Does cyclicity of growth rate in rainbow trout exist?

Ninety rainbow trout Oncorhynchus mykiss were reared in three tanks ( n= 30), and their growth rate was monitored for 25 weeks. During the experiment, fish were fed ad libitum , and kept under simulated natural photoperiod and constant temperature (14 ± 1°C). Throughout the experiment, water quality (pH, O₂, N-NH₃, N-NH₄, NO₂) was considered optimum. Two growth rate periods were observed on the population: first an acclimation period (weeks 1–5), followed by a period of general decrease in growth rate (weeks 5–25). This trend was modelled with a third-order polynomial function. The autocorrelation analysis of the fluctuations revealed a cyclicity of the growth rate with a 4–5-week period. This cyclicity was independent of the tanks and of the growth rate trend type (long- v . short-term acclimation period). However, at the individual level, trends as well as short-term fluctuations were heterogeneous and no clear cyclicity could be detected. The biological relevance of the population growth rate cyclicity and the apparent absence of similar individual fluctuations are discussed.     

Does larder-hoarding affect the condition of chicks in urban kestrels?

Hoarding by urban kestrels and its subsequent exploitation significantly increases the frequency and regularity of feeding during the early stage of the nestling period. Twelve kestrels’ nests situated in various part of the city were chosen to test whether hoarding could affect the chicks’ condition. Four nests (with 22 nestlings) were provided with food — one dead mouse per chick per day (F group) and 8 (43 nestlings) were used as a control group (NF). Nestlings were weighed daily, and the length of their tarsus was also measured when the oldest chick in the nest was 11 days old. 50% of the NF nests experienced a decrease in the number of nestlings but no nestlings were lost in any of the F nests. However, no significant differences were found between the groups either in body mass or tarsus length. A possible reason was the behaviour of the adults which could be interpreted as the regulation of the frequency of prey delivery depending on its presence or absence in the nest.     

Does seed mass drive the differences in relative growth rate between growth forms?

The idea that herbaceous plants have higher relative growth rates (RGRs) compared with woody plants is fundamental to many of the most influential theories in plant ecology. This difference in growth rate is thought to reflect systematic variation in physiology, allocation and leaf construction. Previous studies documenting this effect have, however, ignored differences in seed mass. As woody species often have larger seeds and RGR is negatively correlated with seed mass, it is entirely possible the lower RGRs observed in woody species is a consequence of having larger seeds rather than different growth strategies. Using a synthesis of the published literature, we explored the relationship between RGR and growth form, accounting for the effects of seed mass and study-specific effects (e.g. duration of study and pot volume), using a mixed-effects model. The model showed that herbaceous species do indeed have higher RGRs than woody species, and that the difference was independent of seed mass, thus at all seed masses, herbaceous species on average grow faster than woody ones.     

Does Rubisco control the rate of photosynthesis and plant growth? An exercise in molecular ecophysiology

Experiments are described in which tobacco (Nicotiana tabacum L.) transformed with antisense rbcS to decrease expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) was used to evaluate the contribution of Rubisco to the control of photosynthetic rate, and the impact of a changed rate of photosynthesis on whole plant composition, allocation and growth. (1) The concept of flux control coefficients is introduced. It is discussed how, with adequate precautions, a set of wild-type and transgenic plants with varying expression of an enzyme can be used to obtain experimental values for its flux control coefficient. (2) The flux control coefficient of Rubisco for photosynthesis depends on the short-term conditions. It increases in high light, or low CO₂. (3) When plants are grown under constant irradiance, the flux control coefficient in the growth conditions is low (<0.2) at irradiances of up to 1000μmol quanta m⁻² s⁻¹. In a natural irradiance regime exceeding 1500μmol quanta m⁻² s⁻² over several hours the flux coefficient rose to 0.8–0.9. It is concluded that plants are able to adjust the balance between Rubisco and the remainder of the photosynthetic machinery, and thereby avoid a one-sided limitation of photosynthesis by Rubisco over a wide range of ambient growth irradiance regimes. (4) When the plants were grown on limiting inorganic nitrogen, Rubisco had a higher flux control coefficient (0.5). It is proposed that, in many growth conditions, part of the investment in Rubisco may be viewed as a nitrogen store, albeit bringing additional marginal advantages with respect to photosynthetic rate and water use efficiency. (5) A change in the rate of photosynthesis did not automatically translate into a change in growth rate. Several factors are identified which contribute to this buffering of growth against a changed photosynthetic rate. (6) There is an alteration in whole plant allocation, resulting in an increase in the leaf area ratio. The increase is mainly due to a higher leaf water content, and not to changes in shoot/root allocation. This increased investment in whole plant leaf area partly counteracts the decreased efficiency of photosynthesis at the biochemical level. (7) Plants with decreased Rubisco have a lower intrinsic water use efficiency and contain high levels of inorganic cations and anions. It is proposed that these are a consequence of the increased rate of transpiration, and that the resulting osmotic potential might be a contributory factor to the increased water content and expansion of the leaves. (8) Starch accumulation in source leaves is decreased when unit leaf photosynthesis is reduced, allowing a more efficient use of the fixed carbon. (9) Decreased availability of carbohydrates leads to a down-regulation of nitrate assimilation, acting via a decrease in nitrate reductase activity.     

Does the growth rate hypothesis apply to aquatic hyphomycetes?

The growth rate hypothesis states that in many organisms or tissues, the specific growth rate μ correlates with RNA concentrations. Since RNA often accounts for much of the phosphorus content of cells, μ may also correlate positively with P concentrations and negatively with C:P and N:P ratios. We tested this hypothesis with broth cultures of five aquatic hyphomycete species. Samples were harvested on eight occasions after 3–56 d of incubation. Accumulation of biomass was fitted to a rectangular hyperbola, whose parameters were used to estimate μ. There were no consistent trends related to culture age or μ for C, N, P or ergosterol concentrations. RNA and DNA concentrations and RNA:DNA ratios were significantly and negatively correlated with culture age. Only RNA concentrations were positively and linearly correlated with μ. While RNA or DNA concentrations are unsuitable as indicators for total biomass, levels of fungal RNA combined with markers for fungal biomass may allow estimates of the extent to which the mycelia are metabolically active.     

Does global warming threaten the dynamics of Arctic charr in Lake Geneva?

In France, the Arctic charr (Salvelinus alpinus) is native in only two lakes (Lakes Bourget and Geneva), in the most southerly part of its distribution area. It is a profundal morph living at depths of between 30 and 100 m in Lake Geneva. Following considerable stocking of Lake Geneva with juvenile Arctic charr and some good results during the 1980s, catches are currently declining. Several hypotheses have been proposed to explain this decrease, but the potential influence of warming of the lake in the 1990s has not been considered. This article studies the relationship between the strength of the cohorts and the temperature in Lake Geneva from 1992 to 2002, and discusses the various potential causes of the population collapse observed. The findings reveal close correlation between water temperature and the strength of the cohorts. It is concluded that the recent warming of Lake Geneva may have a significant direct or indirect impact on the Arctic charr population.     

Does the rate of German chamomile growth and development influence the response of plants to soil drought?

The response of the wild type (WT) and a strain C6/2 of German chamomile to 7-d soil drought and subsequent 7-day rehydration was studied. Shoot and leaf growth, vegetative development, water and protein contents, ascorbate peroxidase activity and gas exchange were compared. At the stress stage, water content of WT plants was slightly influenced and the effect was ceased after rehydration. Also the decrease in gas exchange was temporary. New leaves were formed, although their area was diminished. On the contrary, leaves of C6/2 plants were more desiccated and the durable decrease in water content was accompanied by the impairment in gas exchange also at the recovery stage (20–40% loss when compared to the control). At both stages of the experiment the growth of the long shoots of this genotype was drastically decreased, as well as leaf formation. Ascorbate peroxidase activity was increased by drought in leaves of both genotypes, but the pattern of changes in WT plants reflected the enhancement of metabolism resulting from proper water content and gas exchange at the recovery stage. Different pattern of changes in the protein content during drought was also noticed: a slight increase in WT, while the decrease by ¼ in C6/2 leaves. The response of WT plants to desiccation and rewatering was found to be more elastic than that of C6/2.     

Validation of the doubly labeled water method in Japanese Quail Coturnix c. japonica chicks: is there an effect of growth rate?

The Doubly Labeled Water (DLW) method was validated against respiration gas analysis in growing Japanese Quail chicks (between 1 week and 3 weeks of age) as well as in birds after having achieved sexual maturity (7 weeks of age). A comparison was made between a strain selected for high growth rates (P-strain, n=18), and a non-selected strain (C-strain, n=18). Relative growth rates of individual chicks during the measurement ranged from −13.8% day⁻¹ to 23.1% day⁻¹. When employing a single-pool model (eq. 34, Lifson and McClintock 1966), it was found that the relative error of the DLW method was sensitive to assumptions concerning fractional evaporative water loss. The best fit was obtained after taking a fractional evaporative water loss value of 0.33. When applying this value for all chicks, it was found that neither strain, relative growth rate of the chick during measurement, nor age significantly contributed to the explained variance. When employing two-pool models, it was found that the DLW method significantly underestimated the true rates of CO₂ production at all assumed levels of fractional evaporative water loss. Based on an evaluation of DLW validation studies in growing shorebirds, terns, and quail we recommend Speakman's Eq. 7.17 (Speakman 1997) for general use in young birds. Accepted: 14 April 2000     

Does the size of small objects influence chemical reactivity in living systems?

Previous theoretical works showed that chemical reactions in micro- and nano-droplets, bubbles and solid particles were strongly affected by their confinement. In particular, the smallness of the systems leads to high internal pressure compared to the external pressure, which then significantly modifies the values of chemical equilibrium and kinetic constants. In addition, surface tension or surface stress, reactional dilatation and surface charge play also a major role on the chemical reactivity. As living systems are also made of very complex dispersed subsystems, i.e. organelles, it seemed obvious to illustrate our theory by some biological actual examples encountered in pulmonary alveolae, in vacuolae and in medical applications, such as dissolution of gallstones.     

Does the availability of arboreal honeydew determine the prevalence of ecologically dominant ants in restored habitats?

Ants are extensive users of arboreal sugars, but little is known about how ecological dominance or habitat succession influences this interaction. We investigated how the availability and use of arboreal sugar resources by ants changes across a restoration chronosequence. We surveyed the use and availability of hemipteran honeydew and floral nectar on the two dominant plant genera, Eucalyptus and Acacia, in study sites in south eastern Australia. Sugars used by ants are likely to drive their role as ecosystem engineers, while sugars not used by ants remain available to other organisms. We also tested whether the use of sugars differed between ecologically dominant and non-dominant ants; taxa likely to perform different functions in ecosystems. No floral nectar was available on Acacia, but later successional eucalypts supported more floral resources and fewer mutualist hemiptera. Successional stage significantly affected how much sugar remained unexploited by ants, with similar trends for ant use of sugars. Non-dominant ants used mainly floral nectar, while hemipteran honeydew resources were used disproportionately by dominant ants, consistent with the prediction that this group monopolises persistent carbohydrate resources. This pattern was similar across successional stages, but the difference was least in habitats with the greatest availability of floral nectar, suggesting that high sugar availability may reduce the incentive to defend honeydew. Across habitat types, the proportion of dominant ants increased with the availability of hemipteran honeydew. This suggests that honeydew availability may regulate ecological dominance, thus affecting ant-driven ecosystem processes.     

Does lowering glutamine synthetase activity in nodules modify nitrogen metabolism and growth of Lotus japonicus?

A cDNA encoding cytosolic glutamine synthetase (GS) from Lotus japonicus was fused in the antisense orientation relative to the nodule-specific LBC3 promoter of soybean (Glycine max) and introduced into L. japonicus via transformation with Agrobacterium tumefaciens. Among the 12 independent transformed lines into which the construct was introduced, some of them showed diminished levels of GS1 mRNA and lower levels of GS activity. Three of these lines were selected and their T(1) progeny was further analyzed both for plant biomass production and carbon and nitrogen (N) metabolites content under symbiotic N-fixing conditions. Analysis of these plants revealed an increase in fresh weight in nodules, roots and shoots. The reduction in GS activity was found to correlate with an increase in amino acid content of the nodules, which was primarily due to an increase in asparagine content. Thus, this study supports the hypothesis that when GS becomes limiting, other enzymes (e.g. asparagine synthetase) that have the capacity to assimilate ammonium may be important in controlling the flux of reduced N in temperate legumes such as L. japonicus. Whether these alternative metabolic pathways are important in the control of plant biomass production still remains to be fully elucidated.     

Does lemming winter grazing impact vegetation in the Canadian Arctic?

In low-productivity environments such as the tundra, it has been proposed that regular, multi-annual population cycles of lemmings could be driven by winter food depletion in years of peak abundance. If lemming population dynamics is controlled by food resources, we predict that (1) winter grazing should negatively impact the abundance of food plants, (2) this impact should be proportional to lemming density and (3) high lemming winter grazing pressure should result in reduced plant growth during the following summer. We tested these predictions on Bylot Island, Nunavut, Canada, where two species of lemmings are present: the brown (Lemmus trimucronatus) and collared lemming (Dicrostonyx groenlandicus). We installed 16 exclosures in their preferred wintering habitat (snowbeds) and annually sampled plant biomass inside and outside exclosures at snow melt and at peak growth during the summers of 2009–2012, covering a full population cycle. Winter grazing had no impact on total vascular plant or moss biomass at snow melt in all years. Among plant families, only Caryophyllaceae, which was uncommon, showed a decline. In moss taxa, a negative effect was found on Polytrichum in only 1 year out of three. Overall, plant regrowth during the subsequent summer showed annual variation and tended to be reduced in the 2 years of high lemming abundance. However, this could be a consequence of summer grazing. Overall, the impact of lemming winter grazing on plants was weak and short-lived, even in years of high lemming abundance. Therefore, our results are not consistent with the hypothesis that food depletion during winter was the cause of the lemming decline following peak abundance at our study site. Other factors may limit lemming populations and prevent them from reaching densities high enough to exhaust their food resources.     

Localization of pectins in the pollen tube wall of Ornithogalum virens L. Does the pattern of pectin distribution depend on the growth rate of the pollen tube?

Monoclonal antibodies that recognize pectins were used for the localization of esterified (JIM7) and acidic, unesterified (JIM5) forms of pectin in pollen tube walls of Ornithogalum virens L. (x = n = 3). The results indicated that the distribution of the two forms of pectin in the pollen tube wall depended on the medium (liquid or solid) used for pollen germination. In pollen tubes grown in the liquid medium, the localization of JIM7 was limited to the very tip of the pollen tube, whereas the localization of JIM5 indicated a uniform distribution of unesterified pectins in the very tip of the tube and along the subapical parts of the tube wall. In tubes germinated on the medium stabilized with agar (1–2%) the localization of JIM7 and JIM5 indicated the presence of both forms of pectin in the tube tip and along the whole length of the pollen tube wall in a ring-like pattern. Thus, the localization of esterified pectins in the sub-apical part of the pollen tube wall, below the apex of the tube, is described for the first time. Measurements of the growth rates of pollen tubes growing on the two types of medium indicated that oscillations in tube growth rate occur but these do not coincide with the pattern of pectin distribution in the tube wall. Our results complement the previous data obtained for the localization of JIM5 and JIM7 in pollen tube walls of other plant species. (Y.-Q. Li et al. 1994, Sex Plant Reprod 7: 145–150) and provide new insight into an understanding of the construction of the pollen tube wall and the physiology of pollen grain germination. Received: 25 January 1999 / Accepted: 23 June 1999     

Does the T gene determine the anteroposterior axis of a mouse embryo?

The t complex in the mouse is essential to embryonic development. The semidominant mutation, T, is embryonic lethal in homozygotes. In T/T embryos, proper morphogenetic movement is hindered, causing the number of mesodermal cells to be reduced. The other effect of T mutation is shortening of the tail in heterozygotes, T/+ and T/t. t is a series of recessive mutations in the t complex. A detailed examination of tail shortening indicated the T and t mutations to exert various effects, such as the derangement of the pattern of necrosis, fusion or duplication of the neural tube and gut. The most severely affected structure is the notochord. The t mutation augments the effect of T mutation in the formation of normal notochord. A gradient of phenotypic severity along anteroposterior axis of an embryo appeared to exist correlative to the dosage of the T gene. Should the products of the T gene be responsible for inducing mesoderm and the establishment of the anteroposterior axis of an embryo, diverse effects of the T mutation on embryogenesis can be explained collectively.     

Does a fibroblast membrane proteinase affect the binding, uptake and metabolism of epidermal growth factor?

Pre-treatment of human fibroblasts to inhibit a cell-surface growth-related proteinase inhibits the mitogenic action of epidermal growth factor. It also reduces the binding of epidermal growth factor to these cells, and lowers the rate of internalisation and degradation of the growth factor, but quantitative considerations render it unlikely that these parameters contribute directly to the inhibition of mitogenesis.     

Do random fluctuations in daily ration affect the growth rate of juvenile three-spined sticklebacks?

The effect of random fluctuations in daily ration on the growth performance of individual juvenile three-spined sticklebacks Gasterosteus aculeatus was studied in experiments lasting 21 days at 14°C and a photoperiod of 10L:14D. Two mean ration levels were used: a maintenance ration of 2%, and a high ration of 6% of initial body weight per day. For experimental fish, the daily ration varied randomly about the required mean value with a coefficient of variation of 33%. The controls received a constant daily ration. The experiment was replicated in winter (Dec.-Jan.) and spring (Mar.-Apr.). At a given ration, there was no significant difference between the specific growth rates of fish receiving constant or varying ration. Neither the final dry weight, final body water content nor final lipid content (% dry weight) differed significantly. As expected, ration had a significant effect on growth rate, final dry weight and body lipid and water content. There was a significant difference in mean growth rate between the winter and spring replicates. The growth rates observed in these experiments were compared with those predicted from a previously described empirical growth model developed for sticklebacks fed constant rations. The model underestimated mean growth rates.     

Hypoxia and temperature: Does hypoxia affect caiman embryo differentiation rate or rate of growth only?

In crocodilians, the rate of embryonic development and consequently many posthatch attributes are affected by temperature. Since temperature exhibits strong influences on fitness (embryo survivorship and phenotype) by shaping development, we manipulated oxygen concentration in order to uncouple the effects of developmental rate from the direct effects of temperature. Here we consider whether oxygen constrains either differentiation rate (progression from one stage to the next) or embryonic growth (size). Thus, we incubated Caiman latirostris eggs at various oxygen concentrations, and at two temperatures (31 °C, 100% female-producing temperature, and 33 °C, 100% male-producing temperature). We monitored the developmental stages of these embryos within the thermosensitive period (stages 20–24), and assessed several physiological and morphological hatchling traits. While embryonic size was strongly influenced by oxygen, differentiation rate did not seem to be affected. Very low oxygen concentrations and high temperatures inhibited embryo survival. In addition, oxygen availability affected incubation period and hatchling size, whereas temperature did not cause a significant variation in hatchling size. By investing energy in differentiation hypoxic embryos decreased their size.