bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scaling of visual acuity with body size in mammals and birds
Authors: Kiltie R. A. 
Published: March 2003

Abstract1. Kirschfeld (1976)suggested that visual acuity is directly proportional to body length across a wide range of animal species. A survey of eye size, visual acuity and body size of birds and mammals that is consistent with Kirschfeld's suggestion is reported. Hypoallometry (scaling factor < 1) for eye sizevsbody size combines with hyperallometry (scaling factor > 1) for acuityvseye size to produce roughly linear scaling between acuity and body size.2. Kirschfeld (1976)also suggested that the distance at which important objects are typically viewed is a linear function of body length. ‘Subjective distance’ (viewing distance/body length) was therefore thought to be independent of body size across species. However, for prey detection by mammalian and avian predators, it is doubtful that subjective visual distances are size independent because prey size and visual acuity both scale by factors > 0·5 with predator body size; hence, detection distance should scale with size by a factor > 1. Scaling analyses also suggest that subjective visual distances for intraspecific social interactions are size dependent.3. A positive association between body size and viewing distance has implications for the scaling of coat pattern features. In environments with fractal visual backgrounds (in which perceived sizes of background pattern elements do not change as distance from the background changes), larger animal species should have larger coat patches than smaller species if they are adapted to be cryptic at greater viewing distances than smaller species are.
Sons and daughters: age‐specific differences in parental rearing capacities
Authors: Daunt F. , Monaghan P. , Wanless S. , Harris M. P. , Griffiths R. 
Published: March 2003

Abstract1. Numerous studies of iteroparous breeders have demonstrated an increase in average breeding performance with parental age.2. One of the most widely suggested mechanisms to explain this pattern is that the foraging performance of young breeders is relatively poor. Where this is coupled to differences in the costs of rearing male and female offspring, for example because of sexual size dimorphism, young breeders may have difficulties rearing the more expensive sex.3. This was investigated in the Shag, a monogamous seabird in which adult males are on average 20% heavier than adult females. Young pairs breed later in the season than older pairs, and lay smaller eggs. Differences in timing of breeding and egg quality were controlled for in a cross‐fostering experiment in which older and young individuals reared chicks simultaneously from eggs of similar quality.4. Male chicks reared by young parents grew more slowly and attained a lower peak mass than those reared by older parents, whereas there was no equivalent difference for female chicks.5. These results suggest that sons are energetically more demanding on their parents than daughters, and the more expensive sex fledges in significantly poorer condition when the parents are young. Therefore, it is predicted that optimal offspring sex ratio will vary with parental age.
Field and laboratory evidence for acclimation without costs in an egg parasitoid
Authors: Thomson L. J. , Robinson M. , Hoffmann A. A. 
Published: March 2003

Abstract1. Acclimation responses are normally assumed to increase the fitness of an organism, but supporting evidence is generally lacking, especially under field conditions. Even where an advantage arises from acclimation, this can be offset by other fitness costs. Heat hardening is a well‐known form of acclimation in many invertebrates where exposure to high but sub‐lethal temperatures protects against subsequent heat‐induced death.2. Previous laboratory work has shown that hardening occurs in wasp egg parasitoids of the genus Trichogramma because pretreatment with a mild temperature shock can increase survival at high temperatures. This system allowed fitness benefits and costs of hardening under the more stringent conditions in nature to be tested.3. Heat hardening in Trichogramma carverae was considered at the pupal and adult stages and it was shown that hardening had a beneficial effect on heat resistance in the laboratory. Moreover, hardening enhanced adult fitness in the field under hot conditions. No costs of acclimation were detected under mild field and laboratory conditions. Conditions leading to hardening without costs were different from another Trichogramma species.4. Hardening can therefore have fitness benefits without costs under field and laboratory conditions, and this process can be used to enhance parasitism rates in inundative commercial releases of Trichogramma against moth pests.
Functional traits, productivity and effects on nitrogen cycling of 33 grassland species
Authors: Craine J. M. , Tilman D. , Wedin D. , Reich P. , Tjoelker M. , Knops J. 
Published: March 2003

Summary

Our goal was to determine the relationships among ecophysiological, whole‐plant and ecosystem traits of a wide variety of grassland species grown under field conditions in the long term. We measured 87 traits for 33 species (32 perennial, one annual) grown in monoculture for 5 years on sandy soils, and determined the relationship among traits and their correspondence with current functional classifications.
Among non‐legumes, species that produced and maintained large amounts of biomass had tough, low‐activity leaves and roots, high root : shoot ratios, and low extractable inorganic nitrogen and N mineralization in their soils. The set of correlations among the functional traits of fine roots for non‐legumes parallels the set of correlations for leaf functional traits. Low‐N species maintained greater biomass than high‐N species, more by producing tissues with low N concentrations and greater longevity than by acquiring more N. Greater relative production below ground, and the production of long‐lived below‐ground structures, were both important in determining the high root : shoot ratio of species.
For legumes, N2 fixation not only led to greater above‐ground biomass production, but also was associated with low fine root production; greater relative production of stem biomass; and accelerated ecosystem N cycling compared to non‐legumes.
The measured traits, as condensed via principal components analysis, differentiated the 32 species into groups that corresponded with a common grassland functional classification scheme (C3 grasses, C4 grasses, forbs, legumes, woody species) as well as an alternative, continuous approach. For all traits, species can be arrayed well along two continuous axes. The first axis separates cool‐season and warm‐season legumes; the second low‐N and high‐N non‐legumes.
These continuous classifications show the generality of the two strategies for dealing with low nitrogen availability (N2 fixation and the low‐N suite of traits) and extends the strategies to span organ‐level traits to ecosystem processes including roots, whole‐plant patterns of productivity, and nutrient cycling. The correlations of traits among species will also be useful in predicting a large number of important parameters associated with plant growth from the measurement of a few, key traits.
Environmental randomness underlies morphological complexity of colonial diatoms
Authors: Passy S. I. 
Published: March 2003

Summary

The morphology and distribution of six benthic colonial diatoms were investigated from the perspective of fractal geometry and stream ecology to test whether colonial complexity of benthic diatoms is associated with a tolerance to environmental variability, that is, if a random force, such as the unpredictability of current velocity, could be responsible for the development of a high morphological organization.
The fractal dimension of diatom colony perimeters ranged from 1·06 to 1·54, indicating a vast morphological variation from simple geometric shapes to very complex outlines. The niche breadth of the six colonial diatoms, defined from regression models of species abundance along a current velocity gradient, also showed a substantial variation, from 0·48 to 0·79 m s−1.
There was a strong positive relationship between diatom morphological complexity and species niche breadth, suggesting that increased morphological complexity in colonial diatoms is a possible evolutionary strategy for survival in unpredictable environments.
Leaf senescence and resorption as mechanisms of maximizing photosynthetic production during canopy development at N limitation
Authors: Franklin O. , Ågren G. I. 
Published: March 2003

Summary

A canopy N distribution model optimizing photosynthesis was combined with mechanisms for senescence and N resorption to predict canopy leaf area index (LAI) development as a function of canopy nutrient content, Nc.
Shedding of leaves at the bottom of the canopy was initiated when it increased canopy photosynthesis, through resorption and redistribution of N from lost leaves. The amount of N resorbed was modelled as a fraction (Rf) of the N in the leaf prior to senescence.
For a fixed Nc, the LAI at which leaf shedding was initiated was calculated for different Rfs for canopies of Amaranthus cruentus, Glycine max, Oryza sativa and Sorghum bicolor.
Predicted LAIs exceeded optimal LAIs estimated without leaf shedding and N resorption. LAI increased with increasing Rf. For all four species, the model closely predicted the observed LAIs with Rf = 0·7.
Area‐based resorption efficiency increased and litter N concentration decreased with increasing LAI and average canopy N concentration (mol N m−2 leaf). A reduction of Rf, e.g. in response to increased soil N availability, decreases resorption efficiency.
The model provides a mechanistic basis for interpreting plant nutrient–resorption–LAI relations.
Nutrients, arbuscular mycorrhizas and competition interact to influence seed production and germination success in Achillea millefolium
Authors: Allison V. J. 
Published: March 2003

Summary

Environmental variables that positively affect one aspect of plant fitness, may have no effect, or even negatively affect some other component of fitness.
Using individuals of Achillea millefolium grown under field conditions in Michigan, USA, the hypothesis was tested that seed number was determined largely by plant biomass, while seed germination success depends on tissue nutrient concentrations. The impact was assessed of four biotic and abiotic factors on seed number and germination success: root competition, shoot competition, fertilizer, and removal of fungi by fungicide application.
Using a path analysis, it was found that total plant biomass positively affected both seed number and germination success, while inclusion of other variables did not greatly affect the amount of variation the model was able to explain. Fertilizer and fungicide increased, while root and shoot competition decreased both seed number and germination.
Fungicide applied to the maternal plant increased biomass but decreased tissue phosphorus concentrations. In species where germination responds to nutrient concentrations, the potential exists for opposing impacts of environmental treatments on different components of fitness.
This study suggests that environmental impacts on seed number will outweigh impacts on germination success under field conditions, and that biomass is an adequate surrogate for fitness in herbaceous plants.
The physiology of host feeding in parasitic wasps: implications for survival
Authors: Giron D. , Rivero A. , Mandon N. , Darrouzet E. , Casas J. 
Published: March 2003

SummaryModels developed to predict behavioural and life‐history decisions of parasitoids rely heavily on assumptions concerning the nature and function of the nutrients that the female obtains from the host.Using a combination of colorimetric and thin‐layer chromatography techniques, we analysed the composition of the host‐feeding fluid consumed by the parasitoidEupelmus vuillettiand found it to be consistent with the composition of the host's haemolymph.The analysis of the haemolymph revealed that it was rich in proteins but also rich in sugars, trehalose and sucrose in particular.Injections of these sugars at haemolymph concentrations directly into the parasitoid's haemolymph showed that these sugars are solely responsible for the increased longevity observed in host‐fed females.This study is the first to identify the constituents of host‐feeding meals and their impact on parasitoid longevity and provide further evidence of the extent to which parasitoid behavioural decisions are determined by physiological variables. Our study demonstrates that the integration of nutritional physiology, behaviour, life history and population dynamics is essential in order to understand parasitoid foraging ecology.
Measures of reproductive allometry are sensitive to sampling bias
Authors: Bonnet X. , Shine R. , Lourdais O. , Naulleau G. 
Published: March 2003

SummaryIn both interspecific and intraspecific comparisons, maternal body size is the strongest predictor of fecundity for many kinds of animals. However, it has not been widely appreciated that the usual empirical descriptors of this relationship (correlation coefficient, slope andP‐value of the linear regression between maternal body size and offspring number) are sensitive to a factor that is very labile and subject to methodological bias: the degree of maternal investment, specifically the ratio of litter mass to maternal body mass (relative clutch mass, RCM).Samples of females used to assess reproductive allometry may often be biased with respect to RCM. For example, RCMs may vary through time within a single population as a consequence of prey availability, or may vary geographically among populations. Also, females with low RCMs may be more difficult to capture, or may be discarded by researchers who do not realize that they are reproductive.Our analyses on 173 litters of aspic vipers (Vipera aspisLinné) from central western France show that estimates of reproductive allometry are very sensitive to RCM: samples composed of high‐RCM females show a positive and highly significant reproductive allometry, whereas samples composed of low RCM females do not. Conclusions also depend on the method of regression analysis used. This result has strong implications for methodology (i.e. selection of samples, choice of analytical methods and timescales of study) in this field of research.
A measure of the mitotic index: studies of the abundance and half‐life of p34cdc2 in cultured cells and normal and neoplastic tissues
Authors: Gannon Julian V. , Nebreda Angel , Goodger  , Morgan  , Hunt Tim 
Published: March 2003

BackgroundThe cdc2 gene encodes a protein kinase, p34cdc2, that is essential for mitosis, and is present at high levels in dividing cells. Classical studies of the levels of this protein in dividing and resting cells used antibodies that cross‐react with other members of the CDK family, in particular with CDK2. We have therefore re‐examined the abundance of p34cdc2 in a variety of tissues and cell lines, using a highly specific, epitope‐mapped monoclonal antibody that does not react with CDK2.ResultsWe observed high levels of p34cdc2 in proliferating cells, especially those in neoplastic tissues. Cells that have withdrawn from the cell cycle have low or undetectable levels. At the end of mitosis, the level of p34cdc2 declines, with simple first‐order kinetics, with a half‐life which is never less than 6 h and is more typically about 18 h. The persistence of p34cdc2 after the last cell division is comparable to that of PCNA, a commonly used marker of proliferation.ConclusionsThe immunochemical detection of p34cdc2 provides an accurate, reliable and meaningful measure of the proliferative activity of cells in tissues. We suggest that p34cdc2 should be considered as the most authentic molecular marker of the mitotic index.
Region‐specific expression of murine Hox genes implies the Hox code‐mediated patterning of the digestive tract
Authors: Sekimoto Tomohisa , Yoshinobu Kumiko , Yoshida Michio , Kuratani Shigeru , Fujimoto Shoji , Araki Masatake , Tajima Naoya , Araki Kimi , Yamamura Ken‐ichi 
Published: March 2003

Background Hox genes encode transcription factors which are involved in the establishment of regional identities along the anteroposterior (AP) body axis. To elucidate the AP patterning of the digestive tract, we have systematically examined the expression patterns of Hox genes belonging to paralogue groups 6, 7, 8 and 9 by whole‐mount in situ hybridization and by section in situ hybridization analyses.ResultsThe expression patterns of these genes showed co‐linearity along the wall of the digestive tract, thereby yielding the Hox code of the gut. The expression boundaries of the Hox genes at later stages (12.5 d.p.c.) corresponded to the morphological boundaries of individual gut subdomains.ConclusionsThe visceral mesoderm‐restricted expression suggested that the Hox code primarily functions in the mesenchymal specification which eventually leads to the regional differentiation of gut subdomains as the result of epithelial–mesenchymal interactions. Overlapping expression patterns were found among the paralogous Hox genes, indicating that the paralogues may have redundant functions in the specification of the gut.
Tip60 acetylates six lysines of a specific class in core histones in vitro
Authors: Kimura Akatsuki , Horikoshi Masami 
Published: March 2003

Background: Tip60, an HIV‐1‐Tat interactive protein, is a nuclear histone acetyltransferase (HAT) with unique histone substrate specificity. Since the acetylation of core histones at particular lysines mediates distinct effects on chromatin assembly and gene regulation, the identification of lysine site specificity of the HAT activity of Tip60 is an initial step in the analysis of its molecular function. Results: Tip60 significantly acetylates amino‐terminal tail peptides of histones H2A, H3 and H4, but not H2B, consistent with substrate preference on intact histones. Preferred acetylation sites for Tip60 are the Lys‐5 of histone H2A, the Lys‐14 of histone H3, and the Lys‐5, ‐8, ‐12, ‐16 of histone H4, determined by a method which combined matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) measurements and Lys‐C endopeptidase digestion, or a method detecting the incorporation of radiolabelled acetate into synthetic peptides. Conclusion: The lysine site specificity of Tip60 in histone amino‐terminal tail peptides in vitro has been characterized by an assay measuring the molecular mass of endopeptidase digested peptides, or a previously described assay. These results agree well with our proposed classification of lysines in core histones. The classification may be useful for an analysis of the relationships between HATs and the substrates of other uncharacterized HATs.
Enhancer and silencer binding proteins involved in the rat cdc2 promoter activation at the G1/S boundary
Authors: Takeuchi Arata , Shimizu Mamoru , Nishina Mitsue , Shirasuna Kenna , Miura Akihiko , Nakajima Takuma , Oda Kinichiro 
Published: March 2003

BackgroundExpression of the rat cdc2 gene during G1‐S phase progression is negatively and positively regulated by the silencer and enhancer elements located upstream of the basal promoter. The silencer and enhancer sequences resemble each other, but the silencer contains extra internal AG residues.ResultsThe cDNA clones encoding the enhancer binding proteins cdc2E1 and cdc2E2 were isolated by South‐Western blotting. cdc2E1 and cdc2E2 comprise 436 and 256 amino acids and have two RNA binding domains which contain an RNP1 octamer and an RNP 2 hexamer. Both cdc2E1 and cdc2E2 bind to the double‐stranded and single‐stranded silencer and enhancer sequences, but their binding affinity to the enhancer was stronger than that to the silencer. Transfection of quiescent 3Y1 cells with the cdc2 promoter‐luciferase constructs, followed by serum stimulation, showed that the promoter activation at the G1‐S phase boundary was reduced greatly by base substitutions within the enhancer, but not within the silencer. Gel shift assays with oligonucleotides containing both the silencer and enhancer showed that formation of the large complex was greatly reduced if base‐substitutions were introduced into the enhancer, but not within the silencer. The complex was supershifted completely by anti‐cdc2E1 antibody and partially by anti‐cdc2E2 antibody.ConclusionThese results suggest that cdc2E1 and cdc2E2 preferentially form the multimeric complex at the enhancer site after the late G1 phase for activation of the cdc2 promoter.
Competitive interaction of Seven in absentia homolog‐1A and Ca2+/calmodulin with the cytoplasmic tail of group 1 metabotropic glutamate receptors
Authors: Ishikawa Kenji , Nash S. Russell , Nishimune Atsushi , Neki Akio , Kaneko Satoshi , Nakanishi Shigetada 
Published: March 2003

BackgroundGroup 1 metabotropic glutamate receptors (mGluR1 and mGluR5) are coupled to inositol trisphosphate/Ca2+ signaling via G proteins and play an important role in excitatory synaptic transmission. To explore the regulation of group 1 mGluR function, we applied the yeast two‐hybrid system using the intracellular carboxy‐terminal domain of group 1 mGluRs (group 1 ct‐mGluRs) and attempted to identify novel protein–protein interactions of group 1 mGluRs.ResultsThe two‐hybrid screening revealed a specific interaction between group 1 ct‐mGluRs and Siah‐1A, the mammalian homolog of Drosophila seven in absentia which is involved in photoreceptor cell differentiation via the ubiquitin/proteasome‐dependent mechanism. This interaction occurs within a homologous 27–28 amino acid stretch within group 1 ct‐mGluRs and requires the latter two‐thirds of Siah‐1A. Following coexpression in COS‐7 cells, myc‐tagged Siah‐1A was coimmunoprecipitated with the flag‐tagged ct‐mGluR1 by anti‐flag antibody. Furthermore, in vitro binding revealed that Siah‐1A and Ca2+/calmodulin (CaM) binding sites overlap, such that Siah‐1A binding is competitively inhibited by CaM in a Ca2+‐dependent manner.ConclusionsThe results demonstrate a direct interaction between group 1 mGluRs and Siah‐1A and suggest a novel modulatory mechanism mediated by a competitive interaction between Ca2+/CaM and Siah‐1A.