Does growth rate determine the rate of metabolism in shorebird chicks living in the Arctic?

We measured resting and peak metabolic rates (RMR and PMR, respectively) during development of chicks of seven species of shorebirds: least sandpiper (Calidris minutilla; adult mass 20-22 g), dunlin (Calidris alpina; 56-62 g), lesser yellowlegs (Tringa flavipes; 88-92 g), short-billed dowitcher (Limnodromus griseus; 85-112 g), lesser golden plover (Pluvialis dominicana; 150-156 g), Hudsonian godwit (Limosa haemastica; 205-274 g), and whimbrel (Numenius phaeopus; 380 g). We tested two opposing hypotheses: the growth rate-maturity hypothesis, which posits that growth rate in chicks is inversely related to functional maturity of tissues, and the fast growth rate-high metabolism hypothesis, which suggests that rapid growth is possible only with a concomitant increase in either RMR or PMR. We have found no evidence that chicks of shorebirds with fast growth rates have lower RMRs or lower PMRs, as would be predicted by the growth rate-maturity hypothesis, but our data suggested that faster-growing chest muscles resulted in increased thermogenic capacity, consistent with the fast growth-high metabolism hypothesis. The development of homeothermy in smaller species is a consequence primarily of greater metabolic intensities of heat-generating tissues. The maximum temperature gradient between a chick's body and environment that can be maintained in the absence of a net radiative load increased rapidly with body mass during development and was highest in least sandpipers and lowest among godwits. Chicks of smaller species could maintain a greater temperature gradient at a particular body mass because of their higher mass-specific maximum metabolic rates.     

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.     

Cell cycle: the key to plant growth control?

Experimental evidence on the role of the cell cycle in plant growth regulation does not exclusively fit the cellular (division drives growth) or the organismal perspective (division merely accompanies growth). Here we present a broader, integrated concept of plant growth regulatory interactions, which accommodates experimental results gathered to date. This model can serve as a basis for future research, and prompts experimental approaches to encompass both measurements of cell growth and division parameters.     

Are there associations between grain-filling rate and photosynthesis in the flag leaves of field-grown rice?

Rate of grain filling in terms of dry mass accumulated per panicle per day was measured in field-grown rice in the dry season in the Philippines and compared to rates of light-saturated photosynthesis per unit leaf area (P(max)) measured at 350 micro l l(-1) CO(2) for 21 d after flowering. Five new plant type (tropical japonica) varieties (NPT) and one indica variety (IR72) were used and these gave some variation in rates and patterns of grain filling. A rapid grain-filling phase (RGFP) occurred approximately 10 d after flowering in most varieties. There was no consistent relationship in any variety between the rate of grain-filling and P(max) and chlorophyll content, both of which remained mostly unchanged throughout grain filling. Significant declines in the amount of total leaf protein and ribulose bisphosphate carboxylase-oxygenase (Rubisco) occurred, but these did not occur at the same time as the RGFP in all varieties. A decrease in the ratio of chlorophyll a/b preceded these changes and a transient rise in chlorophyll content was also observed in four varieties at this time. There was no significant change in leaf non-structural carbohydrate content during or following the RGFP. It is concluded that the decline in Rubisco and protein content in NPT was not reflected in photosynthetic activity. Hence in these field experiments Rubisco accumulated to a level in excess of photosynthetic requirements, serving as a store of nitrogen for grain filling.     

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 the type of exercise affect tryptophan catabolism in horses?

Tryptophan (Trp) is an essential amino acid which metabolises via the kynurenine pathway to generate a number of bioactive substances referred to as kynurenines. Among those are 3-hydroxykynurenine (3-HKyn) and quinolinic acid, which are neurotoxic, as well as kynurenic acid (Kyna) and xanthurenic acid (XA), which, similarly to nicotinamide (NAm), show neuroprotective and anti-depressive effects. Routine exercise is known to modulate Trp metabolism in skeletal muscle and is thus believed to reduce the risk of depressive states in humans and laboratory animals. Analogously, it was hypothesised that exercise can influence Trp metabolism in horses as well. The aim of this study was to evaluate the influence of two different types of exercise on Trp metabolism in horses of the same breed. A total of 32 purebred Arabian horses were involved in the study. The 22 three-year-old racehorses were subjected to short-time intense exercise. Ten other horses were made to perform endurance competitions at a distance of 80 km. Blood samples were collected at rest and following the end of the exercise period. Plasma concentrations of Trp, kynurenine (Kyn), Kyna, 3-HKyn, XA and NAm were determined using Ultra-High Performance Liquid Chromatography-Electrospray Ionisation-Tandem Mass Spectrometry. Short-time intense exercise led to an increase in plasma concentrations of Kyn, Kyna and XA. The endurance effort induced an increase in Kyna and a decrease in Trp and NAm levels. Both types of exercise, short-time intensive exercise and endurance exercise induced an increase in Trp metabolites, especially Kyna, and did not induce an increase in Trp level. Thus, from a pathophysiological perspective of the kynurenine pathway’s influence on mental state, both types of exercise induced beneficial effects in horses.     

Partitioning the components of relative growth rate: how important is plant size variation?

Plant growth plays a key role in the functioning of the terrestrial biosphere, and there have been substantial efforts to understand why growth varies among species. To this end, a large number of experimental analyses have been undertaken; however, the emergent patterns between growth rate and its components are often contradictory. We believe that these conflicting results are a consequence of the way growth is measured. Growth is typically characterized by relative growth rate (RGR); however, RGR often declines as organisms get larger, making it difficult to compare species of different sizes. To overcome this problem, we advocate using nonlinear mixed-effects models so that RGR can be calculated at a standard size, and we present easily implemented methods for doing this. We then present new methods for analyzing the traditional components of RGR that explicitly allow for the fact that (log)(RGR) is the sum of its components. These methods provide an exact decomposition of the variance in (log)(RGR). Finally, we use simple analytical and simulation approaches to explore the effect of size variation on growth and its components and show that the relative importance of the components of RGR is influenced by the extent to which analyses standardize for plant size.     

Does pre-dispersal seed predation limit reproduction and population growth in the alpine clonal plant Geum reptans?

We studied the impact of the seed damaging gall midge larva Geomyia alpina on its perennial alpine host plant Geum reptans. We analysed the effect of seed predation on reproduction by seeds, i.e. seed number, seed mass, and seed viability and on growth and clonal propagation of non-protected plants in comparison to plants protected from predation by an insecticide. Additionally, we assessed the consequences of seed predation for population growth using matrix projection modelling. Seed predation resulted in a decrease in total seed mass per flower head by 23.8% in non-protected plants (P < 0.05). Individual seed mass decreased with increasing infestation intensity (P < 0.05). Seed number remained unaffected because the sucking feeding behaviour by gall midge larvae does not evoke seed abortion. Percent germination of seeds from non-protected plants was reduced by 97.9% compared to seeds from protected plants. According to reduced seed viability, modelling revealed a decrease in population growth rate from λ = 1.055 to λ = 1.041. Predation did neither influence total plant biomass nor biomass fractions. But stolon dry-weight of non-protected plants increased by 24.1% (P < 0.05), which may indicate a trade-off between sexual reproduction and clonal propagation. Our results demonstrate that despite substantial reduction of viable seeds, predation by gall midge larvae only slightly affected population growth of G. reptans suggesting that in this alpine species, persistence by longevity and clonal propagation can balance potential seed losses by predation, at least for local population growth.     

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.     

Are differences in FSH concentrations involved in the control of ovulation rate in Romanov and Ile-de-France ewes?

Despite differences in FSH concentrations ranging from 1.5 ng/ml (Romanov ewes) to 4 ng/ml (Ile-de-France ewes) between the follicular and luteal phases, follicular growth (numbers of follicles growing, growth rates, maximum size reached) was morphologically similar between the two stages of the cycle. Injection of 750 i.u. hCG at Day 6 or 16 of the cycle triggered ovulation of 4.1 +/- 0.7 and 4.0 +/- 1.3 follicles in Romanov and 2.2 +/- 0.5 and 1.7 +/- 0.5 follicles in Ile-de-France ewes, respectively, demonstrating that functional differentiation was similar between the two stages of the cycle. As gonadotrophin environment differs between these two stages of the cycle, this suggests that there is a wide flexibility in the amount of gonadotrophins required to trigger terminal follicular growth and that ovarian requirements for gonadotrophins might work through thresholds. When Romanov and Ile-de-France ewes were given similar amounts of exogenous gonadotrophins (1250 i.u. PMSG, 750 i.u. hCG) after hypophysectomy, ovulation rates were close to the usual values (Romanov, 5.5 +/- 3.9; Ile-de-France, 1.4 +/- 0.5), demonstrating that differences in gonadotrophin concentrations during the follicular phase do not play a major role in the high ovulation of the Romanov compared to the Ile-de-France ewes.     

Does Ramadan fasting affect acylated ghrelin and growth hormone concentrations during short-term maximal exercise in the afternoon?

Ghrelin is an important stomach hormone that influences several metabolic activities and influences growth hormone (GH) release in response to change in energy homeostasis. The aim of this study was to investigate the effect of Ramadan fasting on acylated ghrelin and GH concentrations during a short-term maximal exercise. Eleven male soccer players (age, 22.11 ± 1.3 years; height, 1.76 ± 0.2 m; body mass, 75.3 ± 2.2; mean ± SD) were asked to perform a 30-s Wingate test, during which we recorded the peak (PP) and mean (MP) powers and fatigue index. Measurements were performed in the afternoon at 18:00 h, after three different occasions: (i) one week before Ramadan (BR), (ii) the first week of Ramadan (FWR), and (iii) the fourth week of Ramadan (ER). Blood samples were taken before, immediately and 60 min after the exercise. Our results show that PP and MP were affected by Ramadan fasting with a significant decrease during Ramadan (i.e. FWR and ER) in comparison with ER (p < 0.05). However, no significant difference was observed between BR and FWR (p > 0.05). Also, a significant decrease in body weight and body fat percentage was observed during Ramadan in comparison with ER. From diet record analysis, protein, fat, and carbohydrate decreased significantly during FWR (p < 0.01), often with further decreases by ER. A significant increase in plasma concentrations of ghrelin was observed during the ER (p < 0.001) compared with BR and FWR, and GH levels were significantly higher during ER (p < 0.01) in comparison with BR and FWR. However, the 30-s Wingate tests had no significant effect on plasma concentrations of ghrelin before or during Ramadan. Our study shows that the concentrations of ghrelin and GH change in the last week of Ramadan fasting, though it is unclear if these changes are related to the changes in body composition during Ramadan, or if they are responsible for the change in performance at the short-duration anaerobic test.     

Does gender influence neuromotor control of the knee and hip?

Patellofemoral pain (PFP) is a common condition that occurs more frequently in females. Anatomical, hormonal and neuromuscular factors have been proposed to contribute to the increased incidence of PFP in females, with neuromuscular factors considered to be of particular importance. This cross-sectional study aimed to evaluate differences in the neuromotor control of the knee and hip muscles between genders and to investigate whether clinical measures of hip rotation range and strength were associated with EMG measures of hip and thigh motor control. Twenty-nine (16 female and 13 male) asymptomatic participants completed a visual choice reaction-time stair stepping task. EMG activity was recorded from vastus medialis oblique, vastus lateralis, anterior and posterior gluteus medius muscles. In addition hip rotation range of motion and hip external rotation, abduction and trunk strength were assessed. There were no differences in the timing or peak of EMG activation of the vasti or gluteus medius muscle between genders during the stepping task. There were however significant associations between EMG measures of motor control of the vasti and hip strength in both females and males. These findings are suggestive of a link between hip muscle control and vasti neuromotor control.     

Is auxin the repressor signal of branch growth in apical control?

"Apical control" is the repression of branch growth by a higher dominating branch or shoot. There has been some confusion in the literature concerning the meaning and causal mechanisms of this correlative phenomenon with those of "apical dominance," which term is often used in a strict sense to connote the repression of the initiation of axillary bud outgrowth by an active shoot apex. Although the term "apical control" is most commonly employed with respect to woody species, this phenomenon also widely occurs in herbaceous plants. Because of the strong evidence for a role of auxin as a repressor signal in apical dominance and partly because of this lack of distinction in terminology, a similar role for auxin in apical control is often assumed in spite of the obvious acropetal auxin transport difficulty and the lack of direct evidence for the acropetal transport of any inhibitor influence. In the present study with the herbaceous Ipomoea nil, it has been clearly demonstrated that while exogenous auxin (1% NAA) strongly restores apical dominance in the Thimann-Skoog experiment, auxin treatments to decapitated dominant shoots do not, in any observable way, restore apical control in lower dominated branches. Hence, in this fast-growing species, the hypothesis for the role of auxin as a repressor signal for apical control is not supported.     

Is the rate of photosynthesis under blue light altered in the 7B-1 tomato mutant?

Changes of photosynthesis under blue light were examined in the ABA-overproducing 7B-1 mutant in tomato. Net photosynthetic rate (P _N), stomatal conductance (g _s), intrinsic water-use efficiency (WUE_i) and chlorophyll (a+b) [Chl (a+b)] content in leaves of different insertion (1^st, 4^th and 9^th ones) were measured in 5-, 7- and 9-week-old plants. P _N, g _s, and Chl (a+b) content were mostly similar in young leaves of 7B-1 and wild type (WT) plants. With the aging of leaves, a blue-light-induced increase in P _N and g _s to steady-state was delayed and steady-state values of P _N and g _s were lower in 7B-1 plants compared with WT. Steady-state values of WUE_i were increased in 4^th and 9^th leaves of 7B-1 plants compared with WT. The results can be explained by the higher endogenous level of ABA in 7B-1 plants and their lower sensitivity to ABA in earlier growth stage.     

Is intensity of plant root mycorrhizal colonization a good proxy for plant growth rate,dominance and decomposition in nutrient poor conditions?

Questions

Mycorrhizae may be a key element of plant nutritional strategies and of carbon and nutrient cycling. Recent research suggests that in natural conditions, intensity of mycorrhizal colonization should be considered an important plant feature. How are inter‐specific variations in mycorrhizal colonization rate, plant relative growth rate (RGR ) and leaf litter decomposability related? Is (arbuscular) mycorrhizal colonization linked to the dominance of plant species in nutrient‐stressed ecosystems?

Location

Teberda State Biosphere Reserve, northwest Caucasus, Russia.

Methods

We measured plant RGR under mycorrhizal limitation and under natural nutrition conditions, together with leaf litter decomposability and field intensity of mycorrhizal colonization across a wide range of plant species, typical for alpine communities of European mountains. We applied regression analysis to test whether the intensity of mycorrhizal colonization is a good predictor of RGR and decomposition rate, and tested how these traits predict plant dominance in communities.

Results

Forb species with a high level of field mycorrhizal colonization had lower RGR under nutritional and mycorrhizal limitation, while grasses were unaffected. Litter decomposition rate was not related to the intensity of mycorrhizal colonization. Dominant species mostly had a higher level of mycorrhizal colonization and lower RGR without mycorrhizal colonization than subordinate species, implying that they were more dependent on mycorrhizal symbionts. There were no differences in litter decomposability.

Conclusions

In alpine herbaceous plant communities dominated by arbuscular mycorrhizae, nutrient dynamics are to a large extent controlled by mycorrhizal symbiosis. Intensity of mycorrhizal colonization is a negative predictor for whole plant RGR . Our study highlights the importance of mycorrhizal colonization as a key trait underpinning the role of plant species in carbon and nutrient dynamics in nutrient‐limited herbaceous plant communities.

     

Which plant traits promote growth in the low-light regimes of vegetation gaps?

Nine temperate grass species were screened for their potential to grow in the low-light conditions typical of gaps in dense vegetation. To this end, photosynthetic photon flux densities (PFD) were simulated in a growth chamber (PFD 100, 50 or 25 μmol photons m⁻² s⁻¹). Relative and absolute growth rates (RGR and AGR, respectively) of the species were regressed on ten different ecophysiological and morphogenetic plant attributes. No significant relationships were found between plant attributes and relative growth rate, while six attributes explained a significant proportion of the interspecific variance in absolute biomass growth: net photosynthetic rate at growth PFD (P _net ) (75.5%), leaf apparent quantum yield of CO₂ fixation (62.5%), leaf dark respiration rate (65.2%), leaf compensation PFD (71.0%), root: shoot ratio (66.4%) and plant nitrogen content on a mass basis (42.0%). Only species with extremely low allocation to roots and very high (relatively speaking) net photosynthetic rates were able to grow fast in low light. Specific leaf area (SLA), instantaneous photosynthetic nitrogen use efficiency (PNUE) and leaf nitrogen content on a mass basis as well as on an area basis were not significantly related to growth. The absence of effects of plant traits on RGR, unlike for AGR, could arise from a relationship that we observed between AGR and a fitted start value of the biomass-time course (i.e. seed mass or germination time). This suggests that interspecific differences in the very early growth stages of the plants were responsible for differences in successful development under low light, rather than differences in RGR. Based on its high explanatory power, its relative constancy with plant age and the lack of effect of growth PFD, P _net would be the best candidate for characterizing potentially shade-tolerant species that are likely to establish in dense vegetation in the field.     

Does host plant influence parasitism and parasitoid species composition in Lygus rugulipennis? A molecular approach

Lygus Hahn plant bugs (Hemiptera: Miridae) are serious pests of a wide variety of economically important crops in North America. European Peristenus digoneutis Loan and P. relictus Ruthe (Hymenoptera: Braconidae) are being considered for release in Canada as part of a classical biological control program for Lygus. The attractiveness of different host plants to European Peristenus has not been addressed, but may be an important consideration prior to parasitoid release. Lygus rugulipennis Poppius nymphs were collected in the Northern Temperate Atlantic (NTA) ecoregion on red clover (Trifolium pratense L.; Fabaceae) and chamomile (Matricaria recutita L.; Asteraceae), and in the Western European Broadleaf Forest (WEBF) ecoregion on red clover and alfalfa (Medicago sativa L.; Fabaceae). Parasitism levels and parasitoid species were determined using a multiplex PCR assay for P. digoneutis, P. relictus, and P. pallipes Curtis. Mean parasitism levels in L. rugulipennis were 45-49% in the NTA ecoregion and 25-32% in the WEBF ecoregion. However, in neither ecoregion were parasitism levels and parasitoid species compositions significantly different in nymphs from different host plant species. Furthermore, multiparasitism was low despite the fact that P. digoneutis and P. relictus share the same host species.     

Does microbiological testing of foods and the food environment have a role in the control of foodborne disease in England and Wales?

This review looks at the contribution of microbiological sampling to the safety of retail foods in England and Wales. It compares sampling methods available and assesses the value of testing as part of outbreaks of foodborne disease, as part of routine management by local authorities, as part of work done or commissioned by the food industry, and as part of research. It confirms that microbiological testing has a role during outbreaks as it makes a significant contribution to help identify foods and other areas of greatest risk for future study. The review suggests that routine testing by local authorities is often of limited use and could be improved by more targeted surveillance. Testing could be better used to validate primary control methods, such as Hazard Analysis and Critical Control Point (HACCP) system. Any public health benefit from testing in the food industry is often restricted by client confidentiality. Microbial research on foods is important as it can lead to significant improvements in safety. Current microbiological methods are slow and, in future, rapid molecular methods may make an even bigger contribution to the control of foodborne disease.