack. In this paper the concentration of three preformed defences (resin, total polyphenols and lignified stone cell masses) was measured at different heights on the stem of Norway and Sitka Spruce to determine their effect on the size of lesions formed during the DWR to inoculation with three facultatively pathogenic fungi (Phacidium coniferarum, Ophiostoma piceae and Cryptosporiopsis sp.) inoculated during the dormant season. 2. There was considerable within‐tree variation in concentration of lignin and there was a dose‐dependent negative effect of lignin on lesion size. The form of the relationship, however, was influenced by fungal and tree species and for some fungi, also by an individual tree effect. 3. Results suggest that resistance of conifer bark to pests and pathogens depends on an interaction between preformed and induced defences.
Latitudinal compensation in oyster ciliary activity
Authors: DITTMAN D. E. 
Published: November 2003

1. Theories of latitudinal compensation predict that individuals living in colder temperature regimes should physiologically compensate for the slowing of standard physiological rates, owing to the relatively low temperature of their local environments, by increasing their metabolic rate in colder water temperatures relative to individuals living in warmer water temperature regimes. 2. This hypothesis was tested with oyster strains originally from geographically separated populations that were raised in a common environment for seven generations. The physiological parameter measured was ciliary activity across a temperature gradient. 3. Support for the latitudinal compensation hypothesis was found: the strain originally from the colder temperature regime had more active cilia at lower experimental temperatures than individuals originally from the warmer temperature regime. Ciliary activity of the more northern Long Island Sound oysters was significantly greater than activity in the more southern Delaware Bay oysters at temperatures of –1, 2 and 6 °C. 4. These results suggest that there is genetically based physiological differentiation between these populations of oysters consistent with the latitudinal compensation for local temperature regime.
Periodic arousals in hibernating mammals: is evaporative water loss involved?
Authors: THOMAS D. W. , GEISER F. 
Published: November 2003

1. Using existing data on the rate of cutaneous and pulmonary evaporative water loss (EWL) for hibernating Little Brown Bats (Myotis lucifugus) and on the duration of torpor bouts, body temperature (Tb) and oxygen uptake (VO2) of Golden‐mantled Ground Squirrels (Spermophilus saturatus), the rate of EWL was modelled for ground squirrels hibernating at ambient temperatures (Ta) of –2, 2, 4 and 8 °C. 2. Total EWL showed a curvilinear response to Ta, being lowest at 2 °C and increasing with both increasing and decreasing Ta. EWL at –2 °C was about equal to that at 4 °C. The duration of torpor bouts showed the same curvilinear response to Ta and torpor bout duration at –2 °C was similar to that at 4 °C (8·5 vs 8·3 days, respectively). 3. At Ta≥ 2 °C, where Tb of torpid S. saturatus is not metabolically defended, torpor bout duration is significantly related to Tb, VO2 and EWL, with the three variables having similar r2 values. 4. Using the regression equations generated at Ta≥ 2 °C to predict torpor bout durations at –2 °C, where Tb is metabolically defended, shows that the three variables do not have equivalent predictive abilities. Tb and VO2 predicted torpor bout durations of 15·2 and –40·4 days, respectively, compared with observed durations of 8·5 days at –2 °C. EWL predicted torpor bout durations of 8·4 days or only 0·1 days less than that observed at –2 °C. 5. The relation between torpor bout duration and total EWL was insensitive to major variations in cutaneous EWL. Over Ta ranging from –2 °C to 8 °C, a stepwise multiple regression including Tb, VO2 and EWL as independent variables identified EWL as the only variable significantly correlated with torpor bout duration. 6. Our analyses suggest that torpor bout duration may be influenced by EWL, indicating that animals may need to obtain free water when they arouse. An analysis of the structural and temperature characteristics of ground squirrel hibernacula suggests that they may function as a biological condensing tower. Throughout winter, water should evaporate from the warm lower levels and condense in the colder upper regions and so free water may be available to animals when they arouse.
Reduced tail regeneration in the Common Lizard, Lacerta vivipara, parasitized by blood parasites
Authors: OPPLIGER A. , CLOBERT J. 
Published: November 2003

1. Many lizards will lose their tail through autotomy as an antipredator device even though there must be significant costs during tail regeneration. 2. Parasites are energetically costly to the host, and may reduce the rate of cell regeneration. The relation between the presence of haemogregarines (phylum Sporozoa) and the rate of tail regeneration in the Common Lizard Lacerta vivipara (Jacquin) was examined. 3. Experimentally induced autotomy in parasitized lizards resulted in a significantly reduced rate of tail regeneration compared with non‐parasitized lizards. On the other hand, tail loss was not associated with an abnormal increase of parasite load, suggesting that the physiological stress (induced by tail loss) did not cause a decrease in parasite defence.
Non‐structural carbohydrate accumulation and use in an understorey rain‐forest shrub and relevance for the impact of leaf herbivory
Authors: MARQUIS R. J. , NEWELL E. A. , VILLEGAS A. C. 
Published: November 2003

1.
Piper arieianum, an evergreen, understorey shrub of lowland moist forests of Central and South America, exhibits marked seasonal variation in reproductive activity even though climatic variation is low at the study site. Despite a lack of climatic seasonality, previous experimental leaf removal suggested that carbohydrate accumulation is seasonal, occurring prior to flowering. 2. We first tested the hypothesis that carbohydrates necessary for reproduction are accumulated prior to flowering, rather than during or after. By measuring non‐structural carbohydrate production in the form of glucose and starch we found that the concentration of these reserves is greatest 1–3months before flowering, decreasing by 50% during peak fruit maturation. 3. The hypothesis that reproduction was the cause of this decrease in carbohydrate reserves was then tested by comparing reserves in plants that were prevented from flowering with those that flowered and produced fruit naturally. As predicted, reserves declined more in flowering than in non‐flowering plants. A smaller decline in reserves of non‐flowering plants was accompanied by greater stem and leaf production, suggesting that stored carbohydrates are also required for growth. 4. Because concentrations of non‐structural carbohydrates were similar in roots, stems and leaves, and because the greatest amount of plant biomass is in stems for plants of a range of sizes, stems appear to be the main storage site of carbohydrate reserves in this plant species. 5. These results, together with previous studies, demonstrate that the impact of leaf herbivory on seed production in P. arieianum depends on the timing of that herbivory relative to the accumulation and use of non‐structural carbohydrates.
An optimum body size for mammals? Comparative evidence from bats
Authors: JONES K. E. , PURVIS A. 
Published: November 2003

1. The distribution of body sizes among mammalian species has been modelled by Brown, Marquet & Taper (1993), who suggest that reproductive power (the rate at which energy from the environment is channelled into offspring production) is maximized at a size of 100 g, and the observed size distribution among species reflects the way reproductive power depends on size. The model makes a testable prediction about life‐history allometries: namely, that components of reproductive power should not scale linearly with body size but should change sign at the optimum size. 2. A large set of life‐history data from a single clade of small mammals, the bats (Order: Chiroptera), was analysed to test this key prediction. The analyses in this study offer no support for the idea that allometries of reproductive power change sign in bats, either at 100 g or at any other size. Furthermore the life‐history allometries of bats, which are mostly below the 100 g optimum, were broadly the same as in mammalian taxa larger than the optimum size. 3. These findings together contradict a key prediction of Brown et al.’s (1993) model to explain the skewed body size distribution across mammalian species.
Geographic variation in ‘costs of reproduction’ in the scincid lizard Lampropholis guichenoti
Authors: QUALLS F. J. , SHINE R. 
Published: November 2003

1. A major focus of life‐history research has been the analysis of reproductive effort (RE). However, while clearly defined in theory, RE has proved very difficult to measure. Consequently, researchers have looked for indices that estimate the components of RE. Uncritical use of indices of reproductive investment, such as measures of costs of reproduction, without verification of the underlying assumptions of the link between these traits, may lead to spurious conclusions. In this paper, the common assumption that the physical burden of the clutch impairs locomotor ability in gravid reptiles is examined. 2. Two neighbouring populations of Australian scincid lizards (Lampropholis guichenoti) are similar in adult body sizes, body shapes and reproductive output (egg sizes, clutch sizes, relative clutch masses). 3. Despite morphological and reproductive similarities, the effects of pregnancy on maternal locomotor ability (running speeds, as measured in a laboratory raceway) differed dramatically between the two populations. 4. Lizards from the two populations ran at similar speeds when nongravid (i.e. after egg‐laying), but pregnancy significantly reduced running speeds in one population and increased them in the other. Thus, superficial similarities in body size and reproductive output masked a strong divergence in the locomotor ‘costs’ of reproduction. 5. Caution is advised if using simple measures of reproductive output (e.g. relative clutch mass) as indices of reproductive effort, or to generalize results even among conspecific populations.
Dissection of fission yeast microtubule associating protein p93Dis1: regions implicated in regulated localization and microtubule interaction
Authors: Nakaseko Yukinobu , Nabeshima Kentaro , Kinoshita Kazuhisa , Yanagida Mitsuhiro 
Published: November 2003

Background: Fission yeast microtubule associating protein (MAP) p93Dis1 functions for sister chromatid separation: dis1 mutants fail to separate chromosomes, while the spindle elongates but without cyclin destruction. p93Dis1 localizes along microtubules in interphase cytoplasm, but shifts to the spindle pole body (SPB) and spindle microtubules upon the entry into mitosis. In this study, regions of p93Dis1 were dissected to examine their role. Results: Nitrocellulose filter blotting shows that recombinant Dis1 binds to bovine brain microtubules in vitro. A basic central region rich in S, T and P is essential for this association. However, the whole p93Dis1 with N‐ and C‐termini containing a conserved repeat motif and heptad repeats, respectively, is necessary for normal microtubule association in vivo. The N‐truncated region also binds to microtubules but only to the portions near the SPBs. Overproduction phenotypes indicate that p93Dis1 greatly affects spindle formation and cell morphogenesis. The central region is essential but, by itself, not sufficient for generating such effects. Conclusions: We propose that p93Dis1 consists of three regions which carry distinct properties for localization: the N‐region for cell cycle dependent localization, the central region for direct microtubule association, and the C‐region for SPB and nuclear localization. The essential role of p93Dis1 is carried out in the C‐region, while the N‐region acts as a regulator.
Enhancer analysis of the mouse HNF‐3β gene: regulatory elements for node/notochord and floor plate are independent and consist of multiple sub‐ elements
Authors: Sasaki Hiroshi , Hogan Brigid L. M. 
Published: November 2003

Background:  Axial pattern formation in vertebrate embryos depends on signals from the node and, later, from the notochord and floor plate. Previous studies have shown that HNF‐3β, a member of the winged‐helix transcription factor family, plays key roles in the development of all three organizing centres. Results:  Enhancer analysis of HNF‐3β has therefore been performed using lacZ reporter gene constructs in transgenic mouse embryos. This has led to the identification of independent node/notochord and floor plate enhancers, at positions far upstream (−15 to −14 kb) and downstream (+6 to +11 kb) of the transcription start site, respectively. The node/notochord enhancer activity has been localized to a 520 bp fragment. Floor plate gene expression requires a combination of two separate fragments of the enhancer. Deletion analysis of one of these fragments (400 bp) has identified subregions required for the initiation and the maintenance of floor plate expression, and for the suppression of ectopic expression within the neural tube. Conclusion:  We conclude that HNF‐3β gene expression in the node/notochord and in the floor plate are controlled through different enhancers, which consist of positive and negative elements.
A one‐hybrid system for detecting RNA–protein interactions
Authors: Wilhelm James E. , Vale Ronald D. 
Published: November 2003

Background : mRNA translation, stability, and localization are controlled by regulatory proteins that bind to specific RNA motifs. Since biochemical isolation of such proteins has often proven to be difficult, a genetic system for studying RNA–protein interactions would be of great utility in the identification of novel RNA binding proteins and in understanding how these proteins recognize particular RNA sequences.  The bacteriophage lambda gene product N protein is a sequence specific RNA binding protein that when bound to its target sequence allows RNA polymerase to ignore transcription termination signals. The fact that the binding of N protein to RNA is directly coupled to gene expression suggests that N protein could be used to develop a general system for studying RNA–protein interactions.Results : Our results show that fusion of the RNA binding protein, R17, to N causes antitermination in a β‐galactosidase reporter construct that has the R17 binding site substituted for the normal N target sequence. This system can both detect low affinity interactions as well as discriminate between binding events with equilibrium dissociation constants from 10−5 to 10−8 m. The differences in antitermination activity with various mutant binding sites can be reliably detected by colony colour on X‐Gal plates as well as by liquid culture assay.Conclusions: We have demonstrated that N protein can cause antitermination through a heterologous RNA–protein interaction and that the system is capable of detecting RNA–protein interactions of differing affinities. This approach may also be useful in screening libraries for proteins that bind to novel RNA regulatory elements. Our results are also consistent with a model of N protein function in which binding to the nascent transcript increases the effective concentration of N in the vicinity of RNA polymerase leading to antitermination.
Molecular anatomy of the β′ subunit of the E. coli RNA polymerase: identification of regions involved in polymerase assembly
Authors: Luo Jianying , Sharif Karim A. , Jin Ruzhong , Fujita Nobuyuki , Ishihama Akira , Krakow Joseph S. 
Published: November 2003

Background: The E. coli RNA polymerase is a multisubunit enzyme, which is present in two different forms: the catalytic competent core enzyme (α2ββ ′) and the promoter selective holoenzyme (α2ββ ′σ). Correct assembly of individual subunits into core or holoenzyme is essential for the function of this enzyme. Results: Mutant β ′ proteins truncated near the centre or at the C‐terminus were able to form stable core enzyme‐like complexes under reconstitution conditions. Mutant β ′ proteins lacking the region between amino acids 201–477 failed to form holoenzyme complexes while retaining the ability to form core enzyme complexes. Furthermore, free β ′ subunit interacted with free σ subunit to form a stable β ′σ subassembly. Removal of amino acids 201–477 from the β ′ subunit strongly interfered with this interaction. Conclusion: Our results suggest that the N‐terminal region of the β ′ subunit is involved in the assembly of core enzyme. The region between amino acids 201 and 477 on β ′ may be directly or indirectly involved in the interaction between the β ′ subunit and the σ subunit.