bluuebunny/crossref_metadata_2025 huggingface dataset:
Trade‐offs in low‐light CO2 exchange: a component of variation in shade tolerance among cold temperate tree seedlings
Authors: Walters M. B. , Reich P. B.
Published: March 2003

1. Does enhanced whole‐plant CO2 exchange in moderately low to high light occur at the cost of greater CO2 loss rates at very‐low light levels? We examined this question for first‐year seedlings of intolerant Populus tremuloides and Betula papyrifera, intermediate Betula alleghaniensis, and tolerant Ostrya virginiana and Acer saccharum grown in moderately low (7·3% of open‐sky) and low (2·8%) light. We predicted that, compared with shade‐tolerant species, intolerant species would have characteristics leading to greater whole‐plant CO2 exchange rates in moderately low to high light levels, and to higher CO2 loss rates at very‐low light levels.

2. Compared with shade‐tolerant A. saccharum, less‐tolerant species grown in both light treatments had greater mass‐based photosynthetic rates, leaf, stem and root respiration rates, leaf mass:plant mass ratios and leaf area:leaf mass ratios, and similar whole‐plant light compensation points and leaf‐based quantum yields.

3. Whole‐plant CO2 exchange responses to light (0·3–600 µmol quanta m−2 s−1) indicated that intolerant species had more positive CO2 exchange rates at all but very‐low light (< 15 µmol quanta m−2 s−1). In contrast, although tolerant A. saccharum had a net CO2 exchange disadvantage at light > 15 µmol quanta m−2 s−1, its lower respiration resulted in lower CO2 losses than other species at light < 15 µmol quanta m−2 s−1.

4. Growth scaled closely with whole‐plant CO2 exchange characteristics and especially with integrated whole‐plant photosynthesis (i.e. leaf mass ratio × in situ leaf photosynthesis). In contrast, growth scaled poorly with leaf‐level quantum yield, light compensation point, and light‐saturated photosynthetic rate.

5. Collectively these patterns indicated that: (a) no species was able to both minimize CO2 loss at very‐low light (i.e. < 15 µmol quanta m−2 s−1) and maximize CO2 gain at higher light (i.e. > 15 µmol quanta m−2 s−1), because whole‐plant respiration rates were positively associated with whole‐plant photosynthesis at higher light; (b) shade‐intolerant species possess traits that maximize whole‐plant CO2 exchange (and thus growth) in moderately low to high light levels, but these traits may lead to long‐term growth and survival disadvantages in very‐low light (< 2·8%) owing, in part, to high respiration. In contrast, shade‐tolerant species may minimize CO2 losses in very‐low light at the expense of maximizing CO2 gain potential at higher light levels, but to the possible benefit of long‐term survival in low light.
Very early detection of canopy presence by seeds through perception of subtle modifications in red:far red signals
Authors: Batlla D. , Kruk B. C. , Benech‐Arnold R. L.
Published: March 2003

1. An early inhibition of germination in seeds of Silene gallica and Brassica campestris which were continuously exposed to the light environment under an establishing wheat canopy, was observed in two different experiments. Inhibition occurred c.15 days after crop emergence, when the canopy leaf area index (LAI) was below one and the red (R):far‐red (FR) ratio recorded under the canopy was well above 0·8.

2. This inhibitory effect was either overcome by filtering FR light through a solution of CuSO4 or could be artificially imposed by simulating the canopy with filters yeilding a R:FR ratio of 0·95 and 0·8. These results show that light subtly enriched with FR was the environmental factor regulating germination below the developing canopy.

3. Exposure to canopy‐filtered light pulses of 1 h (presumably sufficient to saturate a low fluence response, LFR) did not inhibit seed germination. Moreover, such treatment promotes germination up to an extent similar to that previously observed in the laboratory after a saturating pulse of R light. Instead, prolonged exposures were required to inhibit germination. These results, together with the relatively high R:FR ratios measured below the canopy in early stages of its establishment, suggest that a high irradiance response (HIR) would be involved in such a regulation.

4. This capacity to detect small environmental light‐quality modifications when exposed to high irradiances, would allow the seeds from these species to detect the presence of a canopy in the very early stages of its establishment and to stay in ‘safe’ pre‐germination phases when the probability of successful seedling establishment is low.
Maternal basking opportunity affects juvenile phenotype in a viviparous lizard
Authors: Wapstra E.
Published: March 2003

1. The effects of external conditions on embryonic development have been repeatedly examined in oviparous reptile species, but the effect of gestation conditions on offspring traits in viviparous species has rarely been examined.

2. The influence of maternal basking opportunities on gestation length and juvenile phenotype was investigated in a viviparous scincid lizard,Niveoscincus ocellatus. Females were housed under one of two experimental regimes (10 or 4 h access to basking) which reflected the natural variation in temperature, potentially one of the most important proximate sources of life‐history variation.

3. Females with longer access to basking gave birth significantly earlier than those with reduced basking opportunities. Maternal access to basking significantly affected the phenotype and growth rate of her offspring.

4. Offspring born after relatively rapid development were longer, heavier and in better condition than offspring born after slower development.

5. In standard laboratory conditions, offspring born after rapid development grew more rapidly than those born after slower development, thus amplifying the difference in body size between these two groups postpartum.

6. These results suggest the existence of a strong selective pressure on female basking behaviour through the effect of the maternal environment on embryo development and offspring phenotype and highlight the role of temperature as a proximate source of variation in both the timing of reproductive events and in key life‐history traits of neonates.
The use of anhydrobiosis by soil nematodes in the Antarctic Dry Valleys
Authors: Treonis A. M. , Wall D. H. , Virginia R. A.
Published: March 2003

1. Anhydrobiosis is a survival strategy used by soil nematodes that confers protection from environmental stress and is induced by desiccation.

2. To study the use of anhydrobiosis by soil nematodes from the Antarctic Dry Valleys, soil was collected from field sites, and nematodes were extracted using an anhydrobiotic extraction technique. Nematodes were found in a coiled form that characterizes the anhydrobiotic state.

3. The proportion of nematodes coiled ranged from 30 to 80% and appeared to reach a maximum in soils drier than 2% gravimetric soil moisture content.

4. Wetting of dry soils to 12% gravimetric soil moisture content resulted in rapid uncoiling of nearly 100% of nematodes within 6 h.

5. In this cold desert ecosystem, long periods of inactivity appear to be an important aspect of soil nematode life history as their activity may be restricted to the period following infrequent snowfall and melt.
Effects of growing conditions and source habitat on plant traits and functional group definition
Authors: A. R. Dyer , D. E. Goldberg , R. Turkington , C. Sayre
Published: March 2003

Plant functional groups are used to describe patterns of community organization. However, they are defined either by suites of correlated traits or by species groupings, and the responses of these two definitions to changing environmental conditions are unknown.

 We assessed 14 growth and morphological traits under low‐ and high‐resource conditions of 42 annual plant species from two source communities in Israel that differed in resource availability. As current theory predicts, plants growing in the high‐resource treatment were larger, had twofold greater relative growth rate (RGR) and thinner leaves, and allocated less biomass to roots than plants grown in the low‐resource treatment. Differences in these traits were less consistent between the two source communities. Instead, taxonomic groups (grasses, legumes and a group of other forbs), regardless of source, differed in most characteristics.

 Three general groups of species (functional groups) were identified in both resource treatments using cluster analysis on all 14 traits. In both resource treatments monocots were almost completely separated into one distinct cluster, regardless of source habitat, while the two other, mainly dicot, clusters were partially separated by habitat. However, the species composition and trait characterization of the dicot clusters differed strongly between treatments. Under low‐resource conditions the two dicot clusters were separated by size traits and seed mass, but under high‐resource conditions, they were separated by above‐ground size, morphology and RGR.

Principal components analysis demonstrated inconsistency in relationships among traits and species groupings between treatments. The first two principal components emphasized different aspects of growth depending on the treatment; the third axis was defined by growth rates. As with the cluster analysis, plots of species scores revealed relatively little separation of species by habitat.

 The response of each species varies for different traits and with growing conditions. Variation may differ among species within a functional group, producing different definitions of functional groups under different experimental conditions. Because most functional group analyses are performed on data collected without manipulation of growing conditions, conclusions concerning the response of species or communities to changes in environmental conditions may be problematic.
Plasticity in reproductive effort of male dung flies (Scatophaga stercoraria) as a response to larval density
Authors: Stockley P. , Seal N. J.
Published: March 2003

Explaining variation in reproductive effort is fundamental to understanding diversity in male mating and life‐history strategies, although relatively little is known about environmental influences on such variation and associated trade‐offs.

 Plasticity in reproductive effort was examined in male Yellow Dung Flies (Scatophaga stercoraria) reared under two larval density treatments. Relative testis size, thorax size and mate‐searching effort were compared, and relationships between these traits examined to look for correlational evidence of predicted trade‐offs in gonadal and mate‐searching expenditure.

 Males reared under high larval density conditions developed relatively larger testes than those reared at low density but no evidence was found for a corresponding reduction in mean mate‐searching effort at the population level.

 A negative relationship was found between testis size and mate‐searching activity among males within the high larval rearing density treatment but not among those reared at low density.

Willingness to engage in struggles for possession of females increased in relation to body size among males reared at high larval density, and the opposite relationship was found among those reared at low density.

Plasticity in male reproductive effort in relation to environmental conditions may be more widespread among insects than has previously been appreciated.
Light‐dependent changes in biomass allocation and their importance for growth of rain forest tree species
Authors: L. Poorter
Published: March 2003

Sapling growth of six rain forest tree species was compared to evaluate whether species respond in a similar way to a natural light gradient. Saplings were measured non‐destructively; production and loss of leaves, stem and branches were analysed in detail.

 Sapling height growth was positively related to light environment and leaf area. No single descriptor of light environment explained sapling growth best. Direct or diffuse light could explain plant growth, depending on species.

 Seventeen percent of the saplings had negative relative biomass growth rates, although they occurred in fairly bright conditions. Negative growth rates were caused by leaf shedding and stem breakage. Sapling relative growth rate increased with irradiance, mainly because of an increase in net assimilation rate.

 On a shoot basis, shaded plants had a smaller leaf mass fraction (LMF) and a larger specific leaf area, resulting in similar leaf area ratios (LAR) to those of sun plants. This contrasts with the results of seedling studies under controlled conditions, where LMF and LAR increased with shade.

 Biomass partitioning to leaf growth decreased with irradiance and relative growth rate of the sapling. This leaf partitioning ratio was better correlated with RGR than with irradiance.

 Species differed in the effect of light‐dependent changes in specific leaf area (SLA) on growth. This underscores the importance of SLA in explaining differences in species performance in a forest environment. Nevertheless, the effect of SLA was not related to the shade tolerance of the species.
Origins of interspecific variation in lizard sprint capacity
Authors: Van Damme R. , Vanhooydonck B.
Published: March 2003

1. Data were compiled on maximal sprint speed, body mass and temperature in squamate lizards from the literature and from our own data on lacertid lizards.

2. Both traditional (i.e. non‐phylogenetic) and phylogenetic statistical analyses showed that sprint speed is positively correlated with body mass (‘bigger is better’) and temperature (‘hotter is better’).

3. Additionally, we tested whether sprint speed correlates with behavioural and ecological characteristics, i.e. foraging mode (sit‐and‐wait or active), activity (diurnal or nocturnal), microhabitat use (saxicolous, arboreal or terrestrial) and climate (Mediterranean, xeric, cool or temperate). Lizards from Mediterranean and xeric climates, diurnal lizards, sit‐ and wait predators and terrestrial species are expected to run the fastest. Traditional tests suggest that lizards from Mediterranean and desert areas are faster than lizards from cool and tropical regions; that diurnal species are faster than nocturnal species; and that saxicolous animals have higher sprint capacities than do arboreal and terrestrial species. No difference was found between sit‐and‐wait predators and actively foraging animals.

4. However, the effects of climate, activity period and microhabitat use were no longer significant when the data were analysed in a proper phylogenetic context. This seems to suggest that differences in sprint speed reflect phylogeny, rather than ecology. The discrepancy between the results of phylogenetic and traditional analyses forms a strong case for the use of phylogenetic information in comparative studies.
Foraging effort, food intake and lactation performance depend on maternal mass in a small phocid seal
Authors: Bowen W. D. , Iverson S. J. , Boness D. J. , Oftedal O. T.
Published: March 2003

Female mammals increase energy expenditure during lactation to support the high cost of milk production. The extent to which lactation in a small phocid species, the Harbour Seal Phoca vitulina L., was fuelled by food vs body stores, how this allocation varied with maternal body mass and the consequences of maternal expenditure on offspring growth were studied.

 The proportional body composition of 30 females was independent of initial postpartum body mass, but larger females had absolutely more stored energy than smaller ones.

 Females lost 32% of postpartum body mass and 62% of body energy by late lactation; 97% of energy loss was derived from body fat. Percentage loss of body energy was independent of initial body mass, indicating that females limit their allocation of body stores to offspring by expending a constant proportion of stores rather than a constant amount.

 Females spent more time diving and individual dives were deeper and longer as lactation progressed. By late lactation, these characteristics of diving were inversely proportional with initial postpartum mass.

 During early lactation, female expenditures were covered mainly by a reduction in body energy stores. By late lactation, food intake increased six‐fold but the extent of this increase varied inversely with postpartum mass.

 Pup growth rate and weaning mass were positively related to postpartum mass and total daily energy expenditure of females, but were independent of the source of energy used by females during lactation. Pups of heavy females had higher survival than pups of light females.

 Our results support the hypothesis that maternal body mass is an important determinant of lactation strategies in pinnipeds.
Adaptive self superparasitism in a solitary parasitoid wasp: the influence of clutch size on offspring size
Authors: Mackauer M. , Chau A.
Published: March 2003

In solitary parasitoid Hymenoptera, normally only one offspring per host survives. Parasitism with more than one egg by the same female results in siblicide and hence is generally maladaptive.

The braconid wasp Monoctonus paulensis Ashmead is a solitary parasitoid of aphids, including the Pea Aphid. Although all but one offspring are eliminated by competition between first‐instar larvae, females often produce a multiple‐egg clutch, even when searching alone. The hypothesis that the size and, presumably, the fitness of the surviving offspring in a clutch are greater than that of singly developing counterparts was tested in the laboratory. Adult size was measured as dry mass in parasitoids developing in Pea Aphids that differed in size (instar) and growth potential.

Parasitoid size increased with host size, and females were larger than males. Parasitoids developing in aphids reared under crowded conditions (which had low growth potential) were smaller relative to initial host size. As predicted, the male offspring of virgin mothers developing in a clutch were 4–5% larger than counterparts developing alone. Clutch size had no consistent effect on the size of male or female offspring of mated mothers, however.

A female of M. paulensis laying a multiple‐egg clutch can gain in fitness in terms of increased offspring size. The surviving offspring has access to greater nutritional resources because superparasitized aphids feed more than single‐parasitized aphids; the former also contain proportionately more teratocytes, which are egg‐derived cells aiding in parasitoid nutrition.

Evidence that some species of solitary parasitoids do better when developing in a clutch suggests that the solitary lifestyle may not be an evolutionary absorbing state.
Hormonal modification of resource sharing in the clonal plant Fragaria chiloensis
Authors: Alpert P. , Holzapfel C. , Benson J. M.
Published: March 2003

Clonal plants can share resources such as carbon and nitrogen among connected, separately rooted plant units or ramets. In many cases, resource sharing tends to equalize the performance of ramets, suggesting that differences in resource supply drive the sharing process, with resources moving from ramets with high access to resources to those with low access to resources. However, some patterns of apparent C and N sharing in the stoloniferous wild strawberry Fragaria chiloensis make the growth of ramets less equal, which is inconsistent with this model of resource sharing. As hormones are a mechanism by which non‐clonal plants can make the growth of the branches of a shoot less equal, we hypothesized that clonal plants might use hormones to modify patterns of resource sharing between ramets.

 Auxin (IAA) or cytokinin (BA) was applied to the shoot tip of ramets using a non‐invasive protocol previously shown to increase internal hormone concentrations. 14C or 15N was then fed to connected ramets, and the amounts of 14C or 15N imported by the hormone‐treated ramets and by suitable controls were measured.

 Ramets treated with IAA showed greater C import from connected ramets than did control ramets when the IAA‐treated and control ramets were shaded and the connected ramets were not. Ramets treated with IAA showed increased N import from connected ramets compared with the controls when the IAA‐treated and control ramets were given less N than the connected ramets, and were also younger than the connected ramets. IAA had no consistent effect on C or N sharing between ramets given the same resource treatments as one another and did not affect the direction of N sharing, which is strongly acropetal in F. chiloensis. BA showed little effect on resource sharing.

 The results supported the hypothesis that hormones can modify patterns of resource sharing between ramets in clonal plants. In F. chiloensis, auxin can enhance resource import by ramets in relatively resource‐poor microsites. Clonal plants may use hormones as a mechanism for physiological integration of connected ramets.
Nutrient allocation of Macaranga triloba ant plants to growth, photosynthesis and indirect defence
Authors: Heil M. , Hilpert A. , Fiala B. , Bin Hashim R. , Strohm E. , Zotz G. , Linsenmair K. E.
Published: March 2003

1. Allocation patterns are an important aspect of plant life strategies. In particular, many hypotheses on plant antiherbivore defence – such as the growth differentiation balance hypothesis and the resource availability hypothesis – concern constraints on resource allocation to defence, and assume defence to be limited by nutrient supply under most, yet not all, conditions.

2. Field‐grown Macaranga triloba saplings were fertilized, and temporal and spatial patterns in the response of growth, photosynthesis and investment in biotic defence against herbivores and pathogens were measured simultaneously. Macaranga triloba produces food bodies to nourish mutualistic ants which protect their hosts against herbivores and pathogens. Food body production rate is quantitatively related to ant colony structure, and the latter is correlated with defensive efficacy. Food body production can therefore serve as a measure of the plant's investment in defence.

3. Food body production responded quickly, and on all food body‐producing stipules, to increased nutrient supply. In contrast, photosynthetic capacity responded much more slowly, to a smaller degree, and only in leaves that emerged after the onset of fertilization. No significant effects on plant growth were seen.

4. Our results show that food body production by M. triloba is regulated directly by nutrient availability. There was no evidence that increased nutrient supply was preferably allocated to growth and/or photosynthesis, which forms a central assumption of most hypotheses on plant antiherbivore defence.

5. Phenotypic plasticity and the ability to make use of short pulses in nutrient supply are of particular importance in pioneer plants inhabiting rapidly changing habitats. New theoretical frameworks are required for the inclusion of phenotypically plastic defence traits in the theory of plant antiherbivore defence.
Linkages between plant litter decomposition, litter quality, and vegetation responses to herbivores
Authors: Wardle D. A. , Bonner K. I. , Barker G. M.
Published: March 2003

There is increasing awareness that similar suites of plant traits may govern foliage palatability and litter decomposability, but whether there is an association between the response of vegetation to herbivory and litter decomposition rates across plant species remains unexplored.

We collected 141 samples of litter from 59 understorey and 18 canopy tree species from a total of 28 sites under natural forest throughout New Zealand. We assessed whether variables related to decomposition and quality of litter of the understorey species showed a statistical relationship with the response of vegetation density (assessed using a pole‐intercept method) of the same species at the same locations to browsing by deer and goats. Decomposition and nutrient‐loss data from litter were obtained using standardized laboratory bioassays.

There was a significant positive correlation between litter decomposition rate and the extent to which vegetation density was reduced by browsing mammals (r = 0·488, P < 0·001). Further, decomposition rate and vegetation response to herbivory were both correlated with several of the same litter quality variables.

The proportion of total initial phosphorus and nitrogen released from litter during decomposition was correlated with litter decomposition rate, but not with vegetation density response to browsing. This suggests that effects of browsers on vegetation composition are more likely to influence ecosystem carbon flow than nitrogen or phosphorus flow.

Litter‐mixing experiments showed that good quality litters produced by plant species reduced by browsers tended to promote the decomposition of other litters. Meanwhile, poor quality litters from species promoted by browsers tended to decompose more rapidly when mixed with other litter types than when by themselves. However, these effects were weak and likely to be less important than the more direct effects of browsing mammals on vegetation composition.

The relationships between litter decomposition and effect of herbivory on vegetation density were driven primarily by differences among the main plant functional groups, which showed the same decreasing rank order for both variables: large‐leaved dicots, small‐leaved dicots, Nothofagus, ferns, and monocots.

The implications of these results for understanding how herbivores affect the decomposer subsystem are considered. Because the results of this work are only partially consistent with those of an earlier study on how browsers affect decomposer organisms and processes, conducted at the same 28 field sites, other mechanisms through which browser effects are manifested below‐ground must often override that investigated in this study.
Temporospatial constraints in resources available to and used by hermit crabs: tests of models
Authors: Barnes D. K. A. , De Grave S.
Published: March 2003

Resources vary critically in space and time so the ability of animals to utilize them necessarily does so in sympathy. For hermit crabs in coastal SW Madagascar, a critical resource is a suitable shell to habit, as is typical of the group. Quantification of resource status should therefore be as straightforward as counting shells on a beach. Only certain shells are exploitable, however, based on their condition, occupier status and attributes (such as size).

The total, total exploitable and empty shell densities (size classed) per unit area were measured from the shallow subtidal to landward range (100 m inland) of hermit crabs. The population density of resource exploiters (hermit crabs) was also measured (grouped by size classes) over a similar area, enabling calculation of the total number of exploitable shells per individual (based on appropriate match of resource and resource user) and the nested subset of empty exploitable shells per individual.

Resource bottlenecks and surpluses occurred at different (resource exploiter) life stages and at different positions on the shore. The proportion of available shell types used by hermit crabs was found to increase down shore despite the number of shell types availability showing the converse pattern.

4.  Multiple regression models of shell use by hermit crabs were constructed that showed species and genus level trends. Five or more variables were almost equally significant in each of the models. Overall hermit crab size, site, habitat and local shell diversity were most important in determining the number of shell types used.

The proportion of interspecific vs intraspecific competition at each shore level was estimated using observed species‐specific shell use patterns and population size class sizes. Observed competition followed the predicted sigmoidal pattern across the littoral zone but that of intensity of competition was different and bimodal.

Ordination (detrended correspondence analysis) showed that resource exploiter (species) specific shell suites heavily overlap in multidimensional niche space as is near universally described in the literature. When shell suites are ordinated by size class, however, species niches separate, even across sites, except at sizes where resources are not restricted. Niches are distinct but cryptic.
Relationships between head size, bite force, prey handling efficiency and diet in two sympatric lacertid lizards
Authors: Verwaijen D. , Van Damme R. , Herrel A.
Published: March 2003

Relationships between morphology, bite force capacity, prey handling efficiency and trophic niche were explored in two sympatric species of lacertid lizards, Podarcis melisellensis (Braun 1877) and Lacerta oxycephala Duméril & Bibron 1839.

Head shape showed little variation, but head size (absolute and relative to snout–vent length, SVL) differed between species and sexes. Males have larger heads than females, both absolute and relative to their SVL. In absolute terms, male P. melisellensis have larger heads than male L. oxycephala, but the reverse case was true for the females. Relative to SVL, L. oxycephala have larger heads than P. melisellensis.

Bite force capacity was estimated by having the lizards bite on two metal plates, connected to a piezoelectric force transducer. Differences in maximal bite force between species and sexes paralleled differences in absolute head size. Differences in body size and head size explain the higher bite force of males (compared with females), but not the higher bite force of P. melisellensis (compared with L. oxycephala). Among individual lizards, bite force correlated with body size and head size.

Prey handling efficiency, estimated by the time and number of bites needed to subdue a cricket in experimental conditions, also showed intersexual and interspecific variation. This variation corresponded to the differences in maximal bite capacity, suggesting that bite force is a determining factor in prey handling. Among individual lizards, both estimates of handling efficiency correlated with maximal bite force capacity.

Faecal pellet analyses suggested that in field conditions, males of both sexes select larger and harder prey than females. There was no difference between the species. The proportion of hard‐bodied and large‐sized prey items found in a lizard's faeces correlated positively with its bite force capacity.

It is concluded that differences in head and body size, through their effect on bite force capacity, may affect prey selection, either directly, or via handling efficiency.
Energy balance in the Whitebellied Sunbird Nectarinia talatala: constraints on compensatory feeding, and consumption of supplementary water
Authors: Nicolson S. W. , Fleming P. A.
Published: March 2003

Avian nectarivores consume a simple food which is generally dilute, but may vary widely in concentration and thus in water content.

Energy intake over 24 h was investigated in the Whitebellied Sunbird Nectarinia talatala (A. Smith) (mean mass 9·3 ± 1·0 SD g, n = 7) fed a wide range of sucrose concentrations (0·07–2·5 m), with and without access to supplementary water.

On diet concentrations between 0·25 and 2·5 m sucrose, birds showed perfect compensatory feeding by adjusting volumetric intake to maintain constant energy intake.

However, reduced intake on the two lowest concentrations of 0·07 and 0·1 m meant that the birds could not meet their energetic requirements and lost mass. We propose that physiological constraints associated with ingestion of large volumes of preformed water restrict intake at these very low concentrations.

Drinking of supplementary water varied greatly among individuals, but increased as diet concentration increased. This free water consumption effectively diluted the most concentrated diets of 1·5–2·5 m sucrose to an average value of 1·05 m, thus providing an indirect assessment of the birds’ concentration preferences.
Drosophila dSmad2 and Atr‐I transmit activin/TGFβ signals
Authors: Das Pradeep , Inoue Hirofumi , Baker Julie C. , Beppu Hideyuki , Kawabata Masahiro , Harland Richard M. , Miyazono Kohei , Padgett Richard W.
Published: March 2003

Background

Much is known about the three subfamilies of the TGFβ superfamily in vertebrates—the TGFβs, dpp/BMPs, and activins. Signalling in each subfamily is dependent on both shared and unique cell surface receptors and Smads. In invertebrates, mutants for BMP pathway components have been extensively characterized, but thus far, evidence for an activin‐ or TGFβ‐like pathway has been lacking, preventing the use of the extensive genetic tools available for studying several key issues of TGFβ signalling.

Results

Here we report the identification of dSmad2, a new Drosophila Smad which is most related to the activin/TGFβ‐pathway Smads, Smad2 and Smad3. We show that dSmad2 induces activin responsive genes in Xenopus animal cap assays. dSMAD2 is phosphorylated by ATR‐I and PUNT, but not by activated THICK VEINS, and translocates to the nucleus upon activation. Furthermore, we show that dSMAD2 complexes with MEDEA only in the presence of ATR‐I and PUNT. dSmad2 is expressed in the imaginal disks and in the outer proliferation centre of the larval brain, suggesting that it may have important proliferative and patterning roles during Drosophila development.

Conclusion

Our data provide evidence for the existence of an activin/TGFβ pathway in Drosophila. We show that dSmad2 participates in this pathway, and that it functions with Atr‐I and punt. We show that Medea also participates in this pathway, indicating the conservation of roles for Co‐Smads in diverse phyla. Expression patterns of dSmad2 suggest that it functions in imaginal disks and in the brain, in tissues that undergo extensive patterning and proliferation.
kel‐1, a novel Kelch‐related gene in Caenorhabditis elegans, is expressed in pharyngeal gland cells and is required for the feeding process
Authors: Ohmachi Mitsue , Sugimoto Asako , Iino Yuichi , Yamamoto Masayuki
Published: March 2003

Background

Kelch‐related proteins constitute an expanding family, members of which carry two conserved motifs named the BTB/POZ and the kelch repeat domains. The best‐characterized member, Drosophila Kelch, constitutes the ring canals in the egg chamber in association with actin. However, physiological and biochemical functions of the members of this family remain largely uncharacterized.

Results

We identified the kel‐1 gene encoding a Kelch‐related protein in the nematode Caenorhabditis elegans. The deduced KEL‐1 protein had 618 amino acid residues and was most similar to Drosophila Kelch. Loss of kel‐1 function caused growth arrest at an early larval stage, most likely at the beginning of L2. The kel‐1 deletion mutant appeared normal in morphology, movement and pumping action for the initial two to three days after hatching, but it failed to convey foods effectively to intestine and could hardly increase in body size. Analyses using immunostaining and reporter gene expression indicated that kel‐1 was expressed almost exclusively in the g1 pharyngeal gland cells during late embryogenesis and at all developmental stages thereafter.

Conclusions

C. elegans KEL‐1 protein is essential for the larval development, probably performing a function required for feeding in the pharyngeal g1 gland cells, which are supposed to secrete materials aiding digestion.
Overproduction of elongation factor 1α, an essential translational component, causes aberrant cell morphology by affecting the control of growth polarity in fission yeast
Authors: Suda Masako , Fukui Mikiko , Sogabe Yuki , Sato Kazuhito , Morimatsu Akeshi , Arai Ritsuko , Motegi Fumio , Miyakawa Tokichi , Mabuchi Issei , Hirata Dai
Published: March 2003

Background

Elongation factor 1α (EF1α), an essential component of the eukaryotic translational machinery, has been shown to possess various biochemical and biological activities, including F‐actin‐binding and ‐bundling, microtubule‐ severing, and the activity of making fibroblasts highly susceptible to transformation. However, our understanding of the biological significance of EF1α with respect to these various biochemical or biological activities remains limited. Here we report the identification of EF1α‐encoding genes as genes whose over‐expression causes aberrant cell morphology in fission yeast.

Results

Overproduction of EF1α caused aberrant cell morphology—elliptic, curved or branched—and growth defects in yeast cells at high temperatures. EF1α‐overproducing cells showed a supersensitivity to the actin inhibitor cytochalasin D and to the tubulin inhibitor thiabendazole. Genetic analyses using cdc mutants suggested that excess EF1α disturbed the establishment and the maintenance of growth polarity in the G1 phase by pre‐ venting the localization of F‐actin to the polarized growing site and the organization of microtubules. Results from DNase I column chromatography indicated that EF1α was bound to G‐actin. Indeed, the fission yeast actin was immunoprecipitated along with EF1α. Moreover, the temperature sensitivity caused by the overproduction of EF1α was restored by co‐overproduction of actin.

Conclusions

Fission yeast EF1α has the ability to alter the cell morphology of yeast by affecting the control of actin and microtubule cytoskeletons.
Bloom's syndrome gene suppresses premature ageing caused by Sgs1 deficiency in yeast
Authors: Heo Seok‐Jin , Tatebayashi Kazuo , Ohsugi Itaru , Shimamoto Akira , Furuichi Yasuhiro , Ikeda Hideo
Published: March 2003

Background

Bloom's syndrome (BS) is an autosomal recessive disorder causing short stature, immunodeficiency, and an increased risk of cancer. Increased rates of sister chromatid exchange and chromosomal aberration have been observed in cells having defects in the BLM gene. Among five kinds of human RecQ helicases cloned, the mutations in WRN and RecQL4 have been known as the causes of premature ageing. Little is, however, known about the function of BLM helicase in ageing.

Results

We show that human BLM, but not WRN can prevent the premature ageing and the increased homologous recombination at the rDNA loci caused by sgs1 mutation. Unexpectedly, the levels of ERCs (extrachromosomal rDNA circles), the products of homologous recombination, formed in 7‐generation cells of the wild‐type or the sgs1::BLM strain were comparable with those of the sgs1 or the sgs1::WRN age‐matched‐old cells.

Conclusion

These results imply that BLM helicase may have an important role in human ageing. In addition, these data suggest that the accumulated ERCs per se may be not the cause of premature ageing in yeast, inconsistent with the model proposed by Sinclair & Guarente. We discuss a new model, which explains how Sgs1 or BLM helicase suppresses premature ageing in yeast.
Mutation enhancement by DINB1, a mammalian homologue of the Escherichia coli mutagenesis protein DinB
Authors: Ogi Tomoo , Kato Tomohisa , Kato Takesi , Ohmori Haruo
Published: March 2003

Background

The Escherichia coli dinB gene is an SOS gene known to be required for λ phage untargeted mutagenesis. When over‐expressed, it exhibits a potent mutagenic activity without any exogenous treatment to damage DNA. Frameshift mutations at a run of identical bases are most enhanced. The product DinB is structurally related to the E. coli UmuC protein and the Saccharomyces cerevisiae Rev1 and Rad30 proteins, all of which are shown to be involved in bypass synthesis at a DNA lesion.

Results

We have cloned and sequenced human and mouse cDNAs encoding a DinB homologue. Their products are highly similar to DinB and less similar to UmuC, Rev1 or Rad30, and hence the genes were named DINB1 for human and Dinb1 for mouse. Both genes were expressed most abundantly in testis. Transient expression of the mouse cDNA in cultured mouse cells resulted in a nearly 10‐fold increase in the incidence of point mutations, among which about 30% were frameshift mutations.

Conclusions

The above results suggest that a mutagenic mechanism, a so‐called untargeted type, also operates in mammalian cells. Taken together with recent findings that human cells have multiple DNA polymerases for translesion synthesis which are homologous to the S. cerevisiae Rev3 and Rad30 proteins, our results imply that multiple mutagenic pathways are conserved from bacteria to higher eukaryotes.
The whorl‐specific action of a petunia class B floral homeotic gene
Authors: Tsuchimoto Suguru , Mayama Tomoko , Van Der Krol Alexander , Ohtsubo Eiichi
Published: March 2003

Background

GREEN PETAL (GP) is thought to be a petunia class B floral homeotic gene, because the gp mutant flower displays a severe homeotic conversion of petals into sepals in the second whorl. However, since the third whorl stamens remain unaffected in the gp null mutant, gp is different from class B mutants in Arabidopsis and Antirrhinum, which also show a conversion of the third whorl stamens into the carpelloid tissue. BLIND (BL) is thought to be a petunia class A floral homeotic gene, because the bl mutant flower displays homeotic conversions of sepals into the stigmatoid tissue in the first whorl and of the corolla limb into antheroid structures in the second whorl.

Results

A double mutant line homozygous for both bl and gp mutations was constructed. The bl gp double mutant flower displays homeotic conversions of sepals into the stigmatoid tissue in the first whorl and of the corolla limb into antheroid structures with stigmatoid tips in the second whorl. In the third and fourth whorls of the mutant flower, organs remained unchanged. In the gp flower, a petunia B‐type gene FBP1 is expressed strongly in the third whorl organs, but much more weakly in the second whorl organs. In the bl gp flower, FBP1 was found to be expressed strongly in the second whorl organs as well as in the third whorl organs.

Conclusions

Petunia has a class B gene other than GP that determines organ identities, both in the second and third whorls of the double mutant flower, and the action of the postulated class B gene (here called PhBX) is prevented by the BL gene in the second whorl of the gp flower. PhBX appears to be a gene that specifically interacts with the FBP1 gene, and is involved in the up‐regulation of FBP1.
Large‐scale screening of intracellular protein localization in living fission yeast cells by the use of a GFP‐fusion genomic DNA library
Authors: Ding Da‐Qiao , Tomita Yuki , Yamamoto Ayumu , Chikashige Yuji , Haraguchi Tokuko , Hiraoka Yasushi
Published: March 2003

Background

Intracellular localization is an important part of the characterization of a gene product. In an attempt to search for genes based on the intracellular localization of their products, we constructed a green fluorescent protein (GFP)‐fusion genomic DNA library of S. pombe.

Results

We constructed the S. pombe GFP‐fusion genomic DNA library by fusing, in all three reading frames, random fragments of genomic DNA to the 5′ end of the GFP gene in such a way that expression of potential GFP‐fusion proteins would be under the control of the own promoters contained in the genomic DNA fragments. Fission yeast cells were transformed with this plasmid library, and microscopic screening of 49 845 transformants yielded 6954 transformants which exhibited GFP fluorescence, of which 728 transformants showed fluorescence localized to distinct intracellular structures such as the nucleus, the nuclear membrane, and cytoskeletal structures. Plasmids were isolated from 516 of these transformants, and a determination of their DNA sequences identified 250 independent genes. The intracellular localizations of the 250 GFP‐fusion constructs was categorized as an image database; using this database, DNA sequences can be searched for based on the localizations of their products.

Conclusions

A number of new intracellular structural components were found in this library. The library of GFP‐fusion constructs also provides useful fluorescent markers for various intracellular structures and cellular activities, which can be readily used for microscopic observation in living cells.
Blockade of cadherin‐6B activity perturbs the distribution of PSD‐95 family proteins in retinal neurones
Authors: Honjo Yasuko , Nakagawa Shinichi , Takeichi Masatoshi
Published: March 2003

Background

Synaptic junctions have cadherin–catenin complexes, but their functions are poorly understood. Using retinal neurones, we investigated the role of this adhesion machinery in synaptic organization.

Results

In cultures of chicken retinal cells, cadherin‐6B (cad6B) and cadherin‐7 (cad7) are expressed by distinct neurones, each being distributed in a punctate pattern along their neurites as well as in the soma. Double‐immunostaining for cad6B and PSD‐95/SAP90 or other PSD‐95 family members, known to localize in the postsynaptic density, showed that their distributions overlapped each other. To assess the role for cad6B, we incubated retinal cells with antibodies that could specifically block cad6B‐mediated adhesion. In the antibody‐treated neurones, the localization pattern of PSD‐95 family proteins was altered, that is, their staining signals tended to be reduced or disarranged. We then examined whether cadherins interacted molecularly with PSD‐95: Cadherin immunoprecipitates from brain lysates did not contain PSD‐95; nevertheless, this protein was co‐precipitated with αN‐ and β‐catenins. When PSD‐95 proteins were ectopically expressed in epithelial cells, some of these molecules were concentrated in cell–cell junctions, co‐localizing with E‐cadherin, and this junctional localization of PSD‐95 was abolished by blocking of E‐cadherin activity.

Conclusion

These results suggest that cadherins play a role in the subcellular organization of postsynaptic density components through some, perhaps indirect, molecular interactions.
Modulation of TFIIH‐associated kinase activity by complex formation and its relationship with CTD phosphorylation of RNA polymerase II
Authors: Watanabe Yoshinori , Fujimoto Hiroyuki , Watanabe Tomomichi , Maekawa Takafumi , Masutani Chikahide , Hanaoka Fumio , Ohkuma Yoshiaki
Published: March 2003

Background

The general transcription factor TFIIH plays important roles in initiation and the transition to elongation steps of transcription by RNA polymerase II (PolII). Both roles are dependent on the protein kinase, DNA‐dependent ATPase and DNA helicase activities of TFIIH. However, how these enzyme activities of TFIIH contribute to transcription has remained elusive. TFIIH consists of nine subunits, and one of them, Cdk7, possesses kinase activity. Here the substrate specificities of TFIIH and two forms of the Cdk7‐containing kinase complex are compared, and the relationship between transcription activity and the TFIIH‐dependent phosphorylation of the carboxy terminal domain of the largest subunit of PolII (CTD) is studied.

Results

We prepared TFIIH and two Cdk7‐containing kinase complexes, Cdk7/Cyclin H and CAK (Cdk7/Cyclin H/MAT1). Consistent with previous reports, CAK strongly phosphorylated Cdk2, Cdk4, CTD and intact PolII. In contrast, Cdk7/Cyclin H, which lacks MAT1, did not phosphorylate these substrates, except for weak phosphorylation of Cdk2. The kinase activity of TFIIH displayed stronger substrate preference for Cdk4 than did CAK. In addition, TFIIH phosphorylation of PolII was stimulated by TFIIE both in solution and during preinitiation complex formation, whereas Cdk7/Cyclin H and CAK phosphorylation of PolII was not. In combination with other general transcription factors, TFIIH, but not Cdk7/CycH or CAK, promoted transcription on a linear DNA template. This transcription was well correlated with TFIIE stimulated TFIIH phosphorylation of serine at position 5 (Ser‐5) within the heptapeptide repeat of the PolII CTD.

Conclusion

These results provide clues about the roles of CTD phosphorylation at Ser‐5 in transcription.