bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sexual dimorphism of head size in Gallotia galloti: testing the niche divergence hypothesis by functional analyses
Authors: Herrel A. , Spithoven L. , Van Damme R. , DE Vree F. 
Published: March 2003

1. Two often cited hypotheses explaining sexual head size dimorphism in lizards are: sexual selection acting on structures important in intrasexual competition, and reduction of intersexual competition through food niche separation. 2. In this study some implicit assumptions of the latter hypothesis were tested, namely that an increase in gape distance and bite force should accompany the observed increase in head size. These assumptions are tested by recording bite forces, in vivo, for lizards of the species Gallotia galloti. In this species, male lizards have significantly larger heads than female conspecifics of similar snout–vent length. 3. Additionally, the average force needed to crush several potential prey species was determined experimentally and compared with the bite force data. This comparison clearly illustrates that animals of both sexes can bite much harder than required for most insect food items, which does not support the niche divergence hypothesis. The apparent ‘excess’ bite force in both sexes might be related to the partially herbivorous diet of the animals. 4. To unravel the origin of differences between sexes in bite capacity, the crushing phase of biting was modelled. The results of this model show different strategies in allocation of muscle tissue between both sexes. The origin of this difference is discussed and a possible evolutionary pathway of the development of the sexual dimorphism in the species is provided.
Towards a predictive description of forest canopies from litter properties
Authors: ROBERTS J. , HOPKINS R. , MORECROFT M. 
Published: March 2003

1.Specific leaf area (SLA), carbon isotope ratio (δ13C) and leaf nitrogen content (N) were measured in litter in 1993 and in the litter layer and canopy in 1996 in a pedunculate Oak (Quercus robur) wood at Wytham, Oxford.2.The frequency distribution of SLA of leaves falling through the late summer and autumn of 1993 changed with a greater contribution of leaves of high SLA earlier in the period. For the same SLA leaves falling earlier in the season had less negative δ13C and higher N content than leaves falling later.3.The frequency distribution of SLA of litter leaves was similar in both years but litter leaves had lower N and less negative δ13C in 1996.4.In the canopy, there was a highly significant negative relationship between height in the canopy and SLA in green and senescent leaves. The relationship between SLA and both δ13C ratio and leaf N was different between green, senescent and litter leaves.5.The frequency distribution of foliage in the canopy estimated from the frequency of SLA in the litter and the vertical pattern of SLA in the canopy was similar to the distribution measured by the ‘drop‐line’ method.
Simplifying the phytohaemagglutinin skin‐testing technique in studies of avian immunocompetence
Authors: Smits J. E. , Bortolotti G. R. , Tella J. L. 
Published: March 2003

1. Researchers involved in ecology and toxicology, as well as many other aspects of avian biology, use phytohaemagglutinin (PHA) skin testing as a means of evaluating the immune status of individuals. 2. Immune function, one measure of individual quality, can be used as a sensitive, non‐lethal variable that may be negatively affected in animals exposed to degraded, contaminated or otherwise disturbed ecological zones. 3. Typically this test has been applied by challenging one wing web with the immunostimulant PHA, while the other ‘control’ wing is injected with phosphate buffered saline (PBS). Injection sites on the wing web are measured before and 24 h after injection with PHA or PBS. The immune response is considered to be the difference between the two wings. 4. Results from PHA skin tests conducted on 608 birds in seven studies representing passerines, waterfowl, upland game birds and raptors are examined. 5. Numerous advantages to eliminating the PBS injection as the experimental control are: (i) decrease by half, the time required for testing; (ii) decrease handling‐related stress on the birds (proportional to handling time); (iii) reduce the probability of errors at injection time; (iv) spare the other wing for different tests or uses (e.g. tuberculin DTH testing); and (v) decrease the coefficient of variation that is due to measurement inaccuracies. 6. The only disadvantage identified is that hypersensitive individuals (outliers) could be missed, which in this case represents 2 of 608 individuals.
Interacting components of interspecific relative growth rate: constancy and change under differing conditions of light and nutrient supply
Authors: Meziane D. , Shipley B. 
Published: March 2003

1. One thousand three hundred and twenty plants from 22 species of herbaceous angiosperms, typical of open sunny habitats, were grown from seed for 35 days under controlled conditions in four experimental environments: high (1100 μmol m–2 s–1 PAR) and low (200 μmol m–2 s–1 PAR) light, combined with high (full‐strength) and low (1/6 dilution) levels of hydroponic nutrient solution. Plants of each species were harvested at 15, 20, 25, 30 and 35 days post‐germination. 2. Relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA) and leaf mass ratio (LWR) were estimated for each species in each treatment combination. 3. Both light and nutrient levels affected RGR and each of the growth components. Average NAR increased, while SLA and LWR decreased, with increasing light. Increasing nutrient levels increased all three growth components. Light and nutrient levels interacted in their effects on NAR and SLA, but not in their effects on LWR. 4. Those species having the highest RGR in the most productive environment were most severely depressed in the less productive environments. This same pattern also occurred with NAR and SLA, but not with LWR. 5. The rank order of species with respect to SLA and LWR remained similar across the treatment environments; with respect to NAR the rank order remained similar in only four of the six treatment contrasts; with respect to RGR the rank order remained similar in only two of the six treatment contrasts and the rank order actually reversed in one treatment contrast. 6. RGR did not display strong bivariate correlations with any of the growth components in any of the treatment groups. It had positive, moderately strong correlations with NAR but only in the low‐nutrient treatments. It had positive, moderately strong correlations with LWR only in the high‐nutrient treatments. After controlling for the other growth components, each showed strong positive relationships with RGR. Furthermore, the effects of the treatments disappeared after controlling for the components, showing that the treatment effects were completely mediated through their effects on these underlying components. 7. There were also strong negative partial correlations between each of the growth components. These compensatory relationships buffered RGR from large changes in response to changing environments.
Diurnal and seasonal changes in cladode photosynthetic rate in relation to canopy age structure in the leguminous shrub Retama sphaerocarpa
Authors: Haase P. , Pugnaire F. I. , Clark S. C. , Incoll L. D. 
Published: March 2003

1. Changes in canopy area and canopy age structure of the leguminous shrub Retama sphaerocarpa were estimated non‐destructively by monitoring growth and survivorship of cladodes on marked shoots. 2. Gas exchange of cladodes of different age classes was measured by infra‐red gas analysis during a period of 18 months. The effects of seasonal and year‐to‐year variation in the area and age structure of the canopy on daily carbon assimilation were assessed. 3. New canopy area produced by spring growth was highly variable between years and also affected the age structure of canopies because of differential survivorship of older cohorts of cladodes. 4. During the first year (1993), predawn water potential of cladodes and, therefore, their maximum diffusive conductance (0·35–0·45 mol m–2 s–1) and photosynthetic rate (20–26 μmol CO2 m–2 s–1), changed little with the season because the deep‐rooted shrubs had access to permanent water sources. Lack of rainfall in the winter of 1993/1994 constrained predawn water potential and rates of gas exchange in the following growing season when daily maxima of A declined continuously and fell to a minimum of 10 μmol CO2 m–2 s–1 in July 1994. 5. Nitrogen concentration and specific cladode area, but not nitrogen content, were significantly different between annual cohorts. Mainly as a result of secondary diameter increment of cladodes, specific cladode area and nitrogen concentration and therefore photosynthetic rate generally declined with increasing age of cladodes, but the differences in the photosynthetic rate between cohorts were insignificant during the cool season. 6. Variation in canopy area caused variation in daily carbon assimilation by 30–36% within years and by 37–52% between years. Seasonal and between‐year variation in the age structure of canopies, however, only accounted for changes in daily carbon assimilation of ± 2%. Canopy age structure thus appears to be an insignificant variable affecting carbon gain in R. sphaerocarpa.
Influence of tree growth rate, shoot size and foliar chemistry on the abundance and performance of a galling adelgid
Authors: Mckinnon M. L. , Quiring D. T. , Bauce E. 
Published: March 2003

1. The abundance and performance of the Eastern Spruce Gall Adelgid, Adelges abietis, was evaluated on young, open‐grown trees of White Spruce, Picea glauca, whose growth rates had been increased through fertilization or decreased through root‐pruning. 2. In general, gall densities were highest on control trees and on mid‐crown branches. Reduced galling success on fertilized trees was largely due to higher overwintering mortality of first‐generation nymphs. Foliar magnesium, total tannin and total phenol contents were positively, and nitrogen and total monoterpene contents negatively, related to gall density and/or galling success. 3. Although short shoots were more abundant, shoot length was parabolically related to gall density. There was a non‐significant parabolic trend between shoot size and galling success and volume. The number and average size of A. abietis females emerging from galls were positively related to gall volume, and realized fecundity was positively correlated to female size. Consequently, fitness was approximately twice as high for nymphs colonizing intermediate‐sized than small or large shoots. 4. These results do not support the plant vigour or plant stress hypotheses. The results do, however, agree with predictions of the modified plant stress hypothesis for sucking insects. It is speculated that Adelges abietis lacks the necessary resources for successful gall formation on small shoots and is unable to produce a stimulus large enough to induce gall formation on large shoots.
Maintenance of the alcohol dehydrogenase polymorphism in Tiger Salamanders, II. Differences in biochemical function among allozymes
Authors: Carter P. A. , Mitton J. B. , Kocher T. D. , Coelho J. R. 
Published: March 2003

Abstract1. Previous studies of Tiger Salamanders demonstrated that variation in alcohol dehydrogenase (Adh) contributed significantly to associations between multilocus heterozygosity and oxygen consumption traits, and that Adh variation was associated with levels of pond‐oxygen and metamorphic ability in extreme oxygen environments. Here Adh allozymes are characterized kinetically, and relationships between Adh and oxygen‐related physiological traits (ATP/Hb, 2,3‐DPG/Hb) are measured.2. Kinetic differences were measured among Adh allozymes in the acetaldehyde‐to‐ethanol direction:kcat/Kmratios (the catalytic constant divided by the Michaelis–Menton constant) were significantly higher in Adh‐SF than the other two genotypes, and in Adh‐SS compared with Adh‐FF. No significant differences were measured in the ethanol to acetaldehyde direction.3. Adh‐SS had a significantly higher ATP/Hb than Adh‐FF, with the Adh‐SF intermediate. In addition, a significant interaction between Hb and body mass was measured, such that Adh‐FF showed a negative relationship between Hb concentration and body mass while the other two genotypes showed a positive relationship.4. These results are consistent with the hypothesis that variation at the Adh locus has adaptive and physiological significance, and that functional differences among Adh allozymes partly explain significant associations between multilocus genotype and organismal traits.
Optimal timing of corolla abscission: experimental study on Erythronium japonicum (Liliaceae)
Authors: Ishii H. S. , Sakai S. 
Published: March 2003

Abstract1. We analysed how male and female success affects the floral longevity in Erythronium japonicum. We found that flower senescence is advanced by deposition of pollen grains on the stigma but that there exists a minimum longevity (13·64 days in 1996 and 12·20 days in 1997) during which the flower never abscises, even if it is pollinated with a sufficient number of pollen grains.2. We suggest that this floral longevity does not exist to benefit the female function, because the time needed for corolla abscission reacting to ovule fertilization was not so long and the female function was completed within about 3 days.3. Flowers of E. japonicum do not react to pollen removal, as shown by the fact that anther removal experiments did not affect floral longevity. However, it would be advantageous to have some duration of longevity which benefits male success such that most of pollen grains can be expected to be exported. The duration needed to disperse most pollen grains of a flower was about 12 days, very close to the minimum floral longevity.4. We conclude that a minimum longevity may exist for male functions and that floral longevity may be influenced differently by the male and the female functions of flowers.
Escape flight in moulting Tree Sparrows (Passer montanus)
Authors: J. Lind 
Published: March 2003

Summary

Impaired predator evasion in birds as a cost in different life‐history periods has received increasing attention in the last decade. Evasive abilities in birds have been found to be detrimentally affected by migratory fuel load, reproduction and moult. These results suggest that during these periods of their lives birds suffer from increased predation risk due to impaired evasive abilities.
Theoretically, moult should have a detrimental effect on flight, and empirical work on starlings has shown impaired escape ability due to moult. However, a recent theoretical investigation found a surprisingly small effect of moult on flight in birds.
In this study, 31 Tree Sparrows, a sedentary species with a slow moult, were used to investigate the effect of natural and manipulated moult on escape ability. No effect was found due to natural moult, however, when experimentally increasing moult gap size a strong negative effect was found.
With support from empirical and theoretical work, this is the first study to suggest that slow moult may not increase predation risk due to impaired evasive abilities. Compensatory physiological adaptations probably cause this result and may be very important during moult.
Predation risk is probably an important factor in the evolution of moult patterns and moult strategies.
Canopy‐level photosynthetic compensation after defoliation in a tropical understorey palm
Authors: N. P. R. Anten , D. D. Ackerly 
Published: March 2003

Abstract1. Increases in photosynthesis of leaves remaining after defoliation may result from shifts in leaf photosynthetic characteristics or from an improved light penetration in the canopy. However, few studies have tried to estimate the relative contribution of these factors to mitigating the negative effects of defoliation. We present a quantitative framework for such an analysis.2. In a field and greenhouse experiment, plants of the rain forest understorey palm Chamaedorea elegans were subjected to three levels of defoliation (0, 50 or 66% of leaves removed) and, in the greenhouse, grown at two irradiances (5 or 16% of daylight, ‘low light’ and ‘high light’ hereafter). For each plant, leaf photosynthesis and light penetration in the canopy were measured and these data were used to calculate whole‐canopy carbon gain.3. Defoliation significantly increased the light available to the remaining leaves. In the field and in the ‘high‐light’ greenhouse plants, defoliation also resulted in an increase in the light‐saturated photosynthesis per unit leaf area (Pmax), although in the ‘low‐light’ plants this was not the case.4. A sensitivity analysis revealed that in the ‘low‐light’ plants, a proportional increase in leaf Pmax did not result in increased canopy‐level carbon gain, while in the ‘high‐light’ and field plants, it did. This suggests that the lack of plasticity in Pmax in response to defoliation, at low light, may be the appropriate pattern to maximize carbon gain.5. Defoliated plants had 10–18% more average photosynthesis per unit leaf area (Parea) than the control plants, and this increase was mostly the result of an improved light penetration in the canopy.6. A relatively small fraction (5–30%) of the total estimated loss in canopy carbon gain caused by the removal of leaves was compensated for by an increase in Parea. This suggests that in rain forest understorey plants, an increase in diurnal photosynthesis of remaining leaves has limited potential for mitigating the negative effects of defoliation.
Fat stores in birds: an overlooked sink for carotenoid pigments?
Authors: Negro J. J. , Figuerola J. , Garrido J. , Green A. J. 
Published: March 2003

Summary

Carotenoids are responsible for the most striking colours in birds, but also play an important role as enhancers of the immune system. Consequently, a trade‐off between the ornamental and health functions of carotenoids in birds has been proposed.
Although it is well known that birds can store carotenoids in different organs and tissues, including the fat stores, until now all field studies of the regulation of carotenoid stores have focused on plasma carotenoids.
Carotenoids in the fat of 44 wild Greylag Geese (Anser anser L.) wintering in south‐western Spain were identified and quantified. In addition, the relationships between carotenoids and the size of the fat stores, as well as the sex and age of the geese, were analysed.
The major carotenoid in goose fat was lutein. This and related carotenoids are also the most prevalent pigments in bird plasma and secondary sexual characters. We also detected β‐cryptoxanthin, β‐carotene, neochrome and neoxanthin. Total carotenoid concentration was negatively correlated with the size of the fat stores. Males had higher concentrations of carotenoids than females.
A possible explanation for these patterns is that male birds tend to have higher plasma carotenoids than females, a difference that could be transposed to fat if carotenoids diffused passively from the blood into adipose tissues. Carotenoids, however, may tend to remain in the fat stores. If this were true, fat would not be a reservoir of carotenoids, but a sink where a significant amount of these pigments would be sequestered, being no longer available for other functions.
Competition mediates costs of jasmonate‐induced defences, nitrogen acquisition and transgenerational plasticity inNicotiana attenuata
Authors: Van Dam N. M. , Baldwin I. T. 
Published: March 2003

Summary Plants adjust their phenotype in response to environmental signals, but little is known about the interaction of plastic responses to simultaneously occurring environmental stresses. To examine the costs of induced resistance on reproductive performance in plants subjected to other important environmental variables, resistance was elicited with a jasmonate treatment (MeJA) to one, both or neither of twoNicotiana attenuataplants growing competitively in either high‐ or low‐N soils. Half the plants were subjected to leaf removal (LR). K15NO3was used to quantify differences in N acquisition and allocation. Transgenerational effects were measured with seed germination and seedling performance tests. An induced plant competing with an uninduced plant produced significantly fewer seeds, acquired less15N and allocated less15N to seed production. Uninduced plants competing with induced plants realized a comparable fitness benefit. The costs of induction were greater under high N. Plants grown under low N minimized costs by allocating significantly more N to seeds. LR decreased seed production independently of any other effect. Low N and LR both reduced germination rates. The effects of MeJA on seed germination depended on competition and N supply. The differences in germination rates resulted in dramatic fitness differences among offspring. N. attenuataplants appear to use N availability and their induced status to alter their current phenotype and their offspring’s phenotype to adjust to environmental changes that occur predictably over time in their natural environment.
Metabolic rate and aggressiveness between Brown Trout populations
Authors: Lahti K. , Huuskonen H. , Laurila A. , Piironen J. 
Published: March 2003

Summary Studies focusing on the physiological variation between populations and its connection to fitness‐related traits are rare, even though integrating these fields would increase knowledge on the evolution of traits. Standard metabolic rate (SMR) has been suggested to influence an individual’s social status and the level of aggressiveness, as dominant individuals tend to have higher SMR than subordinate individuals. The SMR of juvenile Brown Trout (Salmo trutta) from four populations was measured, and the population‐level relationship between SMR and aggressiveness, which is a fitness‐related behavioural trait, was investigated. SMR differed between the populations, but no differences were found in the amount of aggression. Nevertheless, a significant positive correlation between aggressiveness and SMR between the populations was found. Unlike many previous studies on geographical variation of metabolic rate, SMR correlated negatively with the latitude of origin of the populations. The results suggest that SMR and aggressiveness are correlated not only at the individual level as shown by previous studies, but also at the population level. The costs and benefits of high metabolic rate depend largely on the environment, and local differences in environmental conditions, as for example in food availability, may select for local differences in SMR.